Solid state 13C NMR study of the char forming processes in polychloroprene

Polychloroprene, also known as neoprene, is an elastomer commonly utilised in the electrical and automobile industries. Its degradation is known to occur predominantly in a two stage process: HCl is lost in the initial step, whilst the second step involves the production of volatile hydrocarbons through chain scission. In this paper we describe the use of solid state C-13 NMR as a probe for structural changes in the condensed phase during these degradative steps. Cross polarisation-magic angle spinning (CP-MAS) analysis of virgin polychloroprene and a series of samples degraded at temperatures between 275 and 550 degreesC reveals that as degradation becomes more advanced there is a steady loss of sp(3) carbon with a commensurate growth in sp(2) carbon. The bulk of the chlorine loss occurs by 350 degreesC with the aliphatic carbon lost by 550 degreesC, by which temperature the residue is essentially aromatic carbon. Dipolar dephasing experiments show that this residue is essentially a network of, on average, tri-substituted phenyl rings. (C) 2001 Elsevier Science Ltd. All rights reserved.