PHOTOOXIDATION OF POLY(VINYL-CHLORIDE) AT 254 NM IN THE ABSENCE AND PRESENCE OF PHTHALATE PLASTICIZERS

Irradiation of neat PVC at lambda(inc) = 254 nm under air induces the formation of conjugated double bonds, -(CH=CH)(n)-(quantum yield phi approximate to 1.6 10(-4) for n = 3). Simultaneously, C-Cl bonds are split (phi approximate to 8.10(-2)). With the aid of FTIR spectroscopy the following oxidation products were detected: -OH, -CH=CH-C(=O)-, -CHCl-CH2-C(=O)-OH, -CHCl-CH2-C(=O)-H, -CHCl-C(=O)-CHCl-, -CHCl-C(=O)-Cl. Irradiation of PVC plasticized with about 42 wt.-% phthalate results in similar chemical changes. However, to some extent the chemical alterations are due to an indirect radiation effect. PVC, isolated from plasticizer after irradiation, was found to contain phthalate fragments attached to the polymer. Moreover, in plasticized PVC the formation of carbonyl groups is enhanced as was evidenced regarding the generation of -CHCl-C(=O)-CHCl- groups. On the other hand, cleavage of C-Cl bonds and intermolecular crosslinking is retarded by phthalates. The exposure gel doses for unplasticized and plasticized PVC are 3.10(-5) and 2.10(-4) Einstein cm(-2), respectively.