Unstabilized PVC and its mixtures with two sulphur-free and two sulphur-containing organotin stabilizers were exposed at 35° to radiation 300-420 nm wavelength with dominant λ = 345 nm. The significant increase in the chloroallyl group content during the irradiation affects the rate of thermal dehydrochlorination. Measurements of the conjugated double bond systems, colour stability, increase in the carbonyl group content, products content, changes in thermal stability of the exposed mixtures, etc., gave evidence for a negative effect of the sulphur-containing substances on the photostability of the polymer. The higher sensitivity of these substances brings about their photochemical decomposition followed by reaction of the products with chlorine atoms of the polymer chain. In this sense, sulphur-containing organotin thermal stabilizers can be regarded as sensitizers of photodegradation of PVC. The character of the dependences examined was unaffected by the structure of maleate or thioglycolate in the stabilizers. © 1991.
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