Vinyl acetate polymerization tacticity

For free-radical polymerization, classical results have been obtained concerning the tacticity of hydroxytelechelic poly(methyl methacrylate)109) and copolymers, 46) initiated by H202/UV. Most of the units are in a syndiotactic (64 %) or heterotactic (30 %) configuration. For poly(vinyl acetate) obtained in the presence of H202 at 120 °C 98), the polymer contains less syndiotactic (22%) and somewhat more heterotactic (38%) units with 80% of head-to-tail linkage mode. For the copolymerization of alkyl methacrylate by the H202/UV system113) quite different results, explained by the nature of the medium, especially by the solubility effect (see Table 1.1), have been obtained. 

The PVA in Fig. 6a used in this experiment was purchased from Nacalai Tesque, Inc. and is atactic with a degree of polymerization of 2.0 x 10 and a degree of saponification of 99-100 mol%. As the polymer backbone of PVA is formed by the polymerization of vinyl acetate (Fig. 6b) before saponification, the tacticity of PVA... 

Normally, free radical polymerization results in essentially atactic polymers although steric and electrostatic effects generally favour one conHguration or the other and truly random pol5miers are probably rare. In some cases, free radical polymerization results in polymers which are largely syndiotactic examples of monomers which behave in this way are chlorotrifluoroethylene, methyl methacrylate and vinyl acetate. More commonly, however, highly tactic... 

As mentioned already in the polymerization of meth of-phenylacrylate a steri-cally random pdymer was obtained. However, the fraction of heterotactic triad in the polymer did not exceed 50 % under any polymerization conditions with BuLi Initiator (Table 10). On the other hand, methyl a-(p-bromophenyl)acrylate and methyl ce-(p-chlorophenyl)acrylate gave the polymers whose heterotactic contents were 59 and 61 %, respectively, in THF by BuLi at -78 (Table 10). The tacticity was determined by the C-NMR spectra of poly(2-phenylallyI acetate)s derived from the original polymers via pdy(2-phenylallyl alcohol)s. The bulkiness of the o-substituent seems to be important for the heterotactic propagation in these cases, as pointed out by Nozakuia et al. in the formation of heterotactic poty(vinyl alcohol) derived from poly(vinyl trimethylsilyl ether). However, method o-phenylacrylate formed a heterotactic pdymer whose heterotactic content was 66 %, by octylpotassium in THF (Table 10),... 

The polymerization of optically active acetals and vinyl acrylamides has been described but only in a few cases. Poly-[(-)-7V-propyl-7V-phenylethyl-acrylamide] and poly-[(+)-A -methyl-A -phenyl-ethyl-acrylamide] (VIII) of different tacticity were prepared by Schultz and Kaiser [18] from the corresponding monomers using radical or ionic initiators. No assumptions on polymer conformation in solution have been made. 

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