Microstructure of ethylene–vinyl chloride copolymers. I. Direct verification of terminal radical effects on copolymerization by a simplified NMR approach

The sequence distributions of monomer units in a series of high-pressure, bulk ethylene–vinyl chloride copolymers have been determined by high-resolution NMR spectroscopy. The concentrations of EE, VV, and EV (VE) monomer pairs or diads were used with NMR-determined compositions to calculate, in addition to the sequence distribution parameters, the reactivity ratio product for the system. Inclusion of feed data allowed the calculation of individual reactivity ratios. Well within experimental error, the reactivity ratio product (r₁r₂ = 0.7) determined from microstructure analysis—independent of monomer feed data—was equal to that determined by the standard Fineman-Ross technique. Terminal monomer unit effects on the copolymerization were observed. The nonrandom structures result from a copolymerization described by first-order Markoffian statistics.