Hybrid organic?inorganic materials prepared by photopolymerization of methacrylate-functionalized silsesquioxanes

SILVANA V. ASMUSSEN; CLAUDIA I. VALLO

Hybrid Systems: Performance, Applications and Technology

Nova Science Publishers

Año: 2017; p. 179 - 209

Silsesquioxanes have been the subject of intensive study in the past, and are becoming important again as a vehicle for the manufacture of novel hybrid organic?inorganic materials. In particular, organosilsesquioxanes can be prepared through the hydrolysis and condensation of organotrialkoxysilanes, which undergo a complex series of hydrolysis and self-condensation reactions leading to dimers, trimers, tetramers and ultimately oligomers and polymers designed as silsesquioxanes (SSQO). In this study, methacrylate-functionalized silsesquioxanes were synthesized by the hydrolysis and condensation of (3-methacryloxypropyl)-trimethoxysilane (MPTMS) using methacrylate monomers as reactive solvents. The methacrylate monomers were selected with regards to their ability to form copolymers with the (methacryloxypropyl) silsesquioxanes. The SSQO were characterized by size exclusion chromatography (SEC), Fourier-transform infrared spectra (FTIR), matrix-assisted ultraviolet laser desorption ionization time of flight mass spectra (UV-MALDI-TOF MS), and 29Si NMR spectroscopy. The hydrolytic condensation of MPTMS at 60 ºC in different methacrylate monomers generates incompletely condensed SSQO with a very large fraction of intramolecular cycles. In that way, methacrylate monomers are modified with around 40 wt.% of nanosized methacrylate-functionalized polyhedral SSQO generated in situ by the hydrolysis and polycondensation of MPTMS. Figure 1 shows structures of representative partially condensed polyhedra. Although the polycondensation of the SSQO continues during the storage at room temperature, the reaction proceeds at a slow rate. The absence of higher molar mass oligomers after a prolonged storage period is attributed to the fact that dilution of the reacting medium with polar solvents discourages bimolecular reactions that lead to polymer growth. The methacrylate monomers modified with SSQO were photopoly-merized with visible light, and the performance of the resulting hybrid organic-inorganic materials was assessed by measuring the volumetric shrinkage during polymerization, the leachable monomer content, the flexural modulus, and compressive yield strength