A study has been made of the effect of amines, particularly those used as catalysts in the preparation of polyurethane foams, on the dehydrochlorination of poly(viny1 chloride) (PVC). It has been shown that when PVC is heated at a temperature of 80°C in the presence of amines the levels of dehydrochlorination produced are considerably greater than those found if no amine is present. This has been attributed to a chemical dehydrochlorination reaction and could well have implications with respect to the physical and mechanical properties of the polymer for certain of its commercial applications.
A comparison has been made of the effect of ultraviolet and solar radiation on plasticised and unplasticised PVC. It has been shown that, when the polymer, plasticised with either a phthalate or trimellitate ester, is exposed to short-wavelength ultraviolet radiation (<292 nm), the photodehydrochlorination of the polymer is retarded by the plasticiser. It has also been shown that, when longer-wavelength radiation is used, the dehydrochlorination is accelerated by the plasticiser. In each case, the effect of the trimellitate is greater than that of the phthalate. Possible mechanisms for the reactions at both long and short wavelengths are considered, and the role of the plasticiser is explained in terms of its electronic absorption spectrum.
Samples of PVC, plasticized with a range of dialkyl phthalates, linear and branched, have been naturally weathered by exposure for one year in Arizona. The results confirm previous findings, that aromatic plasticizers can act to accelerate the photodehydrochlorination of PVC and that the low photostability of phthalates with long, branched side chains results in a greater level of dehydrochlorination than that produced by either linear or branched shorter alkyl chains. For alkyl groups of the same carbon number, the branched chains produce a greater level of dehydrochlorination than the straight chains. Possible explanations for these observations are considered.
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