THERMAL-DEGRADATION OF SEGMENTED POLYURETHANES

Thermal degradation of polyurethane samples was studied by a thermogra vimetric method. The effect of soft-segment length and soft-segment co ncentration on activation energy of the degradation process was measur ed. Three methods of calculation gave activation energies at different stages of the very complex weight loss process. It was shown that at initial stages of the weight loss the process was dominated by hard-se gment degradation. Activation energy of the whole process calculated b y the Ozawa-Flynn method did not offer clear insight into the structur e-stability relationship of polyurethanes. The second method showed th at activation energy of the initial stage of degradation increased wit h decrease in hard-segment length. The Flynn method of calculating act ivation energy produced fairly constant activation energy of the first 40% degradation, at around 150 kJ/mol, for polymers in the C series. Generally, calculation of kinetic parameters of a complex degradation process as in polyurethanes gives results that are not easy to interpr et. It has been shown qualitatively that polymers with higher soft-seg ment concentration display lower initial weight loss and higher onset temperatures of degradation. (C) 1994 John Wiley & Sons, Inc.