EFFECT OF ISOCYANATES ON THE CRYSTALLINITY AND THERMAL-STABILITY OF POLYURETHANES

Polyurethanes were synthesized from polyester and butanediol with thre e different diisocyanates, i.e., 4,4'-diphenylmethane diisocyanate (MD I), m-xylene diisocyanate (XDI), and 2,4-toluene diisocyanate (TDI). T he effect of chemical structures of diisocyanate compounds on the degr ee of crystallinity and the thermal stability were observed. Different ial scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) were used to determine the degree of crystallinity of the hard segmen t. The thermal degradation of polyurethanes was studied by the thermog ravimetric method. It has been shown that the polyurethane hard-segmen t crystallinity decreases in the following order: MDI > XDI > TDI. The experimental results also indicated that polyurethanes with aralkyl d iisocyanates, i.e., XDI, had the best thermal stability. The polyureth anes synthesized from aromatic diisocyanates, i.e., MDI and TDI, had w orse thermal stability than from XDI. However, owing to the higher deg ree of hard-segment crystallinity for polyurethanes from MDI, these po lyurethanes had a better thermal stability than those based on TDI. (C ) 1996 John Wiley & Sons, Inc.