Vinyl acetate carbon centered radicals

A different form of retardation occurs when a radical species formed from transfer (S in Scheme 4.3) reinitiates at a slow rate. In addition to the slower reaction rate with monomer to form a polymer radical, the termination of S with other radicals in the system may also need to be considered (Scheme 4.8). Explicit balances must be written for S, and the extra mechanisms must be included when deriving expressions for [Ptot], Rpoi, and DP . As solvent/transfer agent is generally not completely consumed, the retardation effect will last the duration of the polymerization (curve b in Figure 4.2). The degree of retardation depends on the value of which can vary with monomer type many carbon-centered radicals show much lower reactivity toward vinyl esters (for example, vinyl acetate) than (meth)acrylates [3]. 

For efficient cationic polymerization of vinyl monomers, it is necessary that the carbon-carbon double bond be the strongest nucleophile in the molecule. Thus vinyl acetate would be classed as an electron-donor-type monomer (Section 7.10.2) but it cannot be polymerized cationically because the carbonyl group complexes the active center. (It is polymerized only by free radicals anionic initiators attack the ester linkage.)... 

In contrast to most other oxygen-centered radicaLs e.g. benzoyloxy (3.4.2.2.1), hydroxy (3.4.2.3)1, t-butoxy radicals and other r-alkoxy radicals (3.4.2.1.2) show relatively high regiospecificity in reactions with carbon-carbon double bonds (Table 3.8). Nonetheless, significant amounts of head addition are observed with the halo-olcfins, simple alkcncs, vinyl acetate and methyl acrylate. " Head addition is generally not observed with 1,1-disubstituted monomers. The exception is vinylidene niioride" where head addition predominates (Section... 

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