On the structure of chlorinated natural rubber. 1H- and 13C-NMR data

Abstract

1H- and 13C-NMR spectra of compositionally homogeneous samples of chlorinated natural rubber containing 0.4-3.0 Cl/C 5 have been investigated. In the samples of composition Cl/C 5 ⩽ 1 there are no units containing > 1 chlorine atom, meaning that chlorine docs not add to CC double bond. Simultaneously, unsaturation of the polymer decreases by approx. 10%. These data support a hypothesis about cyclization of the chain during the fast stage of chlorination (up to Cl/C 5 = 1). However, quaternary C atoms typical of 6-membered cyclic structures, as postulated in the literature, have not been observed in spectra. Weak signals in the region 75–76 ppm indicate the existence of ▪ fragments. The data obtained suggest that 5- not 6-membered cycles are formed during chlorination of natural rubber. With an increase of the chlorination degree, signals in the olefinic region of spectra appear, indicating formation of exo- and internal CC double bonds differing from analogous fragments forming in the fast stage of the reaction.