Thermal degradation of cross-linked polyisoprene and polychloroprene

Polyisoprene and polychloroprene have been cross-linked either in solution or in solid state using free radical initiators. In the comparable experime ntal conditions higher cross-linking density was observed in the solid stat e process. Independent of the crosslinking method, polychloroprene tended t o give a higher gel content and cross-link density than does polyisoprene. Infrared characterization of the cross-linked materials showed cis-trans is omerization occurred in the polyisoprene initiated by benzoyl peroxide, whe reas no isomerization was found in the samples initiated by dicumyl peroxid e. Polyisoprene does not cross-link by heating in a thermal analyzer, where as polychloroprene easily undergoes cross-linking in such conditions. Infra red spectroscopy showed that in the case of polyisoprene, rearrangements oc cur upon heating which lead to the formation of terminal double bonds, whil e polychloroprene loses hydrogen chlorine which leads to a conjugated struc ture. There is apparently some enhancement of the thermal and thermal oxida tive stability of polyisoprene because of the cross-linking. Cross-linked p olychloroprene is less thermally stable than the virgin polymer. Cross-link ing promotes polymers charring in the main step of weight loss in air, whic h leads to enhanced transitory char. (C) 2000 Elsevier Science Ltd. All rig hts reserved.