n‐Butyl methacrylate/styrene/n‐butyl acrylate (BMA/ST/BA) high‐temperature starved‐feed solution semibatch copolymerization and terpolymerization experiments with varying monomer feed composition, final polymer content, monomer feed time, and reaction temperature were carried out. A comprehensive mechanistic terpolymerization model implemented in PREDICI includes methacrylate depropagation, acrylate backbiting, chain scission, and macromonomer propagation, as well as penultimate chain‐growth and termination kinetics. The generality of the model was verified by comparison with terpolymerization data sets from two laboratories that demonstrate the impact of high‐temperature secondary reactions on polymerization rate and polymer molecular weight. © 2010 American Institute of Chemical Engineers AIChE J, 2011