The synthesis of branched chain polyvinyl acetates

A mode of synthesis of well characterised branched polyvinyl acetate is described. Linear polymer is first produced by a low temperature photopolymerisation carried to a low degree of conversion. Partial hydrolysis of this „backbone”︁ material introduces a small number of hydroxyl groups into the polymer which is then condensed with low molecular weight polymer having an acid chloride endgroup. This is prepared by initiating the polymerisation of vinyl acetate with 4,4′ azo‐bis‐4‐cyanopentanoic acid, and subsequently treating this carboxyl‐ended polymer with thionyl chloride. This method has the distinct advantage that both constituents of the branched polymer can be fractionated prior to the grafting process (condensation). The degree of branching has been estimated using both a radiochemical method based upon 14C, and infra‐red analysis. The viscosities of the branched and linear polymers have been measured in the tetrahydrofuran solutions. Within the limits of these investigations, the limiting viscosity number appears to be insensitive to the extent of branching, for molecules having the same overall degree of polymerisation. There is however considerable variation in k′ (HUGGINS constant), k′ increasing with the extent of branching.