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 H-1 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 with those calculated from Harwood＇s program using the terminal model reactivity ratios determined by EVM method. A C-13 DEFT (distortionless enhancement by polarization transfer) spectrum was used to differentiate the resonance signals for methine and methylene carbons in the copolymer.