Vinyl copolymerizations

Vinyl monomers are often copolymerized, usually with free-radical or coordination metal catalysis, but occasionally by other mechanisms. Random copolymers are important items of commerce. The two monomers are present together in the reaction mixture and copolymerize to give more-or-less random arrangements of the monomers along the pol5aner chain. 

Consider the pol5merization of two vinyl monomers denoted by X and Y. Each propagation reaction can add either an X or a Y to the growing polymer chain, and it is unrealistic to assume that the monomers have equal reactivities. Furthermore, reaction probabilities can depend on the composition of the polymer chain already formed. We suppose that they depend only on the last member added to the chain. The growing chain to which an X-mer was last added is denoted as IX , and I denotes the catalytic site. There are four propagation reactions to consider  

The initiation and termination steps may also come in several varieties, but they will have little effect on overall chain composition provided the chains are long. The monomer consumption rates are 

The ratio of these propagation rates is the ratio in which the two monomers are incorporated into the pol5mier  

This result can be simplified considerably by observing that, except for end effects, the number of transitions from X to Y along the polymer chain (i.e., structures like XY ) must equal the number of transitions from Y to X (i.e., structures like YX ). This requires that 

Consider the polymerization of two vinyl monomers denoted by X and Y. Each propagation reaction can add either an X or a Y to the growing polymer chain, and 

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One reactant is charged to the reactor in small increments to control the composition distribution of the product. Vinyl copolymerizations discussed in Chapter 13 are typical examples. Incremental addition may also be used to control the reaction exotherm. 

Several examples of calculated changes in q and the composition of the monomer mixture as well as that of the polymer are given in Fig. 2. It is seen that in the ideal case the constancy of the composition of the polymer and monomer mixture (which is the sign of ideality in mono-vinyl copolymerization) does not apply, whereas for rx = 1, rs — 0.5 the composition of the monomer mixture remains constant, but the copolymerization is not ideal. 

Scheme 13 General route to branched poly(acrylic acid) (PAA) via self-condensing vinyl copolymerization (SCVCP) of an inimer, AB and a monomer, M, followed by hydrolysis...

Problem 7.23 Predict the extent of reaction at which gelation would occur in (a) vinyl acetate-ethylene glycol dimethacrylate and (b) methyl methaciylate-divinyl adipate systems, both containing 15 mol% of the divinyl compound. Assume that the reaction conditions for the two systems are such as to yield the same DP. of 1000 for the uncrosslinked polymer. Take rj and values from Table 7.1 for the respective analogous vinyl-vinyl copolymerizations. 

Scheme 2 Schematic representation of self-condensing vinyl copolymerization (SCVCP, top) and ROMBP (bottom). Note The asterisks in the structures indicate an initiating site small letters stand for reacted groups.

Agarwal, S. (2007) Radical ring opening and vinyl copolymerization of 2,3,4,5,6 pentafluorostyrene with 5,6-benzo-2-methylene-13-dioxepane synthesis and structural characterization using ID and 2D NMR techniques. / Polym. Res., 13 (5), 403. 

As has been noted previously, the cross-linking of unsaturated linear polyesters involves the reaction of the unsaturated sites in the polymer chain with a vinyl-type monomer. This reaction is analogous to conventional vinyl copolymerization and proceeds by an essentially similar mechanism. As carried out in commercial practice, cross-linking of unsaturated polyesters is invariably a free radical reaction. Two types of initiating systems are commonly employed for this reaction, namely those effective at elevated temperatures and those effective at room temperature. 

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