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1
Chen, Mao, Honghong Gong i Yu Gu. "Controlled/Living Radical Polymerization of Semifluorinated (Meth)acrylates". Synlett 29, nr 12 (18.04.2018): 1543–51. http://dx.doi.org/10.1055/s-0036-1591974.
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Fluorinated polymers are important materials for applications in many areas. This article summarizes the development of controlled/living radical polymerization (CRP) of semifluorinated (meth)acrylates, and briefly introduces their reaction mechanisms. While the classical CRP such as atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization and nitroxide-mediated radical polymerization (NMP) have promoted the preparation of semifluorinated polymers with tailor-designed architectures, recent development of photo-CRP has led to unprecedented accuracy and monomer scope. We expect that synthetic advances will facilitate the engineering of advanced fluorinated materials with unique properties.1 Introduction2 Atom Transfer Radical Polymerization3 Reversible Addition-Fragmentation Chain Transfer Polymerization4 Nitroxide-Mediated Radical Polymerization5 Photo-CRP Mediated with Metal Complexes6 Metal-free Photo-CRP7 Conclusion
2
Ma, Jiashu, Jiahao Li, Bingbing Yang, Siwen Liu, Bang-Ping Jiang, Shichen Ji i Xing-Can Shen. "A Simple Stochastic Reaction Model for Heterogeneous Polymerizations". Polymers 14, nr 16 (11.08.2022): 3269. http://dx.doi.org/10.3390/polym14163269.
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The stochastic reaction model (SRM) treats polymerization as a pure probability‐based issue, which is widely applied to simulate various polymerization processes. However, in many studies, active centers were assumed to react with the same probability, which cannot reflect the heterogeneous reaction microenvironment in heterogeneous polymerizations. Recently, we have proposed a simple SRM, in which the reaction probability of an active center is directly determined by the local reaction microenvironment. In this paper, we compared this simple SRM with other SRMs by examining living polymerizations with randomly dispersed and spatially localized initiators. The results confirmed that the reaction microenvironment plays an important role in heterogeneous polymerizations. This simple SRM provides a good choice to simulate various polymerizations.
3
Wen, Shao Guo, Shi Gao Song, Hong Bo Liu, Ji Hu Wang, Qian Xu i Yan Shen. "Application of a Novel Initiator on Acrylic Emulsion Polymerization". Advanced Materials Research 233-235 (maj 2011): 1415–18. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.1415.
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New initiator of FFM6 is used to initiate the acrylic emulsion polymerization. The influences of concentration of FFM6 (c[I]) and polymerization temperature (T) on polymerization reaction rate (Rp) were discussed. Rp is proportional to (c[I])1.4 which is different with classical emulsion polymerization whose Rp is proportion to (c[I])0.4, that indicate polymerization mechanism of the reaction in the study is different with classical mechanism. The value of Ea, 56.4 kJ/mol, is lower than the value of general radical polymerization’s Ea (80.0-96.0 kJ/mol), which indicates the FFM6 can initiate acrylic emulsion polymerization at a lower temperature compared with the other kinds of initiator.
4
Nestorovic, Gordana, Katarina Jeremic i Slobodan Jovanovic. "Kinetics of aniline polymerization initiated with iron(III) chloride". Journal of the Serbian Chemical Society 71, nr 8-9 (2006): 895–904. http://dx.doi.org/10.2298/jsc0609895n.
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The reaction kinetics of the chemical polymerization of aniline in aqueous acid solutions with FeCl3 as the oxidant (initiator) was investigated at 25?C. The polymerization was performed in a special reactor which enabled the initial concentration of oxidant to be kept constant during the polymerization reaction. The order of the reaction of ANI polymerization with respect to FeCl3 was calculated as n=0.18. The rate constant k of the polymerization reaction was found to be 9.1x10-5(mol dm-3)-1,18 s-1. The theoretical yield of the reaction was calculated using the Faraday law and the experimentally determined quantity of electricity exchanged during the polymerization reaction. There was a discrepancy between the experimentally and theoretically determined yield, indicating that the oxidant was being consumed in some side reactions, which is an accordance with the fact that the order of the reaction of ANI polymerization with respect to FeCl3 is a non-integer number.
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Li, Hua-Rong, Liming Che i Zheng-Hong Luo. "Modeling intraparticle transports during propylene polymerizations using supported metallocene and dual function metallocene as catalysts: Single particle model". Chemical Industry and Chemical Engineering Quarterly 20, nr 2 (2014): 249–60. http://dx.doi.org/10.2298/ciceq120722006l.
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Two improved multigrain models (MGMs) for preparing homopolypropylene and long chain branched polypropylene via propylene polymerization using silica-supported metallocene or dual function metallocene as catalysts are presented in this paper. The presented models are used to predict the intraparticle flow fields involved in the polymerizations. The simulation results show that the flow field distributions involve dare basically identical. The results also show that both the two polymerization processes have an initiation stage and the controlling step for them is reaction-diffusion-reaction with the polymerization proceeding. Furthermore, the simulation results show that the intra particle mass transfer resistance has significant effect on the polymerization but the heat transfer resistance can be ignored.
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Yang, D. Billy. "Direct Kinetic Measurements of Vinyl Polymerization on Metal and Silicon Surfaces Using Real-Time FT-IR Spectroscopy". Applied Spectroscopy 47, nr 9 (wrzesień 1993): 1425–29. http://dx.doi.org/10.1366/0003702934067739.
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A real-time FT-IR (RT/FT-IR) technique has been used to perform direct kinetic measurements of vinyl polymerization on metal and silicon surfaces. Here, we are reporting our results in studies of anaerobic and photo-induced anionic polymerizations of monomers containing vinyl functional groups (>C=C<) for adhesive and coating applications. For anaerobic polymerization we are investigating the hydroperoxide-initiated free radical polymerization of model multifunctional methacrylate monomer systems. We will report the results of our studies on the catalytic effects of different dithiolate complexes and related accelerators. In photo-induced anionic polymerization we will report our studies for ethyl cyanoacrylate (CA) polymerization initiated by a controlled release of anion from a stable chromium complex precursor ( trans-Cr-(NH3)2(NCS)4−K+). Because of high surface sensitivity of the CA monomer, the polymerization kinetic studies were performed on a clean silicon surface at room temperature. The effect of the initiator concentration and irradiation wavelengths on polymerization kinetic rate will be discussed. The acrylic polymerization was monitored with the use of the C=C stretching band at 1634 and 1627 cm−1 for polyglycol dimethacrylate and cyanoacrylate, respectively. Both the degree of polymerization and the intrinsic rates of the polymerization reactions were calculated for kinetic comparisons. For anaerobic polymerization studies, GC/FT-IR software was used which provided a real-time screen display of IR spectral changes as the reaction proceeded. For very fast cyanoacrylate anionic polymerization studies, new FT-IR kinetic software was used to collect 204 spectra per minute with one spectrum per scan. In this case, the interferograms were collected first; post-Fourier transform conversion and spectral script reduction were then performed. Some detailed experimental techniques and polymerization reaction mechanisms will also be discussed.
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Wang, Yu, Mary Nguyen i Amanda J. Gildersleeve. "Macromolecular Engineering by Applying Concurrent Reactions with ATRP". Polymers 12, nr 8 (29.07.2020): 1706. http://dx.doi.org/10.3390/polym12081706.
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Modern polymeric material design often involves precise tailoring of molecular/supramolecular structures which is also called macromolecular engineering. The available tools for molecular structure tailoring are controlled/living polymerization methods, click chemistry, supramolecular polymerization, self-assembly, among others. When polymeric materials with complex molecular architectures are targeted, it usually takes several steps of reactions to obtain the aimed product. Concurrent polymerization methods, i.e., two or more reaction mechanisms, steps, or procedures take place simultaneously instead of sequentially, can significantly reduce the complexity of the reaction procedure or provide special molecular architectures that would be otherwise very difficult to synthesize. Atom transfer radical polymerization, ATRP, has been widely applied in concurrent polymerization reactions and resulted in improved efficiency in macromolecular engineering. This perspective summarizes reported studies employing concurrent polymerization methods with ATRP as one of the reaction components and highlights future research directions in this area.
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Monteiro, M. J., R. Bussels, S. Beuermann i M. Buback. "High Pressure 'Living' Free-Radical Polymerization of Styrene in the Presence of RAFT". Australian Journal of Chemistry 55, nr 7 (2002): 433. http://dx.doi.org/10.1071/ch02079.
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Reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene was studied at high pressure, employing two dithioester RAFT agents with an isopropylcyano (5) and a cumyl (6) leaving group, respectively. The high-pressure reaction resulted in low polydispersity polymer. It was found that controlled polymerizations can be performed at increased pressures with a high degree of monomer conversion, which signifies that high-pressure polymerizations can be utilized for the production of higher molecular weight polystyrene of controlled microstructure. Retardation of styrene polymerization was also observed at high pressure in the presence of RAFT agents (5) and (6). It is postulated that the retarding potential of these two RAFT agents is associated with an intermediate radical termination mechanism. High-pressure free-radical polymerizations open the way to producing living polymers with high rates, and thus lower impurities such as 'dead' polymer that are formed through bimolecular termination reactions.
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HU, ZHIGANG, i DAN ZHAO. "POLYMERIZATION WITHIN CONFINED NANOCHANNELS OF POROUS METAL-ORGANIC FRAMEWORKS". Journal of Molecular and Engineering Materials 01, nr 02 (czerwiec 2013): 1330001. http://dx.doi.org/10.1142/s2251237313300015.
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Metal-organic frameworks (MOFs) have been increasingly investigated as templates for precise control of polymerization. Polymerizations within confined nanochannels of porous MOFs have shown unique confinement and alignment effect on polymer chain structures and thus are promising ways to achieve well-defined polymers. Herein, this review will focus on illustrating the recent progress of polymerization within confined nanochannels of MOFs, including radical polymerization, coordination polymerization, ring-opening polymerization, catalytic polymerization, etc. It will demonstrate how the heterogeneous MOF structures (pore size, pore shapes, flexible structures, and versatile functional groups) affect the polymeric products' molecular weight, molecular weight distribution, tacticity, reaction sites, copolymer sequence, etc. Meanwhile, we will highlight some challenges and foreseeable prospects on these novel polymerization methods.
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Forte, Leonard, Min H. Lien, Alan C. Hopkinson i Diethard K. Bohme. "Carbocationic polymerization in the gas phase: polymerization of acetylene induced by BF2+". Canadian Journal of Chemistry 68, nr 9 (1.09.1990): 1629–35. http://dx.doi.org/10.1139/v90-252.
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Gas-phase measurements for the primary reaction of BF2+ with acetylene and the ensuing higher-order reactions with acetylene have been performed at 296 ± 2 K in helium at 0.35 torr using the Selected-Ion Flow Tube (SIFT) technique. The primary reaction was observed to be rapid and to produce two species which both initiated rapid polymerization of acetylene. The major primary product, C2HBF+, was observed to initiate the sequential addition of four molecules of acetylene, most likely by termolecular association reactions. The first few steps in this polymerization were also followed using abinitio molecular orbital theory. The calculations and measurements provide structural, energetic, and kinetic information and, in combination, reveal several intrinsic features of the initial steps of the cationic polymerization of acetylene initiated by BF2+. Keywords: polymerization, acetylene, aromaticity.
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Korkut, Ibrahim, Fuat Erden i Salih Ozbay. "Cost-Effective Control of Molecular Weight in Ultrasound-Assisted Emulsion Polymerization of Styrene". Acta Chimica Slovenica 69, nr 4 (15.12.2022): 884–95. http://dx.doi.org/10.17344/acsi.2022.7655.
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This paper focuses on the determination of economically most feasible conditions to obtain polystyrene with various target molecular weights through ultrasound-assisted emulsion polymerization. Briefly, batch polymerizations of styrene have been performed by ultrasound-assisted emulsion polymerization process using different reaction feed compositions. Polymerization rates were calculated using the monomer conversions at various reaction times. Also, molecular weights of the synthesized polymers, as well as the Mark-Houwink constants, were determined by intrinsic viscosity and gel permeation chromatography measurements. It was found that the polydispersity index of the polymers is ranging from 1.2 to 1.5, and the viscosity average molecular weights are in between 100000–1500000 g/mol depending on the reaction conditions. Finally, model equations were also developed for response variables, and the most economical ways of reaching various target molecular weights were interpreted by response surface methodology based multi objective optimization.
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Banetta, Luca, Giuseppe Storti, George Hoggard, Gareth Simpson i Alessio Zaccone. "Predictive model of polymer reaction kinetics and coagulation behavior in seeded emulsion co- and ter-polymerizations". Polymer Chemistry 11, nr 41 (2020): 6599–615. http://dx.doi.org/10.1039/d0py01138j.
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Webb, Don W., i William Bard. "Control of polymerization reaction". Nuclear and Chemical Waste Management 8, nr 4 (styczeń 1988): x. http://dx.doi.org/10.1016/0191-815x(88)90064-2.
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Weinberger, Simone, Alessandro Pellis, James Comerford, Thomas Farmer i Georg Guebitz. "Efficient Physisorption of Candida Antarctica Lipase B on Polypropylene Beads and Application for Polyester Synthesis". Catalysts 8, nr 9 (31.08.2018): 369. http://dx.doi.org/10.3390/catal8090369.
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In the present work, Candida antarctica lipase B (CaLB) was adsorbed onto polypropylene beads using different reaction conditions, in order to investigate their influence on the immobilization process and the enzyme activity of the preparations in polymerization reactions. In general, lower salt concentrations were more favorable for the binding of enzyme to the carrier. Polymerisation of dimethyl adipate (DMA) and 1,4-butanediol (BDO) was investigated in thin-film systems at 70 °C and at both atmosphere pressure (1000 mbar) and 70 mbar. Conversion rates and molecular masses of the reaction products were compared with reactions catalyzed by CaLB in its commercially available form, known as Novozym 435 (CaLB immobilized on macroporous acrylic resin). The best results according to molecular weight and monomer conversion after 24 h reaction time were obtained with CaLB immobilized in 0.1 M Na2HPO4\NaH2PO4 buffer at pH 8, producing polyesters with 4 kDa at conversion rates of 96% under low pressure conditions. The stability of this preparation was studied in a simulated continuous polymerization process at 70 °C, 70 mbar for 4 h reaction time. The data of this continuous polymerizations show that the preparation produces lower molecular weights at lower conversion rates, but is comparable to the commercial enzyme concerning stability for 10 cycles. However, after 24 h reaction time, using our optimum preparation, higher molecular weight polyesters (4 kDa versus 3.1 kDa) were obtained when compared to Novozym 435.
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Zhu, Ning, Zilong Zhang, Weiyang Feng, Yuqiang Zeng, Zhongyue Li, Zheng Fang, Kai Zhang, Zhenjiang Li i Kai Guo. "Sn(OTf)2 catalyzed continuous flow ring-opening polymerization of ε-caprolactone". RSC Advances 5, nr 40 (2015): 31554–57. http://dx.doi.org/10.1039/c5ra02583d.
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A simple PTFE tubular microreactor based platform was successfully developed to conduct Sn(OTf)2 catalyzed ε-caprolactone polymerization with better control of reaction conditions, faster polymerizations and narrower molecular weight distributions.
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Ramírez, Jesús Miguel Contreras, Dimas Medina, Francisco López-Carrasquero i Ricardo Rafael Contreras. "Ring-Opening Polymerization of L-lactide Initiated by Samarium(III) Acetate". Current Applied Polymer Science 3, nr 2 (10.10.2019): 112–19. http://dx.doi.org/10.2174/2452271602666181114094536.
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Background: The synthesis of the aliphatic polyesters obtained by the ring opening polymerization has been achieved using as initiators a large amount of organometallic compounds derivative from: Alkali metals, alkaline earth metals, transition metals and lanthanide metals. Of all these compounds, the lanthanide derivatives have acquired great importance in the synthesis of aliphatic polyesters, since these show a greater catalytic activity and also can provide polymer with characteristics that will be very useful in the design of biomaterials. Objective: It was proposed the synthesis of poly(L-lactida) (PL-LA) through a ring opening polymerization process of L-lactide initiated with samarium(III) acetate (Sm(OAc)3) under solvent-free melt conditions. The influence of different parameters of reaction, such as temperature, time, molar ratio monomer to initiator, on typical variables of polymers, e.g., conversion, dispersity, and molar mass, were analyzed. Methods: All polymerizations were carried out under solvent-free melt conditions in ampoules-like flasks, equipped with a magnetic stirrer. The obtained polyesters were characterized by size exclusion chromatography (SEC) and 1H-NMR. Results: The Sm(OAc)3 induces the polymerization of L-LA at high conversion, and produce polyesters with number-average molecular weights of 1.00 x 103 to 30.00 x 103 Dalton. The 1H-NMR analysis indicates a typical polymerization mechanism of coordination-insertion, with a breakdown of the acyl-oxygen bond of the L-LA. Conclusion: Sm(OAc)3 was an effective initiator for the ring-opening polymerization of L-LA. SEC chromatography showed that, at high temperatures and prolonged reaction times, the molar mass of the polyester decreases, which is associated with the transesterification collateral reactions that occur during the polymerization process.
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Su, Jing, Euijin Shim, Jennifer Noro, Jiajia Fu, Qiang Wang, Hye Kim, Carla Silva i Artur Cavaco-Paulo. "Conductive Cotton by In Situ Laccase-Polymerization of Aniline". Polymers 10, nr 9 (14.09.2018): 1023. http://dx.doi.org/10.3390/polym10091023.
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Conductive cotton fabrics were obtained via in situ aniline polymerization by laccase from Myceliophthora thermophila under mild reaction conditions without the addition of strong proton acids. The reactions were conducted using two types of reactors, namely a water bath (WB) and an ultrasonic bath (US), and the role of a mediator, 1-hydroxybenzotriazol (HBT), on the laccase-assisted polymerization of aniline was investigated. A similar polymerization degree was obtained when using both reactors—however, the ultrasonic bath allowed the experiments to be conducted in shorter periods of time (24 h for WB vs. 2 h for US). The data obtained also revealed that the mediator (1-hydroxybenzotriazol-HBT) played a crucial role in aniline oxidation. A higher conversion yield and polymerization degree were obtained when the reaction was conducted in the presence of this compound, as confirmed by MALDI-TOF analysis. The cotton fabrics coated with polyaniline presented deep coloration and conductivity, especially when the mediator was included on the reactional system. The results obtained are a step forward in the enzymatic polymerization of aniline with the purpose of obtaining coloured conductive textile surfaces, with potential applications in wearable electronics.
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Reyhani, Amin, Thomas G. McKenzie, Qiang Fu i Greg G. Qiao. "Redox-Initiated Reversible Addition–Fragmentation Chain Transfer (RAFT) Polymerization". Australian Journal of Chemistry 72, nr 7 (2019): 479. http://dx.doi.org/10.1071/ch19109.
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Reversible addition–fragmentation chain transfer (RAFT) polymerization initiated by a radical-forming redox reaction between a reducing and an oxidizing agent (i.e. ‘redox RAFT’) represents a simple, versatile, and highly useful platform for controlled polymer synthesis. Herein, the potency of a wide range of redox initiation systems including enzyme-mediated redox reactions, the Fenton reaction, peroxide-based reactions, and metal-catalyzed redox reactions, and their application in initiating RAFT polymerization, are reviewed. These redox-RAFT polymerization methods have been widely studied for synthesizing a broad range of homo- and co-polymers with tailored molecular weights, compositions, and (macro)molecular structures. It has been demonstrated that redox-RAFT polymerization holds particular promise due to its excellent performance under mild conditions, typically operating at room temperature. Redox-RAFT polymerization is therefore an important and core part of the RAFT methodology handbook and may be of particular importance going forward for the fabrication of polymeric biomaterials under biologically relevant conditions or in biological systems, in which naturally occurring redox reactions are prevalent.
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Sarker, P., J. R. Ebdon, S. Rimmer, M. A. J. Miah i H. Ahmad. "Synthesis Kinetics of Polymer / Copolymer Latexes via Radical Ring-Opening Emulsion Polymerization of Vinylcyclopropane". Journal of Scientific Research 8, nr 3 (1.09.2016): 463–72. http://dx.doi.org/10.3329/jsr.v8i3.28183.
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Radical emulsion polymerization of 1,1-bis(ethoxycarbonyl)-2-vinylcyclopropane (ECVCP) was examined in the presence of potassium persulfate (KPS) as an initiator. ECVCP underwent both emulsifier-in emulsion and emulsifier-free emulsion polymerizations to afford the ring-opened polymer in good yields. The copolymerization efficiency of this monomer was also evaluated with methyl methacrylate (MMA) and butyl methacrylate (BMA) as comonomers under the same reaction conditions. The emulsion copolymerization of ECVCP with a relatively hydrophobic monomer, lauryl methacrylate (LMA) was also investigated in presence of ?-cyclodextrin hydrate (?-CD) as a phase transfer agent. Polymerization/copolymerization kinetics, change in particle size and olefin contents were followed during the reaction.
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Wibowo, Heri Budi, Widhi Cahya Dharmawan, Ratih Sanggra Murti Wibowo i Adi Yulianto. "Kinetic study of HTPB (Hydroxyl Terminated Polybutadiene) Synthesis Using Infrared Spectroscopy". Indonesian Journal of Chemistry 20, nr 4 (10.06.2020): 919. http://dx.doi.org/10.22146/ijc.49863.
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A kinetic study of HTPB synthesis by radical polymerization of butadiene with hydrogen peroxide initiator was conducted using infrared spectroscopy. HTPB conversion was determined based on the conjunction termination rate constant, and all polymerization kinetics were evaluated to identify the constant. All polymerization steps (decomposition, initiation, propagation, conjunction, and proportional termination) can be evaluated based on polymer conversion and functionality from data provided by infrared spectroscopy. The investigation variables included the initial molar ratio of initiator to monomer (H2O2/butadiene) and the reaction temperature. These steps were assumed as the first-order reactions, giving constant reaction rates of kd, ka, kp, kt, ktc, and ktd. The reaction rates obtained for these constants were 4.2 × 10–5 sec–1, 8.9 × 10–4, 7.7 × 103, 8.5 × 107, 3.2 × 107 and 5.3 × 107 L mol–1 sec–1, respectively, with activation energy of 7608, 14188, 2247, 105, 87 and 135 kJ mol–1, respectively. The determining step of the reaction rate was identified as the initiation reaction. HTPB conversion can be measured if all polymerization kinetics constants have been evaluated.
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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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Wang, Chao, Thomas J. Vickers i Charles K. Mann. "Use of Water as an Internal Standard in the Direct Monitoring of Emulsion Polymerization by Fiber-Optic Raman Spectroscopy". Applied Spectroscopy 47, nr 7 (lipiec 1993): 928–32. http://dx.doi.org/10.1366/0003702934415183.
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Direct analysis of the organic phase of an emulsion polymerization is described. Quantification uses the bending mode peak of water, which makes up the bulk of the reaction medium, as an internal standard. Although demonstrated with methyl methacrylate, the process is generally applicable to emulsion polymerizations. It does not require the introduction of an extraneous internal standard component into the reaction mixture.
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Li, Fang, Jingqin Xu, Yajie Wang, Haiyan Zheng i Kuo Li. "Pressure-Induced Polymerization: Addition and Condensation Reactions". Molecules 26, nr 24 (14.12.2021): 7581. http://dx.doi.org/10.3390/molecules26247581.
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Under pressure of 1–100 GPa, unsaturated organic molecules tend to form covalent bond to each other for a negative enthalpy change, which often produces polymeric materials with extended carbon skeleton. The polymerization reactions typically happen in crystal, which promotes the topochemical process. This review summarized the topochemical polymerization processes of several alkynes, aromatics, and alkynylphenyl compounds, including the critical crystal structures before the reaction, bonding process, and the structure of the products. Secondly, this review also summarized the condensation reaction identified in the polymerization process, including the elimination of small molecules such as NH3, etc.
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Quirk, Roderic P., Jian Yin, Shao-Hua Guo, Xiao-Wei Hu, Gabriel J. Summers, Jungahn Kim, Lin-Fang Zhu, Jing-Jing Ma, Toshiki Takizawa i Thomas Lynch. "Recent Advances in Anionic Synthesis of Functionalized Polymers". Rubber Chemistry and Technology 64, nr 4 (1.09.1991): 648–60. http://dx.doi.org/10.5254/1.3538580.
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Abstract There has been growing interest and research on new synthetic methods for the preparation of well-defined polymers with in-chain and chain-end functional groups. These functional groups in polymers can participate in (a) reversible ionic association; (b) chain extension, branching or crosslinking reactions with polyfunctional reagents; (c) coupling and linking with reactive groups on other oligomer or polymer chains; and (d) initiation of polymerization of other monomers. It is noteworthy that the use of end-functionalized polybutadienes formed by reaction of poly(butadienyl)lithium with 4,4′-bis(diethylamino)-benzophenone has been reported to provide marked improvements in the wear and traction properties of tires. In order to exploit the unique potential of functionalized polymers, it is important to consider the scope and limitations of current functionalization methodology using anionic polymerization. Anionic polymerization approaches the goal of synthesizing polymers with predictable, well-defined structures in certain systems such as diene, styrene, methacrylate, and heterocyclic monomers, which proceed in the absence of chain termination and chain transfer reactions. These living polymerizations generate stable, anionic polymer chain ends when all of the monomer has been consumed. In principle, these anionic chain ends can react with a variety of electrophilic species to generate a diverse array of functional groups. Unfortunately, many of the reported functionalization reactions have not been well characterized. Another limitation of the use of specific electrophilic functionalization reactions is the necessity of developing, optimizing, and characterizing new procedures for each different functional group. Variables such as chain-end structure, solvent, temperature, concentration, stoichiometry, mode of addition of reagents, and polar additives can have dramatic effects on yield and product distributions. This review will first provide a critical overview of some recent developments in the use of specific functionalization reactions to prepare polymers labeled with carboxyl, hydroxyl, amino, and sulfonate end groups via alkyllithium-initiated polymerization methods. In addition, a recently developed methodology will be described which utilizes the addition reactions of organolithium compounds to substituted 1,1-diphenylethylenes as a general, quantitative functionalization reaction, independent of the specific functional group.
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Maafa, Ibrahim M. "Inhibition of Free Radical Polymerization: A Review". Polymers 15, nr 3 (17.01.2023): 488. http://dx.doi.org/10.3390/polym15030488.
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Polymerization reactions have caused several severe accidents in the past since they are prone to runaways due to their highly exothermic and auto-accelerating nature. The heat generated during these uncontrolled runaway reactions surpasses the heat removal capacity of the cooling system leading to the auto-acceleration of the reactions. If proper measures are not taken to attenuate this auto-accelerative nature, dangerous consequences ensue, such as rampant boiling of the reaction system fluids or vapor production from secondary reactions. Both these consequences may eventually lead to over-pressurization followed by a thermal explosion. Thus, to eliminate the associated risk, polymerization reactions in industries are carried out in the presence of inhibitors which are injected into the reaction system before the initiation of polymerization. In this review, I have summarized various accidents that have happened in the past due to runaway polymerization implicating that there is an urgent necessity to do further research in this relatively less explored field of polymerization inhibition. To this end, I have completed an exhaustive survey of the various types of inhibitors used in industries and their inhibition mechanisms focusing mainly on the auto-initiated polymerization of styrene, methyl methacrylate, and acrylic acid monomer. Lastly, the synergism in the inhibition performance of a mixture of two types of inhibitors was also compared and discussed in detail.
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Johnson, CHJ, G. Moad, DH Solomon, TH Spurling i DJ Vearing. "The Application of Supercomputers in Modeling Chemical Reaction Kinetics: Kinetic Simulation of 'Quasi-Living' Radical Polymerization". Australian Journal of Chemistry 43, nr 7 (1990): 1215. http://dx.doi.org/10.1071/ch9901215.
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A computer program has been written which employs an implicit Euler method to solve directly the complete set of coupled differential equations which result from an analysis of polymerization kinetics. The program was written to make full use of the speed and power of modern supercomputers, and is suited to the solution of very large stiff systems of differential equations. The benefit of treating each propagation step as a discrete reaction is that information on the evolution of the molecular weight distribution is obtained directly without the need to make perhaps unjustified assumptions such as the steady-state approximation. For illustrative purposes, the method has been applied in the kinetic simulation of 'quasi-living' radical polymerization to assess the effect of experimental variables on the molecular weight, molecular weight distribution, and rate of polymerization. The calculations show that 'quasi-living' radical polymerization can produce polymers with polydispersities approaching those obtained with anionic 'living' polymerizations. Some necessary conditions for the formation of polymers with narrow molecular weight distribution are defined.
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Yilmaz, Gorkem. "One-Pot Synthesis of Star Copolymers by the Combination of Metal-Free ATRP and ROP Processes". Polymers 11, nr 10 (27.09.2019): 1577. http://dx.doi.org/10.3390/polym11101577.
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A completely metal-free strategy is demonstrated for the preparation of star copolymers by combining atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP) for the syntheses of block copolymers. These two different metal-free controlled/living polymerizations are simultaneously realized in one reaction medium in an orthogonal manner. For this purpose, a specific core with functional groups capable of initiating both polymerization types is synthesized. Next, vinyl and lactone monomers are simultaneously polymerized under visible light irradiation using specific catalysts. Spectral and chromatographic evidence demonstrates the success of the strategy as star copolymers are synthesized with controlled molecular weights and narrow distributions.
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Esen, C., T. Kaiser i G. Schweiger. "Raman Investigation of Photopolymerization Reactions of Single Optically Levitated Microparticles". Applied Spectroscopy 50, nr 7 (lipiec 1996): 823–28. http://dx.doi.org/10.1366/0003702963905501.
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Raman spectroscopy was used to investigate polymerization reactions in a single micrometer-sized monomer droplet. An Ar+ laser levitated the microparticles and simultaneously excited the Raman scattering. The polymerization reaction was initiated by exposing the monomer droplets to the UV radiation of a mercury arc excitation lamp. The Raman spectrum of the reacting particle was investigated on-line. The results demonstrate that the combination of the technique of optical levitation and Raman spectroscopy allows nondestructive in situ measurements of single particles and is therefore very useful for the study of fundamental processes.
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LEE, J. C. "POLYMERIZATION-INDUCED PHASE SEPARATION: INTERMEDIATE DYNAMICS". International Journal of Modern Physics C 11, nr 02 (marzec 2000): 347–58. http://dx.doi.org/10.1142/s0129183100000328.
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When phase separation is induced by polymerizating monomers in a mixture of monomers and nonreacting molecules, the dynamics is different depending on the time scale of polymerization τpl and the time scale of phase separation τps. Previous studies have explored the dynamic regimes where τpl ≪ τps and that where τpl ≫ τps. In the former, a spanning gel emerges before the phase separation and the phase separation is driven largely by activation. In the latter, phase separation occurs first between polymers and nonbonding molecules and then the polymers turn into a gel, and therefore the driving mechanism is the same as in the usual liquid–liquid demixing processes. Using Molecular Dynamics simulations, we explore in this paper the intermediate dynamic regime where the two time scales are comparable. When the polymerization is done by means of the thermal condensation reaction, we observe the expected crossover, one limit behavior at early times and then the other at late times. When the polymerization is done by means of the radical addition reaction, the results suggest that the driving mechanism changes more than once.
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Zhang, Jinghan, Yibo Wu, Kaixuan Chen, Min Zhang, Liangfa Gong, Dan Yang, Shuxin Li i Wenli Guo. "Characteristics and Mechanism of Vinyl Ether Cationic Polymerization in Aqueous Media Initiated by Alcohol/B(C6F5)3/Et2O". Polymers 11, nr 3 (14.03.2019): 500. http://dx.doi.org/10.3390/polym11030500.
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Aqueous cationic polymerizations of vinyl ethers (isobutyl vinyl ether (IBVE), 2-chloroethyl vinyl ether (CEVE), and n-butyl vinyl ether (n-BVE)) were performed for the first time by a CumOH/B(C6F5)3/Et2O initiating system in an air atmosphere. The polymerization proceeded in a reproducible manner through the careful design of experimental conditions (adding initiator, co-solvents, and surfactant or decreasing the reaction temperature), and the polymerization characteristics were systematically tested and compared in the suspension and emulsion. The significant difference with traditional cationic polymerization is that the polymerization rate in aqueous media using B(C6F5)3/Et2O as a co-initiator decreases when the temperature is lowered. The polymerization sites are located on the monomer/water surface. Density functional theory (DFT) was applied to investigate the competition between H2O and alcohol combined with B(C6F5)3 for providing a theoretical basis. The effectiveness of the proposed mechanism for the aqueous cationic polymerization of vinyl ethers using CumOH/B(C6F5)3/Et2O was confirmed.
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Satoh, Masaharu, i Etsuo Hasegawa. "Reaction Mechanism of Electrochemical Polymerization." Kobunshi 41, nr 8 (1992): 602–5. http://dx.doi.org/10.1295/kobunshi.41.602.
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Hamielec, Archie E., i Joao B. P. Soares. "Polymerization reaction engineering — Metallocene catalysts". Progress in Polymer Science 21, nr 4 (styczeń 1996): 651–706. http://dx.doi.org/10.1016/0079-6700(96)00001-9.
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Zecchina, Adriano, i Elena Groppo. "Surface chromium single sites: open problems and recent advances". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 468, nr 2143 (21.03.2012): 2087–98. http://dx.doi.org/10.1098/rspa.2012.0101.
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The results of decades of studies on the Phillips chromium (Cr)/silica polymerization catalyst are briefly summarized. The application of several characterization methods has allowed a detailed knowledge of the structure and reactivity of Cr centres to be obtained. In particular, many aspects of this apparently simple single-site catalyst, including the heterogeneity, the modification of the ligand sphere upon interaction with many molecules and the initiation mechanism of the ethylene polymerization reaction, have been clarified. It is shown that based on the acquired knowledge, it is now possible to proceed further towards the intelligent modification of the ligand sphere with the scope to increase the reaction rate and selectivity. It is also illustrated that, besides polymerization/oligomerization reactions, it is possible to extend the study of Cr II reactivity towards new reactions.
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Duty, Ryan, i Christopher E. Hobbs. "Post-Polymerization Modification of Ring Opening Metathesis Polymerization (ROMP)-Derived Materials Using Wittig Reactions". Polymers 12, nr 6 (29.05.2020): 1247. http://dx.doi.org/10.3390/polym12061247.
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This communication describes our recent efforts to utilize Wittig olefination reactions for the post-polymerization modification of polynorbornene derivatives prepared through ring opening metathesis polymerization (ROMP). Polymerizing α-bromo ester-containing norbornenes provides polymers that can undergo facile substitution with triphenylphosphine. The resulting polymeric phosphonium salt is then deprotonated to form an ylide that undergoes reaction with various aryl aldehydes in a one-pot fashion to yield the respective cinnamates. These materials can undergo further modification through photo-induced [2 + 2] cycloaddition cross-linking reactions.
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Issa, Ahmed, i Adriaan Luyt. "Kinetics of Alkoxysilanes and Organoalkoxysilanes Polymerization: A Review". Polymers 11, nr 3 (21.03.2019): 537. http://dx.doi.org/10.3390/polym11030537.
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Scientists from various different fields use organo-trialkoxysilanes and tetraalkoxysilanes in a number of applications. The silica-based materials are sometimes synthesized without a good understanding of the underlying reaction kinetics. This literature review attempts to be a comprehensive and more technical article in which the kinetics of alkoxysilanes polymerization are discussed. The kinetics of polymerization are controlled by primary factors, such as catalysts, water/silane ratio, pH, and organo-functional groups, while secondary factors, such as temperature, solvent, ionic strength, leaving group, and silane concentration, also have an influence on the reaction rates. Experiments to find correlations between these factors and reaction rates are restricted to certain conditions and most of them disregard the properties of the solvent. In this review, polymerization kinetics are discussed in the first two sections, with the first section covering early stage reactions when the reaction medium is homogenous, and the second section covering when phase separation occurs and the reaction medium becomes heterogeneous. Nuclear magnetic resonance (NMR) spectroscopy and other techniques are discussed in the third section. The last section summarizes the study of reaction mechanisms by using ab initio and Density Functional Theory (DFT) methods alone, and in combination with molecular dynamics (MD) or Monte Carlo (MC) methods.
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Monroy, V. M., G. Guevara, I. Leon, A. Correa i R. Herrera. "In-situ Titration of Initiator-Consuming Impurities in Solution Anionic Polymerization". Rubber Chemistry and Technology 66, nr 4 (1.09.1993): 588–93. http://dx.doi.org/10.5254/1.3538331.
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Abstract An in situ titration of initiator-consuming impurities in amonic polymerizations, using 1,10-phenantroline as an indicator, was developed. The results show that even when impurities are present, it is possible to destroy them prior to the initiation of the polymerization reaction and achieve a better control of molecular weights by adding accurate known quantities of initiator.
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Satti, Angel J., Augusto G. O. de Freitas, M. Loreta Sena Marani, Marcelo A. Villar, Enrique M. Vallés, Cristiano Giacomelli i Andrés E. Ciolino. "Anionic Ring Opening Polymerization of ε-Caprolactone Initiated by Lithium Silanolates". Australian Journal of Chemistry 70, nr 1 (2017): 106. http://dx.doi.org/10.1071/ch16270.
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Ring-opening homo- and co-polymerization reactions of ϵ-caprolactone were performed by employing anionic polymerization (high vacuum techniques) and lithium silanolates (LS) as initiators. LS were obtained by reaction between hexamethyl(cyclotrisiloxane) and sec-Bu–Li+, or from living poly(dimethylsiloxanyl)lithium chains. The results indicated that LS are efficient initiators for the ring-opening polymerization of ϵ-caprolactone, providing the respective homogeneous polymers in good yields.
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Ren, Kewei, i Yunting Tsai. "Thermal Hazard Characteristics of Unsaturated Polyester Resin Mixed with Hardeners". Polymers 13, nr 4 (10.02.2021): 522. http://dx.doi.org/10.3390/polym13040522.
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Unsaturated polyester resin (UP) is a critical polymer material in applications of many fields, such as the chemical industry, military, and architecture. For improving the mechanical properties, some hardeners, such as methyl ethyl ketone peroxide (MEKPO) or tert-butyl peroxy-2-ethylhexanoate (TBPO), can trigger the curing reaction in UP polymerization, which causes that UP changes the structure from monomer to polymer. However, polymerization is a strong exothermic reaction, which can increase the risk of thermal runaway reaction in UP. Therefore, the mechanisms and characteristics in the thermal runaway reaction of UP mixed with hardeners should be studied for preventing and controlling UP explosion. The thermal hazards of UP mixed with hardeners were determined by thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC) analysis. According to the results, UP mixed with MEKPO exhibited a more violent mass loss and exothermic reaction than UP mixed with TBPO. Furthermore, the thermal runaway reactions of UP mixed with MEKPO or TBPO with different mixing proportions of 1:1, 3:1, and 5:1 were determined. Irrespective of MEKPO or TBPO, the mixing proportions of 3:1 exhibited a high onset temperature and low enthalpy of curing reaction (ΔHexo). This demonstrated that this proportion was safer during UP polymerization. The results of this study can provide useful information for preventing UP explosion and developing polymerization technology.
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Malkanduev, Yusuf A., Aneta A. Kokoeva i Аblulakhat T. Dzhalilov. "Peculiar Properties of Spontaneous Methacrylate Derivatives Polymerization with Haloidallyl Compounds". Key Engineering Materials 899 (8.09.2021): 262–68. http://dx.doi.org/10.4028/www.scientific.net/kem.899.262.
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The reaction of spontaneous polymerization in the system of N, N-diethylaminoethyl methacrylate with allyl chloride and bromide, orthophosphoric acid in ethanol and dimethyl sulfoxide solutions is considered. Spontaneous polymerization proceeds, consisting of two stages: the quaternization reaction and the polymerization reaction. It was shown that the accompanying reaction of quaternization, spontaneous polymerization, takes place both in a mixture of reagents and in the presence of a solvent, in other words, and by mixing an unsaturated amine and an alkyl halide.
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Choudhury, Goutam Ghosh, Bhabatarak Bhattacharyya i Birendra Bijoy Biswas. "Kinetic and thermodynamic analysis of taxol-induced polymerization of purified tubulin". Biochemistry and Cell Biology 65, nr 6 (1.06.1987): 558–64. http://dx.doi.org/10.1139/o87-072.
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The kinetic and thermodynamic behavior of in vitro taxol-induced polymerization of purified tubulin has been studied. The assembly of tubulin initiated by taxol has a critical concentration of 0.1 mg/mL at 37 °C and consists of two consecutive pseudo first-order processes, a fast phase followed by a slow phase. The rate constants of the fast and slow phase polymerizations increase linearly with increasing tubulin concentration. This implies that the polymerization is a true pseudo first-order process. The In (1/t0.5) of polymerization for both fast and slow phases follows a linear function with ln [tubulin] fulfilling one of the criteria of condensation polymerization mechanism. From the Arrhenius plot, the temperature dependence of the rate of tubulin polymerization in the presence of taxol is biphasic. The apparent activation enthalpies for the overall polymerization reaction are 13.0 and 50.8 kcal/mol (1 cal = 4.1868 J), respectively, above and below 26 °C. The apparent activation enthalpies for the elongation reaction have also been determined. The values are 11.6 and 28.4 kcal/mol above and below 28 °C. The temperature dependence of the equilibrium constants as revealed by the van't Hoff plot is also biphasic. The standard enthalpy and entropy values are ΔH° = 7.4 and 22.5 kcal/mol above and below 30 °C, and ΔS° = 50.3 and 101.0 cal/(deg∙mol), at high and low temperatures, respectively. This suggests that the taxol-induced assembly of purified tubulin is a process driven by the effect of entropy.
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Aouissi, Ahmed, Zeid Abdullah Al-Othman i Abdurrahman Salhabi. "Keggin-Type Heteropolyacid for Ring-Opening Polymerization of Cyclohexene Oxide: Molecular Weight Control". International Journal of Polymer Science 2015 (2015): 1–6. http://dx.doi.org/10.1155/2015/826512.
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Polymerization of 1,2-cyclohexene oxide (CHO) in dichloromethane was catalyzed by 12-tungstophosphoric acid (H3PW12O40·13H2O) as a super solid acid. The effect of polymerization parameters such as reaction time, temperature, and catalyst amount was investigated. The effect of acetic anhydride as a ring-opening agent was also investigated. The resulting poly(1,2-cyclohexene oxide) (PCHO) was characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance spectroscopy (1HNMR), gel-permeation chromatography (GPC), and differential scanning calorimetry (DSC). It has been found that the PCHO prepared over H3PW12O40·13H2O has a stereoregularity higher than that prepared over clay and Aluminium alkoxide catalysts. TheTgvalue obtained is due to the microstructure but not to molecular weight. The yield and the molecular weight of the polymer depend strongly on the reaction conditions. Molecular weights can be readily controlled by changing reaction temperature, reaction time, and catalyst amount. Contrary to most polymerization reactions, the molecular weight increases with the temperature increase. Addition of acetic anhydride to the reaction medium increased the yield threefold.
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Bellotti, Valentina, i Roberto Simonutti. "New Light in Polymer Science: Photoinduced Reversible Addition-Fragmentation Chain Transfer Polymerization (PET-RAFT) as Innovative Strategy for the Synthesis of Advanced Materials". Polymers 13, nr 7 (1.04.2021): 1119. http://dx.doi.org/10.3390/polym13071119.
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Photochemistry has attracted great interest in the last decades in the field of polymer and material science for the synthesis of innovative materials. The merging of photochemistry and reversible-deactivation radical polymerizations (RDRP) provides good reaction control and can simplify elaborate reaction protocols. These advantages open the doors to multidisciplinary fields going from composite materials to bio-applications. Photoinduced Electron/Energy Transfer Reversible Addition-Fragmentation Chain-Transfer (PET-RAFT) polymerization, proposed for the first time in 2014, presents significant advantages compared to other photochemical techniques in terms of applicability, cost, and sustainability. This review has the aim of providing to the readers the basic knowledge of PET-RAFT polymerization and explores the new possibilities that this innovative technique offers in terms of industrial applications, new materials production, and green conditions.
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EL-Rafie, M. H., S. A. Abdel Hafiz, S. M. Hassan i A. Hebeish. "Grafting of Methacrylic Acid to Loomstate Viscose Fabric Using KMnO4/NaHSO3 System". Engineering Plastics 2, nr 2 (styczeń 1994): 147823919400200. http://dx.doi.org/10.1177/147823919400200204.
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Potassium permanganate/sodium bisulphite redox system induced polymerization of methacrylic acid (MAA) with viscose fabric was studied under a variety of conditions. The polymerization reaction was studied with respect to graft yield, homopolymer, total conversion and graft efficiency. Results obtained indicated that increasing the MAA concentration, duration and temperature of polymerization enhances the graft yield, total conversion and homopolymer. Similar situations were encountered with KMnO 4 and NaHSO 3 concentrations but up to a certain limit after which these polymerization criteria decrease Meanwhile, the graft efficiency exhibits different maxima, depending upon the factors determining the polymerization reaction. Conversely, all the polymerization criteria decrease as the liquor ratio increases. A tentative mechanism for the polymerization reaction is also reported.
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EL-Rafie, M. H., S. A. Abdel Hafiz, S. M. Hassan i A. Hebeish. "Grafting of Methacrylic Acid to Loomstate Viscose Fabric Using KMnO4/NaHSO3 System". Polymers and Polymer Composites 2, nr 2 (luty 1994): 99–104. http://dx.doi.org/10.1177/096739119400200204.
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Potassium permanganate/sodium bisulphite redox system induced polymerization of methacrylic acid (MAA) with viscose fabric was studied under a variety of conditions. The polymerization reaction was studied with respect to graft yield, homopolymer, total conversion and graft efficiency. Results obtained indicated that increasing the MAA concentration, duration and temperature of polymerization enhances the graft yield, total conversion and homopolymer. Similar situations were encountered with KMnO 4 and NaHSO 3 concentrations but up to a certain limit after which these polymerization criteria decrease Meanwhile, the graft efficiency exhibits different maxima, depending upon the factors determining the polymerization reaction. Conversely, all the polymerization criteria decrease as the liquor ratio increases. A tentative mechanism for the polymerization reaction is also reported.
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Bednarczyk, Paulina, Izabela Irska, Konrad Gziut i Paula Ossowicz-Rupniewska. "Synthesis of Epoxy Methacrylate Resin and Coatings Preparation by Cationic and Radical Photocrosslinking". Molecules 26, nr 24 (17.12.2021): 7663. http://dx.doi.org/10.3390/molecules26247663.
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This work involves the synthesis of hybrid oligomers based on the epoxy methacrylate resin. The EA resin was obtained by the modification of industrial-grade bisphenol A-based epoxy resin and methacrylic acid has been synthesized in order to develop multifunctional resins comprising both epoxide group and reactive, terminal unsaturation. Owing to the presence of both epoxy and double carbon–carbon pendant groups, the reaction product exhibits photocrosslinking via two distinct mechanisms: (i) cationic ring-opening polymerization and (ii) free radical polymerization. Monitoring of EA synthesis reactions over time using PAVs, MAAC and NV parameters, and the FT-IR method reveals that esterification reactions proceed faster at the start, exhibiting over 40% of conversion within the initial 60 min, which can be associated with a relatively high concentration of reactive sites and low viscosity of the reaction mixture at the initial reaction stage. With the further increase in the reaction time, the reaction rate tends to decrease. The control of the EA synthesis process can guide how to adjust reactions to obtain EAs with desired characteristics. Based on obtained values, one can state that the optimum synthesis time of about 4–5 h should be adopted to prepare EAs having both epoxy groups and unsaturated double bonds. The structure of the obtained EA was confirmed by FT-IR and NMR methods, as well as the determination of partial acid value and epoxy equivalent. Samples at various stages of synthesis were cured with UV radiation in order to study the kinetics of the process according to cationic and radical polymerization determined via photo-differential scanning calorimetry (photo-DSC) and real-time infrared spectroscopy (RT-IR) and then the properties of the cured coatings were tested. It turned out that the cationic polymerization was slower with a lower conversion of the photoreactive groups, as compared to the radical polymerization. All the obtained EA coatings were characterized by good properties of cured coatings and can be successfully used in the coating-forming sector.
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Sheka, Elena F. "Virtual Free-Radical Polymerization of Vinyl Monomers in View of Digital Twins". Polymers 15, nr 14 (10.07.2023): 2999. http://dx.doi.org/10.3390/polym15142999.
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The first case of virtual polymerization based on the concept of digital twins (DTs) is presented. The free-radical polymerization of vinyl monomers is considered to be a chain reaction consisting of a set of elementary ones. Those three types, related to the polymerization initiation and propagation as well as to the termination of polymer chain growth, are discussed. Special sets of DTs, whose total number approaches 60, distinguish each reaction type. The calculations are carried out using a semi-empirical version of the unrestricted Hartree–Fock approximation. The main energy and spin-density parameters of the ground state of the DTs are determined. The barrier profiles of two pairs of DTs are calculated, based on which two Evans–Polanyi–Semenov relations, attributed to elementary reactions of type (1) and (2), are constructed. These provide a quite reliable evaluation of the activation energy for the initiation and propagation of the free-radical polymerization of vinyl monomers in all the cases. The decisive role of spins in the formation of the elementary reaction transition states is established.
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Salmeia, Khalifah A., Akef T. Afaneh, Reem R. Habash i Antonia Neels. "Trivinylphosphine Oxide: Synthesis, Characterization, and Polymerization Reactivity Investigated Using Single-Crystal Analysis and Density Functional Theory". Molecules 28, nr 16 (17.08.2023): 6097. http://dx.doi.org/10.3390/molecules28166097.
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Organophosphorus chemicals are versatile and important in industry. Trivinylphosphine oxide (TVPO), for example, exhibited a promising precursor as a flame-retardant additive for industrial applications. Density functional theory (DFT) simulations were used to explore the kinetic and thermodynamic chemical processes underlying the nucleophilic addition reactions of TVPO in order to better understand their polymerization mechanisms. An experimental X-ray single-crystal study of TVPO supported this work’s theory based on its computed findings. TVPO was prepared using POCl3 and VMB in a temperature-dependent reaction. TVPO, the thermodynamically favourable product, is preferentially produced at low temperatures. The endothermic anionic addition polymerization reaction between TVPO and VMB begins when the reaction temperature rises. An implicit solvation model simulated TVPO and piperazine reactions in water, whereas a hybrid model modelled VMB interactions in tetrahydrofuran. The simulations showed a pseudo-Michael addition reaction mechanism with a four-membered ring transition state. The Michael addition reaction is analogous to this process.
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Zhu, Xiaoyan, Feng Liu, Xinwu Ba i Yonggang Wu. "Tandem Suzuki Polymerization/Heck Cyclization Reaction to Form Ladder-Type 9,9′-Bifluorenylidene-Based Conjugated Polymer". Polymers 15, nr 16 (10.08.2023): 3360. http://dx.doi.org/10.3390/polym15163360.
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The synthesis of ladder-type 9,9′-bifluorenylidene-based conjugated polymer is reported. Unlike the typical synthetic strategy, the new designed ladder-type conjugated polymer is achieved via tandem Suzuki polymerization/Heck cyclization reaction in one-pot. In the preparation process, Suzuki polymerization reaction occurred first and then the intramolecular Heck cyclization followed smoothly under the same catalyst Pd(PPh3)4. The model reaction proved that the introduction of iodine (I) for this tandem reaction can effectively control the sequential bond-forming process and inhibit the additional competitive side reactions. Thus, small-molecule model compounds could be obtained in high yields. The successes of the synthesized small molecule and polymer compounds indicate that the Pd-catalyzed tandem reaction may be an effective strategy for improving extended π-conjugated materials.
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Reyes-Miguel, Tania, Ana L. Roa-Espitia, Rafael Baltiérrez-Hoyos i Enrique O. Hernández-González. "CDC42 drives RHOA activity and actin polymerization during capacitation". Reproduction 160, nr 3 (wrzesień 2020): 393–404. http://dx.doi.org/10.1530/rep-19-0577.
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Mammalian sperm cells acquire fertilizing capacity as a result of a process termed capacitation. Actin polymerization is important for capacitation; inhibiting actin polymerization prevents the adhesion and fusion of the sperm with the ovule. The main function of RHO proteins CDC42 and RHOA is to direct actin polymerization. Although these two RHO proteins are present in mammalian sperm, little is known about their role in capacitation, the acrosome reaction, and the way in which they direct actin polymerization. The purpose of this study was to determine the participation of CDC42 and RHOA in capacitation and the acrosome reaction and their relationship with actin polymerization using guinea pig sperm. Our results show that the inhibition of CDC42 and RHOA alters the kinetics of actin polymerization, capacitation, and the acrosome reaction in different ways. Our results also show that the initiation of actin polymerization and RHOA activation depend on the activation of CDC42 and that RHOA starts its activity and effect on actin polymerization when CDC42 reaches its maximum activity. Given that the inhibition of ROCK1 failed to prevent the acrosomal reaction, the participation of RHOA in capacitation and the acrosomal reaction is independent of its kinase 1 (ROCK1). In general, our results indicate that CDC42 and RHOA have different roles in capacitation and acrosomal reaction processes and that CDC42 plays a preeminent role.
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Lang, Margit, Stefan Hirner, Frank Wiesbrock i Peter Fuchs. "A Review on Modeling Cure Kinetics and Mechanisms of Photopolymerization". Polymers 14, nr 10 (19.05.2022): 2074. http://dx.doi.org/10.3390/polym14102074.
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Photopolymerizations, in which the initiation of a chemical-physical reaction occurs by the exposure of photosensitive monomers to a high-intensity light source, have become a well-accepted technology for manufacturing polymers. Providing significant advantages over thermal-initiated polymerizations, including fast and controllable reaction rates, as well as spatial and temporal control over the formation of material, this technology has found a large variety of industrial applications. The reaction mechanisms and kinetics are quite complex as the system moves quickly from a liquid monomer mixture to a solid polymer. Therefore, the study of curing kinetics is of utmost importance for industrial applications, providing both the understanding of the process development and the improvement of the quality of parts manufactured via photopolymerization. Consequently, this review aims at presenting the materials and curing chemistry of such ultrafast crosslinking polymerization reactions as well as the research efforts on theoretical models to reproduce cure kinetics and mechanisms for free-radical and cationic photopolymerizations including diffusion-controlled phenomena and oxygen inhibition reactions in free-radical systems.