Enhanced degradation polymers with

Water, methanol, and n-hexane do not influence the photooxidation of PVC (43), but the photodegradation is accelerated by ferric chloride (70,71) and certain other compounds containing iron (70,71,72). Purification of the polymer might be expected to enhance its photostability by removing deleterious impurities such as iron compounds that are derived from metal equipment. This type of result was obtained in one recent study (58) but not in others (30,59). In contrast, the photo-oxidative degradation of PVC should be enhanced by admixture of the polymer with materials that are unusually susceptible to photooxidation themselves. Such behavior has been observed for impact-modified PVC containing polybutadiene-based polyblends (69,73). 

The work described here supports the view that the chemical combination of metal ions with organic molecules leads to coordination complexes and polymers with enhanced stability with respect to weight loss, thermal degradation, or oxidation. Bis(8-hydroxyquinoline) derivatives were used to prepare a series of coordination polymers containing first-row transition metals, and the thermal stabilities of the polymers were evaluated. The influence of the structure of the organic molecule and the role of the metal are discussed. 

Optically active polyaldehydes possessing optically active side chains, such as poly-(R)(+)-citronellal, poly-(R)(+)-6-methoxy-4-methylhexanal, and poly-(S)(+)-2-methylbutanal, have been prepared by Goodman (1, 22). The optical activity of the polymers was enhanced as compared with their model compounds. It was concluded that the enhancements of the optical activity arose from a conformational rigidity around the asymmetric center in the side chain of the polymer. From degradation studies of the polymers it was concluded that the optical activity of the monomer was unchanged, and no racemization had occurred during polymerization and degradation. 

The first commercial aliphatic diisocyanate to be available is 1,6-hexa-methylene diisocyanate (HDI). It is a colourless liquid with a boiling point of 127 C at 10 mm Hg. It is less reactive than either TDI or MDI, but in the presence of a catalyst the rate of reaction is enhanced. The use of HDI leads to urethane polymers with better resistance to discolouration, hydrolysis and heat degradation than has TDI (Frisch, 1969). A number of aliphatic diisocyanates have become available commercially. These aliphatic diisocyanates have been reported to give excellent colour stability. Some important ahphatic diisocyanates are illustrated in Figure 2.16. 

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