Methyl methacrylate (MATA)/tert-butyl methacrylate (tBMA) gradient copolymers having linear and hyperbolic composition profiles were synthesized. These special copolymer products were achieved via a model-based computer-controlled semibatch atom transfer radical copolymerization (ATRcoP) process. A simple ATRcoP model was developed based on the terminal model. The equilibrium constants in the ATRP of MMA and tBMA were estimated by the data correlation. The model was verified by batch experiments and was found to give good correlation for the polymerization rate, molecular weight, and copolymer composition data. The model coupled with a reactor model was then applied to the semibatch ATRcoP and was used to calculate comonomer feeding rates for the targeted gradient composition profiles. It was found that the experimental monomer conversion, molecular weight, and cumulative copolymer composition were in good agreement with their targeted theoretical values. The gradient copolymers had low polydispersities close to 1.1. This work demonstrated the feasibility of the model-based semibatch ATRcoP in fine-tuning gradient copolymer composition profiles. (c) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 69-79, 2009