Emulsion copolymers of alpha‐methylstyrene and styrene

This article reports molecular weights and mechanical and processing properties of a series of styrene/alpha‐methylstyrene copolymers produced by emulsion polymerization at various temperatures. Molecular weights were measured by solution viscosity, membrane osmometry, light scattering, and gel‐permeation chromatography. Molecular weight development is controlled by chain transfer to monomer, but the molecular weight distributions are broader than would be expected for such reactions. This is attributed to polymer branching resulting from chain‐transfer events. Molecular weight distributions of copolymers were multimodal. Thermal stability of the copolymers is somewhat lower than that of polystyrene, but addition of conventional antioxidants produces compositions with good stability in thermoplastic processing operations. Copolymers containing 25 wt. % of alpha‐methylstyrene have usage temperatures about 12°C higher than that of polystyrene.