DOCSLIB.ORG

Kinetic Study of Coordinative Chain Transfer Polymerization of Ethylene by Neodymium Metallocene Catalysts

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Kinetic Study of Coordinative Chain Transfer Polymerization of Ethylene by Neodymium Metallocene Catalysts Kinetic study of coordinative chain transfer polymerization of ethylene by neodymium metallocene catalysts Rodolfo André da Costa Fialho Ribeiro Thesis to obtain the Master of Science Degree in Chemical Engineering Supervisors Prof.ª Dr.ª Maria do Rosário Gomes Ribeiro Dr. Christophe Boisson Examination Committee Chairperson: Prof. Dr. Carlos Manuel Faria de Barros Henriques Supervisor: Prof.ª Dr.ª Maria do Rosário Gomes Ribeiro Member of the Committee: Prof. Dr. João Carlos Moura Bordado November 2015 This page was intentionally left blank. ii Abstract Ethylene polymerizations at 70-90ºC in toluene were performed using a combination of ∗ Cp2NdCl2Li(OEt2)2 (Cp* = C5Me5) or {Me2SiFlu2Nd(µ-BH4)[(µ-BH4)Li(THF)]}2 (Flu = C13H8) neodymium complexes with n-butyl-n-octyl-magnesium used as both alkylating and chain transfer agent. Kinetic studies were performed for the two catalytic systems by varying the Mg/Nd ratio, which is a critical parameter for polymerization control. Both systems were able to perform a controlled polymerization of ethylene and displayed the same phases on the kinetic profiles, reflecting the Coordinative Chain Transfer Polymerization mechanism. The effect of the polymerization temperature was studied for the determination of the propagation activation energy using the Arrhenius equation. A -1 ∗ value of 17.3 kcal.mol was obtained for the Cp2NdCl2Li(OEt2)2/n-butyl-n-octyl-magnesium system. The {Me2SiFlu2Nd(µ-BH4)[(µ-BH4)Li(THF)]}2/n-butyl-n-octyl-magnesium system did not display a linear Arrhenius plot and consequently the activation energy was not determined for this catalyst. Specific molar masses were targeted in order to evaluate the polymerization control efficiency. The co-solvent effect was also explored via addition of dibutyl ether (Bu2O). Unimodal molar mass distributions were obtained, and polymerization rates were enhanced in the presence of the co-solvent without affecting the polymerization control. Finally, a sampling experiment was performed to observe the pseudo-living behaviour of the Coordinative Chain Transfer Polymerization mechanism. Keywords: Neodymium, polyethylene, metallocene, kinetics, mechanism, coordinative chain transfer polymerization iii This page was intentionally left blank. iv Resumo Polimerizações de etileno a 70-90ºC em tolueno foram realizados usando uma combinação de ∗ complexos de neodímio Cp2NdCl2Li(OEt2)2 (Cp* = C5Me5) ou {Me2SiFlu2Nd(µ-BH4)[(µ-BH4)Li(THF)]}2 (Flu = C13H8) com n-butil-n-octilmagnésio, sendo este usado tanto como agente alquilante e como agente de transferência de cadeia. Estudos cinéticos foram realizados para os dois sistemas catalíticos variando a razão Mg/Nd, que é um parâmetro critíco para o controlo da polimerização. Ambos os sistemas permitiram realizar polimerizações controladas de etileno e mostraram as mesmas fases nos perfis cinéticos, reflectindo o mecanismo de polimerização de coordenação por transferência de cadeia. O efeito da temperatura na polimerização foi estudada de modo a determinar a energia de activação da propagação usando a -1 ∗ equação de Arrhenius. Um valor de 17.3 kcal.mol foi obtido para o sistema Cp2NdCl2Li(OEt2)2/n-butil- n-octilmagnésio. Para o sistema {Me2SiFlu2Nd(µ-BH4)[(µ-BH4)Li(THF)]}2/n-butil-n-octilmagnésio não foi obtido um ajuste linear do gráfico de Arrhenius, pelo que a energia de activação da propagação não foi determinada. Polimerizações tendo como alvo massas molares específicas foram realizadas a fim de avaliar a eficiência do controlo da polimerização. O efeito do co-solvente foi também explorado pela adição de éter dibutílico (Bu2O). Distribuições unimodais de massas molares foram obtidas e a velocidade de polimerização aumentou na presença do co-solvente sem afectar o controlo da polimerização. Por último, foi realizada uma reacção de polimerização com extracção de amostras ao longo do tempo de forma a observar o comportamento pseudo-vivo do mecanismo de polimerização de coordenação por transferência de cadeia. Palavras-Chave: Neodímio, polietileno, metaloceno, cinética, mecanismo, polimerização de coordenação por transferência de cadeia v This page was intentionally left blank. vi Acknowledgments This thesis is the end of a life chapter. It would not be possible without the help, advice and collaboration of some great people, to whom I express a word of gratitude. First of all, I would like to thank my supervisors at the C2P2 laboratory, Dr. Christophe Boisson and Dr. Frank D’Agosto, for their guidance, scientific advice and support during this internship and the final revision of this manuscript. Also, I would like to thank my IST supervisor, Professor Maria Rosário Ribeiro, for the opportunity to do this internship, fruitful discussions and suggestions/remarks given for the revision of this work. I am very grateful to Islem Belaid for her advice, support and patience throughout my entire internship. I also would like to thank Dr. Sébastien Norsic for teaching me all the techniques and polymerization skills which were essential to the completion of this work. A word of appreciation to Manel Taam and Olivier Boyron for all the knowledge and guidance in the SEC analysis. I would like to thank my colleagues from C2P2 for making my stay in Lyon a great experience and also my university colleagues for the friendship during the last five years. A huge thanks to all my closest friends for their friendship and companionship during this last five years, and especially over the course of my life. We shared good and bad moments and I am sure we will be great friends for life. I am deeply grateful to my entire family for their support, especially to my uncle Miguel and to my grandmothers Conceição and Albertina. Last but not least, I would like to dedicate this thesis to my parents, António and Luísa, as a sign of respect and recognition for all their efforts and dedication throughout my entire life. Their love and unconditional support are essential for my happiness and without them I could not achieve my life objectives. A todos, muito obrigado! vii This page was intentionally left blank. viii Table of Contents ABSTRACT ............................................................................................................................................ III RESUMO ................................................................................................................................................. V ACKNOWLEDGMENTS ....................................................................................................................... VII TABLE OF CONTENTS ......................................................................................................................... IX LIST OF FIGURES ................................................................................................................................. XI LIST OF TABLES .................................................................................................................................XIV LIST OF ACRONYMS ..........................................................................................................................XVI LIST OF SYMBOLS ............................................................................................................................XVII 1. INTRODUCTION .............................................................................................................................. 1 1.1. CONTEXT AND OBJECTIVE ............................................................................................................ 1 1.2. THESIS STRUCTURE ..................................................................................................................... 2 2. LITERATURE REVIEW .................................................................................................................... 3 2.1. BRIEF POLYETHYLENE OVERVIEW ................................................................................................ 3 2.2. POLYETHYLENE SYNTHESIS AND NEODYMIUM METALLOCENE CATALYSTS ....................................... 5 2.2.1. Free Radical Polymerization .............................................................................................. 5 2.2.2. Coordination Polymerization .............................................................................................. 6 2.2.2.1. Phillips Catalysts .......................................................................................................................... 8 2.2.2.2. Ziegler-Natta Catalysts ................................................................................................................ 8 2.2.2.3. Late Transition Metals Catalysts .................................................................................................. 8 2.2.2.4. Metallocenes ................................................................................................................................ 8 2.2.3. Conclusion ........................................................................................................................ 11 2.3. COORDINATIVE CHAIN TRANSFER POLYMERIZATION .................................................................... 12 2.3.1. Concept ............................................................................................................................ 12 2.3.2. Specialty Polymers .......................................................................................................... 15 Production of olefin multiblock copolymers via chain shuttling polymerization:
Load more

Recommended publications
  • Cationic/Anionic/Living Polymerizationspolymerizations Objectives
    Chemical Engineering 160/260 Polymer Science and Engineering LectureLecture 1919 -- Cationic/Anionic/LivingCationic/Anionic/Living PolymerizationsPolymerizations Objectives • To compare and contrast cationic and anionic mechanisms for polymerization, with reference to free radical polymerization as the most common route to high polymer. • To emphasize the importance of stabilization of the charged reactive center on the growing chain. • To develop expressions for the average degree of polymerization and molecular weight distribution for anionic polymerization. • To introduce the concept of a “living” polymerization. • To emphasize the utility of anionic and living polymerizations in the synthesis of block copolymers. Effect of Substituents on Chain Mechanism Monomer Radical Anionic Cationic Hetero. Ethylene + - + + Propylene - - - + 1-Butene - - - + Isobutene - - + - 1,3-Butadiene + + - + Isoprene + + - + Styrene + + + + Vinyl chloride + - - + Acrylonitrile + + - + Methacrylate + + - + esters • Almost all substituents allow resonance delocalization. • Electron-withdrawing substituents lead to anionic mechanism. • Electron-donating substituents lead to cationic mechanism. Overview of Ionic Polymerization: Selectivity • Ionic polymerizations are more selective than radical processes due to strict requirements for stabilization of ionic propagating species. Cationic: limited to monomers with electron- donating groups R1 | RO- _ CH =CH- CH =C 2 2 | R2 Anionic: limited to monomers with electron- withdrawing groups O O || || _ -C≡N -C-OR -C- Overview of Ionic Chain Polymerization: Counterions • A counterion is present in both anionic and cationic polymerizations, yielding ion pairs, not free ions. Cationic:~~~C+(X-) Anionic: ~~~C-(M+) • There will be similar effects of counterion and solvent on the rate, stereochemistry, and copolymerization for both cationic and anionic polymerization. • Formation of relatively stable ions is necessary in order to have reasonable lifetimes for propagation.
    [Show full text]
  • Living Free Radical Polymerization with Reversible Addition – Fragmentation
    Polymer International Polym Int 49:993±1001 (2000) Living free radical polymerization with reversible addition – fragmentation chain transfer (the life of RAFT) Graeme Moad,* John Chiefari, (Bill) YK Chong, Julia Krstina, Roshan TA Mayadunne, Almar Postma, Ezio Rizzardo and San H Thang CSIRO Molecular Science, Bag 10, Clayton South 3169, Victoria, Australia Abstract: Free radical polymerization with reversible addition±fragmentation chain transfer (RAFT polymerization) is discussed with a view to answering the following questions: (a) How living is RAFT polymerization? (b) What controls the activity of thiocarbonylthio compounds in RAFT polymeriza- tion? (c) How do rates of polymerization differ from those of conventional radical polymerization? (d) Can RAFT agents be used in emulsion polymerization? Retardation, observed when high concentra- tions of certain RAFT agents are used and in the early stages of emulsion polymerization, and how to overcome it by appropriate choice of reaction conditions, are considered in detail. Examples of the use of thiocarbonylthio RAFT agents in emulsion and miniemulsion polymerization are provided. # 2000 Society of Chemical Industry Keywords: living polymerization; controlled polymerization; radical polymerization; dithioester; trithiocarbonate; transfer agent; RAFT; star; block; emulsion INTRODUCTION carbonylthio compounds 2 by addressing the following In recent years, considerable effort1,2 has been issues: expended to develop free radical processes that display (a) How living is RAFT polymerization?
    [Show full text]
  • Polymer Chemistry
    Polymer Chemistry Properties and Application Bearbeitet von Andrew J Peacock, Allison Calhoun 1. Auflage 2006. Buch. XIX, 399 S. Hardcover ISBN 978 3 446 22283 0 Format (B x L): 17,5 x 24,5 cm Gewicht: 1088 g Weitere Fachgebiete > Chemie, Biowissenschaften, Agrarwissenschaften > Biochemie > Polymerchemie Zu Inhaltsverzeichnis schnell und portofrei erhältlich bei Die Online-Fachbuchhandlung beck-shop.de ist spezialisiert auf Fachbücher, insbesondere Recht, Steuern und Wirtschaft. Im Sortiment finden Sie alle Medien (Bücher, Zeitschriften, CDs, eBooks, etc.) aller Verlage. Ergänzt wird das Programm durch Services wie Neuerscheinungsdienst oder Zusammenstellungen von Büchern zu Sonderpreisen. Der Shop führt mehr als 8 Millionen Produkte. Produktinformation Seite 1 von 1 Polymer Chemistry Allison Calhoun, Andrew James Peacock Properties and Application ISBN 3-446-22283-9 Leseprobe Weitere Informationen oder Bestellungen unter http://www.hanser.de/3-446-22283-9 sowie im Buchhandel http://www.hanser.de/deckblatt/deckblatt1.asp?isbn=3-446-22283-9&style=Leseprobe 05.05.2006 2 Polymer Chemistry 2.1 Introduction In this chapter, we will see how polymers are manufactured from monomers. We will explore the chemical mechanisms that create polymers as well as how polymerization methods affect the final molecular structure of the polymer. We will look at the effect of the chemical structure of monomers, catalysts, radicals, and solvents on polymeric materials. Finally, we will apply our molecular understanding to the real world problem of producing polymers on a commercial scale. 2.2 Thermoplastics and Thermosets Thermoplastics consist of linear or lightly branched chains that can slide past one another under the influence of temperature and pressure.
    [Show full text]
  • Effect of Chain Transfer to Polymer in Conventional and Living Emulsion Polymerization Process
    processes Article Effect of Chain Transfer to Polymer in Conventional and Living Emulsion Polymerization Process Hidetaka Tobita ID Department of Materials Science and Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507, Japan; [email protected]; Tel.: +81-776-27-8767 Received: 28 December 2017; Accepted: 5 February 2018; Published: 7 February 2018 Abstract: Emulsion polymerization process provides a unique polymerization locus that has a confined tiny space with a higher polymer concentration, compared with the corresponding bulk polymerization, especially for the ab initio emulsion polymerization. Assuming the ideal polymerization kinetics and a constant polymer/monomer ratio, the effect of such a unique reaction environment is explored for both conventional and living free-radical polymerization (FRP), which involves chain transfer to the polymer, forming polymers with long-chain branches. Monte Carlo simulation is applied to investigate detailed branched polymer architecture, including 2 the mean-square radius of gyration of each polymer molecule, <s >0. The conventional FRP shows a very broad molecular weight distribution (MWD), with the high molecular weight region conforming to the power law distribution. The MWD is much broader than the random branched 2 polymers, having the same primary chain length distribution. The expected <s >0 for a given MW is much smaller than the random branched polymers. On the other hand, the living FRP shows a much narrower MWD compared with the corresponding random branched polymers. Interestingly, 2 the expected <s >0 for a given MW is essentially the same as that for the random branched polymers. Emulsion polymerization process affects branched polymer architecture quite differently for the conventional and living FRP.
    [Show full text]
  • Molecular Weight Control in Emulsion Polymerization by Catalytic Chain Transfer : Aspects of Process Development
    Molecular weight control in emulsion polymerization by catalytic chain transfer : aspects of process development Citation for published version (APA): Smeets, N. M. B. (2009). Molecular weight control in emulsion polymerization by catalytic chain transfer : aspects of process development. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR642709 DOI: 10.6100/IR642709 Document status and date: Published: 01/01/2009 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.
    [Show full text]
  • 1.1 Basic Polymer Chemistry 1.2 Polymer Nomenclature 1.3 Polymer
    1.1 Basic Polymer Chemistry 1.2 Polymer Nomenclature Polymers are the largest class of soft materials: over Polymer = 100 billion pounds of polymers made in US each year Monomer = Classification systems Polymer = Typical physical state? Mechanisms of chain growth Oligomer = Typical physical state? Polymerization = 1.3 Polymer Synthesis 1.4 Chain Growth Polymerization Two synthetic methods Addition polymerization Chain growth/addition polymerization One molecule adds to another with no net loss of atoms (high atom economy) Individual steps are typically rapid (msec, sec) Discrete steps Step growth polymerization Propagation rate >> termination rate What happens if the reaction runs longer? Do the chains get longer? Do you just get more chains? 1 1.5 Chain Growth Polymerization 1.6 Monomers for Chain Growth Addition polymerization Polymers form by… What’s in the polymerization mixture? Defining features Useful monomers for chain growth CH3 Cl CH2 CH CH CH Monomer Polymer H2C H2C H2C H2C ethylenepropylene styrene vinyl chloride nCH2 CH (CH2 CH)n X X O N X X C O O-CH3 CH2 O CH3 C HC C nCH2 CH (CH2 CH O)n CH C CH CH CH O H2C H2C 3 H2C H2C vinyl acetate methyl methacrylate butadiene acrylonitrile 1.7 Chain Growth Polymerization 2.1 Radical Polymerization Mechanisms to link monomers together Three steps to radical polymerization Radical Initiation Cationic (1) RO OR 2RO Anionic Transition metal catalysis (2) RO + H2C CH RO CH2 CH R R Propagation RO CH2 CH + H2C CH RO CH2 CH CH2 CH R R R R Termination 2 2.2 Radical
    [Show full text]
  • Hyperbranched Polymers with Step-Growth Chemistries from Transfer-Dominated Branching Radical Telomerisation (TBRT) of Divinyl Monomers Polymer Chemistry
    Volume 11 Number 48 28 December 2020 Polymer Pages 7575-7730 Chemistry rsc.li/polymers ISSN 1759-9962 PAPER Steve P. Rannard et al. Hyperbranched polymers with step-growth chemistries from transfer-dominated branching radical telomerisation (TBRT) of divinyl monomers Polymer Chemistry View Article Online PAPER View Journal | View Issue Hyperbranched polymers with step-growth chemistries from transfer-dominated branching Cite this: Polym. Chem., 2020, 11, 7637 radical telomerisation (TBRT) of divinyl monomers† Savannah R. Cassin,a,b Pierre Chambona,b and Steve P. Rannard *a,b The commercial synthesis of polymers is generally limited to two main mechanisms that are typically con- sidered to be mutually exclusive, namely step-growth and chain-growth polymerisation. This also defines the vast number of academic advances in macromolecular synthesis including the increasingly studied reversible deactivation radical polymerisation techniques (chain-growth) and complex polymer architec- tures such as dendrimers (step-growth). We report here a new synthetic strategy that utilises conventional free radical chain-growth chemistry, under modified telomerisation conditions, to form branched poly- Creative Commons Attribution 3.0 Unported Licence. mers containing chemistries conventionally formed under step-growth conditions. Telomerisation is typi- cally limited to small molecule synthesis and employs addition across the unsaturated bond of a substrate, whilst minimising intermolecular reaction between substrates. Through the careful manipulation of reac- Received 12th September 2020, tion conditions, we have created a ‘transfer dominated branching radical telomerisation’ mechanism that Accepted 15th November 2020 creates branched polymers containing step-growth motifs from multi-vinyl monomers, with molecular DOI: 10.1039/d0py01309a weights in excess of 1000 kg mol−1, using industrially relevant free radical chain-growth chemistry.
    [Show full text]
  • Kinetics of Chain Transfer Agents in Photopolymer Material
    Kinetics of Chain Transfer Agents in Photopolymer Material Jinxin Guo1, Michael R. Gleeson2, and John T. Sheridan1* 1School of Electrical, Electronic and Communications Engineering, College of Engineering and Architecture, Communications and Optoelectronic Research Centre, The SFI-Strategic Research Cluster in Solar Energy Conversion, University College Dublin, Belfield, Dublin 4, Ireland. 2Department of Computer Science, National University of Ireland Maynooth, Maynooth, Co. Kildare, Ireland. *Corresponding author: [email protected]; Tel: +353 (0)1 716 1927 ABSTRACT The Non-local Photo-Polymerization Driven Diffusion (NPDD) model was introduced to describe the observed drop-off in the material’s response for higher exposing spatial frequencies. Recent work carried out on the modeling of the mechanisms which occur in photopolymers during- and post-exposure, has led to the development of a tool, which can be used to predict the behaviour of these materials under a wide range of conditions. In this article, based on the chemical reactions of chain transfer agents, we explore this extended NPDD model, illustrating some of the useful trends, which the model predicts and we analyse their implications on the improvement of photopolymer material performance. Keywords: Holography, photopolymer material, chain transfer agent. 1. INTRODUCTION Photopolymer materials are being actively studied for practical applications such as holographic data storage, hybrid optoelectronics, photo embossing, including the manufacture of refractive and diffractive optical elements, and the self- trapping of light.1-4 Generally, in photopolymers, the photosensitizer absorbs light of an appropriate wavelength, becoming excited and causing the production of primary radicals, R•. In free radical polymerization systems, the generation of R• leads to monomer being polymerized.
    [Show full text]
  • Computational Study of Chain Transfer to Monomer Reactions In
    Article pubs.acs.org/JPCA Computational Study of Chain Transfer to Monomer Reactions in High-Temperature Polymerization of Alkyl Acrylates † ‡ § ∥ † Nazanin Moghadam, Shi Liu, Sriraj Srinivasan, Michael C. Grady, Masoud Soroush,*, ‡ and Andrew M. Rappe † Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania 19104, United States ‡ The Makineni Theoretical Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States § Arkema Inc., 900 First Avenue, King of Prussia, Pennsylvania 19406, United States ∥ DuPont Experimental Station, Wilmington, Delaware 19898, United States *S Supporting Information ABSTRACT: This article presents a computational study of chain transfer to monomer (CTM) reactions in self-initiated high-temperature homopolymerization of alkyl acrylates (methyl, ethyl, and n-butyl acrylate). Several mechanisms of CTM are studied. The effects of the length of live polymer chains and the type of monoradical that initiated the live polymer chains on the energy barriers and rate constants of the involved reaction steps are investigated theoretically. All calculations are carried out using density functional theory. Three types of hybrid functionals (B3LYP, X3LYP, and M06- 2X) and four basis sets (6-31G(d), 6-31G(d,p), 6-311G(d), and 6-311G(d,p)) are applied to predict the molecular geometries of the reactants, products and transition sates, and energy barriers. Transition state theory is used to estimate rate constants. The results indicate that abstraction of a hydrogen atom (by live polymer chains) from the methyl group in methyl acrylate, the methylene group in ethyl acrylate, and methylene groups in n-butyl acrylate are the most likely mechanisms of CTM.
    [Show full text]
  • 1 051110 Quiz 7 Introduction to Polymers (Chemistry)
    051110 Quiz 7 Introduction to Polymers (Chemistry) 1) Termination of chain growth can occur by coupling/disproportionation or through a variety of chain transfer reactions. a) What does chain transfer mean? b) Does chain transfer affect the rate of consumption of monomers (rate of propagation)? c) Chain transfer to initiator [I2] involves the reaction, P· + I2 => PI + I· (1) write an expression for the rate of chain transfer to initiator using the initiator concentration [I2] and the concentration of propagating species [P·]. 1/2 d) At steady state [P·] ~ [I2] . Write an expression for the kinetic chain length, ν = Rp/Rt, where Rt includes all reactions that end chain growth. e) Explain why 1/ν is a more useful function that ν from part d. f) Write an equation for the rate of chain transfer to polymer and explain why this might be important to the quality of polymer product. 2) Critique the following polymerization of polystyrene (PS) that contains BHT (butylated hydroxyl toluene or t-butylcatechol): To a small amount of PS we add benzyl peroxide (DBP) and expose at room temperature to UV radiation. a) What is BHT and why/how can it be removed? b) Does DBP initiate when exposed to UV? How is DBP initiated? c) When bulk polymerization of PS was successful a viscous liquid with about 60% conversion and a molecular weight of about 4000 g/mole resulted. Is this surprising? Explain the problems with bulk polymerization that can lead to this result. d) When adding solvent to polymerization of MMA, below, the conversion versus time shows several characteristic features.
    [Show full text]
  • Living Radical Polymerization: a Review
    Tran DF sfo P rm Y e Y r B 2 B . 0 A Click here to buy w w m w co .A B BYY. 141 Journal of Scientific Research Vol. 56, 2012 : 141-176 Banaras Hindu University, Varanasi ISSN : 0447-9483 LIVING RADICAL POLYMERIZATION: A REVIEW Vivek Mishra and Rajesh Kumar* Organic Polymer Laboratory, Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi-221005, E-mail: [email protected] E-mail: [email protected] 1. Introduction Free radical polymerization is one of the most widely employed polymerization techniques. This technique is applied to prepare latexes to be used in paints, high ® molecular weight poly (methyl methacrylate) for safety glass (Plexiglas ), or foamed poly (styrene) to be applied in coffee cups. Some advantages of radical polymerizations, with respect to other techniques, are the relative insensitivity to impurities, the moderate reaction temperatures and the multiple polymerization processes available, e.g., bulk, solution, precipitation or emulsion polymerization. Some disadvantages related to the mechanism of free radical polymerization is the poor control of the molecular weight and the molecular weight distribution, and the difficulty (or even impossibility) of preparing well-defined copolymers or polymers with a predetermined functionality. To overcome these disadvantages new techniques were developed based on either reversible deactivation of polymer radicals or a degenerative transfer process, called ‘living’ or controlled radical polymerizations (CRP). It will be worthwhile to discuss the significance of the living radical polymerization process because of which it was selected for the present investigation. Controlled radical polymerizations, like atom transfer radical polymerizations (ATRP) [1], reversible addition-fragmentation chain transfer polymerization (RAFT) [2, 3], and nitroxide-mediated polymerizations (NMP) [4] represent key strategies for the preparation of polymers with narrow molecular weight distributions.
    [Show full text]
  • Chapter 8 Ionic Chain Polymerization
    Chapter 8 Ionic Chain Polymerization The carbon–carbon double bond can be polymerized either by free radical or ionic methods. The difference arises because the p-bond of a vinyl monomer can respond appropriately to the initiator species by either homolytic or heterolytic bond breakage as shown in Eq. 8.1. CC CC CC ð8:1Þ Although radical, cationic, and anionic initiators are used in chain polymeri- zations, they cannot be used indiscriminately, since all three types of initiation do not work for all monomers. Monomers show varying degrees of selectivity with regard to the type of reactive center that will cause their polymerization. Most monomers will undergo polymerization with a radical initiator, although at varying rates. However, monomers show high selectivity toward ionic initiators [1]. Some monomers may not polymerize with cationic initiators, while others may not polymerize with anionic initiators. The coordination polymerization requires coordination catalyst to synthesize polymers. It has been used extensively to polymerize high performance polyolefin but seldom used in the polymerization of polar monomer [2]. The detailed mechanisms of coordination polymerization will be discussed in Chap. 9. The various behaviors of monomers toward polymeri- zation can be seen in Table 8.1. The types of initiation that bring about the polymerization of various monomers to high-molecular-weight polymer are indi- cated. Thus, although the polymerization of all monomers in Table 8.1 is ther- modynamically feasible, kinetic feasibility is achieved in many cases only with a specific type of initiation. The carbon–carbon double bond in vinyl monomers and the carbon–oxygen double bond in aldehydes and ketones are the two main types of linkages that undergo chain polymerization.
    [Show full text]