Phase separation driven by a reversible photo-cross-linking reaction was investigated by using anthracene-labeled polystyrene/poly(vinyl methyl ether) (PSA/PVME) blends. Upon irradiation with 365 nm ultraviolet light, anthracene moieties undergo photodimerization, leading to phase separation of the two polymers. On the other hand, the homogenization process of the phase-separated blend was induced by irradiation with 297 nm which converted photodimer back to anthracene monomer, thus de-cross-linking the PSA networks in the mixture. The kinetics of phase separation and the corresponding homogenization processes driven by these two UV wavelengths were followed in situ under a light scattering instrument equipped with a UV light source. Unlike the conventional kinetics of phase separation in nonreacting mixtures, it was found that the scattering peak shifts toward the side of larger wavenumber as phase separation proceeds under 365 nm light. The local elastic deformation of the blend monitored along the course of irradiation by Mach-Zehnder interferometry reveals a strong correlation between the cross-link-induced elastic deformation and the shift of the scattering peak observed during irradiation. On the other hand, the homogenization process of the cross-linked blends was observed upon irradiation with 297 nm. The scattering intensity decreases while the position of the scattering peak remains unchanged with irradiation time. These experimental results do not only provide basic information for modeling reaction-induced phase separation but also would suggest a method for recycling multicomponent polymer blends by taking advantages of UV-induced reversible phase separation.

Local deformation of a polymer mixture crosslinked by irradiation with ultraviolet light was in situ monitored by using a Mach‐Zehnder interferometer. In combination with the refractive index data obtained from independent measurements, the deformation in the nanometer scales of the crosslinked blends was calculated by using the difference in optical path length of the blend measured before and after irradiation. Upon varying the crosslink density of the blend by changing the light intensity, it was found that the local deformation well correlates with the crosslink density obtained from the reaction kinetics experiments. Furthermore, the strain relaxation of the blends was also monitored in situ and analyzed after irradiation over different time intervals. The results obtained in this study reveal the possibility of monitoring the nanometer‐scale deformation in polymers during radiation curing. These data also provide important information on the correlations between the irradiation‐induced elastic strain and the resulting morphology of reacting polymer blends. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2898–2913, 2005

Phase separation of polymer mixtures is induced and controlled by photo-cross-link and photopolymerization using ultraviolet (UV) light. By taking advantage of the competition between phase separation and chemical reactions, a variety of morphologies such as co-continuous, spatially graded co-continuous and periodic structures with controllable periods, and hexagonal structures, etc, are obtained experimentally. The reaction kinetics (photo-cross-link or photopolymerization), reaction-induced elastic strain and phase separation kinetics are monitored, respectively, by UV–Vis spectroscopy, FTIR, Mach–Zehnder interferometry (MZI), light scattering (LS) and laser-scanning confocal microscopy (LSCM). Spatial modulation of light intensity generated by computer-assisted irradiation (CAI) is also used to induce phase separation of polymer blends. The correlation between the reaction-induced phase separation of polymer mixtures and the competing interactions is discussed with some perspectives on designing polymer materials with high performance.