Phase separation of polymer mixtures driven by photochemical reactions: Complexity and fascination

► Direct measurements of elastic deformation and its relaxation process in polymerizing mixtures. ► Stimulus-response relation between cross-link reactions and shrinking process in polymers. ► Effects of sample shrinkage on the phase separation kinetics and the resulting morphology. Phase separation driven by photochemical reactions was examined for two types of polymer mixtures: one in the liquid and the other in the bulk state. In the former, monomer of the first polymer was photo-polymerized and simultaneously cross-linked in the presence of the second polymer in the liquid state, whereas in the second system, a polymer was photo-cross-linked in the presence of the second polymer in the bulk state. A combination of measurements techniques including FT-IR, UV–VIS spectrometry, confocal microscopy, light scattering and Mach–Zehnder interferometry was utilized in order to elucidate the stimulus–response behavior of these polymer networks. The shrinkage of the mixtures occurring during the photo-polymerization process was in situ observed under a laser-scanning confocal microscope (LSCM), whereas the deformation process during the cross-link process in the bulk state was in situ followed by using Mach–Zehnder interferometry (MZI). The correlation between the emergence of the hexagonal-phase morphology and the reaction-induced shrinkage in the polymerizing mixtures was discussed from the reaction kinetics and the LSCM data. For the mixture in the bulk state, MZI data provide a reasonable explanation for the mechanism of the anomalous light scattering from the reacting polymer blends. These experimental results are finally discussed in the context of systems with competing interactions.