trans-4-Acryloyloxyazobenzene/methyl methacrylate (A/M) copolymers were prepared by free-radical solution polymerization in DMF using AIBN as initiator. The copolymer compositions were obtained from 1 H n.m.r. spectroscopy. The reactivity ratios for the copolymerization of A with M were calculated using the Kelen-Tudos (KT) and non-linear error in variables model (EVM) methods. The reactivity ratios obtained from the KT and EVM methods are r A =0.6±0.1 and r M =1.2±0.1, and r A =0.6±0.1 and r M =1.2±0.1, respectively. The A- and M-centered triad concentrations were calculated from 13 C{ 1 H} n.m.r. spectra of copolymers and correlated with those calculated from Harwood's program using the terminal model reactivity ratios determined by EVM method. A 13 C DEPT (distortionless enhancement by polarization transfer) spectrum was used to differentiate the resonance signals for methine and methylene carbons in the copolymer.