NEW METHOD FOR DETERMINING REACTIVITY LEVELS OF COPOLYMERS BY NUCLEAR MAGNETIC-RESONANCE - APPLICATION TO POLY(METHYL METHACRYLATE-VINYLIDENE CHLORIDE)

Constant-composition copolymers of methyl methacrylate and vinylidene chloride produced by radical copolymerization are studied by **1H-NMR at 60 and 250 MHz. The different methods of the literature for the derivation of reactivity ratios from either the copolymer composition or the sequence average lengths, or even the diad distribution, are applied but lead to rather dispersed results. A new graphical method is proposed, based on the use of peculiar values of the triad distribution functions. It allows us to detect a penultimate effect for the vinylidene chloride-rich region. In the same range, a change in tacticity of the diads and triads on the methylmethacrylate sequences, as compared with homopolymers, is observed; it suggests that the anomaly is caused by the competition of the depropagation reaction.