Influences of wetting and shrinkage on the phase separation process of polymer mixtures induced by photopolymerization

Abstract

Phase separation induced by photopolymerization was investigated for a mixture composed of a polystyrene derivative and methyl methacrylate (MMA) monomer. The photopolymerization kinetics of MMA under irradiation with 405 nm visible light was in situ monitored by Fourier-transform infrared spectroscopy (FT-IR). Laser-scanning confocal microscopy (LSCM) combined with 2D-fast Fourier transform (2D-FFT) was utilized to observe and analyze the morphology resulting from the photopolymerization. By using LSCM together with static light scattering, it was found that the phase separation can be induced via either the spinodal decomposition or the nucleation-and-growth processes depending upon the irradiation intensity. A wide variety of stationary morphologies ranging from bi-continuous, salami structures to tri-layer morphology were separately obtained by changing the irradiation intensity. It was also found that the shrinkage of the sample associated with the photo-polymerization plays an important role in the resulting morphology. In addition, the autoacceleration behavior of the polymerization plays a key role in the phase separation kinetics. These experimental results indicate that photopolymerization can be used as an efficient tool not only to control the wetting process during the phase separation, but also to design polymer materials with various morphologies which would be utilized as templates for various practical applications.