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1
Gillon, Bronwyn H., Kevin JT Noonan, Bastian Feldscher, Jennifer M. Wissenz, Zhi Ming Kam, Tom Hsieh, Justin J. Kingsley, Joshua I. Bates i Derek P. Gates. "Molecular studies of the initiation and termination steps of the anionic polymerization of P=C bonds". Canadian Journal of Chemistry 85, nr 12 (1.12.2007): 1045–52. http://dx.doi.org/10.1139/v07-121.
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The initiation and termination steps of the anionic polymerization of P=C bonds have been modeled. The initiation step was investigated through the stoichiometric reaction of MesP=CPh2 (1) with RLi (R = Me or n-Bu). In each case, the addition was highly regioselective with the formal attack of R– at phosphorus to give the carbanion Li[Mes(R)P–CPh2] (3a, R = Me; 3b, R = n-Bu). To simulate the termination step in the anionic polymerization of 1, carbanions 3a and 3b were quenched in situ with various electrophiles. Through these reactions, several new tertiary phosphines have been prepared, namely, Mes(Me)P–CPh2H (4a), Mes(n-Bu)P–CPh2H (4b), Mes(Me)P–CPh2Me (6a), Mes(Me)P–CPh2–P(NEt2)2 (7a), Mes(Me)P–CPh2–SiMe2H (8a), and Mes(Me)P–CPh2–SiMe3 (9a). In addition, compounds 4a, 7a, 8a, and 9a were characterized by X-ray crystallography. Most of the metrical parameters are typical of tertiary phosphines; however, the P–CPh2H bonds were elongated in all cases reflecting the considerable steric bulk surrounding this bond. Unexpectedly, an unusually large 31P–31P coupling constant (2JPP > 200 Hz) was observed for 7a both in solution and the solid state. This observation may be rationalized by a through space P···P interaction. This rationale is further supported by the short P···P distance [P(1)—P(2) = 2.966(1) Å; cf. Σ rvdw = 3.7 Å] and a small P–C–P bond angle for 7a [P(1)–C(11)–P(1) = 99.17(9)°].Key words: phosphaalkenes, phosphorus polymers, phosphines, anionic polymerization.
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Verebélyi, Klára, Ákos Szabó, Zsombor Réti, Györgyi Szarka, Ákos Villányi i Béla Iván. "Highly Efficient Cationic Polymerization of β-Pinene, a Bio-Based, Renewable Olefin, with TiCl4 Catalyst from Cryogenic to Energy-Saving Room Temperature Conditions". International Journal of Molecular Sciences 24, nr 6 (8.03.2023): 5170. http://dx.doi.org/10.3390/ijms24065170.
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Polymers based on renewable monomers are projected to have a significant role in the sustainable economy, even in the near future. Undoubtedly, the cationically polymerizable β-pinene, available in considerable quantities, is one of the most promising bio-based monomers for such purposes. In the course of our systematic investigations related to the catalytic activity of TiCl4 on the cationic polymerization of this natural olefin, it was found that the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4/N,N,N′,N′-tetramethylethylenediamine (TMEDA) initiating system induced efficient polymerization in dichloromethane (DCM)/hexane (Hx) mixture at both −78 °C and room temperature. At −78 °C, 100% monomer conversion was observed within 40 min, resulting in poly(β-pinene) with relatively high Mn (5500 g/mol). The molecular weight distributions (MWD) were uniformly shifted towards higher molecular weights (MW) in these polymerizations as long as monomer was present in the reaction mixture. However, chain–chain coupling took place after reaching 100% conversion, i.e., under monomer-starved conditions, resulting in considerable molecular weight increase and MWD broadening at −78 °C. At room temperature, the polymerization rate was lower, but chain coupling did not occur. The addition of a second feed of monomer in the polymerization system led to increasing conversion and polymers with higher MWs at both temperatures. 1H NMR spectra of the formed polymers indicated high in-chain double-bond contents. To overcome the polarity decrease by raising the temperature, polymerizations were also carried out in pure DCM at room temperature and at −20 °C. In both cases, rapid polymerization occurred with nearly quantitative yields, leading to poly(β-pinene)s with Mns in the range of 2000 g/mol. Strikingly, polymerization by TiCl4 alone, i.e., without any additive, also occurred with near complete conversion at room temperature within a few minutes, attributed to initiation by adventitious protic impurities. These results convincingly prove that highly efficient carbocationic polymerization of the renewable β-pinene can be accomplished with TiCl4 as catalyst under both cryogenic conditions, applied widely for carbocationic polymerizations, and the environmentally benign, energy-saving room temperature, i.e., without any additive and cooling or heating. These findings enable TiCl4-catalyzed eco-friendly manufacturing of poly(β-pinene)s, which can be utilized in various applications, and in addition, subsequent derivatizations could result in a range of high-added-value products.
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Zhao, Yaqi, Banglei Liang, Zhenxin Zhao i Qiao Feng. "Property and Structure Characterization of High Molecular Weight Polyacrylonitrile Polymers Initiated by 2,2'-Azobis (2-methyl propionamide) Dihydrochloride Using Aqueous Deposited Polymerization Technique". MATEC Web of Conferences 358 (2022): 01028. http://dx.doi.org/10.1051/matecconf/202235801028.
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Powdery high molecular weight polyacrylonitrile (HMW-PAN) polymers were successfully synthesized by aqueous deposited polymerization (ADP) method with 2,2'-azobis (2-methyl propionamide) dihydrochloride (AIBA) as the initiator and itaconic acid (IA) as comonomer. The utilization of IA into the ADP system was conducive to relax the proceeding of thermo-oxidation process. Differential scanning calorimeter (DSC) curves of obtained PAN copolymers showed the doublet peaks character under air atmosphere, attributing to the exothermic cyclization and oxidative reactions during heat-treatment process. With the utilization of IA in the reaction system, crystallinity and grain sizes of the PAN polymers decreased. The stretching vibration of nitrile group (C≡N) at 2240cm-1 was the strongest peak in both Fourier transform infrared spectra (FTIR). And the stretching vibration and bending of CH2 were the stronger peaks in FTIR. Amido group (NH2), carbonyl group (C=O) and C-O single bond existed in FTIR of PAN homopolymer and copolymers, indicating occurrence of C≡N hydrolysis during polymerization process except carboxyl group (COOH) introduced by IA.
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Aprilian, Rafly, Mas Ayu Elita Hafizah, Azwar Manaf i Andreas. "Conversion Enhancement of Vinyl Acetate Monomer to Polyvinyl Acetate Emulsion through Emulsion Polymerization Method". Materials Science Forum 1028 (kwiecień 2021): 263–68. http://dx.doi.org/10.4028/www.scientific.net/msf.1028.263.
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Synthesis of Polyvinyl Acetate (PVAc) through the conversion of Vinyl Acetate Monomer (VAM) was carried out by emulsion polymerization method assisted by thermal initiator Ammonium persulfate (APS) under reaction temperature was kept at 70 °C – 80 °C with 5 hours of reaction time and agitation speed at 300 rpm. The polymerization reaction was running used batch process technique where is all components were mixed all together simultaneously. A set of polymerization reactions was conducted when the absence of surfactant and cationic and amphoteric surfactant presence. The monomer chain's double bond was found at 1645 cm-1 was measured by FTIR Spectrophotometer did not disappear after polymerization reaction was utterly done. The spectrum FTIR of Polyvinyl acetate did not explicitly found at 1644 cm-1. During the reaction, characterization was conducted by measuring the solid content value where the maximum solid content was achieved was 6,1 % when using Amphoteric surfactant while the lowest solid content was obtained when the absence of surfactant. Other parameters were conducted to observe the acidity value by pH Meter.
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Veselý, Ivan, i Václav Dědek. "Reactivity of 2,2-difluoro-3-methyl-3-butenal toward some O-, N- and C-nucleophiles". Collection of Czechoslovak Chemical Communications 50, nr 12 (1985): 2730–42. http://dx.doi.org/10.1135/cccc19852730.
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Addition of nucleophiles to 2,2-difluoro-3-methyl-3-butenal (I) is complicated by its spontaneous polymerization. Compound I afforded neither hydrate nor dimethyl acetal but reacted with ethylene glycol to give the cyclic acetal II. Reaction with acetyl chloride and acetic anhydride led to the respective acetate III and diacetate IV. Satisfactory reaction with N-nucleophiles was observed only in the case of hydroxylamine and dinitrophenylhydrazine. Diethylamine reacted with I only at 150 °C to give the reduction product VI and the ethylaldimine VII. The compound I added nitromethane and sodium cyanide (giving X and XI, respectively); the adducts or products of their reduction with lithium aluminium hydride were hydroxylated at the double bond to give analogues of alcoholic sugars with difluoromethylene group in position 3. Hydroxylation of the butenal I or the acetate III afforded 3,3-difluoro-2,4-dihydroxy-4-methyloxolane (XIX) which was prepared also by cleavage of the acetal XVIII obtained from II by hydroxylation. Addition of bromine to the double bond in III and IV gave the dibromo derivatives XV and XVI; the attempted replacement of bromine in XV and XVI by acetate anion failed. Bromination of I in aqueous medium afforded 3-bromo-2,2-difluoro-3-methyl-4-butanolide (XIV).
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Sari, R. N., i E. Hastarini. "Functional groups of bio-lubricants from crude catfish oil (Pangasius hypothalamus)". IOP Conference Series: Earth and Environmental Science 919, nr 1 (1.11.2021): 012044. http://dx.doi.org/10.1088/1755-1315/919/1/012044.
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Abstract Bio-lubricants have great potential in the production of lubricating in the future. Several studies have developed animal oils as lubricants, which come from a by-product of fish processing. Fish oil extracted from the material and processed into bio-lubricants reached the highest yield of 94%. This research aimed to study the bio-lubricants functional groups. The research steps extracted crude fish oil as raw material, hydrolysis using HCl catalyst, polymerization using benzoyl peroxide, and polyesterification using ethylene glycol. The extraction process used the wet rendering method with a ratio of catfish waste (viscera) to the water of 1:2 (w/v) at 70 °C for 30 minutes. The best bio-lubricants were analyzed for functional groups using an FT-IR instrument with a wave range of 4000-450 cm−1. The results obtained were the absorption wavelength peak of 3472 cm−1, indicating O-H bonds with the sloping peak and the weak bond. The absorption wave peak of 3006-2852 cm−1 indicated a strong C-H bond (alkane). The absorption wave peaks of 1743 cm−1 indicated the presence of a C=O double bond. The adsorption wave peaks at 1465 cm−1 indicated carbon chain bonds between C-C, while the absorption wave peaks at 1115 and 1174 cm−1 indicated C-O bonds. The three spectral indicated that the ester groups formed in bio-lubricants. In the polymerization reaction, there was no absorption wave of 1600-1500 cm−1 which indicated that all C=C groups had been polymerized by benzoyl peroxide. Meanwhile, a sloping absorption wave of 3472 cm−1 was found in the polyesterification reaction due to the weak O-H bond. The analysis obtained above showed the differences in wave peak between bio-lubricant and crude fish oil as raw material but had the same group shape.
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Yu, Ke, Yan Lin, Jinchen Fan, Qiaoxia Li, Penghui Shi, Qunjie Xu i Yulin Min. "Ternary N, S, and P-Doped Hollow Carbon Spheres Derived from Polyphosphazene as Pd Supports for Ethanol Oxidation Reaction". Catalysts 9, nr 2 (26.01.2019): 114. http://dx.doi.org/10.3390/catal9020114.
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Ethanol oxidation reaction (EOR) is an important electrode reaction in ethanol fuel cells. However, there are many problems with commercial ethanol oxidation electrocatalysts today, such as poor durability, poor anti-CO poisoning ability, and low selectivity for C–C bond cleavage. Therefore, it is very meaningful to develop a high-performance EOR catalyst. Herein, we designed ternary N, S, and P-doped hollow carbon spheres (C–N,P,S) from polyphosphazene (PCCP) as Pd supports for EOR. Using SiO2 spheres as the templates, the PCCP was first coated on the surfaces of SiO2 spheres by in situ polymerization. Through high-temperature pyrolysis and hydrofluoric acid-etching, the hollow PCCP has a large surface area and porous structure. After loading Pd nanoparticles (NPs), the Pd/C–N, P, S catalysts with Pd NPs decorated on the surfaces of C–N, P, S can achieve a high mass peak current density of 1686 mA mgPd−1, which was 2.8 times greater than that of Pd/C. Meanwhile, the Pd/C–N, P, S catalyst also shows a better stability than that of Pd/C after a durability test of 3600s.
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Sujono, Sujono, i Zainal A. Mas’ud. "UREA CORE COATING WITH CROSSLINKED HYDROPHILIC POLIMERS FOR CONTROLLED RELEASE FERTILIZER APPLICATION". Helium: Journal of Science and Applied Chemistry 1, nr 2 (31.12.2021): 51–56. http://dx.doi.org/10.33751/helium.v1i2.4539.
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Controlled release fertilizer (CRF) can be made by coating the fertilizer core with a polymer layer. The simultaneous coating reaction of the polymerization needs to be controlled in the reactor. A controlled reactor system was developed for the polymerization of granular fertilizer coating using integrated electronic control of the 8-bit ATTiny 2313 AVR microcontroller chip. Urea granule fertilizer is coated with hydrophilic polymer polyacrylamide and crosslinked polyacrylate with N,N'-methylene-bis acrylamide (MBA). The reaction was initiated by benzoyl peroxide (BPO) at 61 oC. The coating was successfully formed in 45 minutes reaction. The coating process in the control reactor was more effective than without control, thereby reducing the deposition of polymer deposits that did not coat the fertilizer. The characterization of the fertilizer coating layer based on infrared spectroscopy (FTIR) showed that polymerization synthesis had occurred based on the presence of C=C bonds. The IR spectrum showed a reduced absorption of the C=C stretching vibration medium in the acrylamide monomer compared with the polymer (crosslinked polyacrylamide), namely the wavenumbers of 1614 cm-1 in acrylamide and 1601 cm-1 in polyacrylamide spectrum. Similarly, the loss of C=C absorption in the crosslinked polyacrylate spectrum but appeared in the acrylic monomer spectrum at 1636 cm-1 wave. This group is reduced or lost after polymerization due to an addition reaction.
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Mori, Atsunori, Sonoka Yamamoto, Yushin Shibuya, Toyoko Suzuki, Kentaro Okano i Masaki Horie. "One-Shot Deprotonative Metalation/Transmetalation/Polymerization of Halothiophenes Catalyzed by Nickel Complex for Polythiophene Synthesis". Synthesis 53, nr 17 (21.01.2021): 3081–84. http://dx.doi.org/10.1055/a-1368-7072.
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AbstractEffect of divalent metals was studied in the cross-coupling polymerization of thiophenes leading to head-to-tail-type poly-3-hexylthiophene. Deprotonation of the C–H bond at the 5-position of 2-halo-3-hexylthiophene by LDA followed by metal exchange was carried out in one pot and following addition of nickel catalyst underwent polymerization. One-shot reaction involving deprotonation/transmetalation/ cross coupling polymerization was also examined with manganese(II) chloride and nickel(II) catalyst.
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Wappel, Julia, Roland C. Fischer, Luigi Cavallo, Christian Slugovc i Albert Poater. "Simple activation by acid of latent Ru-NHC-based metathesis initiators bearing 8-quinolinolate co-ligands". Beilstein Journal of Organic Chemistry 12 (28.01.2016): 154–65. http://dx.doi.org/10.3762/bjoc.12.17.
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A straightforward synthesis utilizing the ring-opening metathesis polymerization (ROMP) reaction is described for acid-triggered N,O-chelating ruthenium-based pre-catalysts bearing one or two 8-quinolinolate ligands. The innovative pre-catalysts were tested regarding their behavior in ROMP and especially for their use in the synthesis of poly(dicyclopentadiene) (pDCPD). Bearing either the common phosphine leaving ligand in the first and second Grubbs olefin metathesis catalysts, or the Ru–O bond cleavage for the next Hoveyda-type catalysts, this work is a step forward towards the control of polymer functionalization and living or switchable polymerizations.
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Zhang, Ming, Zhi Xiong Huang i Yan Qin. "Quantum Chemical Calculation of Maleic Anhydride Ring-Opening Reaction". Advanced Materials Research 79-82 (sierpień 2009): 1193–96. http://dx.doi.org/10.4028/www.scientific.net/amr.79-82.1193.
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The reaction of maleic anhydride ring-opening was calculated by Gaussian03. The Density Function Theory (DFT) method were employed to study the geometries of maleic anhydride and ethanol on the base of B3LYP/6-31G in the paper. The transitional states(Ts1,Ts2) of maleic anhydride ring-opening reaction were found by TS method and were proved by IRC calculation. The results showed that from the reactant to product, the energy reduced about 129.25337kJ/mol,The computation results showed that the reaction was exothermic and matched up well with experiment. Nowadays the MAH multipolymers were studied extensively.Because of C=C double bond has double substitutions and the great Spatial steric hindrance, MAH was always regarded as representative that couldn’t carry out homopolymerization[1,2]. Much attention has been paid to MAH polymerization(Homopolymerization[4] and Copolymerization[5-15])gradually Long and his colleagues[3] published papers on MAH homopolymerization in 1963. The related reports have been increased since MAH multipolymer was found to possess anti-tumor and biological activity[16]. According to the polymerization mechanism，epoxide ring-opening esterification were divided into three kinds: cationic polymerization, anionic polymerization and coordination polymerization.The saturated polyesters were prepared through maleic anhydride and alkene oxide reaction, generally using anionic polymerization initiated by hydroxyl compound such as alcohol, water and carboxylic acid. maleic anhydride ring-opening reaction initiated by alcohol(Eq. 1) was discussed in this paper.
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Zheng, Haiyan, Kuo Li, George Cody, Chris Tulk, Jamie Molaison, Wenge Yang, Ilia Ivanov, Malcolm Guthrie i Ho-kwang Mao. "Phase Transition and Polymerization of Acetonitrile under High Pressure". Acta Crystallographica Section A Foundations and Advances 70, a1 (5.08.2014): C763. http://dx.doi.org/10.1107/s2053273314092365.
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Successful application of high pressure on synthesis of organic polymer, including the conducting polymer and super hard materials depends on the knowledge of reaction mechanism. The evolution of crystal structure under high pressure especially the structure close to transition pressure is crucial to conclude the reaction mechanism. Nitriles represent a large class of interstellar molecules and are the potential source of amino acids. Understanding its behavior at extreme conditions has gained increasing attention recently. Acetonitrile (CH3CN), the simplest organic compound with C≡N triple bond, can act as a model system for studying the pressure induced polymerization. The phase transition of acetonitrile under high pressure has been studied extensively.[1-3] However, it is still controversial and there is no any detailed discussion about its polymerization mechanism under high pressure. Here, we report the in-situ high pressure Raman spectra and powder neutron diffraction results on CD3CN, which indicates a minor phase transition at 5 GPa. The neutron diffraction shows that CD3CN keeps the orthorhombic phase from 1.66 GPa to 20.58 GPa which is very close to the reaction pressure. The week hydrogen bonding CD...N arranges the molecule into 3-dimensional framework which can be treated as two sets of diamond like structures interpenetrating with each other. Interestingly, the observed N...D distance is 1.984 Å at 20.58 GPa, shorter than the van der Waals distance of N...H (2.75 Å) by 28%. The van der Waals separation is often taken as a reference distance for the molecular instability. Thus, a hydrogen transfer process during the polymerization can be concluded. This deduction is also supported by the solid state NMR and FTIR results of the recovered polymerized CH3CN (p-CH3CN) from high pressure. In addition, the atomic pair distribution function and Raman spectra indicate the p-CD3CN or p-CH3CN has a random packed layer structure with nano-graphene lattice.
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Uhlig, Wolfram. "Zur Darstellung von Organosiliciumpolymeren mit (-SiH2-)n-Gnippen/Synthesis of Organosilicon Polymers Containing ( – SiH2- )n-Units". Zeitschrift für Naturforschung B 54, nr 2 (1.02.1999): 270–77. http://dx.doi.org/10.1515/znb-1999-0216.
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Organosilicon polymers containing (SiH2) or (SiH2)2 units have been prepared via silyltriflate intermediates. Two methods of the formation of silicon-hydrogen bonds are described. Polysilaethylene [SiH2-CH2- ]n has been prepared by ring-opening polymerization of tetraphenyl-1,3-disilacyclobutane followed by a protodesilylation reaction with triflic acid and reduction with LiAlH4. The reaction of H2Si(OTf)2 or (TfO )H2Si- SiH2(OTf) with organolithium or organomagnesium compounds gave poly(silyleneethyne)s [(SiH2)n-C≡C]n and poly(silylenephenylene)s [(SiH2)n-C6H4 -]n. These polymers may serve as suitable precursors for ceramic materials. The TGA studies gave remarkably high ceramic yields. NMR measurements (29Si, 13C, 1H) indicate an regular alternating arrangement of silicon atoms and organic groups in the polymer backbone.
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Li, Zilong, Yanping Ma i Wen-Hua Sun. "Comparison of the Reactivity and Structures for the Neutral and Cationic Bis(imino)pyridyl Iron and Cobalt Species by DFT Calculations". Catalysts 10, nr 12 (30.11.2020): 1396. http://dx.doi.org/10.3390/catal10121396.
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Density Functional Theory (DFT) method was adopted to investigate and compare the reaction mechanisms of ethylene polymerization catalyzed by neutral, cationic bis(imino)pyridyl (PDI) iron and cobalt derivatives. The electronic structure and the oxidation states of the metal center and the PDI ligand were analyzed by taking spin states, natural bond orbital (NBO) charge distribution, etc. into consideration, revealing that the reactivity is closely related to the valence electron numbers instead of the charge numbers. The neutral Co(0) had the lowest reactivity as it possessed the most electrons. During the formation of the cationic Co(+)/Fe(+), one electron was mainly lost from PDI ligand rather than the metal center while the metal center maintained +II valence state through the process. Moreover, a special unsymmetrically bidentate N^N coordination manner was found to provide the deficient metal surroundings with 14e, which may initiate the reactivity of some unsymmetrical species with rich electrons. Finally, an anion [AlMe4]− participating process was proposed to explain the presence of the experimentally observed LCo(+)B(C2H4). A special intermediate, Co(+)B(C2H4) [AlMe4]− with Co in +I and absence of Co–C σ bond, was obtained. These calculation results may provide fundamental information for further understanding and designing the ethylene polymerization catalysts.
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Lin i Jheng. "Mechanistic Insight into the Ring-Opening Polymerization of ɛ-Caprolactone and L-Lactide Using Ketiminate-Ligated Aluminum Catalysts". Polymers 11, nr 9 (19.09.2019): 1530. http://dx.doi.org/10.3390/polym11091530.
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The reactivity and the reaction conditions of the ring-opening polymerization of ɛ-caprolactone (ɛ-CL) and L-lactide (LA) initiated by aluminum ketiminate complexes have been shown differently. Herein, we account for the observation by studying the mechanisms on the basis of density functional theory (DFT) calculations. The calculations show that the ring-opening polymerization of ɛ-CL and LA are rate-determined by the benzoxide insertion and the C–O bond cleavage step, respectively. Theoretical computations suggest that the reaction temperature of L–LA polymerization should be higher than that of ɛ-CL one, in agreement with the experimental data. To provide a reasonable interpretation of the experimental results and to give an insight into the catalyst design, the influence of the electronic, steric, and thermal effects on the polymerization behaviors will be also discussed in this study.
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Muzaffar, Anjum, Ernest Hamel, Rouli Bai i Arnold Brossi. "Synthesis and tubulin interaction of thiocolchicines containing an isothiocyanato group. Synthesis of C(2)-deuterated and C(2)-14C-labeled 7-isothiocyanatodeacetamidothiocolchicine". Collection of Czechoslovak Chemical Communications 56, nr 11 (1991): 2306–12. http://dx.doi.org/10.1135/cccc19912306.
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Synthesis of isothiocyanato substituted thiocolchicines XI - XIV is described. Introduction of an isotope label is demonstrated with the deuterated isothiocyanate XII and the 14C-labeled analog XIII. These isothiocyanates inhibit tubulin polymerization at low concentration. In addition, the 14C-labeled XIII forms covalent bond(s) with tubulin. Unfortunately, the covalent reaction while rapid, is not inhibited by preincubation of tubulin with colchicine. The covalent interaction of XIII with tubulin thus appears to be nonspecific, limiting its use as a marker of the colchicine binding site on tubulin.
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Ilie, Nicoleta. "Comparative Effect of Self- or Dual-Curing on Polymerization Kinetics and Mechanical Properties in a Novel, Dental-Resin-Based Composite with Alkaline Filler". Materials 11, nr 1 (11.01.2018): 108. http://dx.doi.org/10.3390/ma11010108.
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Dental bulk-fill restorations with resin-composites (RBC) are increasing in popularity, but doubts concerning insufficient curing in depth still disconcert clinicians. An alternative might be offered by modern dual-cured RBCs, which additionally provide bioactive properties. This study assessed the impact of additional light-curing on polymerization kinetics, the degree of conversion (DC) and mechanical properties of a novel, dual-cured RBC with alkaline fillers. Since the bioactivity of a material often implies a release of compounds, the mechanical stability in simulated clinical environments was also evaluated. Polymerization kinetics and DC were assessed at 2- and 4-mm specimen depths in real-time up to one hour (n = 6). Incident and transmitted irradiance and radiant exposure were recorded at 2- and 4-mm depths. Micro-mechanical profiles (n = 6) were assessed in 100-µm steps along 6-mm deep specimens at 24 h post-polymerization. Flexural strength and modulus (n = 10) were determined up to three months of immersion in neutral (6.8) and acidic (4) pH conditions. DC variation in time was best described by a sigmoidal function (R2 > 0.98), revealing a retarded (3.4 ± 0.4 min) initiation in C=C double bond conversion in self-cured versus dual-cured specimens. The setting reaction kinetic was identical at 2- and 4-mm depths for the self-cure mode. For the dual-cure mode, polymerization initiated at 2-mm depth instantly with light-irradiation, while being retarded (0.8 min) at 4-mm depth. The material behaves similarly, irrespective of curing mode or depth, later than 11 min after mixing. Flexural strength and modulus was comparable to regular RBCs and maintained up to three months in both neutral and acidic conditions. Additional light-curing initially accelerates the polymerization kinetic and might help shorten the restauration procedure by hardening the material on demand, however with no effect on the final properties.
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Ullah, Mohammad Shahid, Sadia Afrin Chhanda i Shinichi Itsuno. "ADMET Polymerization of Dimeric Cinchona Squaramides for the Preparation of a Highly Enantioselective Polymeric Organocatalyst". Catalysts 10, nr 5 (25.05.2020): 591. http://dx.doi.org/10.3390/catal10050591.
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Under the acyclic diene metathesis (ADMET) reaction condition, the C3-vinyl groups of cinchona alkaloids readily react with each other to form a C-C bond. A novel type of cinchona alkaloid polymers was synthesized from dimeric cinchona squaramides using the Hoveyda-Grubbs’ second-generation catalysts (HG2) by means of ADMET reaction. The chiral polymers, containing cinchona squaramide moieties in their main chains, were subsequently employed as catalysts for the enantioselective Michael reaction to give the corresponding chiral adducts in high yields with excellent enantioselectivity and diastereoselectivity. Both enantiomers from the asymmetric Michael reaction were distinctively prepared while using the polymeric catalysts, possessing pseudoenantiomeric structures. The catalysts were readily recovered from the reaction mixture and recycled several times due to the insolubility of the cinchona-based squaramide polymers.
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Luo, Aoxiang, Yao Yao, Li Zhang i Yuejing Chen. "Influence of different but compatible all-ceramic materials and bonding systems on dentin bonding properties". Materials Express 11, nr 1 (1.01.2021): 116–22. http://dx.doi.org/10.1166/mex.2021.1885.
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This study aimed to investigate the effects of various compatible all-ceramic materials and bonding systems, on the bonding properties of dentin. Five types of commonly used all-ceramic materials (Cerec Blocs, IPS e. max Press, IPS e. max ZirCAD, Incoris Alumina, In-Ceram Alumina) were bonded with three types of adhesives (Multilink N, Variolink N, Relyx Unicem) for nuclear porcelain tile preparation. We evaluated the polymerization conversion rates, shear bonding strength (SBS), and micro-tensile bond strength (TBS) for each combination. The polymerization conversion rates, SBS and TBS differed significantly for all 3 adhesives with each all-ceramic group (P < 0.05). The Relyx Unicem agent had higher adhesive properties compared with the Variolink N and Multilink N agents (P < 0.05). The polymerization conversion rate, SBS and TBS of the five all-ceramic materials differed significantly with each adhesive (P < 0.05). The Cerec Blocs had the highest adhesive performance (P < 0.05). The polymerization conversion rate of adhesives differed with each all-ceramic material, while the dentin bonding strength differed with each all-ceramic material and adhesive. Clinically, all-ceramic materials with a high transparency and low refraction are recommended. For opaque all-ceramic restorations, the curing light time and polymerization reaction rate should be increased to improve the dentin bonding performance.
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MALLAKPOUR, SHADPOUR, i MOHAMMAD DINARI. "IN SITU FABRICATION OF HIGH PERFORMANCE POLYIMIDE/TYROSINE-MODIFIED LAYERED SILICATE NANOCOMPOSITES". Nano 07, nr 03 (czerwiec 2012): 1250021. http://dx.doi.org/10.1142/s179329201250021x.
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Several novel organic–inorganic hybrids consisting of high performance polyimide (PI) and organically modified montmorillonite (OMMT) with trifunctional swelling agent were successfully prepared by in situ polymerization technique. In this way, at first, OMMT was prepared by surface treatment of Cloisite Na+ with protonated form of bioactive L-tyrosine amino acid. Amine functional groups of this swelling agent formed an ionic bond with the negatively charged silicates, whereas the remaining acidic and phenolic functional groups are available for further interaction with PI chains. Then, organo-soluble PI with benzimidazole pendent group was prepared from pyromellitic dianhydride and 4-(3, 5-diaminophenyl)-benzimidazole in dry N,N-dimethylacetamide. PI/OMMT nanocomposites enclosing 1–10 wt.% of OMMT were successfully prepared by an in situ polymerization reaction through thermal imidization up to 300°C. Also, the relationship between the properties and OMMT content of the PI hybrid films were examined using Fourier-transform infrared spectroscopy, X-ray diffraction measurements and electronic microscopy (FE-SEM and TEM). The silicate layers in the polymer matrix were exfoliated as confirmed by XRD, FE-SEM and TEM techniques. The PI/OMMT films have good optical transparencies, and are almost colorless. The thermal stability of hybrids such as the decomposition temperature and weight residue at 800°C were also increased with increasing OMMT content.
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Przesławski, Grzegorz, Katarzyna Szcześniak, Piotr Gajewski i Agnieszka Marcinkowska. "Influence of Initiator Concentration on the Polymerization Course of Methacrylate Bone Cement". Polymers 14, nr 22 (18.11.2022): 5005. http://dx.doi.org/10.3390/polym14225005.
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Background: The amount of oxidant (initiator) and reductant (co-initiator) and their ratio have a significant effect on the properties of polymethacrylate bone cement, such as maximum temperature (Tmax.), setting time (tset.) and compressive strength (σ). The increase in the initiating system concentration causes an increase in the number of generated radicals and a faster polymerization rate, which shortens the setting time. The influence of the redox-initiating composition on the course of polymerization (rate of polymerization and degree of double bond conversion) and the mechanical properties of bone cement will be analyzed. Methods: Bone cement were synthesized by mixing a powder phase composed of two commercially available methacrylate copolymers (Evonic) and a liquid phase containing 2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), and triethylene glycol dimethacrylate (D3). As an initiating system, the benzoyl peroxide (BPO) as an oxidant (initiator) in combination with a reducing agent (co-initiator), N,N-dimethylaniline (DMA), was used. Samples were prepared with various amounts of peroxide BPO (0.05%, 0.1%, 0.2%, 0.3%, 0.5% and 0.7% by weight) with a constant amount of reducing agent DMA (0.5 wt.%), and various amounts of DMA (0.25%, 0.35% and 0.5% by weight) with a constant amount of BPO (0.3 wt.%). The polymerization kinetics were studied by differential scanning calorimetry (DSC). Doughing time and compressive strength tests were carried out according to the requirements of the ISO 5833:2002 standard. Results: The increase in polymerization rate was due to the increase in the amount of BPO. In addition, the curing time was shortened, as well as the time needed to achieve the maximum polymerization rate. The final conversion of the double bonds in the studied compositions was in the range 74–100%, and the highest value of this parameter was obtained by the system with 0.3 wt.% of BPO. The doughing times for each BPO concentration were in the range of 90–140 s. The best mechanical properties were obtained for the cement following the initiating system concentrations: 0.3 wt.% of BPO and 0.5 wt.% of DMA. Nevertheless, all tested cements met the requirements of the ISO 5833:2002 standard. Conclusions: Based on the conducted polymerization kinetic studies, the best reaction conditions are provided by an initiating system containing 0.3 wt.% of BPO oxidant (initiator) and 0.5 wt.% of DMA reductant (co-initiator). A decrease in the DMA amount caused a decrease in the polymerization rate and the amount of heat released during the reaction. The change in BPO and DMA concentrations in the composition had little effect on the doughing time of the studied bone cement. The cement showed similar doughing times, ranging from 90–225 s, which is comparable to the bone cement available on the market.
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Gumidyala, Abhishek, Bin Wang i Steven Crossley. "Direct carbon-carbon coupling of furanics with acetic acid over Brønsted zeolites". Science Advances 2, nr 9 (wrzesień 2016): e1601072. http://dx.doi.org/10.1126/sciadv.1601072.
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Effective carbon-carbon coupling of acetic acid to form larger products while minimizing CO2emissions is critical to achieving a step change in efficiency for the production of transportation fuels from sustainable biomass. We report the direct acylation of methylfuran with acetic acid in the presence of water, all of which can be readily produced from biomass. This direct coupling limits unwanted polymerization of furanics while producing acetyl methylfuran. Reaction kinetics and density functional theory calculations illustrate that the calculated apparent barrier for the dehydration of the acid to form surface acyl species is similar to the experimentally measured barrier, implying that this step plays a significant role in determining the net reaction rate. Water inhibits the overall rate, but selectivity to acylated products is not affected. We show that furanic species effectively stabilize the charge of the transition state, therefore lowering the overall activation barrier. These results demonstrate a promising new route to C–C bond–forming reactions for the production of higher-value products from biomass.
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Miao, Yong Xia, i Jian Ping Liu. "Epoxidation of Soybean Oil under Acid-Free Condition". Advanced Materials Research 881-883 (styczeń 2014): 140–43. http://dx.doi.org/10.4028/www.scientific.net/amr.881-883.140.
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Industrially the epoxidation of soybean oil utilize peracids as oxidizing agents together with strong mineral acids as catalyst. To avoid the corrosive waste and undesirable epoxy-ring opening as well as polymerization under acidic conditions, new green catalytic processes in acid-free system have been paid great attentions in recent years. In this paper, MoO3/Al2O3 simply prepared by impregnation method and mesoporous TS-1 prepared by one-pot hydrothermal method were evaluated as catalysts for the epoxidation of soybean oil with tert-butyl hydroperoxide. Orthogonal experiment design was used to optimize the reaction conditions for MoO3/Al2O3 and the optimized conditions are as reaction temperature of 80°C, reaction time of 4h, the ratio of double bond to TBHP of 1:1.4, and the ratio of Ti to double bond of 1%. Higher than 55.8% of selectivity would be obtained. The synthesized meso-TS-1 displayed worse performance than expected result, only 27.6% of epoxy selectivity at conversion of 38.7%.
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Frech, Christian Manfred, Olivier Blacque i Heinz Berke. "Dinitrosyl rhenium complexes for ring-opening metathesis polymerization (ROMP)". Pure and Applied Chemistry 78, nr 10 (1.01.2006): 1877–87. http://dx.doi.org/10.1351/pac200678101877.
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The treatment of benzene solutions of the cations [Re(NO)2(PR3)2][BArF4] (R = Cy and R = iPr; [BArF4] = tetrakis{3,5-bis(trifluoromethyl)phenyl}borate) with phenyldiazomethane afforded the moderately stable cationic rhenium(I) benzylidene dinitrosyl bis(trialkyl) phosphine complexes as [BArF4]- salts in good yields. The cationic rhenium dinitrosyl bisphosphine complexes catalyze the ring-opening metathesis polymerization (ROMP) of highly strained nonfunctionalized cyclic olefins to give polymers with relatively high polydispersity indices, high molecular weights, and Z configurations of the double bonds in the polymer chain backbones of over 80 %. The benzylidene derivatives are almost inactive in ROMP catalysis with norbornene and in olefin metathesis. NMR experiments gave first hints for the initial formation of carbene complexes when [Re(NO)2(PR3)2][BArF4] was treated with norbornene. The carbene formation is initiated by an unique reaction sequence where the cleavage of the strained olefinic bond starts with phosphine migration forming a cyclic ylid carbene complex. The [2+2] addition of a norbornene molecule to the Re=C bond leads to the rhenacyclobutane complex, which is expected to be converted into an iminate complex by attack of the ylid function onto one of the NNO atoms followed by Wittig-type phosphine oxide elimination. The formation of phosphine oxide was confirmed by NMR spectroscopy. This species is thought to drive the ROMP metathesis with alternating rhenacyclobutane formations and cycloreversions. The proposed mechanism is supported by density functional theory (DFT) calculations.
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DROUILLARD, Sophie, Sylvie ARMAND, J. Gideon DAVIES, E. Constantin VORGIAS i Bernard HENRISSAT. "Serratia marcescens chitobiase is a retaining glycosidase utilizing substrate acetamido group participation". Biochemical Journal 328, nr 3 (15.12.1997): 945–49. http://dx.doi.org/10.1042/bj3280945.
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The stereochemistry of the reaction catalysed by Serratia marcescens chitobiase was determined by HPLC separation of the anomers of N-acetylglucosamine produced during the hydrolysis of p-nitrophenyl N-acetyl-β-D-glucosaminide (PNP-GlcNAc). In the early stages of the reaction, the β-anomer was found to prevail, whereas the α-anomer dominated at mutarotation equilibrium. This established that chitobiase hydrolyses glycosidic bonds with overall retention of the anomeric configuration. Chitobiase-catalysed hydrolysis of PNP-GlcNAc was competitively inhibited by a series of chito-oligosaccharides (degree of polymerization 2-5) that were selectively de-N-acetylated at their non-reducing end. The results are in accord with the participation of the acetamido group at C-2 of the substrate in the catalytic mechanism of chitobiase and related enzymes.
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Zhao, Hong Chi, Juan Li Guo, Jiang Tao Li, Ling Ling Gao i Cong Cong Bian. "Synthesis and Thermal Property of Linear Chloromethylated Polystyrene". Advanced Materials Research 150-151 (październik 2010): 1504–7. http://dx.doi.org/10.4028/www.scientific.net/amr.150-151.1504.
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Polystyrene (PS) was synthesized by emulsion polymerization. 1,4-bis(chloromethoxy)butane (BCMB) was synthesized using 1,4-butanediol, formaldehyde and phosphorus trichloride as raw material. The linear poly(p-chloromethyl styrene) (PS-Meyl-Cl) was prepared high effectively using BCMB and anhydrous aluminium trichloride as the chloromethylation reagent and catalyst, respectively. In this method, carcinogenic compound (chloromethyl ether etc.) was avoided. The resultant polymers were characterized by gel permeation chromatography (GPC), Fourier transform infrared spectrometer (FTIR) and thermogravimetric analyzer. The results show that the molecular weight (Mw) of PS is big. BCMB has been prepared because of the strong absorption band observed at 1130cm-1 (due to C-O-C bond stretching vibration) and two new bands at 640 and 1315cm-1 (due to the bending vibration of C-Cl bond and stretching vibration of C-H bond in -CH2Cl, respectively). Chloromethyl groups were introduced into benzene ring of PS because of the appearance of the absorption peaks at 676 and 1419cm-1 (due to the bending vibration of C-Cl bond and stretching vibration of C-H bond in -CH2Cl, respectively) in the FTIR spectra. The thermal stability of PS-Meyl-Cl was decreased with increasing chloromethyl group. Moreover, there are two decomposing stages. The reaction condition is gentle and the operation is safe, simple and economical.
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Dinh, Tran Trong Hieu, Hoang Hao Lam, Thanh Danh Tran, Hoang Long Tran, Tien Cuong Nguyen, Van Man Tran, Thi Hong Loan Truong i Duy Tap Tran. "Study on the mechanism of graft polymerization and sulfonation of proton exchange membranes for fuel cell". Ministry of Science and Technology, Vietnam 64, nr 6 (25.06.2022): 7–13. http://dx.doi.org/10.31276/vjst.64(6).07-13.
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Poly (styrenesulfonic acid)-grafted poly(ethylene-co-tetrafluoroethylene) polymer electrolyte membrane (ETFE-PEM) applied for fuel cells was prepared by radiation induced-grafting using gamma-ray from 60Co source based on three steps (i) irradiation, (ii) polystyrene-graftedpoly(ethylene-alt-tetrafluoroethylene) (PS-g-ETFE), and (iii) sulfonation (ETFE-PEM). Mechanism of grafting and sulfonation of ETFE-PEM with grafting degree of 22% and sulfonation degree of 93% was revealed by solid 13C nuclear magnetic resonance (solid 13C NMR), Fourier transform infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FE-SEM). The obtained results indicated that the styrene was grafted on the matrix of ETFE polymer by the π bond-breaking reaction which could be attributed to free radicals and formed the polystyrene chain at the surfaces of crystalline phases. The styrene migrated deep into the membrane due to the concentration gradient. The grafting reactions occurred at sites of C-H and C-F in the ETFE backbone but dominantly at the C-F sites while the sulfonation took place at the para position of polystyrene. The signatures related to side (secondary) reactions and by-products were not observed in the spectra indicating that the graft polymerization and sulfonation are well-controlled.
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Monopoli, Antonio, Michele Casiello, Pietro Cotugno, Antonella Milella, Fabio Palumbo, Francesco Fracassi i Angelo Nacci. "Synthesis of Tailored Perfluoro Unsaturated Monomers for Potential Applications in Proton Exchange Membrane Preparation". Molecules 26, nr 18 (15.09.2021): 5592. http://dx.doi.org/10.3390/molecules26185592.
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The aim of the present work is the synthesis and characterization of new perfluorinated monomers bearing, similarly to Nafion®, acidic groups for proton transport for potential and future applications in proton exchange membrane (PEM) fuel cells. To this end, we focused our attention on the synthesis of various molecules with (i) sufficient volatility to be used in vacuum polymerization techniques (e.g., PECVD)), (ii) sulfonic, phosphonic, or carboxylic acid functionalities for proton transport capacity of the resulting membrane, (iii) both aliphatic and aromatic perfluorinated tags to diversify the membrane polarity with respect to Nafion®, and (iv) a double bond to facilitate the polymerization under vacuum giving a preferential way for the chain growth of the polymer. A retrosynthetic approach persuaded us to attempt three main synthetic strategies: (a) organometallic Heck-type cross-coupling, (b) nucleophilic displacement, and (c) Wittig–Horner reaction (carbanion approach). Preliminary results on the plasma deposition of a polymeric film are also presented. The variation of plasma conditions allowed us to point out that the film prepared in the mildest settings (20 W) shows the maximum monomer retention in its structure. In this condition, plasma polymerization likely occurs mainly by rupture of the π bond in the monomer molecule.
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Sun, Qili, Song Ma, Zhen Ge i Yunjun Luo. "Preparation and curing behavior of high-stress solid propellant binder based on polydicyclopentadiene". High Performance Polymers 29, nr 8 (27.09.2016): 931–36. http://dx.doi.org/10.1177/0954008316664797.
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The ring-opening metathesis polymerization reaction of dicyclopentadiene (DCPD) was carried out using Grubbs first generation catalyst. Fourier transform infrared (FTIR), dynamic-thermo mechanical analysis (DMA), and Raman spectroscopy were used to investigate the curing behavior of this polymer. The FTIR results showed that DCPD had not cured completely and the polymers were composed of linear and cross-linked polydicyclopentadiene (PDCPD). The DMA test showed that the polymer possesses the glass transition temperature of linear PDCPD and cross-linked PDCPD, which had also proved the FTIR result. Furthermore, in order to explain the strange phenomenon that the band at 3004 cm−1 should have been detected in infrared spectrum, the Raman spectrum of PDCPD was applied to analyze the bonding mechanism of =C–H bond in the process of polymerization. Moreover, the real-time FTIR result cure formula showed that the cure degree increases first then constants trend with cure time of increasing, the cure degree reached the maximum value (96.76%) at 60°C for 192 h.
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Abid, Nasir Sadoon, Maha T. Sultan i Jumbad H. Tomma. "New Nanocomposite Derivatives From Thiadiazole Polymers /Silica Synthesis and Characterization using Free Radical Polymerization". Ibn AL- Haitham Journal For Pure and Applied Science 32, nr 1 (10.02.2019): 27. http://dx.doi.org/10.30526/32.1.2016.
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A new class of thiadiazole /silica nanocomposites with chemical bonds between thiadiazole monomers and modified nanosilica surface were synthesized by free radical polymerization. Presence silica nanoparticles in the structure of nanocomposite showed effectively improve the physical and chemical properties of Producing polymers. A nanocomposite material with feature properties comparison with their polymers, The structure and morphology of the synthesis materials were investigated by FT-IR spectrum which display preparation new thiadiazole compounds and polymerization monomers. FT-IR showed disappeared double bond (C=C) of monomers, due to produce long chains of thiadiazole polymers and nanocomposite. X-ray diffraction gave idea about crystalline structure of nanoparticles and nanocomposite , X-ray showed that silica nanoparticles have high intensity at 18000 , due to nanoscale of particles which allowed for particles aggregation together. While nanocomposite show low intensity due to reacted thiadaizole polymer chains with silica nanoparticles surface. The distribution of nanoparticles had characterized by Atomic forces microscopy AFM. AFM results shown roughness in the surfaces of nanocomposites C1 and C2, comparison with silica nanoparticles which gave smooth surface. The roughness attributed to reaction between functionalized surface of silica nanoparticles and chains of thiadaizole polymers, which led to change in size particles distribution and surface of particles that refer to nanocomposite.
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Ezazi, Mohammadamin, Qiang Ye, Anil Misra, Candan Tamerler i Paulette Spencer. "Autonomous-Strengthening Adhesive Provides Hydrolysis-Resistance and Enhanced Mechanical Properties in Wet Conditions". Molecules 27, nr 17 (27.08.2022): 5505. http://dx.doi.org/10.3390/molecules27175505.
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The low-viscosity adhesive that is used to bond composite restorative materials to the tooth is readily damaged by acids, enzymes, and oral fluids. Bacteria infiltrate the resulting gaps at the composite/tooth interface, demineralize the tooth, and further erode the adhesive. This paper presents the preparation and characterization of a low-crosslink-density hydrophilic adhesive that capitalizes on sol-gel reactions and free-radical polymerization to resist hydrolysis and provide enhanced mechanical properties in wet environments. Polymerization behavior, water sorption, and leachates were investigated. Dynamic mechanical analyses (DMA) were conducted using water-saturated adhesives to mimic load transfer in wet conditions. Data from all tests were analyzed using appropriate statistical tests (α = 0.05). The degree of conversion was comparable for experimental and control adhesives at 88.3 and 84.3%, respectively. HEMA leachate was significantly lower for the experimental (2.9 wt%) compared to control (7.2 wt%). After 3 days of aqueous aging, the storage and rubbery moduli and the glass transition temperature of the experimental adhesive (57.5MPa, 12.8MPa, and 38.7 °C, respectively) were significantly higher than control (7.4MPa, 4.3 MPa, and 25.9 °C, respectively). The results indicated that the autonomic sol-gel reaction continues in the wet environment, leading to intrinsic reinforcement of the polymer network, improved hydrolytic stability, and enhanced mechanical properties.
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Panchenko, Valentina N., Dmitrii E. Babushkin, John E. Bercaw i Hans H. Brintzinger. "Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates †". Polymers 11, nr 6 (29.05.2019): 936. http://dx.doi.org/10.3390/polym11060936.
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Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)2AlMe2+ B(C6F5)4− (SBI = rac-dimethylsilyl-bis(1-indenyl)) at 23 °C is studied by following the accompanying UV-vis-spectral changes. These indicate that the onset of polymerization catalysis is associated with the concurrent formation of two distinct zirconocene species. One of these is proposed to consist of SBIZr-σ-polyhexenyl cations arising from SBIZr-Me+ (formed from SBIZr(μ-Me)2AlMe2+ by release of AlMe3) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-η3-allyl cations of composition SBIZr-η3-(1-R-C3H4)+ (R = n-propyl), formed by σ-bond metathesis between SBIZr-Me+ and 1-hexene under release of methane. At later reaction stages, all zirconocene-σ–polymeryl cations appear to decay to yet another SBIZr-allyl species, i.e., to cations of the type SBIZr-η3-(x-R-(3-x)-pol-C3H3)+ (pol = i-polyhexenyl, x = 1 or 2). Renewed addition of excess 1-hexene is proposed to convert these sterically encumbered Zr-allyl cations back to catalytically active SBIZr-σ–polymeryl cations within a few seconds, presumably by initial 1-hexene insertion into the η1- isomer, followed by repeated additional insertions, while the initially formed, less crowded allyl cations, SBIZr-η3-(1-R-C3H4)+ appear to remain unchanged. Implications of these results with regard to the kinetics of zirconocene-catalyzed olefin polymerization are discussed.
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Rastogi, A. C., i S. B. Desu. "Structural development and electronic properties of hot filament low pressure chemical vapor deposited fluorocarbon polymer films". Journal of Materials Research 21, nr 1 (1.01.2006): 242–54. http://dx.doi.org/10.1557/jmr.2006.0021.
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Fluorocarbon polymer films in the poly(tetrafluoroethylene) (PTFE)-like structure are formed by a low-pressure chemical vapor deposition technique using the hot filament excitation of the gaseous C3F6O precursor. The filament and substrate temperatures were found to influence the structure of the deposited films. Infrared absorption and electron spectroscopy studies reveal that a PTFE-like (CF2)2n linear molecular chain structure evolves by an adsorption driven nucleation and CF2 polymerization process in the films deposited with low (450 °C) filament and high (70 °C) substrate temperatures. The films formed at a low substrate temperature (–165 °C) show a higher concentration of CF and C–CF bond defects and shorter (CF2)2n chains. A high (8–10 at.%) oxygen concentration in the films deposited at 600 °C filament temperature is attributed to the reaction of the (CF2)2n chains with COF and peroxyradicals arising from the dissociation of CF3C(O)F and affects the thermal stability of the films. Such reactions are not involved in the film growth at a low (450 °C) filament temperature. These films have much lower (<2 at.%) bonded oxygen content. The films having an ordered (CF2)2n chain structure formed at 70 °C are characterized by low leakage currents ∼7 × 10−11 A cm−2 at 0.1 MV cm−1 field. In comparison, high leakage currents ∼1 × 10−8 A cm−2 are observed for the films having a higher concentration of C–F and C–CF bonds.
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Bhushan, Brij, Arunima Nayak i Kamaluddin. "Role of manganese oxides in peptide synthesis: implication in chemical evolution". International Journal of Astrobiology 16, nr 4 (23.12.2016): 360–67. http://dx.doi.org/10.1017/s1473550416000471.
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AbstractDuring the course of chemical evolution the role of metal oxides may have been very significant in catalysing the polymerization of biomonomers. The peptide bond formation of alanine (ala) and glycine (gly) in the presence of various oxides of manganese were performed for a period of 35 days at three different temperatures 50, 90 and 120°C without applying drying/wetting cycling. The reaction was monitored every week. The products formed were characterized by high-performance liquid chromatography and electrospray ionization–mass spectrometry techniques. Trace amount of oligomers was observed at 50°C. Maximum yield of peptides was found after 35 days at 90°C. It is important to note that very high temperatures of 120°C favoured the formation of diketopiperazine derivatives. Different types of manganese oxides [manganosite (MnO), bixbyite (Mn2O3), hausmannite (Mn3O4) and pyrolusite (MnO2)] were used as catalyst. The MnO catalysed glycine to cyclic (Gly)2, (Gly)2 and (Gly)3, and alanine, to cyclic (Ala)2 and (Ala)2. Mn3O4 also produced the same products but in lesser yield, while Mn2O3 and MnO2 produced cyclic anhydride of glycine and alanine with a trace amount of dimers and trimmers. Manganese of lower oxidation state is much more efficient in propagating the reaction than higher oxidation states. The possible mechanism of these reactions and the relevance of the results for the prebiotic chemistry are discussed.
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Zhao, Zhen Qiang, i Xin Ping Ouyang. "Effect of Oxidation on the Structures and Properties of Lignin". Advanced Materials Research 550-553 (lipiec 2012): 1208–13. http://dx.doi.org/10.4028/www.scientific.net/amr.550-553.1208.
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The effect of three kinds of oxidants, hydrogen peroxide, copper oxide and ammonium persulfate, on the structures and properties of modified lignin were investigated. It is found out that a low dosage of oxidant can result in the increase in the content of active phenolic hydroxyl and carboxyl. It is most likely to cleave β-O-4 and C-C bond in lignin molecule. Compared to ammonium persulfate and copper oxide, hydrogen peroxide exhibits relatively mild oxidation to lignin. The oxidation of lignin with excessive ammonium persulfate and hydrogen peroxide can cause free radical polymerization of alkali lignin, leading to the increase of molecular weight and the decrease of the sulfonation degree of the sulfonated lignin followed by oxidation and hydroxymethylation (OSAL). Ammonium persulfate exhibits a stronger capacity to initiate free polymerization reaction compared to hydrogen peroxide, so it is suitable to use a low dosage of ammonium persulfate for the oxidation of alkali lignin. Copper oxide could not cause a free radical polymerization, therefore the molecular weight of the sulfonated lignin is lower, and the sulfonation degree is higher. OSAL with a good dispersive effect to cement paste should simultaneously possess a high sulfonation degree and an appropriate molecular weight.
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Bender, Desiree N., Alan J. Lough, R. Stephen Wylie, Robert A. Gossage i Daniel A. Foucher. "Preparation and DFT Studies of κ2C,N-Hypercoordinated Oxazoline Organotins: Monomer Constructs for Stable Polystannanes". Inorganics 8, nr 5 (13.05.2020): 35. http://dx.doi.org/10.3390/inorganics8050035.
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Tetraorganotin tin(IV) compounds containing a flexible or rigid (4: Ph3Sn-CH2-C6H4-R; 7: Ph3SnC6H4-R, R = 2-oxazolinyl) chelating oxazoline functionality were prepared in good yields by the reaction of lithiated oxazolines and Ph3SnCl. Reaction of 7 with excess HCl resulted in the isolation of the tin monochlorido compound, 9 (ClSn[Ph2]C6H4-R). Conversion of the triphenylstannanes 7 and 4 into their corresponding dibromido species was successfully achieved from the reaction with Br2 to yield 10 (Br2Sn[Ph]C6H4-R) and 11 (Br2Sn[Ph]-CH2-C6H4-R), respectively. X-ray crystallography of 4, 7, 9, 10, and 11 reveal that all structures adopt a distorted trigonal bipyramidal geometry around Sn in the solid state. Compound 4, with an additional methylene spacer group, displays a comparatively long Sn–N bond distance compared to the dibromido tin species, 11. Several DFT methods were compared for accuracy in predicting the solid-state geometries of compounds 4, 7, 9–11. Compounds 10 and 11 were further converted into the corresponding dihydrides (12: H2Sn[Ph]C6H4-R, 13: H2Sn[Ph]-CH2-C6H4-R), via Br–H exchange, in high yield by reaction with NaBH4. Polymerization of 12 or 13 with a late transition metal catalyst produced a low molecular weight polystannane (14: –[Sn[Ph]C6H4-R]n–, Mw = 10,100 Da) and oligostannane (15: –[Sn[Ph]-CH2-C6H4-R]n–, Mw = 3200 Da), respectively.
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An, Xiaowei, Weihong Lu, Jian Zhu, Xiangqiang Pan i Xiulin Zhu. "Selenol-Based Nucleophilic Reaction for the Preparation of Reactive Oxygen Species-Responsive Amphiphilic Diblock Copolymers". Polymers 11, nr 5 (8.05.2019): 827. http://dx.doi.org/10.3390/polym11050827.
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Selenide-containing amphiphilic copolymers have shown significant potential for application in drug release systems. Herein, we present a methodology for the design of a reactive oxygen species-responsive amphiphilic diblock selenide-labeled copolymer. This copolymer with controlled molecular weight and narrow molecular weight distribution was prepared by sequential organoselenium-mediated reversible addition fragmentation chain transfer (Se-RAFT) polymerization and selenol-based nucleophilic reaction. Nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization time-to-flight (MALDI-TOF) techniques were used to characterize its structure. Its corresponding nanomicelles successfully formed through self-assembly from the copolymer itself. Such nanomicelles could rapidly disassemble under oxidative conditions due to the fragmentation of the Se–C bond. Therefore, this type of nanomicelle based on selenide-labeled amphiphilic copolymers potentially provides a new platform for drug delivery.
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Xing, Yunliang, Xianru He, Rui Yang, Kan Zhang i Shengfu Yang. "Design of High-Performance Polybenzoxazines with Tunable Extended Networks Based on Resveratrol and Allyl Functional Benzoxazine". Polymers 12, nr 12 (26.11.2020): 2794. http://dx.doi.org/10.3390/polym12122794.
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A novel resveratrol-based bio-benzoxazine monomer (RES-al) containing an allyl group has been synthesized using resveratrol, allylamine, and paraformaldehyde via Mannich condensation reaction, and its chemical structures have been characterized by FT-IR spectroscopy and NMR techniques. The polymerization behavior of this benzoxazine resin has been investigated using in situ FT-IR and differential scanning calorimeter (DSC) measurements, and the thermal-mechanical properties of its corresponding polybenzoxazines are evaluated by DMA and TGA. We show that by controlling the curing process of the oxazine ring, the C=C bond in resveratrol, and the allyl group in RES-al, the cross-linking network of the polybenzoxazine can be manipulated, giving rise to tunable performance of thermosets. As all curable functionalities in RES-al are polymerized, the resulted polybenzoxazine exhibits a good thermal stability with a Tg temperature of 313 °C, a Td5 value of 352 °C, and char yield of 53% at 800 °C under N2.
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Moccia, Fabio, Luca Rigamonti, Alessandro Messori, Valerio Zanotti i Rita Mazzoni. "Bringing Homogeneous Iron Catalysts on the Heterogeneous Side: Solutions for Immobilization". Molecules 26, nr 9 (6.05.2021): 2728. http://dx.doi.org/10.3390/molecules26092728.
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Noble metal catalysts currently dominate the landscape of chemical synthesis, but cheaper and less toxic derivatives are recently emerging as more sustainable solutions. Iron is among the possible alternative metals due to its biocompatibility and exceptional versatility. Nowadays, iron catalysts work essentially in homogeneous conditions, while heterogeneous catalysts would be better performing and more desirable systems for a broad industrial application. In this review, approaches for heterogenization of iron catalysts reported in the literature within the last two decades are summarized, and utility and critical points are discussed. The immobilization on silica of bis(arylimine)pyridyl iron complexes, good catalysts in the polymerization of olefins, is the first useful heterogeneous strategy described. Microporous molecular sieves also proved to be good iron catalyst carriers, able to provide confined geometries where olefin polymerization can occur. Same immobilizing supports (e.g., MCM-41 and MCM-48) are suitable for anchoring iron-based catalysts for styrene, cyclohexene and cyclohexane oxidation. Another excellent example is the anchoring to a Merrifield resin of an FeII-anthranilic acid complex, active in the catalytic reaction of urea with alcohols and amines for the synthesis of carbamates and N-substituted ureas, respectively. A SILP (Supported Ionic Liquid Phase) catalytic system has been successfully employed for the heterogenization of a chemoselective iron catalyst active in aldehyde hydrogenation. Finally, FeIII ions supported on polyvinylpyridine grafted chitosan made a useful heterogeneous catalytic system for C–H bond activation.
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Ali, Amjad, Ahmad Naveed, Tahir Rasheed, Tariq Aziz, Muhammad Imran, Ze-Kun Zhang, Muhammad Wajid Ullah i in. "Methods for Predicting Ethylene/Cyclic Olefin Copolymerization Rates Promoted by Single-Site Metallocene: Kinetics Is the Key". Polymers 14, nr 3 (24.01.2022): 459. http://dx.doi.org/10.3390/polym14030459.
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In toluene at 50 °C, the vinyl addition polymerization of 4-vinyl-cyclohexene (VCH) comonomers with ethylene is investigated using symmetrical metallocene (rac-Et(Ind)2ZrCl2) combined with borate/TIBA. To demonstrate the polymerizations’ living character, cyclic VCH with linear-exocyclicπ and endocyclicπ bonds produces monomodal polymers, but the dispersity (Ɖ) was broader. The copolymers obtained can be dissolved in conventional organic solvent and have excellent thermal stability and crystalline temperature (ΔHm), and their melting temperature (Tm) varies from 109 to 126 °C, and ΔHm ranges from 80 to 128 (J/g). Secondly, the distribution of polymeric catalysts engaged in polymer chain synthesis and the nature of the dormant state are two of the most essential yet fundamentally unknown aspects. Comprehensive and exhaustive kinetics of E/VCH have shown numerous different kinetic aspects that are interpreted as manifestations of polymeric catalysts or of the instability of several types of active center [Zr]/[C*] fluctuations and formation rates of chain propagation RpE, RpVCH, and propagation rate constants kpE and kpVCH, the quantitative relationship between RpE, RpVCH and kpE, kpVCH and catalyst structures, their constituent polymer Mw, and their reactivity response to the endocyclic and exocyclic bonds of VCH. The kinetic parameters RpE, RpVCH, kpE, and kpVCH, which are the apparent rates for the metallocene-catalyzed E/VCH, RpE, and kpE values, are much more significant than RpVCH and kpVCH at 120 s, RpE and RpVCH 39.63 and 0.78, and the kpE and kpVCH values are 6461 and 93 L/mol·s, respectively, and minor diffusion barriers are recommended in the early stages. Compared with previously reported PE, RpE and kpE values are 34.2 and 7080 L/mol·s. VCH increases the RpE in the initial stage, as we are expecting; this means that the exocyclic bond of VCH is more active at the initial level, and that the chain transfer reaction of cyclic internal π double is increased with the reaction time. The tp versus Rp, kp, and [Zr]/[C*] fraction count may be fitted to a model that invokes deactivation of growing polymer chains. At tp 120–360 s higher, the incorporation rate of VCH suppresses E insertion, resulting in reduced molecular weight.
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Garai, Mousumi, i Kumar Biradha. "Exploration and exploitation of homologous series of bis(acrylamido)alkanes containing pyridyl and phenyl groups: β-sheetversustwo-dimensional layers in solid-state photochemical [2 + 2] reactions". IUCrJ 2, nr 5 (31.07.2015): 523–33. http://dx.doi.org/10.1107/s2052252515009987.
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The homologous series of phenyl and pyridyl substituted bis(acrylamido)alkanes have been synthesized with the aim of systematic analysis of their crystal structures and their solid-state [2 + 2] reactivities. The changes in the crystal structures with respect to a small change in the molecular structure, that is by varying alkyl spacers between acrylamides and/or by varying the end groups (phenyl, 2-pyridyl, 3-pyridyl, 4-pyridyl) on the C-terminal of the amide, were analyzed in terms of hydrogen-bonding interference (N—H...NpyversusN—H...O=C) and network geometries. In this series, a greater tendency towards the formation of N—H...O hydrogen bonds (β-sheets and two-dimensional networks) over N—H...N hydrogen bonds was observed. Among all the structures seven structures were found to have the required alignments of double bonds for the [2 + 2] reaction such that the formations of single dimer, double dimer and polymer are facilitated. However, only four structures were found to exhibit such a solid-state [2 + 2] reaction to form a single dimer and polymers. The two-dimensional hydrogen-bonding layerviaN—H...O hydrogen bonds was found to promote solid-state [2 + 2] photo-polymerization in a single-crystal-to-single-crystal manner. Such two-dimensional layers were encountered only when the spacer between acryl amide moieties is butyl. Only four out of the 16 derivatives were found to form hydrates, two each from 2-pyridyl and 4-pyridyl derivatives. The water molecules in these structures govern the hydrogen-bonding networks by the formation of an octameric water cluster and one-dimensional zigzag water chains. The trends in the melting points and densities were also analyzed.
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Lawson, NC, D. Cakir, P. Beck, L. Ramp i JO Burgess. "Effect of Light Activation on Resin-modified Glass Ionomer Shear Bond Strength". Operative Dentistry 37, nr 4 (1.07.2012): 380–85. http://dx.doi.org/10.2341/11-212-l.
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SUMMARY Objective Recent studies confirmed that resin-modified glass ionomers (RMGIs) set on the basis of two competing mechanisms, an acid-base reaction and a light-activated resin polymerization. This study evaluated the effect of the setting mechanism on bond strength by measuring the shear bond strength of three RMGIs to dentin with and without light activation. Methods Sixty human molars were ground to midcoronal dentin and randomly divided into six even groups: 1) Ketac Nano (KN), 2) KN without light cure (woLC), 3) Fuji Filling LC (FF), 4) FF woLC, 5) Fuji II LC (FII), and 6) FII woLC. The dentin surfaces of the specimens were conditioned/primed according to the manufacturers' instructions. A 1.54-mm diameter plastic tube was filled with RMGI material and affixed to the dentin surface. Groups 1, 3, and 5 were light cured for 20 seconds, and groups 2, 4, and 6 were immediately placed in a damp dark box with no light curing at 37°C for 24 hours. Shear bond strength testing was performed in an Instron device at 1 mm/min. Data were analyzed with a one-way analysis of variance (ANOVA) and Tukey/Kramer test (α=0.05). Results Mean ± standard deviation shear bond strength values (MPa) are: 7.1 ± 4.2 (KN), 11.7 ± 3.9 (FF), 10.2 ± 3.2 (FF woLC), 12.5 ± 5.1 (FII), and 0.3 ± 0.4 (FII woLC). Two KN, all KN woLC, and seven FII woLC specimens debonded before testing. Tukey/Kramer analysis revealed no significant differences in bond strength between the three light-cured RMGIs. KN and FII showed significantly lower bond strength without light cure, but no significant difference was observed between FF and FF woLC. Conclusions The results of this study strongly suggest that light activation is necessary to obtain optimal bond strength between RMGI and dentin. FF may contain components that chemically activate resin polymerization. Clinically, KN and FII need to be light cured after placement of these RMGIs.
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LIU, DONGJING, ZHEN ZHANG, LIANG LIU i JIANG WU. "HONEYCOMB-LIKE MESOPOROUS g-C3N4 FOR ELEMENTAL MERCURY REMOVAL FROM SIMULATED FLUE GAS". Surface Review and Letters 27, nr 12 (14.08.2020): 2050017. http://dx.doi.org/10.1142/s0218625x20500171.
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The [Formula: see text]-conjugated graphitic carbon nitride (g-C3N[Formula: see text] has gained increasing attention due to its unique electronic property, accessible nanoporous framework, chemical and thermal stability. The nanopore structure of g-C3N4 is believed to be favorable for adsorption process owing to the improved mass transfer process. Here, a honeycomb-like mesoporous g-C3N4 is synthesized by direct thermal polymerization of the mixture of urea and ammonium carbonate. It displays an excellent affinity with elemental mercury at reaction temperatures of 50–[Formula: see text]C. The optimal mass ratio of ammonium carbonate/urea is 2 with the highest Hg0 removal efficiency of 87.5% at [Formula: see text]C. NO has a negative effect on Hg0 removal, whereas SO2 slightly reinforces Hg0 adsorption in the presence of oxygen. The Hg0 is probably captured on the carbon atoms of g-C3N4 by producing a covalent carbon-mercury (C–Hg) bond via Lewis acid-base interactions.
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Liu, Xin, Xiaozhou Zhang, Jiawei Jiang, Hongge Jia, Xigao Jian i Jinyan Wang. "Synthesis and Characterization of a Self-Polycondensation Diazaphthalanone Monomer and Its Polymers from Polycondensation Reactions". Polymers 14, nr 18 (19.09.2022): 3904. http://dx.doi.org/10.3390/polym14183904.
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Polyether ketone (PEK) plastics are linear thermoplastic polymers connected by at least one ether bond and at least one ketone bond on the aryl group. The reason for their excellent heat resistance, rigidity, and mechanical strength is that their main molecular chain contains plenty of aromatic rings and polar carbonyl groups, and their molecular chain presents a large rigidity and strong intermolecular force. In addition, the main chain contains a considerable number of ether bonds, resulting in a certain toughness. However, polyether ketone materials have the disadvantage of poor solubility because of their excellent rigidity. To improve the solubility of polyether ketone, the preparation method of a novel nitrogenous heterocyclic polyaromatic ether monomer, 2-(4-chlorophenyl)-2,3-dihydrophthalazine-1,4-dione (CDD), was proposed, and its activity of polymerization was studied. The average molecular weight of the poly(aryl ether ketone) containing a nitrogenous heterocyclic polyaromatic ether group obtained by self-polycondensation of CDD was 4.181 × 103 kg/mol, and the yield was 90.5%. In order to further explore the activity of monomers, novel copolymerized poly(aryl ether ketone) (PBCD) containing a nitrogenous heterocyclic polyaromatic ether structure was prepared by ternary copolymerization with 4,4-difluorobenzophenone (DFBP) and bisphenol fluorene (BHPF) with high activity. The average molecular weight of PBCD was 72.793 × 103 kg/mol, the molecular weight distribution was 2.344, and the yield was 88.1%. Fourier transform infrared spectroscopy (FT-IR) and 1H NMR were used to confirm the structure of the obtained polymer. Through thermogravimetric analysis (TGA), the determined weight loss temperature of 5% under nitrogen was higher than 500 °C, indicating excellent thermal stability. Compared with the solubility of the binary copolymer containing fluorenyl poly(aryl ether ketone) (PBD), the polymer showed reasonable solubility in selective solvents such as chloroform and N,N-dimethylacetamide.
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Peckham, Timothy J., Daniel A. Foucher, Alan J. Lough i Ian Manners. "The synthesis and polymerization behaviour of silicon-bridged [1]- and [2]ferrocenophanes with sterically demanding trimethylsilyl substituents attached to the cyclopentadienyl rings". Canadian Journal of Chemistry 73, nr 11 (1.11.1995): 2069–78. http://dx.doi.org/10.1139/v95-255.
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The silicon-bridged [1]ferrocenophane Fe(η-C5H3SiMe3)2(SiMe2) (5) was synthesized via the reaction of Li2[Fe(η-C5H3SiMe3)2]•tmeda (tmeda = tetramethylethylenediamine) with Me2SiCl2 in hexanes. The disilane-bridged [2]ferrocenophane Fe(η-C5H3SiMe3)2(Si2Me4) (7) was prepared using a similar route from the disilane ClMe2SiSiMe2Cl. Despite the presence of sterically demanding SiMe3 substituents on the cyclopentadienyl rings, compound 5 was found to undergo thermal ring-opening polymerization at 170 °C to produce very soluble, high molecular weight poly(ferrocenylsilane) 6 with Mw = 1.4 × 105, Mn = 8.4 × 104. However, the [2]ferrocenophane 7 was found to be resistant to thermal ring-opening polymerization even at 350 °C and decomposed above 380 °C. A single-crystal X-ray diffraction study of 7 revealed that the steric interactions between the bulky SiMe3 groups are relieved by a significant twisting of the disilane bridge with respect to the plane defined by the centroids of the cyclopentadienyl ligands and the metal atom. The angle between the planes of the cyclopentadienyl rings in 7 was found to be 5.4(6)°, slightly greater than that in the non-silylated analogue Fe(η-C5H4)2(Si2Me4) (4a) (4.19(2)°), and dramatically less than the corresponding tilt angle of the strained, polymerizable, silicon-bridged [1]ferrocenophane Fe(η-C5H4)2(SiMe2) (1) (20.8(5)°). The length of the Si—Si bond in 7 (2.342(3) Å) was found to be close to the sum of the covalent radii (2.34 Å). Crystals of 7 are monoclinic, space group C2/c, with a = 23.689(3) Å, b = 11.174(1) Å, c = 31.027(3) Å, β = 109.16(1)°, V = 7758(2) Å3, and Z = 12. Keywords: ring-opening polymerization, ferrocenophane, organometallic polymers.
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Chang, Chungyu, Brendan R. Amer, Jerzy Osipiuk, Scott A. McConnell, I.-Hsiu Huang, Van Hsieh, Janine Fu i in. "In vitro reconstitution of sortase-catalyzed pilus polymerization reveals structural elements involved in pilin cross-linking". Proceedings of the National Academy of Sciences 115, nr 24 (29.05.2018): E5477—E5486. http://dx.doi.org/10.1073/pnas.1800954115.
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Covalently cross-linked pilus polymers displayed on the cell surface of Gram-positive bacteria are assembled by class C sortase enzymes. These pilus-specific transpeptidases located on the bacterial membrane catalyze a two-step protein ligation reaction, first cleaving the LPXTG motif of one pilin protomer to form an acyl-enzyme intermediate and then joining the terminal Thr to the nucleophilic Lys residue residing within the pilin motif of another pilin protomer. To date, the determinants of class C enzymes that uniquely enable them to construct pili remain unknown. Here, informed by high-resolution crystal structures of corynebacterial pilus-specific sortase (SrtA) and utilizing a structural variant of the enzyme (SrtA2M), whose catalytic pocket has been unmasked by activating mutations, we successfully reconstituted in vitro polymerization of the cognate major pilin (SpaA). Mass spectrometry, electron microscopy, and biochemical experiments authenticated that SrtA2Msynthesizes pilus fibers with correct Lys–Thr isopeptide bonds linking individual pilins via a thioacyl intermediate. Structural modeling of the SpaA–SrtA–SpaA polymerization intermediate depicts SrtA2Msandwiched between the N- and C-terminal domains of SpaA harboring the reactive pilin and LPXTG motifs, respectively. Remarkably, the model uncovered a conserved TP(Y/L)XIN(S/T)H signature sequence following the catalytic Cys, in which the alanine substitutions abrogated cross-linking activity but not cleavage of LPXTG. These insights and our evidence that SrtA2Mcan terminate pilus polymerization by joining the terminal pilin SpaB to SpaA and catalyze ligation of isolated SpaA domains in vitro provide a facile and versatile platform for protein engineering and bio-conjugation that has major implications for biotechnology.
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Li, Sheng Fang, i Wei Dong Huang. "Synthesis of New Benzoxazine from Cardanol-Furfural Resin and the Properties of the Corresponding Polymer". Advanced Materials Research 236-238 (maj 2011): 317–20. http://dx.doi.org/10.4028/www.scientific.net/amr.236-238.317.
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A novel benzoxazine-based phenolic resin containing furan groups and long alkyl side-chain (CFB) was synthesized using cardanol-furfural resin as phenolic raw materials. The new benzoxazine-based cardanol-furfural resin derived from renewable resources was characterized by FTIR,1H NMR spectra and Differential scanning calorimeter (DSC) etc. The thermal ring-opening reaction of the benzoxazine ring and the polymerization of the double bond were demonstrated with FTIR measurement. The thermal behavior of the cured product was also investigated with thermogravimetric analysis. The corresponding polybenzoxazine showed Tgvalue higher than that of polybenzoxazine prepared from cardanol, ammonia and formaldehyde. The char yield value at 800°C of the corresponding polybenzoxazine is 46.2% in N2atmosphere. The results showed that the polybenzoxazine cured from CFB had good heat resistance and toughness.
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Ghani, Salwani A., Sam’an M. Masudi i Norshamsuria Omar. "A cytotoxic evaluation of 7 th generation dentin bonding agent on human pulp cells". Journal of Dentomaxillofacial Science 8, nr 2 (13.12.2016): 63. http://dx.doi.org/10.15562/jdmfs.v8i2.214.
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Dentin bonding agents are resin based materials that used in clinical dentistry inorder to prevent leakage and promote adherent of filling material to the enamel anddentin. However, the polymerization of dentin bonding agents will release residualmonomer that may interact with pulp tissue. This in vitro study is aimed to evaluatethe cytotoxicity of new 7thgeneration dentin bonding agents (G Bond) on stem cellsfrom human exfoliated deciduous teeth (SHEDs). The proliferated human pulp cellswere incubated at 37 C for 48 hours. Under aseptic conditions, extracted testspecimen were plated in 96 well of tissue tray. SHEDs were placed on each well withdifferent concentration of dentin bonding agents, and then incubated at 37 C for 72hours exposure. The cytotoxic effect was recorded by using MTT assay method.Statistical analysis showed that higher concentration of dentin bonding agents (IC=0.035 mg/ml)exerts higher toxic effect to the human pulp cells (SHEDs). This studyconcluded that pulpal reaction to dentin bonding agent may depend on number ofapplication procedure.
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Reetz, Manfred T., Stephan Hütte i Richard Goddard. "Tetrabutylammonium Salts of 2-Nitropropane, Cyclopentadiene and 9-Ethylfluorene: Crystal Structures and Use in Anionic Polymerization". Zeitschrift für Naturforschung B 50, nr 3 (1.03.1995): 415–22. http://dx.doi.org/10.1515/znb-1995-0316.
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Reaction of the CH-acidic compounds 2-nitropropane, cyclopentadiene and 9-ethylfluorene with HON (nBu)4 affords the corresponding tetrabutylammonium salts in crystalline form, which have been characterized by X -ray structure analysis. The nitrostabilized salt is not a “naked ” anion (real carbanion). Rather, the α-methylene entities of the N+(nBu)4 cations form relatively strong hydrogen bonds with the O -atom s of the nitronateanion, forming dimers in a three-dimensional network. In solution dimers in the form of supramolecular ion pairs exist. In contrast, the cyclopentadienyl anion appears to be a real carbanion, since anion and cation do not interact with one another via H -bonding. The structure of the N+(nBu)4 salt of the 9-ethylfluorenyl anion is a special case in that closer contacts between cation and anion occur, which may be indicative of unusual [CH ··· C]- bonding. All three salts function as initiators in the metal-free anionic polymerization of acrylates and methacrylates at room temperature. In the case of tetrabutylammoniumcyclopentadienide, star polymers are formed.
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Tu, Sung-Lin, Chih-Kuang Chen, Shih-Chen Shi i Jason Hsiao Chun Yang. "Plasma-Induced Graft Polymerization of Polyethylenimine onto Chitosan/Polycaprolactone Composite Membrane for Heavy Metal Pollutants Treatment in Industrial Wastewater". Coatings 12, nr 12 (15.12.2022): 1966. http://dx.doi.org/10.3390/coatings12121966.
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The present study manifests an innovative and green approach to graft metal ion adsorbent, polyethylenimine (PEI), onto an electrospun chitosan (CS)/polycaprolactone (PCL) composite membrane via atmospheric pressure nitrogen plasma grafting polymerization. FTIR absorption peak at around 1690 cm−1 was attributed to the bending vibration of N-H from PEI. Since the plasma exposure time is a dependent factor of –NH bond formation, an increased nitrogen content up to 3.3% was observed with an extensive reaction time under plasma treatment. In addition, N1s spectra showed a clear PEI dominating characteristic at 401.7 eV, which suggested a successful grafting of PEI onto the CS/PCL membrane. According to the EDX analysis, a significant amount of copper ions was detected in PEI-CS/PCL membranes. This study showed that a greener wastewater treatment can be realized with the developed plasma synthesis technology.