| Copolymers of methacrylate, acrylate and styrene produced via high-temperature solution polymerization are the base resin component for many automotive coatings. These materials are often manufactured using a semibatch starved-feed reactor policy in order to reduce the solvent level while tightly controlling polymer composition and molecular weight. Methacrylates are known to undergo depropagation reactions at these conditions, while acrylates are affected by backbiting followed by beta-scission and slowed monomer addition to the tertiary radicals. Both mechanisms have a significant impact on polymer molecular weights and free monomer concentrations in the reactor. Meanwhile, a strong penultimate effect has been observed for some of these binary systems at lower temperatures, also affecting the polymerization rate.; The objective of this work is to formulate a generalized model for the terpolymerization of methacrylate, acrylate and styrene, building from our knowledge of mechanisms in the homo- and co-poIymerizations. As part of this investigation, we answered specific questions about penultimate effects at higher temperature, and how they interact with depropagation for the butyl methacrylate/styrene (BMA/ST) system. It is found that penultimate kinetics have a strong impact on the copolymer-averaged propagation rate coefficient at the elevated temperatures at which depropagation is important. The Lowry Case 1 depropagation model adequately describes the effect of methacrylate deproagation over the range of conditions examined. The mechanistic models, implemented in PrediciRTM for high temperature semibatch BMA/ST copolymerization and BMA/ST/butyl acrylate terpolymerization, provide good predictions of monomer conversion and MW. |
