RELAXATION PROPERTIES OF POLYCHLOROPRENES

Fifteen mechanical loss maxima were identified in the spectra of inter nal friction of polychloroprenes in the temperature range from -160 to +450-degrees-C. Eleven of these maxima correspond to various physical relaxation transitions and four to chemical relaxation processes. Low -temperature small-scale beta, beta1, pi, and pi-relaxation (glass tra nsition) processes split into two maxima, as is observed in PVC. The s plitting is caused by the existence of two amorphous structures, which is a common cause for such effects in all linear polymers. At medium temperatures, three lambda-transitions are observed that are due to di ssociation of microvolume physical junctions of the molecular network. At high temperatures, the observed delta(Cl), delta(C), and delta(O) maxima correspond to chemical relaxation processes associated with dis sociation of the C-Cl, C-C, and C-O bonds. An assignment of all relaxa tion transitions is reported both for polychloroprene and PVC. The bet a1, pi, and delta(Cl) transitions are due to the chlorine atom in poly chloroprene and PVC. In addition, in PVC, as compared to polychloropre ne, the more frequently occurring polar atom of chlorine increases the intermolecular interactions, thus shifting the small-scale transition s (only slightly) and alpha- and lambda-transitions (markedly) to high er temperatures. Chemical relaxation processes retain their positions. The number of relaxation transitions in polychloroprene is the same a s in PVC, except for the delta(O) transition, which is due to the scis sion of C-O cross-linkages in cross-linked polychloroprene. The origin of most relaxation processes in polychloroprene is the same as in PVC ; however, the positions on the temperature scale and activation energ ies of the corresponding transitions are different.