Artigos de revistas: "Polymerization"

1

Chen, Mao, Honghong Gong e Yu Gu. "Controlled/Living Radical Polymerization of Semifluorinated (Meth)acrylates". Synlett 29, n.º 12 (18 de abril de 2018): 1543–51. http://dx.doi.org/10.1055/s-0036-1591974.

Texto completo da fonte

Resumo:

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

Estilos ABNT, Harvard, Vancouver, APA, etc.

2

Penczek, Stanislaw, Julia Pretula e Stanislaw Slomkowski. "Ring-opening polymerization". Chemistry Teacher International 3, n.º 2 (15 de março de 2021): 33–57. http://dx.doi.org/10.1515/cti-2020-0028.

Texto completo da fonte

Resumo:

Abstract Ring-opening polymerization is defined by IUPAC (Penczek, S., Moad, G. (2008). Glossary of the terms related to kinetics, thermodynamics, and mechanisms of polymerization. (IUPAC Recommendations 2008), Pure and Applied Chemistry, 80(10), 2163–2193) as (cit.) “Ring-opening polymerization (ROP): Polymerization in which a cyclic monomer yields a monomeric unit that is either acyclic or contains fewer rings than the cyclic monomer”. The large part of the resulting polymerizations is living/controlled; practically all belong to chain polymerizations. After the introduction, providing basic information on chain polymerizations, the paper presents the concise overview of major classes of monomers used in ROP, including cyclic ethers, esters, carbonates, and siloxanes as well as cyclic nitrogen, phosphorus, and sulfur containing monomers. There are discussed also thermodynamics, kinetic polymerizability, and major mechanisms of ROP. Special attention is concentrated on polymers prepared by ROP on industrial scale.

Estilos ABNT, Harvard, Vancouver, APA, etc.

3

Cheah, Pohlee, Caitlin N. Bhikha, John H. O’Haver e Adam E. Smith. "Effect of Oxygen and Initiator Solubility on Admicellar Polymerization of Styrene on Silica Surfaces". International Journal of Polymer Science 2017 (2017): 1–7. http://dx.doi.org/10.1155/2017/6308603.

Texto completo da fonte

Resumo:

Although admicellar polymerization has been termed the surface analog of emulsion polymerization, previous reports utilizing free radical-initiated admicellar polymerization relied on high levels of the free radical initiator when compared to emulsion polymerization, likely due to the presence of oxygen in the reported admicellar polymerization systems. Admicellar polymerizations of styrene on the surface of precipitated silica initiated by either a water-soluble or a water-insoluble initiator were studied to determine the effect of dissolved oxygen and free radical initiator solubility on the kinetics, yield, and molecular weight of the polymer formed. Results show that the presence of oxygen reduces the polymer yield and limits molecular weight. The solubility of the initiator also affected the polymer formed in the admicellar polymerization of styrene. While monomer conversions and polymer yield were similar, the molecular weights of polymerizations initiated by a water-soluble initiator were higher than comparable polymerizations initiated by a water-insoluble initiator.

Estilos ABNT, Harvard, Vancouver, APA, etc.

4

Prescott, S. W., M. J. Ballard, E. Rizzardo e R. G. Gilbert. "RAFT in Emulsion Polymerization: What Makes it Different?" Australian Journal of Chemistry 55, n.º 7 (2002): 415. http://dx.doi.org/10.1071/ch02073.

Texto completo da fonte

Resumo:

Reversible addition-fragmentation chain transfer (RAFT) polymerization techniques have been the focus of a great deal of recent work, particularly in their application to emulsion polymerization, which is the method of choice for implementing most free-radical polymerizations on an industrial scale. RAFT/emulsion polymerizations have considerable technical potential: to 'tailor-make' material properties, to eliminate added surfactant from surface coatings, and so on. However, considerable difficulties have been experienced in using RAFT in emulsion polymerization systems. Here, progress in the application of RAFT techniques to emulsion polymerization is reviewed, summarizing the difficulties that have been experienced and mechanisms that have been postulated to explain the observed behaviour. Possible origins of the difficulties in implementing RAFT in emulsion polymerizations include polymerization in droplets, water sensitivity of some RAFT agents, slow transport of highly hydrophobic RAFT agents across the water phase, and surface activity of some RAFT agents.

Estilos ABNT, Harvard, Vancouver, APA, etc.

5

Lowe, A. B., e C. L. McCormick. "Homogeneous Controlled Free Radical Polymerization in Aqueous Media". Australian Journal of Chemistry 55, n.º 7 (2002): 367. http://dx.doi.org/10.1071/ch02053.

Texto completo da fonte

Resumo:

The ability to conduct controlled radical polymerizations (CRP) in homogeneous aqueous media is discussed. Three main techniques, namely stable free radical polymerization (SFRP), with an emphasis on nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT) are examined. No examples exist of homogeneous aqueous NMP polymerization, but mixed water/solvent systems are discussed with specific reference to the NMP of sodium 4-styrenesulfonate. Aqueous ATRP is possible, although monomer choice is limited to methacrylates and certain styrenics. Finally, homogeneous aqueous RAFT polymerizations are examined. We demonstrate the greater versatility of this technique, at least in terms of monomer variety, by discussing the controlled polymerization of charged and neutral acrylamido monomers and of a series of ionic styrenic monomers. Many of these monomers cannot/have not been polymerized by either NMP or ATRP.

Estilos ABNT, Harvard, Vancouver, APA, etc.

6

Zhang, Xiaoqian, Wenli Guo, Yibo Wu, Liangfa Gong, Wei Li, Xiaoning Li, Shuxin Li, Yuwei Shang, Dan Yang e Hao Wang. "Cationic polymerization of p-methylstyrene in selected ionic liquids and polymerization mechanism". Polymer Chemistry 7, n.º 32 (2016): 5099–112. http://dx.doi.org/10.1039/c6py00796a.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

7

Jenkins, Aubrey D., Richard G. Jones e Graeme Moad. "Terminology for reversible-deactivation radical polymerization previously called "controlled" radical or "living" radical polymerization (IUPAC Recommendations 2010)". Pure and Applied Chemistry 82, n.º 2 (18 de novembro de 2009): 483–91. http://dx.doi.org/10.1351/pac-rep-08-04-03.

Texto completo da fonte

Resumo:

This document defines terms related to modern methods of radical polymerization, in which certain additives react reversibly with the radicals, thus enabling the reactions to take on much of the character of living polymerizations, even though some termination inevitably takes place. In recent technical literature, these reactions have often been loosely referred to as, inter alia, "controlled", "controlled/living", or "living" polymerizations. The use of these terms is discouraged. The use of "controlled" is permitted as long as the type of control is defined at its first occurrence, but the full name that is recommended for these polymerizations is "reversible-deactivation radical polymerization".

Estilos ABNT, Harvard, Vancouver, APA, etc.

8

HU, ZHIGANG, e DAN ZHAO. "POLYMERIZATION WITHIN CONFINED NANOCHANNELS OF POROUS METAL-ORGANIC FRAMEWORKS". Journal of Molecular and Engineering Materials 01, n.º 02 (junho de 2013): 1330001. http://dx.doi.org/10.1142/s2251237313300015.

Texto completo da fonte

Resumo:

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.

Estilos ABNT, Harvard, Vancouver, APA, etc.

9

Wang, Qiao, Jin Liang Li, Ai Ping Fu e Hong Liang Li. "Effect Factors on the Preparation of Polystyrene Microspheres by Emulsifier-Free Emulsion Polymerization". Advanced Materials Research 926-930 (maio de 2014): 304–7. http://dx.doi.org/10.4028/www.scientific.net/amr.926-930.304.

Texto completo da fonte

Resumo:

Emulsifier-free emulsion polymerization is a technique derived from conventional emulsion polymerization in which polymerization is carried out in the absence of emulsifiers. This technique is useful for the preparation of polymer colloids with narrow particle size distributions and well defined surface properties. Emulsifier-free emulsion polymerization eliminates the disadvantages of conventional emulsion polymerizations stemming from the use of emulsifiers, e.g. impurities in products caused by residual emulsifier and poor water-resistance of films induced by polymer latex.

Estilos ABNT, Harvard, Vancouver, APA, etc.

10

Zhang, Jie, Zhiming Zhang, Fulin Yang, Haoke Zhang, Jingzhi Sun e Benzhong Tang. "Metal-Free Catalysts for the Polymerization of Alkynyl-Based Monomers". Catalysts 11, n.º 1 (22 de dezembro de 2020): 1. http://dx.doi.org/10.3390/catal11010001.

Texto completo da fonte

Resumo:

Novel polymerizations based on alkyne monomers are becoming a powerful tool to construct polymers with unique structures and advanced functions in the areas of polymer and material sciences, and scientists have been attracted to develop a variety of novel polymerizations in recent decades. Therein, catalytic systems play an indispensable role in the influence of polymerization efficiencies and the performances of the resultant polymers. Concerning the shortcomings of metallic catalysts, much of the recent research focus has been on metal-free polymerization systems. In this paper, metal-free catalysts are classified and the corresponding polymerizations are reviewed, including organobase-catalyzed polymerizations, Lewis-acid-catalyzed polymerizations, as well as catalyst-free polymerizations. Moreover, the challenges and perspectives in this area are also briefly discussed.

Estilos ABNT, Harvard, Vancouver, APA, etc.

11

Xie, Linghai, Rong Tong, Quanyou Feng e Yongliang Zhong. "Recent Advances in Ring-Opening Polymerization of O-Carboxyanhydrides". Synlett 28, n.º 15 (3 de agosto de 2017): 1857–66. http://dx.doi.org/10.1055/s-0036-1590841.

Texto completo da fonte

Resumo:

Poly(α-hydroxy acids) are important biodegradable polymers with wide applications. Recently O-carboxyanhydrides (OCAs) have emerged as promising monomer equivalents of lactides to synthesize poly(α-hydroxy acids). We will highlight recent advances in controlled ring-opening polymerization of OCAs catalyzed by organocatalysts, enzymes, or organometallic complexes.1 Introduction2 Organocatalysts for O-Carboxyanhydride Polymerization2.1 Synthesis of O-Carboxyanhydride Monomers2.2 Ring-Opening Polymerization of O-Carboxyanhydrides Catalyzed by 4-Dimethylaminopyridine2.3 Epimerization in the Ring-Opening Polymerization of O-Carboxyanhydrides Catalyzed by the Pyridine Base2.4 N-Heterocyclic Carbenes for Ring-Opening Polymerization of O-Carboxyanhydrides3 Enzymes for O-Carboxyanhydride Polymerization4 Organometallic Catalysts for O-Carboxyanhydride Polymerization4.1 Early Efforts4.2 Ring-Opening Polymerization Catalyzed by Zn Complexes4.3 Photoredox Ring-Opening Polymerization Catalyzed by Zn/Ni Complexes5 Conclusion and Perspective

Estilos ABNT, Harvard, Vancouver, APA, etc.

12

Wen, Shao Guo, Shi Gao Song, Hong Bo Liu, Ji Hu Wang, Qian Xu e Yan Shen. "Application of a Novel Initiator on Acrylic Emulsion Polymerization". Advanced Materials Research 233-235 (maio de 2011): 1415–18. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.1415.

Texto completo da fonte

Resumo:

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.

Estilos ABNT, Harvard, Vancouver, APA, etc.

13

Brandl, Florian, Marco Drache e Sabine Beuermann. "Kinetic Monte Carlo Simulation Based Detailed Understanding of the Transfer Processes in Semi-Batch Iodine Transfer Emulsion Polymerizations of Vinylidene Fluoride". Polymers 10, n.º 9 (10 de setembro de 2018): 1008. http://dx.doi.org/10.3390/polym10091008.

Texto completo da fonte

Resumo:

Semi-batch emulsion polymerizations of vinylidene fluoride (VDF) are reported. The molar mass control is achieved via iodine transfer polymerization (ITP) using IC4F8I as chain transfer agent. Polymerizations carried out at 75 °C and pressures ranging from 10 to 30 bar result in low dispersity polymers with respect to the molar mass distribution (MMD). At higher pressures a significant deviation from the ideal behavior expected for a reversible deactivation transfer polymerization occurs. As identified by kinetic Monte Carlo (kMC) simulations of the activation–deactivation equilibrium, during the initialization period of the chain transfer agent already significant propagation occurs due to the higher pressure, and thus, the higher monomer concentration available. Based on the kMC modeling results, semi-batch emulsion polymerizations were carried out as a two pressure process, which resulted in very good control of the MMD associated with a comparably high polymerization rate.

Estilos ABNT, Harvard, Vancouver, APA, etc.

14

Park, Sora, e Jeung Gon Kim. "Mechanochemical synthesis of poly(trimethylene carbonate)s: an example of rate acceleration". Beilstein Journal of Organic Chemistry 15 (23 de abril de 2019): 963–70. http://dx.doi.org/10.3762/bjoc.15.93.

Texto completo da fonte

Resumo:

Mechanochemical polymerization is a rapidly growing area and a number of polymeric materials can now be obtained through green mechanochemical synthesis. In addition to the general merits of mechanochemistry, such as being solvent-free and resulting in high conversions, we herein explore rate acceleration under ball-milling conditions while the conventional solution-state synthesis suffer from low reactivity. The solvent-free mechanochemical polymerization of trimethylene carbonate using the organocatalysts 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) are examined herein. The polymerizations under ball-milling conditions exhibited significant rate enhancements compared to polymerizations in solution. A number of milling parameters were evaluated for the ball-milling polymerization. Temperature increases due to ball collisions and exothermic energy output did not affect the polymerization rate significantly and the initial mixing speed was important for chain-length control. Liquid-assisted grinding was applied for the synthesis of high molecular weight polymers, but it failed to protect the polymer chain from mechanical degradation.

Estilos ABNT, Harvard, Vancouver, APA, etc.

15

Goto, Atsushi, Koji Nagasawa, Ayaka Shinjo, Yoshinobu Tsujii e Takeshi Fukuda. "Reversible Chain Transfer Catalyzed Polymerization of Methyl Methacrylate with In-Situ Formed Alkyl Iodide Initiator". Australian Journal of Chemistry 62, n.º 11 (2009): 1492. http://dx.doi.org/10.1071/ch09229.

Texto completo da fonte

Resumo:

A method utilizing generation of an alkyl iodide (low-mass dormant species) in situ formed in polymerization was adopted to reversible chain transfer catalyzed polymerizations (RTCP) (living radical polymerizations) with several nitrogen and phosphorus catalysts. The polymerization of methyl methacrylate afforded low-polydispersity polymers (Mw/Mn ~1.2–1.4), with Mn values predicted to high conversions; where Mn and Mw are the number- and weight-average molecular weights respectively. This method is robust and would enhance the utility of RTCP.

Estilos ABNT, Harvard, Vancouver, APA, etc.

16

Ma, Jiashu, Jiahao Li, Bingbing Yang, Siwen Liu, Bang-Ping Jiang, Shichen Ji e Xing-Can Shen. "A Simple Stochastic Reaction Model for Heterogeneous Polymerizations". Polymers 14, n.º 16 (11 de agosto de 2022): 3269. http://dx.doi.org/10.3390/polym14163269.

Texto completo da fonte

Resumo:

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.

Estilos ABNT, Harvard, Vancouver, APA, etc.

17

Dumur, Frédéric. "Recent Advances on Visible Light Metal-Based Photocatalysts for Polymerization under Low Light Intensity". Catalysts 9, n.º 9 (30 de agosto de 2019): 736. http://dx.doi.org/10.3390/catal9090736.

Texto completo da fonte

Resumo:

In recent years, polymerization processes activated by light have attracted a great deal of interest due to the wide range of applications in which this polymerization technique is involved. Parallel to the traditional industrial applications ranging from inks, adhesives, and coatings, the development of high-tech applications such as nanotechnology and 3D-printing have given a revival of interest to this polymerization technique known for decades. To initiate a photochemical polymerization, the key element is the molecule capable to interact with light, i.e., the photoinitiator and more generally the photoinitiating system, as a combination of several components is often required to create the reactive species responsible for the polymerization process. With the aim of reducing the photoinitiator content while optimizing the polymerization yield and/or the polymerization speed, photocatalytic systems have been developed, enabling the photosensitizer to be regenerated during the polymerization process. In this review, an overview of the photocatalytic systems developed for polymerizations carried out under a low light intensity and visible light is provided. Over the years, a wide range of organometallic photocatalysts has been proposed, addressing both the polymerization efficiency and/or the toxicity, as well as environmental issues.

Estilos ABNT, Harvard, Vancouver, APA, etc.

18

Quirk, Roderic P., e Jungahn Kim. "Recent Advances in Thermoplastic Elastomer Synthesis". Rubber Chemistry and Technology 64, n.º 3 (1 de julho de 1991): 450–68. http://dx.doi.org/10.5254/1.3538563.

Texto completo da fonte

Resumo:

Abstract A variety of living polymerization systems are now available for the controlled synthesis of block copolymers. Although living anionic polymerization remains as the method of choice for the most precise structural control, living polymerizations proceeding via other mechanistic types provide extremely useful extensions of this methodology to a wider variety of monomers.

Estilos ABNT, Harvard, Vancouver, APA, etc.

19

Mohammadi Hafshejani, Tahereh, Xiaoyang Zhong, John Kim, Bahar Dadfar e Joerg Lahann. "Chemical and Topological Control of Surfaces Using Functional Parylene Coatings". Organic Materials 5, n.º 02 (maio de 2023): 98–111. http://dx.doi.org/10.1055/s-0043-1761309.

Texto completo da fonte

Resumo:

Chemical vapor deposition (CVD) polymerization is a prevalent technique for fabricating conformal, defect-free, and systematically adjustable organic thin films. CVD is particularly beneficial for barrier coatings due to its ability to eliminate solvent-related environmental, health, and safety risk factors and provide a wide spectrum of post-polymerization modification strategies. This review discusses poly-p-xylylene and its functional derivatives. CVD polymerization of [2.2]paracyclophane precursors has undergone a recent renaissance due to advancements in chemical and morphological surface manipulation. This review summarizes emerging trends based on the following outline:Table of content:1 Introduction2 CVD Polymerization as a Sustainable Coating Technology3 CVD Instrumentation4 Poly-p-xylylene Coatings: Background of Polymerization Process and Functionalized Films5 Main Applications of Poly-p-xylylenes6 Area-Selective CVD Polymerization7 Fabrication and Applications of Topological Structures8 Conclusions and Outlook

Estilos ABNT, Harvard, Vancouver, APA, etc.

20

Zhang, Jinghan, Yibo Wu, Kaixuan Chen, Min Zhang, Liangfa Gong, Dan Yang, Shuxin Li e Wenli Guo. "Characteristics and Mechanism of Vinyl Ether Cationic Polymerization in Aqueous Media Initiated by Alcohol/B(C6F5)3/Et2O". Polymers 11, n.º 3 (14 de março de 2019): 500. http://dx.doi.org/10.3390/polym11030500.

Texto completo da fonte

Resumo:

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.

Estilos ABNT, Harvard, Vancouver, APA, etc.

21

Save, Maud, Yohann Guillaneuf e Robert G. Gilbert. "Controlled Radical Polymerization in Aqueous Dispersed Media". Australian Journal of Chemistry 59, n.º 10 (2006): 693. http://dx.doi.org/10.1071/ch06308.

Texto completo da fonte

Resumo:

Controlled radical polymerization (CRP), sometimes also termed ‘living’ radical polymerization, offers the potential to create a wide range of polymer architectures, and its implementation in aqueous dispersed media (e.g. emulsion polymerization, used on a vast scale industrially) opens the way to large-scale manufacture of products based on this technique. Until recently, implementing CRP in aqueous dispersed media was plagued with problems such as loss of ‘living’ character and loss of colloidal stability. This review examines the basic mechanistic processes in free-radical polymerization in aqueous dispersed media (e.g. emulsion polymerization), and then examines, through this mechanistic understanding, the new techniques that have been developed over the last few years to implement CRP successfully in emulsion polymerizations and related processes. The strategies leading to these successes can thus be understood in terms of the various mechanisms which dominate CRP systems in dispersed media; these mechanisms are sometimes quite different from those in conventional free-radical polymerization in these media.

Estilos ABNT, Harvard, Vancouver, APA, etc.

22

Li, Hua-Rong, Liming Che e 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, n.º 2 (2014): 249–60. http://dx.doi.org/10.2298/ciceq120722006l.

Texto completo da fonte

Resumo:

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.

Estilos ABNT, Harvard, Vancouver, APA, etc.

23

Harrisson, Simon. "The Chain Length Distribution of an Ideal Reversible Deactivation Radical Polymerization". Polymers 10, n.º 8 (8 de agosto de 2018): 887. http://dx.doi.org/10.3390/polym10080887.

Texto completo da fonte

Resumo:

The chain length distribution (CLD) of a reversible deactivation radical polymerization at full conversion is shown to be a negative binomial distribution with parameters that are simple functions of the number-average degree of polymerization and either the chain transfer constant (in the case of polymerizations that incorporate a reversible chain transfer step) or the concentrations of dormant polymer chains and deactivating agent and the rate constants of propagation and deactivation (other types of RDRP). Expressions for the CLD at intermediate conversions are also derived, and shown to be consistent with known expressions for the number-average degree of polymerization and dispersity. It is further demonstrated that these CLDs are well-approximated by negative binomial distributions with appropriate choice of parameters. The negative binomial distribution is thus a useful model for CLDs of reversible deactivation radical polymerizations.

Estilos ABNT, Harvard, Vancouver, APA, etc.

24

Theis, Alexander, Martina H. Stenzel, Thomas P. Davis, Michelle L. Coote e Christopher Barner-Kowollik. "A Synthetic Approach to a Novel Class of Fluorine-Bearing Reversible Addition - Fragmentation Chain Transfer (RAFT) Agents: F-RAFT". Australian Journal of Chemistry 58, n.º 6 (2005): 437. http://dx.doi.org/10.1071/ch05069.

Texto completo da fonte

Resumo:

A synthetic route is described to a novel class of reversible addition–fragmentation chain transfer (RAFT) agents bearing a fluorine Z-group. Such F-RAFT agents are theoretically predicted to allow living free radical polymerization of various monomers without affecting the rate of polymerization, and should also facilitate the construction of block copolymers from monomers with disparate reactivity. The class of F-RAFT agents is exemplified by the example of benzyl fluoro dithioformate (BFDF) in styrene free-radical polymerizations and the process is shown to induce living polymerization.

Estilos ABNT, Harvard, Vancouver, APA, etc.

25

Wood, Murray R., David J. Duncalf, Paul Findlay, Steven P. Rannard e Sébastien Perrier. "Investigation of the Experimental Factors Affecting the Trithiocarbonate-Mediated RAFT Polymerization of Methyl Acrylate". Australian Journal of Chemistry 60, n.º 10 (2007): 772. http://dx.doi.org/10.1071/ch07171.

Texto completo da fonte

Resumo:

The reversible addition–fragmentation chain transfer polymerization of acrylates, using methyl acrylate (MA) as a monomer model, mediated by a trithiocarbonate was tested under several conditions where the experimental parameters were systematically altered. The most significant parameter in controlling the rate and control of the polymerization was found to be the ratio of chain transfer agent (CTA) to initiator. Decreasing this ratio increased the rate of polymerization and had little noticeable effect on the control over molecular weight distribution. A ratio of CTA to initiator of unity was shown to give the best compromise between rate and control of the polymerization. Targeted degrees of polymerization (equivalent to ratios of monomer to CTA) had negligible effect on the rate of polymerization and polydispersity index (PDI). Performing the polymerization in the presence of solvent (up to 41.2% (w/w) in toluene) had no negative effect on the rate of polymerization. Indeed, marginally higher conversions and lower PDIs than for bulk polymerization were achieved for similar reaction times. A higher amount of toluene (66.6% (w/w)) induced a lower rate of polymerization, but the evolution of molecular weight and PDI were unaffected. Polymerizations performed in the presence of toluene, N,N′-dimethylformamide, and methyl ethyl ketone showed that solvent polarity and aromaticity had no observable effect on the rate of polymerization and over the control of molecular weight distribution. The optimum conditions for the polymerization of MA, mediated by 2-ethylthiocarbonylsulfanyl-propionic acid ethyl ester at 50°C were found to be [CTA]/[AIBN] = 1/1 and ~40% solvent (w/w).

Estilos ABNT, Harvard, Vancouver, APA, etc.

26

Banetta, Luca, Giuseppe Storti, George Hoggard, Gareth Simpson e Alessio Zaccone. "Predictive model of polymer reaction kinetics and coagulation behavior in seeded emulsion co- and ter-polymerizations". Polymer Chemistry 11, n.º 41 (2020): 6599–615. http://dx.doi.org/10.1039/d0py01138j.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

27

Kohsaka, Yasuhiro, Yusuke Matsumoto e Tatsuki Kitayama. "α-(Aminomethyl)acrylate: polymerization and spontaneous post-polymerization modification of β-amino acid ester for a pH/temperature-responsive material". Polymer Chemistry 6, n.º 28 (2015): 5026–29. http://dx.doi.org/10.1039/c5py00723b.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

28

Kajiwara, Atsushi. "Characterizations of radicals formed in radical polymerizations and transfer reactions by electron spin resonance spectroscopy". Pure and Applied Chemistry 90, n.º 8 (28 de agosto de 2018): 1237–54. http://dx.doi.org/10.1515/pac-2018-0401.

Texto completo da fonte

Resumo:

Abstract Electron spin resonance (ESR, aka electron paramagnetic resonance, EPR) investigations have been conducted on radicals formed during radical polymerizations and provide a detailed characterization of the active radical species. Active propagating radicals can be observed during actual radical polymerizations by ESR/EPR. The chain lengths of the observed radicals were estimated by a combination of atom transfer radical polymerization (ATRP) and ESR/EPR. The structures of the chain end radicals were determined by analysis of the ESR/EPR spectra. An increase in the dihedral angles between terminal p-orbital of radical and Cβ–H bonds was observed with increasing chain lengths of methacrylate polymers. Radical transfer reactions were observed during radical polymerization of acrylates. A combination of ATRP and ESR/EPR clarified a 1,5-hydrogen shift mechanism of the radical transfer reactions using model adamantyl acrylate radicals. Penultimate unit effects were also observed. Time-resolved ESR/EPR (TR ESR) spectroscopy clarified the initiation processes of an alternating copolymerization of styrene with maleic anhydride and the copolymerization of styrene with 1,3-butadiene. Several unsolved problems in conventional radical polymerization processes have been clarified using combinations of ATRP with ESR/EPR and TR ESR. Characterization of the radicals in radical polymerizations using various ESR techniques would definitely provide interesting and useful information on conventional radical polymerizations.

Estilos ABNT, Harvard, Vancouver, APA, etc.

29

Capek, I. "On the inverse miniemulsion copolymerization and terpolymerization of acrylamide, N, N′-methylenebis(acrylamide) and methacrylic acid". Open Chemistry 1, n.º 3 (1 de setembro de 2003): 291–304. http://dx.doi.org/10.2478/bf02476230.

Texto completo da fonte

Resumo:

AbstractThe kinetics of free-radical copolymerization and terpolymerization of acrylamide (AAm), N, N′-methylenebis(acrylamide) (MBA) and methacrylic acid (MA) in the inverse water/monomer/cyclohexane/Tween 85 miniemulsion was investigated. Polymerizable sterically-stable miniemulsions were formulated in cyclohexane as a continuous medium. Polymerizations are very fast and reach the final conversion within several minutes. The dependence of the polymerization rate vs. conversion is described by a curve with two nonstationary rate intervals. The maximum rate of polymerization slightly increases with increasing concentration of crosslinking monomer (MBA) and strongly decreases by the addition of MA. The rate of polymerization is inversely proportional to the 0.9th and 1.8th power of the particle concentration without and with MA, respectively. The number of polymer particles is inversely proportional to the 0.18th and 0.13th power of MBA concentration. The kinetic and colloidal parameters of the miniemulsion polymerization are discussed in terms of microemulsion polymerization model.

Estilos ABNT, Harvard, Vancouver, APA, etc.

30

Zhao, Yanan, Zhenli Zhang e Yi Luo. "DFT Modeling of Coordination Polymerization of Polar Olefin Monomers by Molecular Metal Complexes". Inorganics 12, n.º 9 (28 de agosto de 2024): 233. http://dx.doi.org/10.3390/inorganics12090233.

Texto completo da fonte

Resumo:

Introducing polar functional groups into polyolefin chains through polar olefin monomer coordination (co)polymerization can directly and significantly improve the surface properties of polymer materials and expand their application range. Therefore, the related research has always received considerable attention from both academia and industry. Many experimental studies have been reported in this field, and molecular metal complexes have shown high catalytic activity and selectivity in polar olefin monomer polymerizations. Although considerable DFT calculations have also been conducted for better understanding of the (co)polymerization performance, the factors governing the activity, selectivity, and molecular weight of resulting polymers are still ambiguous. This review mainly focuses on the DFT studies of polar olefin monomer coordination (co)polymerization catalyzed by molecular metal complexes in recent years, discussing the chain initiation and propagation, the origin of polymerization activity and selectivity, and the specific role of additives in the (co)polymerization reactions.

Estilos ABNT, Harvard, Vancouver, APA, etc.

31

Rodríguez, Rocío B., Daniela Iguchi, Rosa Erra-Balsells, M. Laura Salum e Pablo Froimowicz. "Design and Effects of the Cinnamic Acids Chemical Structures as Organocatalyst on the Polymerization of Benzoxazines". Polymers 12, n.º 7 (9 de julho de 2020): 1527. http://dx.doi.org/10.3390/polym12071527.

Texto completo da fonte

Resumo:

This study focuses on the catalytic effect of the two geometric isomers of a cinnamic acid derivative, E and Z-forms of 3-methoxycinnamic acid (3OMeCA), analyzing the influence of their chemical structures. E and Z-3OMeCA isomers show very good catalytic effect in the polymerization of benzoxazines, decreasing by 40 and 55 °C, respectively, the polymerization temperatures, for catalyst contents of up to 10% w/w. Isothermal polymerizations show that polymerizations are easily realized and analyzed at temperatures as low as 130 °C and at much shorter times using Z-3OMeCA instead of E-3OMeCA. Thus, both cinnamic acids are good catalysts, with Z-3OMeCA being better. The molecular reasons for this difference and mechanistic implications in benzoxazine polymerizations are also presented.

Estilos ABNT, Harvard, Vancouver, APA, etc.

32

Kadokawa, Jun-ichi. "Synthesis of Amylosic Supramolecular Materials by Glucan Phosphorylase-Catalyzed Enzymatic Polymerization According to the Vine-Twining Approach". Synlett 31, n.º 07 (30 de janeiro de 2020): 648–56. http://dx.doi.org/10.1055/s-0039-1690804.

Texto completo da fonte

Resumo:

This article overviews the synthesis of amylosic supramolecular materials through inclusion complexation in glucan phosphorylase (GP)-catalyzed enzymatic polymerization. Amylose is a polysaccharide that is known to form inclusion complexes with a number of hydrophobic small guest molecules. A pure amylose can be synthesized by the enzymatic polymerization of α-d-glucose 1-phosphate monomer with a maltooligosaccharide primer catalyzed by GP. The author has reported that the propagating amylosic chain in the enzymatic polymerization twines around hydrophobic polymers present in aqueous reaction media to form supramolecular inclusion complexes. As it is similar to the way that vines of a plant grow around a rod, this polymerization is termed ‘vine-twining polymerization’. Amylosic supramolecular network materials have been obtained through the vine-twining polymerization by using copolymers, where hydrophobic guest polymers are covalently grafted on hydrophilic main-chain polymers. The enzymatically produced amylosic chains form complexes with the guest polymers among graft copolymers, which act as cross-linking points to form supramolecular networks, resulting in the formation of soft materials, such as gels and films. Vine-twining polymerization using appropriately designed guest polymers has also been performed, which leads to supramolecular products that exhibit new functionality.1 Introduction2 Vine-Twining Polymerization to Form Supramolecular Inclusion Complexes3 Selective Complexation of Amylose toward Guest Polymers in Vine-Twining Polymerization4 Hierarchical Architecture of Amylosic Supramolecular Network Materials by Vine-Twining Polymerization Approach5 Hierarchical Fabrication of Amylosic Supramolecular Materials by Vine-Twining Polymerization Using Designed Guest Polymers6 Conclusions

Estilos ABNT, Harvard, Vancouver, APA, etc.

33

Xu, Yuan Qing, Xiao Min Fang, Tao Ding e Yan Rong Ren. "Living Radical Polymerizations of Methyl Methacrylate Mediated by Tris-(4-Carboxyphenyl) Methane". Advanced Materials Research 631-632 (janeiro de 2013): 3–8. http://dx.doi.org/10.4028/www.scientific.net/amr.631-632.3.

Texto completo da fonte

Resumo:

Pseudo-living radical polymerization and reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) were reported, utilizing tris-(4-carboxyphenyl)methane (TCOPM) as the thermal iniferter and initiator, respectively. The polymerization of MMA using TCOPM as thermal iniferter possesses pseudo-living characteristics: Mn increases with conversion in a certain range, and the resulted polymer can be used as the macro-initiator for chain extension. The RATRP using TCOPM as the initiator shows linear kinetic plot, linear increase of Mn with conversion and narrow polydispersity indice (PDI) of the resultant polymers. Effects of temperature on both polymerizations were investigated.

Estilos ABNT, Harvard, Vancouver, APA, etc.

34

Yang, D. Billy. "Direct Kinetic Measurements of Vinyl Polymerization on Metal and Silicon Surfaces Using Real-Time FT-IR Spectroscopy". Applied Spectroscopy 47, n.º 9 (setembro de 1993): 1425–29. http://dx.doi.org/10.1366/0003702934067739.

Texto completo da fonte

Resumo:

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.

Estilos ABNT, Harvard, Vancouver, APA, etc.

35

Barszczewska-Rybarek, Izabela, e Grzegorz Chladek. "Studies on the Curing Efficiency and Mechanical Properties of Bis-GMA and TEGDMA Nanocomposites Containing Silver Nanoparticles". International Journal of Molecular Sciences 19, n.º 12 (7 de dezembro de 2018): 3937. http://dx.doi.org/10.3390/ijms19123937.

Texto completo da fonte

Resumo:

Bioactive dimethacrylate composites filled with silver nanoparticles (AgNP) might be used in medical applications, such as dental restorations and bone cements. The composition of bisphenol A glycerolate dimethacrylate (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) mixed in a 60/40 wt% ratio was filled from 25 to 5000 ppm of AgNP. An exponential increase in resin viscosity was observed with an increase in AgNP concentration. Curing was performed by way of photopolymerization, room temperature polymerization, and thermal polymerization. The results showed that the polymerization mode determines the degree of conversion (DC), which governs the ultimate mechanical properties of nanocomposites. Thermal polymerization resulted in a higher DC than photo- and room temperature polymerizations. The DC always decreased as AgNP content increased. Flexural strength, flexural modulus, hardness, and impact strength initially increased, as AgNP concentration increased, and then decreased at higher AgNP loadings. This turning point usually occurred when the DC dropped below 65% and moved toward higher AgNP concentrations, according to the following order of polymerization methods: photopolymerization < room temperature polymerization < thermal polymerization. Water sorption (WS) was also determined. Nanocomposites revealed an average decrease of 16% in WS with respect to the neat polymer. AgNP concentration did not significantly affect WS.

Estilos ABNT, Harvard, Vancouver, APA, etc.

36

Yilmaz, Gorkem. "One-Pot Synthesis of Star Copolymers by the Combination of Metal-Free ATRP and ROP Processes". Polymers 11, n.º 10 (27 de setembro de 2019): 1577. http://dx.doi.org/10.3390/polym11101577.

Texto completo da fonte

Resumo:

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.

Estilos ABNT, Harvard, Vancouver, APA, etc.

37

Buback, Michael, Wibke Meiser e Philipp Vana. "Mechanism of CPDB-Mediated RAFT Polymerization of Methyl Methacrylate: Influence of Pressure and RAFT Agent Concentration". Australian Journal of Chemistry 62, n.º 11 (2009): 1484. http://dx.doi.org/10.1071/ch09219.

Texto completo da fonte

Resumo:

Reversible addition–fragmentation chain transfer (RAFT) polymerizations of methyl methacrylate (MMA) in bulk at 60°C were performed at five pressures up to 200 MPa using 2-(2′-cyanopropyl)dithiobenzoate (CPDB) as RAFT agent at concentrations between 1.5 × 10–3 and 2.0 × 10–2 mol L–1. Applying high pressure during polymerization increases the rate of polymerization, but no effect on polydispersity was observed. Molecular weight distributions and average molecular weights of the final polymer indicated the successful control of MMA polymerization even at low CPDB concentrations. The slight retardation observed is adequately described by the dependence the termination rate coefficient, kt, on the chain-length.

Estilos ABNT, Harvard, Vancouver, APA, etc.

38

Yılmaz, Görkem, e Yusuf Yagci. "Multi-mode Polymerizations Involving Photoinduced Radical Polymerization". Journal of Photopolymer Science and Technology 31, n.º 6 (15 de dezembro de 2018): 719–25. http://dx.doi.org/10.2494/photopolymer.31.719.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

39

Braun, Dietrich. "Origins and Development of Initiation of Free Radical Polymerization Processes". International Journal of Polymer Science 2009 (2009): 1–10. http://dx.doi.org/10.1155/2009/893234.

Texto completo da fonte

Resumo:

At present worldwide about 45% of the manufactured plastic materials and 40% of synthetic rubber are obtained by free radical polymerization processes. The first free radically synthesized polymers were produced between 1910 and 1930 by initiation with peroxy compounds. In the 1940s the polymerization by redox processes was found independently and simultaneously at IG Farben in Germany and ICI in Great Britain. In the 1950s the systematic investigation of azo compounds as free radical initiators followed. Compounds with labile C–C-bonds were investigated as initiators only in the period from the end of the 1960s until the early 1980s. At about the same time, iniferters with cleavable S–S-bonds were studied in detail. Both these initiator classes can be designated as predecessors for “living” or controlled free radical polymerizations with nitroxyl-mediated polymerizations, reversible addition fragmentation chain transfer processes (RAFT), and atom transfer radical polymerizations (ATRP).

Estilos ABNT, Harvard, Vancouver, APA, etc.

40

Verebélyi, Klára, Ákos Szabó, Zsombor Réti, Györgyi Szarka, Ákos Villányi e 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, n.º 6 (8 de março de 2023): 5170. http://dx.doi.org/10.3390/ijms24065170.

Texto completo da fonte

Resumo:

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.

Estilos ABNT, Harvard, Vancouver, APA, etc.

41

Koopmann, F., A. Burgath, R. Knischka, J. Leukel e H. Frey. "Poly(methylphenylsilylenemethylene) – the carbosilane analog of poly(α ‐methylstyrene)". Acta Polymerica 47, n.º 9 (setembro de 1996): 377–85. http://dx.doi.org/10.1002/j.1521-4044.1996.tb00002.x.

Texto completo da fonte

Resumo:

The carbosilane analog of poly(α‐methylstyrene), poly(methylphenylsilylenemethylene) (PMPSM) has been prepared by ring‐opening polymerization of l,3‐dimethyl‐I,3‐diphenyl‐l,3‐disilacyclobutane (1), using various transition‐metal‐based catalysts in bulk and in solution samples from polymerization in bulk and in solution, respectively, were characterized by GPC coupled with on‐line low‐angle laser light scattering (LALLS) and viscometry. Absolute molecular weights were in the range of 200 000; however, polymerization in solution afforded higher yields of PMPSM. Polymerizations generally yielded atactic PMPSM with strictly alternating SiR1R2/CH2 backbone structure and monomodal molecular weight distribution. Radical and cationic initiators proved to be unable to effect polymerization. Polymerization of pure trans‐1 afforded PMPSM without isotactic triads. Stcreoregularity as well as polymer yields increased when polymerization was performed at low temperatures (–32 °C). Thermal properties of PMPSM were investigated. TGA analysis evidenced better thermal stability of PMPSM than poly(α‐mcthylstyrene). PMPSM shows a Tg at 28 °C, which lies between the glass transition of poly(α‐methylstyrcne) and that of poly(methylphenylsiloxane), suggesting that poly(silylenemethylenes) may structurally be ranged between the analogous carbon‐based polymers and the highly flexible poly(siloxanes).

Estilos ABNT, Harvard, Vancouver, APA, etc.

42

Wang, Jinfang, Peter A. G. Cormack, David C. Sherrington e Ezat Khoshdel. "Synthesis and characterization of micrometer-sized molecularly imprinted spherical polymer particulates prepared via precipitation polymerization". Pure and Applied Chemistry 79, n.º 9 (1 de janeiro de 2007): 1505–19. http://dx.doi.org/10.1351/pac200779091505.

Texto completo da fonte

Resumo:

In this paper, the synthesis and characterization of molecularly imprinted spherical polymer particulates prepared via precipitation polymerization is described. The effects of the monomer and initiator concentrations and the solvent on the polymerizations were investigated systematically. Polymer microspheres with narrow size distributions and average diameters up to ca. 10 μm were prepared under optimized polymerization conditions. The morphologies of the microspheres were characterized by nitrogen sorption porosimetry and the molecular recognition properties of representative products evaluated in high-performance liquid chromatography (HPLC) mode. Imprinting effects were confirmed by analyzing the relative retentions of the analytes on imprinted and non-imprinted packed HPLC columns. Finally, two different agitation/mixing methods for precipitation polymerizations were compared. It was found that the use of a low-profile roller housed inside a temperature-controlled incubator had advantages over a rotavapor-based system. Overall, this study has served to highlight the attractiveness of precipitation polymerization for the routine production of molecularly imprinted polymers in a well-defined spherical particulate form via an efficient one-step synthetic process.

Estilos ABNT, Harvard, Vancouver, APA, etc.

43

Yuan, Ming, Dayun Huang e Yixuan Zhao. "Development of Synthesis and Application of High Molecular Weight Poly(Methyl Methacrylate)". Polymers 14, n.º 13 (28 de junho de 2022): 2632. http://dx.doi.org/10.3390/polym14132632.

Texto completo da fonte

Resumo:

Poly(methyl methacrylate) (PMMA) is widely used in aviation, architecture, medical treatment, optical instruments and other fields because of its good transparency, chemical stability and electrical insulation. However, the application of PMMA largely depends on its physical properties. Mechanical properties such as tensile strength, fracture surface energy, shear modulus and Young’s modulus are increased with the increase in molecular weight. Consequently, it is of great significance to synthesize high molecular weight PMMA. In this article, we review the application of conventional free radical polymerization, atom transfer radical polymerization (ATRP) and coordination polymerization for preparing high molecular weight PMMA. The mechanisms of these polymerizations are discussed. In addition, applications of PMMA are also summarized.

Estilos ABNT, Harvard, Vancouver, APA, etc.

44

Jiang, Jianguo, Weifeng Chen, Aimin Cheng, Jin Guo e Yueshu Liu. "Preparation of Polyacrylamide with Improved Tacticity and Low Molecular Weight Distribution". BIO Web of Conferences 55 (2022): 01028. http://dx.doi.org/10.1051/bioconf/20225501028.

Texto completo da fonte

Resumo:

Polyacrylamide with improved tacticity and low molecular weight distribution was obtained via stereospecific atom transfer radical polymerization (ATRP) using the mixture of Lewis acids Y(OTf)3 and AlCl3 in a certain ratio as stereospecific catalyst and chloroacetic acid/ Cu2O / N,N,N’,N’-tetramethylethylenediamine( TMEDA) as initiating system. The initiating system afforded persistently controlled ATRP of acrylamide with lower polydispersity index ranging from 1.12 to 1.35 as well as a moderate polymerization process. The participation of the mixture of Lewis acids Y(OTf)3 and AlCl3 as stereospecific catalyst in the stereospecific ATRP of acrylamide contributed optimal stereospecific PAM with the meso content 80%~83%. Polymerization kinetics displayed a living/controlled nature of the present polymerizations.

Estilos ABNT, Harvard, Vancouver, APA, etc.

45

Arcens, Dounia, Gaëlle Le Fer, Etienne Grau, Stéphane Grelier, Henri Cramail e Frédéric Peruch. "Chemo-enzymatic synthesis of glycolipids, their polymerization and self-assembly". Polymer Chemistry 11, n.º 24 (2020): 3994–4004. http://dx.doi.org/10.1039/d0py00526f.

Texto completo da fonte

Resumo:

This paper describes the synthesis of bio-based methacrylated 12-hydroxystearate glucose (MASG), and its (co)polymerization with methyl methacrylate (MMA) by either free- or RAFT radical polymerizations.

Estilos ABNT, Harvard, Vancouver, APA, etc.

46

Hatada, K., J. Kahovec, Máximo Barón, K. Horie, T. Kitayama, P. Kubisa, G. P. Moss, R. F. T. Stepto e E. S. Wilks. "Definitions relating to stereochemically asymmetric polymerizations (IUPAC Recommendations 2001)". Pure and Applied Chemistry 74, n.º 6 (1 de janeiro de 2002): 915–22. http://dx.doi.org/10.1351/pac200274060915.

Texto completo da fonte

Resumo:

Asymmetric polymerization has been of interest to many academic and industrial polymer scientists, but no reference has been made by IUPAC explicitly to classification and definitions of reactions involving the asymmetric synthesis of polymers. This document presents definitions concerned with asymmetric and related polymerizations, with examples included to clarify the meaning of the definitions. Asymmetric polymerizations embrace two main categories, "asymmetric chirogenic polymerizations" and "asymmetric enantiomer-differentiating polymerizations".

Estilos ABNT, Harvard, Vancouver, APA, etc.

47

Kang, Yan, Anaïs Pitto-Barry, Helen Willcock, Wen-Dong Quan, Nigel Kirby, Ana M. Sanchez e Rachel K. O'Reilly. "Exploiting nucleobase-containing materials – from monomers to complex morphologies using RAFT dispersion polymerization". Polymer Chemistry 6, n.º 1 (2015): 106–17. http://dx.doi.org/10.1039/c4py01074d.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

48

Zhang, Zhen, Baiyu Jiang, Feng He, Zhisheng Fu, Junting Xu e Zhiqiang Fan. "Comparative Study on Kinetics of Ethylene and Propylene Polymerizations with Supported Ziegler–Natta Catalyst: Catalyst Fragmentation Promoted by Polymer Crystalline Lamellae". Polymers 11, n.º 2 (19 de fevereiro de 2019): 358. http://dx.doi.org/10.3390/polym11020358.

Texto completo da fonte

Resumo:

The kinetic behaviors of ethylene and propylene polymerizations with the same MgCl2-supported Ziegler–Natta (Z–N) catalyst containing an internal electron donor were compared. Changes of polymerization activity and active center concentration ([C*]) with time in the first 10 min were determined. Activity of ethylene polymerization was only 25% of that of propylene, and the polymerization rate (Rp) quickly decayed with time (tp) in the former system, in contrast to stable Rp in the latter. The ethylene system showed a very low [C*]/[Ti] ratio (<0.6%), in contrast to a much higher [C*]/[Ti] ratio (1.5%–4.9%) in propylene polymerization. The two systems showed noticeably different morphologies of the nascent polymer/catalyst particles, with the PP/catalyst particles being more compact and homogeneous than the PE/catalyst particles. The different kinetic behaviors of the two systems were explained by faster and more sufficient catalyst fragmentation in propylene polymerization than the ethylene system. The smaller lamellar thickness (<20 nm) in nascent polypropylene compared with the size of nanopores (15–25 nm) in the catalyst was considered the key factor for efficient catalyst fragmentation in propylene polymerization, as the PP lamellae may grow inside the nanopores and break up the catalyst particles.

Estilos ABNT, Harvard, Vancouver, APA, etc.

49

Monteiro, M. J., R. Bussels, S. Beuermann e M. Buback. "High Pressure 'Living' Free-Radical Polymerization of Styrene in the Presence of RAFT". Australian Journal of Chemistry 55, n.º 7 (2002): 433. http://dx.doi.org/10.1071/ch02079.

Texto completo da fonte

Resumo:

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.

Estilos ABNT, Harvard, Vancouver, APA, etc.

50

Gallaway, Joshua B. L., Justin R. K. McRae, Andreas Decken e Michael P. Shaver. "Ring-opening polymerization of rac-lactide and ε-caprolactone using zinc and calcium salicylaldiminato complexes". Canadian Journal of Chemistry 90, n.º 5 (maio de 2012): 419–26. http://dx.doi.org/10.1139/v2012-012.

Texto completo da fonte

Resumo:

Tridentate Schiff base complexes of zinc and calcium were prepared and tested in the ring-opening polymerization of ε-caprolactone and rac-lactide to generate biodegradable polymeric materials from biocompatible metals. Alteration of the pendant donor arm attached to the imine backbone provides some control over catalyst composition and polymerization activity. Complexes of the formula [ONN]ZnN(SiMe3)2, where [ONN] = 2-(N-donor arm-imine)[4,6-di(tert-butyl)phenoxide], were isolated with ethyldimethylamine, ethylpiperidine, and ethylmorpholine substituents, while disproportionation led to the isolation of [ONN]2Zn complexes with methylpyridine, quinoline, and ethyldiisopropylamine derivatives, two of which were crystallographically characterized. Calcium complexes were more stable and novel [ONN]CaN(SiMe3)2 complexes with ethylpiperidine and ethyldiisopropylamine substituents were reported. Zinc and calcium catalysts coordinated to a single tridentate ligand were effective at initiating the polymerization of ε-caprolactone, but did not control the polymerizations, whereas the bis(ligand) complexes produced no polymer. These catalysts were effective at controlling the polymerization of rac-lactide. Coordinatively saturated complexes inhibit the polymerization, while initiation from either the amido or ligand alkoxide functionalities produces poly(lactic acid) with low polydispersities.

Estilos ABNT, Harvard, Vancouver, APA, etc.

Artigos de revistas sobre o tema "Polymerization"

Crie uma referência precisa em APA, MLA, Chicago, Harvard, e outros estilos