Photolysis of dialkyl phthalates and poly(vinyl chloride) plasticized with dialkyl phthalates at wavelengths exceeding 290 nm

When dialkyl phthalate plasticizers, neat poly(vinyl chloride), PVC, and PVC plasticized with dialkyl phthalate are subjected to near UV radiation at lambda(inc) > 290 nm, chemical alterations are induced by traces of impurities capable of absorbing light in this wavelength range. The main photoproducts formed in the case of neat phthalates are olefins, alcohols, and phthalic acid anhydride. Neat PVC undergoes C-Cl bond cleavage and, in addition, carbonyl and polyene groups are formed. The formation of carbonyl groups is a nonlinear (auto-accelerated) process whereas polyene generation occurs linearly with increasing irradiation time. The photolysis of phthalate-plasticized PVC is characterized by the decomposition of the plasticizer, evidenced by the decrease in the absorption band at 278 nm, and by the formation of carbonyl groups attached to PVC and the cleavage of C-Cl bonds as evidenced by the increase or decrease in the IR absorption bands at about 1710 and 617/639 cm(-1), respectively. Phthalates hardly influence the incorporation of carbonyl groups into PVC tan auto-accelerated process) and retard only slightly the cleavage of C-Cl bonds. By contrast, phthalates sensitize the incorporation of carbonyl groups upon irradiation at lambda(inc) = 254 nm. Within the error limit no effect of the chemical nature of the phthalate on the formation of photoproducts was detectable upon performing irradiations at lambda(inc) > 290 nm.