Effects of framework structure and coupling modification on the properties of mesoporous silica/poly(methyl methacrylate) composites

Mesoporous silicas (MPSs) with two-dimensional (2D) hexagonal framework (SBA-15) and worm-hole framework (MSU-J) were synthesized with poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (P123) and ,-polyoxypropylene diamine (D2000) as templates, respectively. Both SBA-15 and MSU-J were further modified with -(methacryloyloxy) propyl trimethoxy silane (MAPTS) via post-grafting to prepare organic mesoporous silicas (denoted SBA-15-G and MSU-J-G, respectively) with -C=C groups on the surface of mesopores. All mesoporous silicas were employed as filler to prepare improved poly(methyl methacrylate) (PMMA) composites with lower dielectric constant, higher thermal, and mechanical properties. It was found that all mesoporous silicas retained their mesostructure in MPS/PMMA composites to introduce a lot of voids into the composites. So, the dielectric constant of composites decreased with the loading of mesoporous silica and their organic derivatives increased. Also, all composites exhibited stabilized dielectric constant with lower value in comparison to pure PMMA over the whole frequency from 1 to 160MHz. Specifically, with the addition of MPS to PMMA, the dielectric constants of the composite can be reduced from 2.91 of the pure PMMA to 2.73 and 2.64 by incorporating 4wt% SBA-15 and 7wt% MSU-J, respectively. All the composites exhibited improved mechanical properties, glass transmission temperature (T-g), and thermal stability in comparison to PMMA. All these differences in macro-properties are attributed to the different structure between MPS/PMMA composites and PMMA. MSU-J silica with the larger framework pore size provides the composite with the best improvement in dielectric, thermal, and mechanical properties.