Effect of polyol structure and molecular weight on the thermal stability of segmented poly(urethaneureas)

Abstract

The thermal stabilities of two series of segmented poly(urethaneureas) have been correlated with their soft-segment molecular weights and structure. Thermal stability was measured by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) in air and in nitrogen. It was shown that polyurethanes based on polytetramethylene glycol (PTMG) are generally more stable for both series in air and in nitrogen than polyurethanes based on polyethene glycol (PEG) and polypropylene glycol (PPG). In contrast, the lower stability for PPG-based polyurethanes may be attributed to the lower extent of interurethane hydrogen bonding arising from the incomplete phase separation between the soft and hard segments and an inferior mutual stabilization effect in this polyurethane. The TGA curves in air also revealed that higher soft-segment molecular weights increase the thermal stability of polyurethanes based on PTMG or PEG. It is suggested that the crystallization effect in both kinds of polyurethanes enhances the phase separation and increases the degrees of interurethane hydrogen bonding in both samples. In a nitrogen atmosphere, the importance of interurethane hydrogen bonding decreases due to the dissociation of hydrogen bonding at elevated temperature. Hence, the B series polyurethanes show higher decomposition temperatures due to the higher soft segment concentrations in these materials.