Active chlorines in poly(vinyl chloride) (PVC) were quantitatively replaced by pendant allyl groups (-CH2CH=CH2) with allyltrimethylsilane in the presence of Friedel-Crafts acids (e.g., Et2AlCl and TiCl4). The thermal stability of the allylated PVCs was significantly superior to that of the starting material. Our allylation method is essentially quantitative; indeed, it was used for the determination of the active chlorine content in the PVCs. Furthermore, the pendant allyl groups were quantitatively oxidized by m-chloroperbenzoic acid to epoxides; thus, PVCs carrying propylene oxide substituents [-CH2CH-CH2(O)] were prepared. The structures of the products were characterized by high-resolution NMR spectroscopy, and their thermal characteristics were characterized by TGA and color formation. (C) 2000 John Wiley & Sons, Inc.