We report the monomer reactivity ratios for copolymers of methyl methacrylate (MMA) and a reactive monomer, 2-vinyl-4,4'-dimethylazlactone (VDMA), using the Fineman-Ross, inverted Fineman-Ross, Kelen-Tudos, extended Kelen-Tudos, and Tidwell-Mortimer methods at low and high polymer conversions. Copolymers were obtained by radical polymerization initiated by 2,2'-azobisisobutyronitrile in methyl ethyl ketone solutions and were analyzed by NMR, gas chromatography (GC), and gel permeation chromatography. H-1 NMR analysis was used to determine the molar fractions of MMA and VDMA in the copolymers at both low and high conversions. GC analysis determined the molar fractions of the monomers at conversions of less than 27% and greater than 65% for the low- and high-conversion copolymers, respectively. The reactivity ratios indicated a tendency toward random copolymerization, with a higher rate of consumption of VDMA at high conversions. For both low- and high-conversion copolymers, the molecular weights increased with increasing molar fractions of VDMA, and this was consistent with the faster consumption of VDMA (compared with that of MMA). (C) 2003 Wiley Periodicals, Inc.