Polymerisation Reactions

12 Key excerpts on "Polymerisation Reactions"

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  Chemistry of Petrochemical Processes

  • Sami Matar Ph.D., Lewis F. Hatch Ph.D., Sami Matar, Ph.D., Lewis F. Hatch, Ph.D.(Authors)
  • 2001(Publication Date)
  • Gulf Professional Publishing

    (Publisher)

  CHAPTER ELEVEN Polymerization INTRODUCTION Polymerization is a reaction in which chain-like macromolecules are formed by combining small molecules (monomers). Monomers are the building blocks of these large molecules called polymers. One natural polymer is cellulose (the most abundant organic compound on earth), a molecule made of many simple glucose units (monomers) joined together through a glycoside linkage. ~ Proteins, the material of life, are polypeptides made of ~-amino acids attached by an amide 0 II --(- CNH-)-- linkage. The polymer industry dates back to the 19th century, when natural polymers, such as cotton, were modified by chemical treatment to pro- duce artificial silk (rayon). Work on synthetic polymers did not start until the beginning of the 20th century. In 1909, L. H. Baekeland prepared the first synthetic polymeric material using a condensation reaction between formaldehyde and phenol. Currently, these polymers serve as important thermosetting plastics (phenol formaldehyde resins). Since Baekeland's discovery, many polymers have been synthesized and marketed. Many modern commercial products (plastics, fibers, rubber) derive from poly- mers. The huge polymer market directly results from extensive work in synthetic organic compounds and catalysts. Ziegler's discovery of a coordination catalyst in the titanium family paved the road for synthe- sizing many stereoregular polymers with improved properties. This chapter reviews the chemistry involved in the synthesis of polymers. 301 302 Chemistry of Petrochemical Processes MONOMERS, POLYMERS, AND COPOLYMERS A monomer is a reactive molecule that has at least one functional group (e.g.-OH,-COOH,-NH2,-C=C-). Monomers may add to them- selves as in the case of ethylene or may react with other monomers hav- ing different functionalities. A monomer initiated or catalyzed with a specific catalyst polymerizes and forms a macromolecule~a polymer.

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  Principles of Polymer Systems

  • Ferdinand Rodriguez, Claude Cohen, Christopher K. Ober, Lynden Archer(Authors)
  • 2014(Publication Date)
  • CRC Press

    (Publisher)

  107 Polymer Formation 4.1 POLYMERIZATION REACTIONS Polymerization is the process of joining together small molecules by covalent bonds to produce high-molecular-weight polymers. Both natural and synthetic polymers are built from these simple small molecular units known as monomers. However, the range of properties that can be achieved depends on the strategy used to assemble these units. This chapter covers many of the synthetic strategies used to build poly-mers and provides examples of several of the commercial polymers made with these techniques. There are basically two approaches to polymer formation: chain-growth and step-growth polymerization. Chain-growth polymerization involves combining monomers with similar reactive functions starting from a single reactive site and growing the polymer chain from that site. The reactive chain site can be a cation, an anion, or a radical. The type of chain-growth polymerization selected depends on the monomer to be used and the requirements of the target polymer. Among the recent inventions in polymerization chemistry has been living polymerization that permits the growth of polymer chains with identical molecular weights and enables the creation of block copolymers or other polymers with well-controlled structures. Certain transition metals will also catalyze polymer formation with hydrocar-bon vinyl monomers. This work resulted in the Nobel Prize in Chemistry in 1955. Such polymers include polyethylene and polypropylene and are among the largest volume polymers produced. More recently the 2000 Nobel Prize in Chemistry has been awarded for the discovery of conducting polymers, also first made by metal-catalyzed chain-growth polymerization. More recently again, the 2005 Nobel Prize in Chemistry has been awarded for work on ring-opening metathesis polymerization and the development of new functional group-tolerant catalysts for this polymeriza-tion reaction.

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  Handbook of Petrochemical Processes

  • James G. Speight(Author)
  • 2019(Publication Date)
  • CRC Press

    (Publisher)

  The polymer field is versatile and fast growing, and many new polymers are continually being produced or improved. The basic chemistry principles involved in polymer synthesis have not changed much since the beginning of polymer production. Major changes in the last 70 years have occurred in the catalyst field and in process development. These improvements have a great impact on the economy. In the elastomer field, for example, improvements influenced the automobile industry and also related fields such as mechanical goods and wire and cable insulation.

  Recognition that polymers make up many important natural materials was followed by the creation of synthetic analogs having a variety of properties. Indeed, applications of these materials as fibers, flexible films, adhesives, resistant paints, and tough but light solids have transformed modern society. Polymers are formed by chemical reactions in which a large number of monomers are joined sequentially, forming a chain. In many polymers, only one monomer is used. In others, two or three different monomers may be combined.

  Polymers are classified by the characteristics of the reactions by which they are formed. If all atoms in the monomers are incorporated into the polymer, the polymer is called an addition polymer (Table 11.4 ). If some of the atoms of the monomers are released into small molecules, such as water, the polymer is called a condensation polymer. Most addition polymers are made from monomers containing a double bond between carbon atoms and are typical of polymers formed from olefin derivatives (olefin derivatives), and most commercial addition polymers are polyolefin derivatives. Condensation polymers are made from monomers that have two different groups of atoms which can join together to form, for example, ester or amide links. Polyesters are an important class of commercial polymers, as are polyamides (nylon).

  TABLE 11.4Glass Transition Temperatures of Various Polymers

  Hydrocarbon derivatives (in this case, alkene derivatives unsaturated hydrocarbon derivatives) are prevalent in the formation of addition polymers but do not usually participate in the formation of condensation polymers. The term polymer in popular usage suggests plastic but actually refers to a large class of natural and synthetic materials with a wide range of properties.

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  The Chemistry of Polymers

  • John W Nicholson(Author)
  • 2017(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  2 Polymerisation Reactions

  As outlined in Chapter 1, Polymerisation Reactions can be classified as either condensation or addition processes, the basis of the classification suggested by W. H. Carothers in 1929. More useful, however, is the classification based on reaction kinetics, in which Polymerisation Reactions are divided into step and chain processes. These latter categories approximate to Carothers’ condensation and addition reactions but are not completely synonymous with them.

  The study of reaction mechanisms can be a subtle business but in fact the mechanistic basis of classification into step and chain processes arises from major differences in the two types of process. There is no doubt about the nature of the reaction in almost all cases as can be seen by considering the distinguishing features of the two mechanisms which are summarised below.

  Chain polymerisation : Monomer concentration decreases steadily with time. High molar mass polymer is formed at once and the molar mass of such early molecules hardly changes at all as reaction proceeds. Long reaction times give higher yields but do not affect molar mass. The reaction mixture contains only monomer, high molar mass polymer, and a low concentration of growing chains.

  Step polymerisation : Monomer concentration drops rapidly to zero early in the reaction. Polymer molar mass rises steadily during reaction. Long reaction times increase molar mass and are essential to obtain very high molar masses. At all stages of the reaction every possible molecular species from dimers to polymers of large degrees of polymerisation are present in a calculable distribution.

  2.1 Chain Polymerisation

  The Polymerisation Reactions that occur by the chain mechanism are typically those involving unsaturated monomers. The characteristic reaction begins with the chemical generation of reactive centres on selected monomer molecules. These reactive centres are typically free radicals, but may be anions or cations, and they react readily with other monomers without extinguishing the active centre. In this way any given active centre becomes responsible for the reaction of large numbers of monomer molecules which add to the growing polymer, thereby increasing its molar mass. The reactivity of the species involved is high, hence so is the rate constant of reaction in a typical polymerisation, which leads to the rapid formation of high molar mass polymers right from the beginning of the reaction. A consequence of this is that almost no species intermediate between monomer and polymer are found in such reacting systems.

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  Monitoring Polymerization Reactions

  From Fundamentals to Applications

  • Wayne F. Reed, Alina M. Alb(Authors)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  SECTION 1

  OVERVIEW OF POLYMERIZATION REACTIONS AND KINETICS

  Passage contains an image

  1

  FREE RADICAL AND CONDENSATION POLYMERIZATIONS

  MATTHEW KADE AND MATTHEW TIRRELL

  1.1 INTRODUCTION

  Polymers are macromolecules composed of many monomeric repeat units and they can be synthetic or naturally occurring. While nature has long utilized polymers (DNA, proteins, starch, etc.) as part of life’s machinery, the history of synthetic polymers is barely 100 years old. In this sense, man-made macromolecules have made incredible progress in the past century. While synthetic polymers still lag behind natural polymers in many areas of performance, they excel in many others; it is the unique properties shared by synthetic and natural macromolecules alike that have driven the explosion of polymer use in human civilization. It was Herman Staudinger who first reported that polymers were in fact many monomeric units connected by covalent bonds. Only later we learned that the various noncovalent interactions (i.e., entanglements, attractive or repulsive forces, multivalency) between these large molecules are what give them the outstanding physical properties that have led to their emergence.

  In recent years, the uses of synthetic polymers have expanded from making simple objects to much more complex applications such as targeted drug delivery systems and flexible solar cells. In any case, the application for the polymer is driven by its physical and chemical properties, notably bulk properties such as tensile strength, elasticity, and clarity. The structure of the monomer largely determines the chemical properties of the polymer, as well as other important measurable quantities, such as the glass transition temperature, crystallinity, and solubility. While some important determinants of properties, such as crystallinity, can be affected by polymer processing, it is the polymerization itself that determines other critical variables such as the molecular weight, polydispersity, chain topology, and tacticity. The importance of these variables cannot be overstated. For example, a low-molecular-weight stereo-irregular polypropylene will behave nothing like a high-molecular-weight stereo-regular version of the same polymer. Thus, it is easy to see the critical importance the polymerization has in determining the properties and therefore the potential applications of synthetic polymers. It is therefore essential to understand the polymerization mechanisms, the balance between thermodynamics and kinetics, and the effect that exogenous factors (i.e., temperature, solvent, and pressure) can have on both.

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  Fundamentals of Materials Engineering - A Basic Guide

  • Shashanka Rajendrachari, Orhan Uzun(Authors)
  • 2021(Publication Date)
  • Bentham Science Publishers

    (Publisher)

  Polymers R. Shashanka , Orhan Uzun

  Abstract

  In the present chapter, we have discussed the classification of polymers, structure, properties, fabrication process, and polymerization mechanism. Generally, polymers are made up of a series of molecules joining together and the average molecular weight of chains ranges from 10,000 to more than one million. The process of chemically joining the monomers together to create giant molecules is called polymerization. In polymers, atoms are joined together by a strong bond called covalent bonding. Many of the polymers are organic (carbon-based polymers) and inorganic (non-carbon based polymers like polysiloxanes, polyphosphazene, polysilanes, etc.).

  Keywords: Addition and condensation polymerization, Bakelite, Branched and cross-linking polymers, Classification, Homo and co-polymers, Linear, Mechanisms, Molding techniques, Natural polymers, Nylon, Polymers, Properties of polymers, Polyethylene, PVC, Poly propylene, Synthetic polymers, Tacticity, Thermosetting and thermoplastics.

  1. INTRODUCTION

  The word polymer comes from the Greek language “poly” meaning many and “mers” means units. A polymer is defined as a group of many units or it is a combination of a large number of monomers together to form a giant structure. Most of the time the word polymer is used for “plastic” also; but, all plastics are polymers, but not all polymers are plastics [2 ]. Fig. (

  1

  ) shows the polymers [1 ].

  Polyvinyl chloride (PVC), polyethylene, polymethyl methacrylate (PMMA), nylons, bakelite, etc. are some of the examples of polymers. Polymers are very popular due to their wide range of applications as mentioned below [1 ]:

  • Automobile industries
  • Constructional purposes
  • Aerospace applications
  • Medical applications
  • Packaging applications
  • Electronic goods etc.

  Fig. (1)) Polymers [1 ].

  2. PROPERTIES OF A POLYMER

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  The Chemistry of Polymers

  • John Nicholson(Author)
  • 2007(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  there are no intramolecular reactions. It is found experimentally that these assumptions are not completely valid and tend to lead to an underestimate of the extent of reaction required to bring about gelation. 2.9 COPOLYMERISATION Step polymerisations tend to be carried out using two different bifunctional molecules so that these give rise to molecules which are essentially copoly-mers. For example, nylon 6,6 is prepared from hexamethylenediamine and adipic acid; it thus consists of alternating residues along the polymer chain and may be thought of as an alternating copolymer. On the other hand, nylon 6 is prepared from caprolactam, which behaves as a bifunctional monomer bearing two different functional groups, and hence the polymer is made up of just one type of unit along the backbone; it is therefore a homopolymer. Chain reactions carried out on one type of monomer give rise to homopolymers; when using two types of monomer the situation is more complicated. For example, polymerising mixtures of vinyl chloride with acrylate esters gives rise to a range of molecules, the first of which are rela-tively rich in acrylate; molecules formed later, when the amount of acrylate monomer is relatively depleted, are richer in vinyl chloride. In a number of instances, reactions of this kind can be used to prepare polymers containing monomers which will not homopolymerise, e.g. maleic anhydride and stil-bene (vinylbenzene). In a copolymerisation involving two monomers, A and B, reacting poly-mer chains can have either monomer A or monomer B at the growing end. As a result, there are four possible reactions: Chain-end A (written A·) with monomer A or monomer B, and chain-end B ( B·) with A or with B. Each has a different rate constant, which can be designated k AA , k AB , k BA , and k BB respectively. Once the copolymerisation reaction has become properly established, the radical chains A· and B· each achieve a steady-state concentration.

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  Polymer Chemistry

  • Timothy P. Lodge, Paul C. Hiemenz(Authors)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  2 Step-Growth Polymerization

  2.1Introduction

  In Section 1.4 , we discussed the classification of polymers into the categories of addition or condensation. At that time we noted that these classifications could be based on the following criteria:

  1. Stoichiometry of the polymerization reaction (small molecule eliminated?)
  2. Composition of the backbone of the polymer (atoms other than carbon present?)
  3. Mechanism of the polymerization (stepwise or chain reaction?)

  The third criterion offers the most powerful insight into the nature of the polymerization process for this important class of materials. We shall sometimes use the terms step-growth and condensation polymers as synonyms, although step-growth polymerization encompasses a wider range of reactions and products than the first two criteria would indicate.

  The chapter is organized as follows. First, we examine how the degree of polymerization and its distribution vary with the progress of the polymerization reaction, with the latter defined both in terms of composition and kinetics (Section 2.2 through Section 2.4 ). We consider these topics for simple reaction mixtures, that is, those in which the proportions of reactants agree exactly with the stoichiometry of the reactions. Also, the treatment is entirely generic – it applies to all step-growth polymerizations. After this, we consider two important classes of condensation or step-growth polymers – polyesters and polyamides – in Sections 2.5 and 2.6 , respectively, taking into consideration some of the chemical details. Section 2.7 extends this analysis to a few other important polymers that are produced in this way. Finally, we consider nonstoichiometric proportions of reactants (Section 2.8 ). The important case of multifunctional monomers, which can introduce branching and cross-linking into the products, is deferred until Chapter 10

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  Mechanism and Kinetics of Addition Polymerizations

  • M. Kucera(Author)
  • 1991(Publication Date)
  • Elsevier Science

    (Publisher)

  Chapter I Polymerization Even liquid water is ~i kind nf polymer A finding documenting our dependence on polymers Macromolecules are formed by polycondensation and polymerization. Both reactions have been and are precisely defined and differentiated. For formal reasons, the term polymerization is superior to polycondensation (both lead to the formation of polymers) and polycondensation is then designated by the compromise term condensation polymerizationt. In my opinion, due to the differences in the mechanism and kinetics of polymerizations and polycondensa- tions, a separate treatment of each of these polyreactions is justified. The trivial scheme of polymerization is simple ( 1 ) b P Ad IM, + M e IM,,, However, it comprises an enormous number of possible ways by which the monomer M can be added to the initiator I or to the chain IM, growing on the reactive end group, usually called the active centre. In addition, the real situation is complicated by the occurrence of competing and consecutive reactions. To this day, a general theory of polymerizations suitable for 'a unified explanation of observed phenomena and predicting the behaviour of real polymerizing systems has not been formulated. Truly speaking, present findings are so varied that so far nobody has attempted to unify them. The progress of our knowledge has led to the description of many kinds of polymerization. Each kind is composed of a large number of special cases but it always exhibits some common features. Let us present some such sets as examples without claiming completeness. ' Until recently it has becn customary to classify synthetic polyreactions as polymerizations, polycondensations and polyadditions [I]. According to the IUPAC nomenclature [2] the temi polymerization is supcrior to the concepts of addition polymerization and condensation polymcriza- tion.

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  The Chemistry of Polymers

  • John Nicholson(Author)
  • 2007(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  It can then be continuously removed by pulling out the interface. Ring-opening reactions may also be used in order to make polymers by the step polymerisation mechanism. One commer- cially important example of this is the manufacture of nylon 6, which uses caprolactam as the starting material and proceeds via the ring-opening reaction shown in Reaction 2.15. STEP POLYMERISATION WITH POLYFUNCTIONAL MONOMERS If monomers which have functionalities greater than 2 are used for step polymerisation the product that forms consists of an infinitely large three-dimensional network and the polymerisation is characterised by sudden gelation at some point before the reaction is complete. The gel point is observed readily as the time when the mixture suddenly loses fluidity as viscosity rises sharply n 15) and any bubbles present no longer rise through the medium. The gel component at this point represents only a fraction of the total mixture and since it is insoluble in all non-degrading solvents it can be readily freed of the soluble component (the so-called ‘sol’) by extraction with solvent. As reaction proceeds beyond the gel point so the proportion of gel increases at the expense of the sol. Gelation occurs at relatively low conversions of monomer to polymer; hence the number-average molar mass at the gel point is low. By contrast, however, the weight-average molar mass becomes infinite at the gel point. In considering step polymerisation with polyfunc tional mole- cules a number of assumptions are made. They are (i) that all functional groups are equally reactive, (ii) that reactivity is independent of molar mass or solution viscosity, and (iii) that all reactions occur between functional groups on different mole- cules, ie. there are no intramolecular reactions. It is found experi- mentally that these assumptions are not completely valid and tend to lead to an underestimate of the extent of reaction required to bring about gelation.

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  Macromolecular Chemistry

  Volume 1

  • A D Jenkins, John F Kennedy(Authors)
  • 2007(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  Polymer Symp. Ser. No. 20, 1969. 1976. Ellis Horwood, London, 1974. 105 106 Macromolecular Chemistry the two year period covered by this Report over lo00 relevant papers and patents have appeared as the apparently inexhaustible quest continues to find new polymeric materials, to exploit new chemical reactions or to achieve a better understanding of existing processes. The present Report makes no pretence at covering the field in all its many facets. Only work related to copolymerization chemistry will be reported and that is taken from the scientific literature, ignoring multitudinous patents which have appeared. The Report is largely confined to addition polymerization proces- ses, although the sharp demarcation between the traditional classifications of polymerization reactions is to some extent becoming blurred, particularly when attempts have been made to incorporate both non-polar and polar structural units within a polymer chain, as will be seen later. In selecting material for comment emphasis has been given to work which, either directly or indirectly, leads to the production of polymeric materials with controlled structures, composition, or molecular size. Whilst the chemist is mainly preoccupied with achieving control over his synthetic processes by essentially chemical means, selecting the right initiator, monomer cornbination, or reaction conditions, it should be remembered that the polymerization reactor and its operating conditions can have a particularly profound effect on molecular composition and chain size distribution in reactions involving two or more monomers. The influence of the reactor type and operating conditions is most noticeable for statistically random addition copolymerizations taken to high conversion in a batch reactor.

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  Essentials of Modern Materials Science and Engineering

  • James A. Newell(Author)
  • 2012(Publication Date)
  • Wiley

    (Publisher)

  Thus, the new monomer may add head to head only, head to tail only, or a blend of the two, depending on the relative stabilities of the free radicals. 2. Although the polymer may have thousands (or millions) of identical monomer units added, there will be only two end groups. In this case, both will be —OH groups. The end groups have little significance on the mechanical properties of most polymers but can be used to deter- mine the number of chains formed through titration. 3. Many different chains are reacting at the same time, and whether they react with another vinyl monomer or with a free radical is probabi- listic. Therefore, a distribution of chain lengths will form, as shown in Figure 5-23. Controlling that distribution is a major challenge for polymer scientists and engineers. 5.4 CONDENSATION POLYMERIZATION T he alternative to addition polymerization is condensation polymeriza- tion, which sometimes is referred to as step-growth polymerization. Unlike addition polymerization, condensation polymerization does not require sequential steps or any initiation. In condensation, potentially reac- tive functional groups on the ends of molecules react. A new covalent bond forms between the functional groups, and a small molecule (usually water) is | Free Radical | Molecule containing a highly reactive unpaired electron. | Propagation | Second stage of the polymerization process during which the polymer chain begins to grow as monomers are added to the chain. | Termination | Final step in the polymerization process, which causes the elongation of the polymer chain to come to an end. | Mutual Termination | One of the two different types of termination in the polymerization process. During this type of termination, the free radicals from two different polymer chains join to end the propagation process. | Primary Termination | Last step in the polymerization process, which occurs when the free radical of a polymer chain joins with the free radical on an end group.

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