Mesoporous silica/polymer nanocomposites.

摘要

The primary purpose of this work is to investigate the different methods from the literature to synthesize mesoporous silica/polymer nanocomposites, the possibility of synthesizing highly oriented polymer inside mesoporous silica channels and to use mesoporous silica as reinforcements in composites. Literature contains some methods to synthesize mesoporous silica/polymer composites, but these reported methods only used nano-channels as nano-reactor and the synthesized polymers had no direct connection with silica surface. To address some of the limitations found in the literature, new approaches through grafting initiators onto the surface of inner-wall of mesoporous silica were developed and investigated. Using the newly developed approach, PMMA was successfully synthesized through free radical polymerization and nylon 6 though in situ anionic ring-opening polymerization inside the nano-channels. The synthesized polymer had direct covalent bonds with silica surface and they couldn't be removed by solvent. This research involved two main parts: development of approaches and characterization of properties of newly synthesized composites and polymer.;ABCC, a kind of azo-initiator, was grafted onto silica surface through multiple grafting steps. The resulting ABCC-immobilized-MS could be used to initiate monomers with ethyl groups using free radical polymerization. Monomer of MMA was used as an example to be initiated inside the nano-channels and spherical mesoporous silica/PMMA composites were synthesized. The resulting composites showed a higher glass transition temperature, higher decomposition temperature and narrower decomposition range than pure commercially available PMMA. Spherical PMMA capsules were obtained after the silica network was dissolved with hydrofluoric acid, these pure PMMA spheres had the same thermal properties and morphology as they had with in the composites.;Most grafting steps based on silica surface involved APTMS grafting which grafted amine groups on silica surface. The existence of amine groups on the surface of mesoporous silica would terminate the anionic ring-opening polymerization of epsilon caprolactam and produced caprolactactam salt with catalysts of magnesium bromide ethyl etherate. N-3-((N-3-(trimethoxysilanyl)n-propyl)benzamidyl)-benzoyl-epsilon-caprolactam was synthesized and directly grafted onto the surface of inner-walls of mesoporous silica, and nylon 6 propagated inside the nano-channels from the initiator center from the walls. The resulting nylon 6/BMS nanocomposites were spheres with the same diameter as pure BMS. About 50 wt% of the composites was newly synthesized nylon 6. The synthesized nylon 6 was proven to contain both alpha-form crystallite and gamma-form crystallites with covalent bonds with the surface of silica inside the nano-channels. The synthesized spherical composites had the same glass transition temperature and melting temperature as pure commercial nylon 6, having the same decomposition temperature as N-acyllactam-immobilized BMS but lower than commercial pure nylon 6.;Traditional surface grafting on the surface of mesoporous silica only produced materials with organic groups occurred mostly near the openings of the channels. To overcome the limitation, one-pot sol-gel synthesis could produce ordered mesoporous silica with organic functional groups homogeneously distributed on the silica surface. Mesoporous silica/polyelectrolyte with high surface and regular morphology was directly synthesized with one-pot sol-gel method. The synthesized mesoporous silica/PSSA could be used as catalyst to initiate the polymerization of epsilon caprolactone. The resulting polycaprolactone showed very low polydispersity index of 1.2, which was much lower than those produced with catalyst of organometallics.