Direct rotating‐sector studies of the systems: Styrene–methyl methacrylate and styrene–methyl acrylate

The rotating‐sector technique was applied directly in a study of two copolymerization systems: styrene–methyl methacrylate and styrene–methyl acrylate. The two coupled rate expressions which describe the change in radical concentrations for two‐component polymerizations degenerate into a single expression identical in form to the radical expression for a homopolymerization when the ratio of the radical concentrations under intermittent illumination is assumed constant and equal to the ratio under steady illumination. Numerical solutions of the complete rate expression by use of constants from the literature confirm that this assumption is valid for a rotating‐sector experiment. The overall lifetimes of these two‐component systems were defined and measured experimentally as a function of monomer composition and then compared with lifetimes calculated by using literature rate constants. The agreement was satisfactory. The direct application of the technique to the two‐component system provides an independent experiment which for some systems seems to be more sensitive to the value of the cross‐termination constant than the usual steady‐state method.