Solution and bulk properties of branched polyvinyl acetates : Part I: Non-Newtonian viscosity behaviour

Abstract

A series of linear and branched fractions of polyvinyl acetate of relatively narrow molecular weight distribution was prepared and characterized by solution viscosity, hydrolysis, and light scattering measurements. At a given molecular weight, the intrinsic viscosity of a branched fraction was less than that of a linear fraction. The viscosity loss which takes place after removal of branches, by hydrolysis followed by re-acetylation, is a sensitive indication of the presence of branching in polyvinyl acetate. However, the process is not quantitative because of the presence of nonhydrolysable branches in the branched polymer. Benzene solutions of linear and branched polymers above a molecular weight of about 2 x 106 were significantly non-Newtonian in character. The major factor contributing to the non-Newtonian behaviour was found to be molecular weight rather than structure. Therefore, even though the intrinsic viscosity of a high molecular weight fraction is dependent on shear rate, the ratio of the intrinsic viscosities of branched to linear fractions of the same molecular weight (a term used in the estimation of the degree of branching) is not sensitive to shear rate. Since the shear sensitivity or degree of non-Newtonian viscosity behaviour is dependent upon molecular weight, it is possible to detect the presence of branching in polymers of molecular weight greater than 2 x 106 by comparison of the shear sensitivities of branched and linear fractions of the same intrinsic viscosity.