Haloaldehyde Polymers LXII. High Resolution Solid State 13C NMR Spectra of Chloral and Bromal Polymers

Abstract

ABSTRACT:Homopolymers of chloral and bromal and copolymers of chloral with bromal were studied by solid-state 13 C NMR spectroscopy operated at 100.5 MHz. The cross polarization/magic angle spinning (CP/MAS) measurements of t-butoxy-initiated, acetate endcapped polychloral samples showed the trichloromethyl carbon atom and the acetal 13 C NMR resonances at 97.2 and 101.0ppm. The signals due to the end-groups were noticed at 24.1, 29-31, and 178.0 ppm; these signals were observed more clearly in the dipolar decoupling/MAS spectrum. The tribromomethyl carbon and the acetal carbon resonances of polybromal were observed as a single broad peak at 100.9ppm. The copolymer of chloral and bromal showed the acetal carbon and the tribromomethyl carbon resonances at 100.9 ppm and the trichloromethyl carbon resonance at 98 ppm as a shoulder peak. In the CP /MAS spectrum of the copolymer of chloral and p-chlorophenyl isocyanate ( 5 mo!%), the acetal carbon and the trichloromethyl carbon resonances were similar to the 13 C resonances in polychloral, suggesting that the p-chlorophenyl isocyanate units are segregated in the polychloral chain.KEY WORDS Polychloral / Polybromal / CP/MAS / DD/MAS / Tacticity / Terminal Group / Aldehyde Polymerization / Polychloral and polybromal are insoluble and infusible polymers. These characteristics limit the techniques available for their characterization. 1 From early IR 2 and solidstate 13 C NMR measurements 3 it was recognized that polychloral has a tactic structure and it was suggested that the structure was most likely the isotactic structure. X-Ray studies on rolled samples 4 and on samples drawn over a _hot pin 5 indicated that polychloral was isotactic and had the structure of a 4/1 helix with a repeat distance of approximately 5.2 A. 5 It has been known for some time that the steric repulsion between the bulky trichloromethyl groups lead the polymerization of chloral to be highly isotacticspecific and conformational specific resulting in a helical polymer structure.