Melting parameters of poly(glycolic acid)

Equilibrium melting temperature T-m(0), heat of fusion DeltaH(f), and entropy of fusion DeltaS(f) of poly(glycolic acid) (PGA) was determined by using Clapeyron-Clausius equation. Equilibrium melting temperature T-m(0) was 504.6 K which was determined by Hoffman-Weeks plots. The pressure dependence of T-m(0) was determined by high pressure DTA up to 150 MPa. Volume change DeltaV(f) at melting was determined by using dilatometer. Heat of fusion in PGA was 183.2 (J g(-1)), which is very close to the value reported by Chujo et al. who determined it by using T-m depression in copolymer with poly(lactic acid). DeltaS(f) of PGA was 0.363 (J g(-1) K (1)), which is about twice that of PLA, and the reason was discussed on the basis of the elastic modulus below T-m. (C) 2004 Elsevier Ltd. All rights reserved.