Studies in chain transfer IV. Catalyzed polymerization of vinyl acetate

Abstract

The chain-transfer coefficients, C s = k s / k p of highly purified vinyl acetate for twenty-five solvents at 60° C using azobisisobutyronitrile as catalyst have been measured. The C s values are in most cases higher by an order than that of styrene or methyl methacrylate, though the relative order is more or less the same with all the three monomers. This is in agreement with the view that the free radical preferentially attacks the a-hydrogen. The absolute values of the rate of chain transfer, k s of vinyl acetate are, however, found roughly about one thousand times higher for vinyl acetate in comparison with the other two monomers for most solvents. A chemical explanation based on the stability of the transferred atom in the typical compound of low molecular weight formed by transfer is found to be in agreement with known facts about vinyl acetate and other monomers. The behaviour of chlorinated solvents is found to be rather difficult to understand because of the simultaneous transfer of chlorine and hydrogen, but the general tendency of high transfer with higher chlorine: carbon ratio is maintained. The theoretical foundation of such measurements has been briefly discussed, and the possibility of obtaining C s values by a single-tube experiment in suitable systems has been indicated.