MOLECULAR-WEIGHT CHARACTERISTICS OF POLYVINYL ACETATE OBTAINED BY DIFFERENT METHODS.

The diversity of the fields of application of PVAc and of polymers based on it and the need to develop processes for synthesis of polymers having predetermined combinations of properties prompted further detailed study of the molecular characteristics of PVAc. The authors carried out a comparative analysis of the molecular characteristics of PVAc synthesized by initiated radical polymerization effected by different technological procedures: in methanol solution, and by a combined bulk-solution technique (two-stage synthesis of the polymer: bulk polymerization of VA to low degrees of conversion at the first stage, and completion of the process in methanol solution). The results showed that the MWD (Molecular Weight Distribution) is unimodal during polymerization in bulk (up to 30 mass % conversion) and in methanol solution, and broadens with increase of the degree of monomer conversion. The MW (Molecular Weight) and polydispersity of PVAc synthesized in bulk are lower than those of the polymer obtained in solution; this is due to reactions of chain transfer to methanol. The MWD of the polymer made by the combined bulk-solution technique is bimodal, and its MW is higher and the polydispersity is lower than those of the solution polymer. By varying the degree of monomer conversion at each polymerization stage, and the amount of solvent at the second stage, it is possible in practice to synthesize polymers having predetermined average MW and polydispersity.