Photopolymerization and photobleaching of n-butyl acrylate/fumed silica composites monitored by real time FTIR-ATR spectroscopy

Using real time Fourier transform infrared (FTIR)-attenuated total reflection (ATR) spectroscopy, photopolymerization and photobleaching of n-butyl acrylate/fumed silica composites were characterized. To simulate and study surface and bulk photopolymerization, experiments were performed with and without metallic spacers above ATR crystal. Different photopolymerization behaviors were observed at the surface (without spacer) and at the bulk (with 1 mm spacer). The difference in photopolymerization kinetics can be explained by photobleaching reaction, which increases with the increase in ultra-violet (UV) intensity. From in situ UV transmission measurement, it was observed that there is a gradual increase in UV intensity with 1 mm thick samples, which means a gradual increase in UV intensity at 1 mm depth in the bulk. It was also found that higher photobleaching rate with higher UV intensity induces lower molecular weight and broader molecular weight distribution.