Thionyl chloride (20 mL; 32.8 g; 0.28 mol) was added to dry Amberlite IR-50 (20 g) in a flask. DMF (10 drops) was added and the mixture left at room temperature overnight. Excess Thionyl chloride was removed in vacuo, the polymer was washed thoroughly with CH2Cl2 and dried and was used without further purification.