Effect of the nucleophilicity and solvent on the chemical modification of flexible poly(vinyl chloride) by substitution

The chemical modification might become an alternative to the thermal degradation of waste polyvinylchloride (PVC). Therefore, the nucleophile substitution of chlorine from flexible PVC by hydroxide (OH^-), thiocyanate (SCN^-), azide (N₃^-), and iodide (I^-) was investigated in ethylene glycol (EG) at 190°C. With the exception of I^-, all nucleophiles used resulted in substitution yields of about 20%. However, also high elimination yields were observed. When SCN was used as the nucleophile, the substitution/elimination ratio increased with decreasing temperature. The product at 150°C contained a mixed structure of thiocyanate and isothiocyanate groups, while at 190°C, only the structure of isothiocyanate was present the product, due to the isomerization of the S-C=N group under the formation of N=C=S at elevated temperatures. The substitution and dehydrochlorination yields increased with an increasing molar SCN/Cl ratio. When EG was replaced by diethylene glycol (DEG) or triethylene glycol (TEG), the dehydrochlorination was found to proceed more rapidly. The use of a solvent with a lower polarity improved the contact between the solvent and the polymer; however, solvents with a lower polarity favor the elimination over the substitution. Therefore, the substitution-elimination ratio increased in the order EG > DEG > TEG. POLYM. ENG. SCI., 2011.