MULTIPHASE STRUCTURE OF SEGMENTED POLYURETHANES - ITS RELATION WITH SPHERULITE STRUCTURE

Small-angle light-scattering (SALS), polarized light microscopy (PLM), differential scanning calorimetry (DSC), and small-angle x-ray scatte ring (SAXS) were used to study morphological changes in segmented poly urethanes with 4,4'-diphenylmethane diisocyanate (MDI) and 1,4-butaned iol (BD) as the hard segment. It was found, for the first time, that s pherulites could form from the melt by quenching the polyurethanes in the melt state to annealing temperatures between 120-degrees-C and T(h ), the highest annealing temperature for spherulite formation. T(h), r anged from 140-degrees-C to ca. 170-degrees-C and depended upon the ha rd- and soft-segment compatibility. Within the range 120-degrees-C to T(h), the radius of the spherulite increased with increasing hard-segm ent content at each fixed annealing temperature. Annealing at 135-140- degrees-C gave rise to the largest spherulites. SAXS was used to inves tigate the phase-separated structures corresponding to the spherulite formation. The interdomain spacing increased with increasing hard-segm ent content and with increasing annealing temperature. The degree of p hase separation first increased with increasing annealing temperature from room temperatures (ca. 25-degrees-C), reached a maximum at ca. 10 7-degrees-C, and then decreased with further increase in the annealing temperature. On the basis of these observations, the mechanisms of ph ase separation, crystallization, and spherulite formation are discusse d.