Synthesis of silsesquioxanes based in (3-methacryloxypropyl)- trimethoxysilane using methacrylate monomers as reactive solvents

摘要

The polycondensation of (3-methacryloxypropyl)-trimethoxysilane in acidic conditions using different methacrylate monomers as reactive solvents resulted in incompletely condensed methacrylate-functionalized silsesquioxanes with a very large fraction of intramolecular cycles. UV-MALDI-TOF-MS analysis demonstrated that the species present after 2 weeks of reaction at 60 °C were: T_6(OH)_2, T_7(OH), T_8(OH) _2, T_9(OH), T_(10)(OH)_2 and T _(11)(OH). Analysis of samples after 30 months of storage at room temperature revealed the presence of T_(12)(OH)_2 and T _(13)(OH) species. The absence of higher molar mass oligomers after prolonged storage periods is attributed to dilution of the reacting medium, which discourages bimolecular reactions that lead to polymer growth. ~(29)Si NMR spectroscopy showed that the conversion in the polycondensation reaction was in the range 0.91-0.96. The methacrylate monomers are not involved in the hydrolysis-condensation reactions with MPTMS and therefore can be polymerized by thermal or photochemical means, thereby cross-linking the preformed nanosized cagelike silsesquioxanes. The formulations containing silsesquioxanes showed a markedly reduced content of extractable monomer after photopolymerization, which makes these resins very attractive for dental filling materials.