Research On The Molecule Design Of Polymeriable Photoinitiators And The UV Curing Behavior Of Silicone Resin

Silicone resin is widely used in Aerospace and other fields due to its high performance such as high temperature resistance, UV resistance, etc. Silicone resin is usually cured under high temperature which limits its application. Ultra violet(UV) curing silicone resin owns properties such as environment friendly, fast curing, ambient temperature curing, so as to overcome the drawbacks of heat curing. Photoinitiator is the most important part of UV curing system, Benzophenone is the most popular hydrogen abstraction-type photoinitiator. However, low molecular benzophenone has many drawbacks such as toxic, odor, yellowing and migration, leading to the decrease properties of silicone resin. In this paper, polymerizable photoinitiators and polymeric photoinitiator were synthesized to overcome the drawbacks of low moleculer benzophenone, and the curing mechanism of the silicone resin cured by different photoinitiators were studied.Three polymerizable photoinitiators containing maleimide group and a polymeric photoinitiator using polyethylene glycol as main chain were synthesised. The pure products were obtained by recrystallization. FT-IR and NMR were taken to characterize the structure. The Ultraviolet Absorption of the photoinitiators were measured by Ultraviolet Absorption Spectrum, it was concluded that the UV maximal absorbtion was redshifted with the introduction of maleimide group, chlorine atom and sulfer atom. The photoinitiator with sulfer atom was significant redshifted, 68 nm higher than BP. The introduction of the PEG enhanced the UV absorbtion; The fluorescence spectra indicated that the introduction of the maleimide group, sulfer atom and the PEG chain will decrease the fluorescence emission, they were benefit for the improving of the efficience of the photoinitiators.The methacrylate silicone resin was synthesised by hydrolysis condensation reaction using methyl propylene acyloxy propyl trimethoxy silane as raw material. The structure was characterized by FT-IR, GPC and NMR. The Silicone resin was cured by the synthesised photoinitiators and the co-initiator, Dimethylaminoethyl methacrylate under high-pressure Hg lamp. The results showed that the polymeric photoinitiator possessed the fastest curing speed, only 70 s when the concentration is 0.2mmol/g. The photoinitiator containing sulfer atom possessed the highest double bond transformation, up to 85%. The thermal property of the cured resin was characterized by Thermogravimetric analysis and Differential Scanning Calorimetry, the results showed that the resin cured by sulfer containing photoinitiator possess the best thermal behavior, the temperature of initial decomposition was 200℃, the final quality retention rate was 33.8%.In this paper, the synthesized polymerizable and polymeric photoinitiators can not only overcome the drawbacks of the low molecular benzophenone such as migration, but also some of them can improve the curing speed of silicone resin and the final double bond conversion, which will give silicone resin a wider application in areas such as food packaging, spacecraft coating.