INSTABILITY OF SOLUTIONS OF HIGH POLYMERS

Abstract

The change in the viscosity property of solutions of high polymers on ageing has been investigated. It has been found that the variations in viscosity are due to changes in the molecular weight of the dissolved polymer, caused by the presence of small amounts of impurities. In particular, oxygen appears to give rise to degradation reactions, while iron salts cause the formation of gel structures. Solutions of the dry polymers in pure solvents, when aged in the absence of air, show only very small variations in viscosity. The investigation has been conducted with three polymers, polyvinyl acetate, polystyrene, and polymethyl methacrylate in solution in three solvents, bis(2-chloroethyl) ether, nitrobenzene, and bis(2-chloroethyl) sulphide.The principal reaction seems to occur between the impurity and the polymer, with the solvent acting as an inert medium. However, it appears that in the case of bis(2-chloroethyl) sulphide, reaction of iron salts with the solvent is possible.The intrinsic viscosity of polyvinyl acetate recovered from the aged solutions has been determined. The k′ factor of Huggins has been evaluated from these measurements, and appears to change during some of the ageing processes.