NMR characterization of the chemical microstructure of vinylidene halide and vinyl halide copolymers.

We have examined the polyvinylidene halides having dichloro, dibromo, bromochloro, and fluorochloro geminal substituents by NMR spectroscopy and determined that the polymers with asymmetrical substitution are stactic. A series of vinylidene bromide-vinylidene chloride copolymers were prepared and analyzed by 500MHz proton and 125.8MHz carbon-13NMR which resolved monomer sequence tetrad structure. The sequence distribution conformed to a first- order Markov model with r(B)=0.9 and r(C)=0.8. Vinyl bromide- vinyl chloride copolymers proved more difficult to examine by NMR owing to complication by tacticity effects. The analysis was rendered tractable by reductively debrominating the copolymers to the structural equivalent of ethylene-vinyl bromide-vinyl chloride terpolymers. Bromine could not be completely eliminated without partial reaction of chlorine. The resulting monomer sequence distribution was described by the reactivity ratios r(B)=1.0 and r(C)=0.8, in good accord with literature values and the Q-e scheme. Bromine and chlorine substituents have very similar effects on monomer and radical reactivities in the above copolymerizations.