Synchrotron SAXS studies of segmented polyurethanes

Abstract

It has been reported by us, for the first time, that segmented polyurethanes (SPUs) based on 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) as the hard segment could form spherulite structures upon melt-quenching to an annealing temperature (T _A) above 120°C. Synchrotron small-angle x-ray scattering (SAXS) experiments were performed to investigate the microphase separated structures corresponding to the spherulite formation. With increasing hard-segment content, both the integrated scattered intensity (Q) and the interdomain spacing (d) increased first and then decreased when the hard segment was above 50%, possibly due to phase inversion. With increasing T _A, the Q values increased first, reached a maximum at ∼107°C, and then decreased with further increase in T _A; the d values showed a monotonic increase. The kinetics of phase separation was investigated after the samples were quenched from the melt to 140°C. Interdomain spacing remained unchanged throughout the whole process. The results indicated that the hard-segment mobility and the system viscosity were the two key factors controlling the phase structure.