In-situ SAXS study of phase segregation and morphology of styrenic block copolymers

The equilibrium morphologies of the styrenic block copolymers have been studied extensively [1,2,3], however the structural developments in dynamic regime are virtually unknown. In-situ Small Angle X-ray Scattering (SAXS) measurements were performed on a series of thermoplastic elastomers at the synchrotron light source at Brookhaven National Laboratory. The results from the scattering experiments were compared to different structural models. It was found that the styrenic blocks segregate very rapidly at high temperatures (200oC - 250oC). It was established that the molten polymers start from the disordered state at high temperatures and on cooling, rapid phase segregation with significant phase fluctuations occurs. The hard block segments segregated into hexagonally packed cylinders before leaving the spinneret of the extruder. The rapid segregation is followed by a slower process of 3-D spatial ordering, which could take up to two weeks for completion depending on the annealing conditions.