High-Temperature Free Radical Copolymerization of Styrene and Butyl Methacrylate with Depropagation and Penultimate Kinetic Effects

Abstract

Copolymers of methacrylate and styrene, the main components of many solvent-based automotive coating formulations, are produced under higher temperature starved-feed conditions in order to reduce the solvent level while controlling polymer composition. Under these conditions methacrylate depropagation has a significant impact on polymer molecular weights and free monomer concentrations in the reactor. Meanwhile, a strong penultimate effect has been observed for this binary system at lower temperatures, also affecting the polymerization rate. In this work, the combined effect of depropagation and penultimate copolymerization kinetics is investigated. The copolymer-averaged propagation rate coefficient for butyl methacrylate and styrene is determined as a function of monomer composition using pulsed-laser polymerization over a range of temperatures. A clear penultimate effect is seen even at the elevated temperatures at which depropagation is important. Radical and monomer reactivity ratios show a negligible temperature dependency between 50 and 150 °C. The Lowry case 1 representation adequately describes the effect of methacrylate depropagation over the range of conditions examined.