Phase separation kinetics and morphology of light-induced IPN confined in micrometer scales

The reaction and phase separation kinetics of interpenetrating polymer networks (IPNs), prepared by photopolymerization of methyl methacrylate (MMA) and photo-crosslinking of polystyrene (PS), were examined in situ by using Fourier-trans form infrared (FT-IR) spectroscopy and phase-contrast and laser-scanning confocal microscopy. Photopolymerization of MMA exhibited an autocatalytic behavior and the reaction yield increased with increasing light intensity. The phase separation process on the other hand, was suppressed by the reaction occurring at the later stage of irradiation, resulting in co-continuous morphology with variable characteristic lengths. By localizing the domains undergoing phase separation by irradiation with a single strip of light, whose width varied from 500 to 60,um, it was found that the characteristic length of the spinodal structures depends on the scale of spatial confinement. These results were discussed in terms of phase separation under thermodynamically open conditions.