A SYNCHROTRON SAXS STUDY OF STRUCTURE DEVELOPMENT KINETICS DURING THE REACTIVE PROCESSING OF FLEXIBLE POLYURETHANE FOAM

The kinetics of microphase separation during the processing of flexible polyurethane foam have been investigated. Forced-adiabatic, time-resolved synchrotron SAXS experiments were employed to probe the evolution of structure. Microphase separation was observed to occur at a critical conversion of isocyanate functional groups and shown to follow the kinetics associated with spinodal decomposition. The isocyanate conversion at the microphase separation transition (MST) was in good agreement with our previously reported FT-IR results. From the scattering data, R(q), the amplification rate of the composition fluctuations was determined. The data have been analyzed in terms of a time-dependent Ginzburg-Landau model (TDGL). Plots of R(q)/q2 versus q2 exhibited a maximum at a finite value of scattering vector (q). These observations were in qualitative agreement with the theoretical predictions of the TDGL theory.