Chain growth polymerization reaction

To determine the rate behavior of chain growth polymerization reactions, we rely on standard chemical techniques. We can choose to follow the change in concentration of the reactive groups, such as the carboxylic acid or amine groups above, with spectroscopic or wet lab techniques. We may also choose to monitor the average molecular weight of the sample as a function of time. From these data it is possible to calculate the reaction rate, the rate constant, and the order of the reacting species. 

In chain growth polymerization reactions the average molecular weight, the molecular weight distribution and in some cases the type of terminal group of the polymer can be varied within certain limits by proper choice of reaction conditions and/or the addition of low-molecular-weight compounds (regula-... 

The reaction is called an addition reaction because two monomers are added to each other with the elimination of a double bond. This is also called a chain growth polymerization reaction. However, the reaction as such does not go without the help of an unstable molecule, called an initiator, that starts the reaction. Benzoyl peroxide or i-butyl benzoyl peroxide are such initiators. Benzoyl peroxide splits into two halves under the influence of heat or ultraviolet light and thus produces two free radicals. A free radical is a molecular fragment that has one unpaired electron. Thus, when the central bond was broken in the benzoyl peroxide, each of the shared pair of electrons went with one half of the molecule, each containing an unpaired electron. 

A. General features of chain-growth polymerization reactions (Section 31.1). 

Biopolymers are naturally occurring polymers that are formed in nature during the growth cycles of all organisms they are also referred to as natural polymersJ Their synthesis generally involves enzyme-catalyzed, chain growth polymerization reactions, typically performed within cells by metabolic processes. 

C YCI.opolymerization has been defined as a chain-growth polymerization reaction of l,X-bis-(multiple bonded) monomers which introduces cyclic structures into the main chain of the resulting polymers. However, polymers containing cyclic units in the main chain can be synthesized by a wide variety of methods. On this basis, the organizers of the symposium upon which this book is based decided to broaden its scope to include both polymers formed by cyclopolymerization and polymers containing chain-ring structures. 

Biopolymers are polymers formed in nature during the growth cycles of all organisms hence, they are also referred to as natural polymers. The biopolymers of interest in this review are those that serve in nature as either structural or reserve cellular materials. Their syntheses always involve enzyme-catalyzed, chain-growth polymerization reactions of activated monomers, which are generally formed within the cells by complex metabolic processes. The most prevalent structural and reserve biopolymers are the polysaccharides, of which many different types exist, but several other more limited types of polymers exist in nature which serve these roles and are of particular interest for materials applications. The latter include the polyesters and proteins produced by bacteria and the hydrocarbon elastomers produced by plants (e.g. natural rubber). In almost all cases (natural rubber is an exception), all of the repeating units of these biopolymers contain one or more chiral centers and the repeating units are always present in optically pure form that is, biopolymers with asymmetric centers are always 100% isotactic. 

Both starch and cellulose are prepared in nature by enzymatic, chain growth polymerization reactions of glucose nucleotide monomers [6]. In both cases, the monomer precursor is glucose-1-phosphate, which is enzymatically converted to the nucleotide derivative. The latter, in turn, complexes with an enzyme to form the activated monomer at the active site on the enzyme, which also contains the growing polymer molecule, as schematically illustrated below for the enzymatic polymerization of cellulose ... 

Although ethylene and substituted ethylenes are the monomers most commonly used for chain-growth polymerization reactions, other compounds can polymerize as well. For example, epoxides undergo chain-growth polymerization reactions. If the initiator is a nucleophile such as HO or RO , polymerization occurs by an anionic mechanism. 

In this type of polymerization the monomer is dispersed in a liquid (usually water) by vigorous stirring and by the addition of stabilizers such as methyl cellulose. A monomer-soluble initiator is added in order to initiate chain-growth polymerization. Reaction heat is efficiently dispersed by the aqueous medium. The polymer is obtained in the form of granules or beads, which may be dried and packed/bagges directly for shipment. Refer to Bulk Polymerization Emulsion Polymerization, and Solution Polymerization. 

Chain-growth polymerization reactions, where caprolactam adds directly to the ends of linear chains, are also important in nylon 6 production [38], for example ... 

Substantial amounts of cyclic dimer form, due to condensation reactions between the end-groups on hnear dimer molecules. Like caprolactam, cyclic dimer molecules are consumed by hydrolytic ring-opening reactions and chain-growth polymerization reactions. 

Common photopolymerization reactions by free radical mechanism follow the same laws of chemistry as do the thermal polymerizations. The differences are primarily in the formations of the initiating radicals. Typical chain growth polymerization reactions are initiated by Ifee radicals that come from thermal decomposition of the initiators. The initiating Ifee radicals in photo polymerizations, on the other hand, come If om photolyses of the photoinitiators. 

Within the deterministic modeling techniques, a first distinction can be made between numerical methods enabling the simulation of only averages of the CLD as a function of monomer conversion, that is, the method of moments, and methods enabling the simulation of the full CLD, that is, the/w// CLD methods. In what follows, the main aspects of these methods are discussed in detail. For illustration purposes, it is assumed that only two populations of macrospecies, namely the living and dead polymer molecules (Fig. 10.1), exist and that only a limited number of chain-growth polymerization reactions can take place. 

In a chain-growth polymerization reaction, the end of the polymer chain remains at the active metal center during monomer enchainment. Thus, the stereogenic center in the polymer chain... 

Torque measurements have been used for online monitoring of the viscosity of polymerization reactions. The advantage of the torque measurement as compared with that of the capillary is that no treatment (dilution and flow) of the reaction medium is needed. Several examples of monitoring chain-growth polymerization reactions [62, 63] and step-growth polymerization reactions (specially curing reactions) can be found in the hterature [64]. 

It is generally assumed that the stereosequence distributions, or tacticity, obtained in polymerization reactions of vinyl and related monomers is primarily a kinetically-controlled process (1). That is, as in other important aspects of chain-growth polymerization reactions (e.g., molecular weight and copolymer composition), tacticity is determined by the relative rates of competitive reactions, in this case the rates of isotatic, kj, and syndiotactic, ks, additions, as shown in Equation 1. 

In a chain-growth polymerization reaction, one end of the polymer chain remains at the active metal center during monomer enchainment. Thus, the stereogenic center in the polymer chain from the last enchained monomer unit will have an influence on the stereochemistry of monomer enchainment. If this influence is significant, the mode of stereochemical regulation is referred to as polymer chain-end control (Scheme 2(a)). If the active site is chiral and overrides the influence of the polymer chain end, the mechanism of... 

There are only a few reports on the ROP of lactides that do not use organometallic promoters. The synthesis of biomacromolecules generally involves in vivo enzyme-catalyzed chain growth polymerization reactions within cells. Enzymes exhibit high, stereo-, reaction- and substrate... 

For many reactions, the number of moles of products is different from the number of moles of reactants. Polymerizations are an extreme example of reactions with a large change in the number of moles. A single polymer molecule may contain as many as 10,000 monomer molecules. The stoichiometry of a chain-growth polymerization reaction can be represented as... 

It would be tempting to consider the step-growth and chain-growth polymerization reactions as if they were independent and one could have the choice of either in any particular situation. The truth is that there are aspects of both types of polymerization in the cure of almost every epoxy structural adhesive. Such multiple-cure reactions often make it difficult to calculate the stoichiometry of an epoxy adhesive formulation. One type might predominate, depending on the formulation and cure conditions, but the effects of the other could not be completely discounted. The significance of... 

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