A starved feed reactor (SFR) is a semibatch polymerization reactor where initiator and monomer are fed slowly into a fixed amount of solvent. The polymerization is carried out isothermally at elevated temperatures. The added initiator decomposes instantaneously and the added monomer polymerizes immediately. The molecular weight of the product polymer can be effectively controlled by the feed ratio of monomer to initiator. This article presents a study on the kinetics of butylacrylate polymerization in an SFR. The model parameters are regressed with experimental data. Although the solids fraction in the SFR is high (>50%), viscosity is not high and the "gel effect" is weak because of the low molecular weight of the products. It is found that the termination rate constant is a power function of molecular weight, and the lumped rate constant k(p)/(k(t)(0))(1/2) can be modeled through an Arrhenius equation. (C) 2004 Wiley Periodicals, Inc.