The high‐resolution NMR spectra at 60 and 100 Mcps of poly(vinyl chloride)‐β,β‐d2 in o‐dichlorobenzene, pyridine, and C2HCl5 solutions are reported. The use of low molecular weight samples and of {D} spin‐decoupling experiments, which yield higher resolution spectra, results in the observation of a number of additional resonances for the α‐proton. These can be interpreted in terms of pentad configurational sequences of monomer units. It is found that, whereas the S syndiotactic pentads cannot be resolved, two components of the H heterotactic and all of the possible I isotactic pentads are clearly discernible. From the tacticity values of polymers prepared at +40, 0, and −40°C, enthalpy and entropy of activation for isotactic and syndiotactic monomer placement are found to be 630 cal/mole and 1.5 eu, respectively.

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SynopsisThe polymerization of vinyl chloride initiated by a mixture of tetraethyllead and ammonium ceric nitrate has been studied a t low temperatures. As (I%)&e(NO& was insoluble in vinyl chloride, methanol was added. Methanol was found to be not only a solvent for the catalyst but also to affect the polymerization reaction by complexing the ceric ions. A reaction order of -0.4 with respect to methanol was cakcdated. Rate curves were shown to decrease fairly rapidly with time, suggesting a decrease of the rate of production of radicals during the polymerization. The apparent activation energy obtained from polymerizations carried out at different temperatures was 7.4 kcal./mole. A maximinn in average polymerization rate on changing the ceric salt concentration was attributed to reactions of radicals with ceric ions. Orders of 1.2 with respect to (NH&Ce(N03)6 and 0.9 with respect to Pb(CzH6)r were obtained. An increase in molecular weight was observed during the polymerization; this could be accounted for by the decreasing rate of production of radicals and by the transfer process involving one component of the initiator system. The results indicate that the mechanism of formation of radicals is described by the equation: Pb(GH,)4 + CeIV --t Pb(C2H&+ + CelI1 + CzHs.