Polymer association. V. Solution behavior and rheology of neutralized styrene-methacrylic acid copolymers

Abstract

The behavior of styrene copolymers containing 2.3 mole % or 5.6 mole % of methacrylic acid and of their lithium, sodium, and barium salts was studied in dilute benzene and dioxane solution. Light-scattering molecular weights were higher in benzene but the extent of molecular aggregation was small except with the barium salt. Intrinsic viscosities of the acid polymers and their salts were very similar but the reduced viscosities of the salts increased rapidly at concentrations above 1 g./100 ml., suggesting an increasing molecular association. Creep and creep recovery studies were carried out on films containing styrene copolymer with 2.3 mole % methacrylic acid, its lithium and barium salt, and a styrene homopolymer of similar chain length, all plasticized with 25% dioctyl phthalate. The rigidity and the tensile viscosity increased as the forces between interacting groups were increased in the order — COOH < —COO −Li + < —COO −Ba ++ 1 2 , but when the materials were compared at temperatures corresponding to the same compliance, the irrecoverable flow was least with samples which had the strongest interacting groups. The activation energy of viscous flow changed in an order opposite to that of the tensile viscosities. Films plasticized with an α-methylstyrene oligomer were more rigid and had less irrecoverable flow than films plasticized with DOP. This difference was much more pronounced with the acid copolymer than with its lithium salt.