Intrinsic viscosities and molecular weights of polyvinyl acetates

Abstract

Abstract A polyvinyl acetate polymer of medium viscosity was fractionated into sixteen fractions (first series) and three of the larger of these further separated into twenty subfractions (second series). The intrinsic viscosities and the osmotic pressure molecular weights were determined at 25°C. and the relation between them was found to be expressed by the equations: first series: [η] = (1.88 × 10 −4 ) M 0.69 ; second series: [η] = (1.76 × 10 −4 ) M 0.68 . The data indicate that little, if any, increase in homogeneity is to be expected by further successive fractionations and that the equations applicable to the second fractionation series are representative of essentially homogeneous polyvinyl acetates in acetone. An equation applicable to fractionated and unfractionated vinyl acetate polymers is described that is useful in obtaining the intrinsic viscosity from a single viscosity measurement. Several unfractionated materials from different sources were also studied and the calculated ratios of the viscosity‐average to the number‐average molecular weight indicate that the degree of heterogeneity of chain‐length distribution increases with increasing average molecular weight.