Free-Radical Copolymerization of Methyl Methacrylate and a-Methacrylophenone. II. Sequence Distribution through13 C-[1H] NMR Spectroscopy

Abstract Sequence distribution in methyl methacrylate (A)-methacrylo-phenone (B) copolymers obtained by free-radical copolymerization at 60°C has been studied by l3C-[1H] NMR spectroscopy. Quantitative analysis of the resonance patterns of the quaternary carbon atom of A units and of the α -CH3 carbon atoms of A and B units has been carried out, considering both compositional and configurational effects. All the kinetic and structural data may be readily taken into account by a scheme in which copolymerization obeys a penultimate unit model characterized by the four reactivity ratios r., = 1.77 ± 0.02, r = 2.30 ± 0.10, rBB = 0.058 ± 0.01, rAB = 0.325 ± 0.03. The stereochemistry of the cross-propagation steps may be described by a single cotacticity parameter: a = σAB = σBA ⋍ 0.40. Its relatively high value probably arises from the great steric hindrance and the high polarizability of the aromatic keto group of methacrylo-phenone.