Microscopically-viewed structural changes in solvent-induced phase transitions of synthetic polymers

Structural changes occurring in the solvent-induced phase transition have been investigated by carrying out the time-resolved measurements of X-ray diffraction, infrared spectra and Raman spectra. First example is about the solvent-induced crystallization of syndiotactic polystyrene glass. By comparing the time evolution of the various infrared and Raman bands and the X-ray reflections, the process of nucleation, growth, and aggregation of regular helical sequences in the crystalline lattice could be traced concretely. It was also found experimentally that the amorphous chain segments started an active motion immediately after absorbing solvent molecules and became a trigger to induce the local regularization of random coils into regular helical segments. The second example is the reversible solid-state phase transition of poly(ethylene imine) between the anhydrate of doubly-stranded helices and the hydrates of planar zigzag chains. By carrying out the time-resolved infrared spectral measurements in water vapor atmosphere (H₂O or D₂O), the characteristic bands could be identified for these crystalline phases and the structural transformation in the hydration process could be clarified in detail.