Local chain configuration dependence of the mechanisms of chemical reactions of PVC. 8. New results from the reductive dechlorination reaction

The reductive dechlorination of poly(vinyl chloride) (PVC) with lithium alu minium hydride, tri-n-butyl tin hydride and lithium triethyl borohydride as reducing agents has been performed in the solution of tetrahydrofuran. A c omparative study of the microstructural evolution with conversion using the three different reducing agents was carried out. The quantitative microstr uctural analysis with conversion has been followed by C-13 NMR spectroscopy . From the evolution of the content of isotactic (mm), heterotactic (mr) an d syndiotactic (rr) triads, and of mmmm, mmmr and rmmr isotactic pentads in the unmodified parts of the polymer, it is unambiguously inferred that onl y the central chlorine atoms of isotactic triads in mmr tetrads or heterota ctic triads in rmmr pentads are reactive. This conclusion was confirmed on the basis of FTIR results. The results provide valuable information regardi ng the effect of tacticity and the related local conformations in the chemi cal reactions of PVC. (C) 2001 Elsevier Science Ltd. All rights reserved.