Starch-g-polycaprolactone copolymerization using diisocyanate intermediates and thermal characteristics of the copolymers

Starch-g-polycaprolactone copolymers were prepared by two-step reactions. T he diisocyanate-terminated polycaprolactone (NCO-PCL) was prepared by intro ducing NCO on both hydroxyl ends of PCL using diisocyanates (DI) at a molar ratio between PCL and DI of 2:3. Then, the NCO-PCL was grafted onto corn s tarch at a weight ratio between starch and NCO-PCL of 2:1. The chemical str ucture of NCO-PCL and the starch-g-PCL copolymers were confirmed by using F TIR and C-13-NMR spectrometers, and then the thermal characteristics of the copolymers were investigated by DSC and TGA. By introducing NCO to PCL (M- n: 1250), the melting temperature (T-m) was reduced from 58 to 45 degrees C . In addition, by grafting the NCO-PCL (35-38%) prepared with 2,4-tolylene diisocyanate (TDI) or 4,4-diphenylmethane diisocyanate (MDI) onto starch, t he glass transition temperatures (T-g's) Of the copolymers were both 238 de grees C. With hexamethylene diisocyanate (HDI), however, T-g was found to b e 195 degrees C. The initial thermal degradation temperature of the starch- g-PCL copolymers were higher than that of unreacted starch (320 versus 290 degrees C) when MDI was used, whereas the copolymers prepared with TDI or H DI underwent little change. (C) 2000 John Wiley & Sons, Inc.