Synthesis, characterization, and properties of new polystyrene-SiO 2 hybrid sol-gel materials
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MaryGail K. Hutchins LNP Engineering Plastics, Inc., 475 Creamery Way, Exton, Pennsylvania 19341 (Received 1 July 1992; accepted 30 December 1992)
A new family of organic-inorganic hybrid materials has been prepared by incorporating polystyrene structure units covalently into the SiO2 glass network via the sol-gel approach. The polymer precursors were synthesized by free-radical copolymerization of styrene with 3-(trimethoxysilyl)propyl methacrylate (MSMA) at various feeds. These copolymers were then hydrolyzed and co-condensed with tetraethyl orthosilicate in tetrahydrofuran at room temperature to afford monolithic polystyrene-SiO2 hybrid sol-gel materials having SiO 2 contents of 15 to 84% by weight. The hybrid materials derived from the copolymers with MSMA contents greater than 22 mol % have excellent optical transparency. In these transparent hybrid materials, the polymer chains should be uniformly distributed in and covalently bonded to the amorphous SiO2 matrices. The bulk properties of these materials including density, refractive index, and hardness were found to be related to their molecular compositions and can be tailored by varying the polymer contents.
I. INTRODUCTION Sol-gel processes have been investigated extensively for many years and have been employed for improving or modifying the processes of making inorganic glasses.1 For example, acid-catalyzed hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) yield a SiO2 glass at temperatures much lower than the conventional fusion process. Many researchers have demonstrated the successful combinations of various polymers and copolymers with inorganic structures like the SiO 2 at the molecular level to form a class of inorganic-organic hybrid materials through the sol-gel process.2^4 A significant feature in many of these new materials is the formation of covalent bonding and therefore elimination of macroscopic interfaces, as existing in the conventional composite materials, between the polymers and the inorganic components. Thus, the physical properties of these hybrid materials could be designed and controlled by varying the nature and composition of both the polymer and inorganic components. A number of polymers have been incorporated into SiO2 and/or TiO 2 glass networks, including polydimethylsiloxane,5 poly(tetramethylene oxide),6 polyimides,7 poly(arylene ether ketone) and
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Author to whom correspondence should be addressed. J. Mater. Res., Vol. 8, No. 5, May 1993
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poly(arylene ether sulfone),8 polymethacrylates,9 14 and polyoxazolines.15 The structure-property relationship in the new materials was studied to a certain extent. Recently we have successfully incorporated trialkoxysilyl-functionalized poly(methyl methacrylate) (PMMA), an important organic glass, into the inorganic SiO2 matrix by co-condensing triethoxysilyl groups of the polymers with TEOS.11"13 The acidity of reaction media, content of water, and solvents are known to play a critical role on the sol-gel rea
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