MICROSTRUCTURAL ANALYSIS OF METHACRYLONITRILE METHYL-METHACRYLATE COPOLYMERS BY C-13 NMR-SPECTROSCOPY

The microstructure and stereochemical configuration of methacrylonitrile, N, and methyl methacrylate, M, copolymers prepared by free-radical polymerization at 60-degrees-C are analyzed on the basis of the classical terminal copolymerization model and with the assumption of Bernoullian statistics for the distribution of the stereochemical configuration of monomer units. From the analysis of H-1 NMR spectra the reactivity ratios were determined, their values being r(N) = 0.883 and r(M) = 0.892. From the analysis of the C-13 NMR resonance signals assigned to the quaternary carbon and the carbonyl group of M units and the alpha-CH3 group of both the M and N units, the statistical parameters sigma-NN = 0.37, sigma-MM = 0.24, and sigma* = sigma-NM = sigma-MN = 0.87 were determined. The coisotacticity parameter sigma* is observably higher than the isotacticity parameters of the corresponding homopolymers, sigma-NN and sigma-MM, which indicates some strong interactions between the nitrile and carbonyl groups of neighboring N and M units.