This study examined the chemical modification of polyvinyl chloride (PVC) by substitution with SCN (thiocyanate) as a nucleophile. The effects of temperature, molar SCN/Cl ratio, and solvent on the substitution by SCN and the elimination of HCl were investigated. In SCN/EG (ethylene glycol) solution, the substitution/dechlorination ratio increased with decreasing temperature. The dechlorination yield increased with an increasing molar SCN/Cl ratio, favoring the substitution over the elimination. When N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) solutions were used as solvents, DMF favored the substitution, whereas DMSO favored the elimination. In the SCN/DMF solution, the substitution yield and the substitution/dechlorination ratio increased with increasing temperature. Higher temperatures favored the substitution over the elimination in SCN/D MF. Furthermore, the reaction of PVC in SCN/tetrahydrofuran (THF)-DMSO (1:2) proceeded at room temperature, favoring the substitution over elimination. The isomerization of SCN was observed, resulting only in -N=C=S (isothiocyanate) at room temperature and -S-C N (thiocyanate) at 190 degrees C. POLYM. ENG. SCI., 50:69-75, 2010. (C) 2009 Society of Plastics Engineers