Ultraviolet Light Catalyzed Gelation of 3-Methacryloxypropyltrimethoxysilane via Altered Silicate Spatial Structure

The gelation of 3-methacryloxypropyltrimethoxysilane (MAPTMS) is much more difficult to achieve in conventional conditions. This article describes a novel and concise approach to acquire transparent and firm hybrid gel material by one step promptly without photoinitiator or other tetraalkoxysilane. MAPTMS was hydrolyzed in acidified aqueous solution, which became homogeneous sol in 3 min, and then the sol was irradiated with UV light for a few minutes to form gel. The experimental results indicated that MAPTMS sol gelled in the presence of UV-irradiation was mainly attributed to altering Si-O-Si skeleton structure through hydroxyl radicals, and the gelation originated from the hydrolytic polycondensation of MAPTMS rather than the polymerization of methacryloxy substituent groups. The hydroxyl radicals could break the Si-O-Si ring structure to form cross-linker like species, and these cross-linkers chemically joined linear chains together to form the gel network. This investigation offers not only the photoinduced gelation strategy for MAPTMS sol but also the new insight into the effect of UV-irradiation on the sol-gel process of organotrialkoxysilanes.