A copolymer of dodecyl methacrylate/styrene (DMA/St) containing the amidine functionality was synthesized and characterized. The one‐step solution copolymerization process was carried out using a mixed solvent, high temperature, and a functional azo initiator, 2,2′‐azobis[N,N′‐dimethylene isobutyramidine]. Copolymers with different compositions (DMA/St 10/1 to 1/2), molecular weight (Mn 2000–9000), and functionality (1.0–2.0) were prepared and characterized by NMR, FTIR, DSC, and elemental analysis. The molecular weight of the copolymers could be controlled by the amount of the initiators. Copolymer composition depends on the feed molar ratio of comonomers. The amidine functionality of the copolymers was determined by elemental analysis. It was found that 72% of the polymer chain has one functionality. The Tg of the copolymer depends on the feed molar ratio. This copolymer could be used as a potential dispersant for lubricant oil. Published 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1684–1691, 2002