The goal of this project was to synthesize and characterize porous inorganic-organic hybrid particles using emulsion polymerization. Specifically, cross-linked poly(methyl methacryl) (PMMA)–poly(orthosiloxane) POSS (PMMA/POSS) particles were synthesized using two reaction approaches: (i) water phase free radical initiated reaction (WI) and (ii) organic phase free radical initiated reaction (OI). Particles were produced with concentrations of methyl-methacrylate (MMA) and methacryl functional POSS (MAPOSS) in the reaction mixtures from 40 to 100 wt% MAPOSS. MAPOSS was used to provide vinyl groups that could participate in the reaction and form a highly cross-linked, connected network of POSS molecules. The MMA was used to provide reactive groups that could link the POSS molecules. Following synthesis, the particles were washed with solvent to remove any unbound MMA, MAPOSS, or PMMA oligomers which was expected to provide more porous structure.
The conversion of monomers to PMMA/POSS particles was monitored as a function of reaction method and initial MMA concentration. Scanning electron microscopy (SEM) was used to monitor the particle size and size distribution. The N2 sorption isotherms in the PMMA/POSS particles were characterized with a Micromeritics accelerated surface area and porosimetry system. The surface area and porosity of the PMMA/POSS particles were characterized using several different models for porous materials; such as, Brunauer-Emmet-Teller analysis, t-plot by Kruk-Jaroniec-Sayari analysis, and non local density functional theory by Tarazona.
The particles synthesized formed hard-spheres with a broad size distribution, from about 100 nm to 15μm diameter, as shown by SEM micrographs. Particles were synthesized with greater than 90% conversion of monomers. The particles were washed with organic solvent and final mass or recovery was from 50% to 95% of prewashed values. There was a general trend of a decrease in surface area with increasing MMA concentration for samples produced using the OI method. The samples produced using OI method were generally higher porosity than those with the WI method. In most cases, the samples were characterized as having mesopores and some samples contained micropores.