Photopolymerization of methacrylate monomers using polyhedral silsesquioxanes bearing side-chain amines as photoinitiator

Organotriethoxysilanes (APS-PGE2) were synthesized by reacting 1 mol of 3-(aminopropyl)triethoxysilane with 2 mol of 1,2-epoxy-3-phenoxypropane (PGE). Polyhedral oligomeric silsesquioxanes functionalized with bulky amino groups (ASSQO) were prepared by hydrolytic condensation of APS-PGE2 catalyzed by formic acid. Methacrylate resins were activated for visible light polymerization by the addition of 1 wt.% CQ in combination with the synthesized ASSQO at loadings between 0 and 30 wt.%. The progress of monomer conversion versus irradiation time showed that the CQ/ASSQO pair is an efficient photoinitiator system because a fast reaction and high conversion result from 60 s irradiation at 600 mW/cm2. The lack of methacrylate groups in the ASSQO, able to polymerize with the methacrylate resin, results in the absence of chemical bond between the ASSQO cages and the matrix. Debonding of ASSQO cages from the polymer give rise to nanovoids; which allows the methacrylate matrix to yield and deform plastically. Consequently, the final effect is a decrease in the flexural modulus and compressive strength with increasing amounts of ASSQO. The present study highlights the surface effect on the overall properties in nanostructured materials.