Yongyuan Yang

Photoinitiating systems and photopolymer materials for holography

In this paper, the kinetics of photosensitive initiating polymerization and photopolymer holographic recording materials were studied. Four sensitizers that could be sensitive to He-Ne (632.8 nm) laser were synthesized and chosen for this study: (1) NK-529, (2) NK-3960, (3) (MCD), (4) ECD. The long-wavelength sensitive photoinitiating system are composed of one of the four compounds above, 2- chlorohexaarrylbiimidazole(o-cl-HABI) and 3-mercapto-4- methyl-4H-1,2,4-triazole (MTA), which acted as sensitizer, initiator and hydrogen-donor respectively. The kinetic study was carried out by using dilatometer, we found the relationships between the rate of polymerization and the concentration of each component. We believe that the photopolymerization was initiated by free radicals which were produced by the electron transfer between the sensitizer and the initiator in the excited state. Comparing the monomer conversion of these four systems, we found: MCD >ECD >NK529 >NK3960. We chose the system (MCD- HABI-MTA) as a photoinitiating system of photopolymer holographic materials. The holographic material was composed of the above photoinitiating system, a binder, a mono- or multi-functional monomer, and other additives. Adding the third beam to expose the photopolymer plate simultaneously during the initial holographic exposure can increase the effective exposure sensitivity of the photopolymer plate. Mechanisms of photoinitiating polymerization and hologram formation are discussed. More than 80% of reflection grating diffraction efficiency can be obtained. The holographic gratings have a good physical and chemical stability under ambient conditions.