HEAT-CAPACITY OF POLY(TRIMETHYLENE TEREPHTHALATE)

The heat capacity of poly(trimethylene terephthalate) (PTT) has been m easured using adiabatic calorimetry, standard differential scanning ca lorimetry (DSC), and temperature-modulated differential scanning calor imetry (TMDSC). The heat capacities of the solid and liquid states of semicrystalline PTT are reported from 5 to 570 K. The semicrystalline PTT has a glass transition temperature of 331 K. Between 340 and 480 K , PTT can show exothermic ordering depending on the prior degree of cr ystallization. The melting endotherm of semicrystalline samples occurs between 480 and 505 K, with a typical onset temperature of 489 K (216 degrees C). The heat of fusion of the semicrystalline samples is abou t 15 kJ mol(-1). For 100% crystalline PTT the heat of fusion is estima ted to be 30 +/- 2 kJ mol(-1). The heat capacity of solid PTT is linke d to an approximate group vibrational spectrum and the Tarasov equatio n is used to estimate the heat capacity contribution due to skeletal v ibrations (theta(1) = 550.5 K and theta(2) = theta(3) = 51 K, N-skelet al = 19). The calculated and experimental heat capacities agree to bet ter than +/-3% between 5 and 300 K. The experimental heat capacities o f liquid PTT can be expressed by: C-p(L) (exp) = 211.6 + 0.434 T J K-1 mol(-1) and compare to +/-0.5% with estimates from the ATHAS data ban k using contributions of other polymers with the same constituent grou ps. The glass transition temperature of the completely amorphous polym er is estimated to be 310-315 K with a Delta C-p of about 94 J K-1 mol (-1). Knowing C-p of the solid, liquid, and the transition parameters, the thermodynamic functions enthalpy, entropy, and Gibbs function wer e obtained. With these data one can compute for semicrystalline sample s crystallinity changes with temperature, mobile amorphous fractions, and resolve the question of rigid-amorphous fractions. (C) 1998 John W iley & Sons, Inc.