Stereoregularity evolution of methyl acrylate and vinyl acetate copolymers by 2D NMR spectroscopy

Copolymers of methyl acrylate (M) and vinyl acetate (V) were synthesized by free radical bulk polymerization using azobisisobutyronitrile (AIBN) as an initiator at 70 °C and their composition were calculated from 1H NMR spectra. These copolymer compositions were further used to calculate reactivity ratios of V/M copolymers. The reactivity ratios obtained from linear Kelen-Tudos (KT) and non-linear error-in-variable methods (EVM) are rM = 6.74 ± 1.03, rV = 0.04 ± 0.01 and rM = 6.72, rV = 0.04, respectively. The copolymers were analyzed for their stereochemical structure utilizing various 1D (1H, 13C{1H}, DEPT) and 2D (HSQC, TOCSY, HMBC) NMR techniques. 2D HSQC and TOCSY NMR experiments were employed to resolve the highly overlapped and complex 1H and 13C{1H} NMR spectra of copolymers. The complete spectral assignment of carbonyl carbons were done with the help of 2D HMBC spectra. The carbonyl carbon was found to be sensitive up to pentad configurational sequences and shows three and four bond couplings with methine and methylene protons.