Radical polymerization in holographic grating formation in PQ-PMMA photopolymer part I: Short exposure

Photochemical radical polymerization in phenathrenequinone doped poly(methyl methacrylate) photopolymer are investigated theoretically and experimentally at short exposure. In experiments, the dynamic evolution of diffraction efficiency in grating formation is measured. Based on the rate equations of chemical reactions, the analytical expressions of components evolution are deduced to compare the contributions of several photochemical processes to the grating formation. The percentages of these radical polymerizations, namely the polymerization of one PQ with one matrix molecule, the bimolecular combination of MMA molecules, and the disproportionation of MMA molecules, are extracted quantitatively by nonlinear fitting experimental curves. Furthermore, the kinetics parameters, quantum yield Φ and molar absorption coefficient ε of photosensitizers, are determined to demonstrate the rationality of chemical processes. The theoretical results indicate that the polymerization of PQ with matrix is primary photochemical process which dominated the grating formation at short exposure. The contribution of chain polymerization of MMA molecules on the grating can be neglected. This investigation can provide a significant foundation for improving holographic characteristics by photochemical mechanism.