Chap._500006 - Photolysis in the presence of oxygen also...

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PVC degrades more rapidly when heated in air than when heated in an inert atmosphere. The rate of dehydrochloration increases substantially. It is generally supported that the acceleration is due to peroxy radicals. chain scission O H Cl CH 2 * + C-CH 2 -CH Cl thermo-oxidative degradation H O O Cl CH 2 -CH-CH 2 -CH Cl * O O CH 2 -CH-CH 2 -CH O 2 Cl Cl CH 2 -CH-CH 2 -CH CH 2 -CH-CH 2 -CH Cl PVC shall be processed under the inert atmostphere (nitrogen) condition. (b) Photodegradation When unstabilized PVC is exposed to UV radiation of wavelengths above 250nm, dehydrochlorination occurs to give polyene sequences. Simultaneously, the polymer chains undergo scission and crosslinking.
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Unformatted text preview: Photolysis in the presence of oxygen also results in dehydrochlorination together with chain scission and cross-linking. Cl Cl-PVC CH 2-CH-CH 2-CH-CH=C- Cl* + * CH 2 O H CH 2-C chain scission O 2 crosslinking * uv Cl CH 2-C PVC labile tertiary Cl PVC- HCl-CH 2-CH-CH 2-CH-Cl Cl-CH 2-CH-CH 2-CH-CH 2-C Cl Cl- HCl Unzipping sequential elimination due to allylic activation-CH=CH-CH=CH-CH=C PVC In addition to polyene formation, photodehydrochlorination of PVC also leads to cross-linking and chain scission....
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