Copolymers of vinylidene cyanide (1a) methacrylonitrile (1b) and acrylonitrile (1c) with alpha captodative monomer, methyl a acetoxyacrylate were synthesized by radical copolymerization and their microstructures were studied by C-13 NMR spectroscopy. The copolymer of 1a with methyl alpha-acetoxyacrylate (2) has mostly an alternating structure but the copolymers of 1b and 1c with 2 are rather statistical. The measurement of their reactivity ratios for these two reactions is in agreement with the proposed structures.