Solventless Transparent High Refractive Index Nanocomposite Resin

This research is focus on developing solventless transparent high refractive index nanocomposite resins. By blending different surface-modified TiO2 into either bisphenol A diacrylate or 4-vinyl benzyl alcohol containing free radical initiator, two different solventless hybrid resins can be made and further polymerized via radical polymerization into bisphenol A polyacrylate and poly(4-vinylbenzyl alcohol) nanocomposite respectively. They exhibit high refractive index (>1.7) with high transparency. First, we investigated the chemical structure effect of surface modifier on the chemical and physical properties of nanocomposite. Acetic acid (AA), phenylacetic acid (PAA) and hexanoic acid (HA) were used to modified the surface of TiO2 nanoparticle by in-situ sol-gel synthesis. AA- TiO2 is a well known, stable particle in aqueous solution, but it is difficult to be dispersed in common organic matrixes like epoxy resin and polyacrylate. As a result, Only PAA-TiO2 and HA-TiO2 were used in the polyacrylate system. The PAA-TiO2/polyacrylate nanocomposite has better performance in refractive index (1.70 vs. 1.67), thermal properties (Td: 284.7℃ vs. 277.8℃; Tg: 64.8℃ vs 61.8℃) and mechanical properties (hardness: 19.02 VHN vs. 14.39 VHN) than HA-modified TiO2/polyacrylate nanocomposite due to the stiff aromatic structure of PAA surface modifier. Second, we studied the chemical structure effect of polymers on the chemical and physical properties of nanocomposite. A polymerizable amphiphilic 4-vinyl benzyl alcohol was synthesized to obtain poly(4-vinylbenzyl alcohol) (PBzOH). The PBzOH exhibits higher refractive index than bisphenol A polyacrylate and is compatible with AA-TiO2. At 18 vol% TiO2, the PBzOH-AA-TiO2 nanocomposite has a refractive index of 1.73 and excellent transparency (>85% from 500nm to 800nm). The refractive index of the nanocomposite can be further increased to 1.77 by replacing AA-TiO2 by PAA-TiO2. This solvent free high refractive index hybrid resin can be casted into thick film (>50μm), which has potential application in the LED encapsulation, optical parts and interconnects