Yj. Li et al., MULTIPHASE STRUCTURE OF SEGMENTED POLYURETHANES - ITS RELATION WITH SPHERULITE STRUCTURE, Journal of polymer science. Part B, Polymer physics, 31(7), 1993, pp. 853-867
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.