The sorption properties of toluene vapor were measured for methyl methacrylate (MMA)-co-chloromethyl styrene (CMSt) copolymers chemically modified with N,N-dimethyl-1,3-propanediamine (DMPDA) to develop a novel quartz crystal microbalance toluene-vapor sensor coating. The influence of the structure of the comonomer, the composition of the copolymer, and the film thickness on the toluene sorption properties were investigated. The modified MMA-CMSt copolymers were capable of large, fast, and reversible sorption versus the modified styrene-CMSt copolymers. The largest sorption capacity was obtained for MMA-CMSt-DMPDA with a 96 mol % CMSt concentration. These behaviors were explained by a combination of the plasticization of the copolymers by the introduction of bulky DMPDA at lower CMSt concentrations and the formation of a loosely crosslinked structure at higher CMSt concentrations. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1086-1093, 2009