The effects of radicals on silica surface, which were formed by c-ray irradiation, on the polymerization of vinyl monomers were investigated. It was found that the polymerization of styrene was remarkably retarded in the presence of c-rayirradiated silica above 60 8C, at which thermal polymerization of styrene is readily initiated. During the polymerization, a part of polystyrene formed was grafted onto the silica surface but percentage of grafting was very small. On the other hand, no retardation of the polymerization of styrene was observed in the presence of c-rayirradiated silica below 50 8C; the polymerization tends to accelerate and polystyrene was grafted onto the silica surface. Poly(vinyl acetate) and poly(methyl methacrylate) (MMA) were also grafted onto the surface during the polymerization in the presence of c-ray-irradiated silica. The grafting of polymers onto the silica surface was confirmed by thermal decomposition GC-MS. It was considered that at lower temperature, the grafting based on the propagation of polystyrene from surface radical (''grafting from'' mechanism) preferentially proceeded. On the contrary, at higher temperature, the coupling reaction of propagating polymer radicals with surface radicals (''grafting onto'' mechanism) proceeded to give relatively higher molecular weight polymer-grafted silica.
Synthesis and polymerization of styrene derivatives with silyl group(s) have been studied extensively' -3 ) , and the applications of silicon-containing polymers as X-ray resists4), oxygen-permselective membranes5) or flame retarders6) have also been studied.Recently, we have reported on a novel synthetic route for styrene derivatives having trimethylsilylmethyl group(s), 4-trimethylsilylmethylstyrene (SMS) and 4-bis(tri-methylsily1)methylstyrene (BSMS), using the unique nucleophilic reactivity of lithium diisopropylamide (LDA) toward 4-methylstyrene (MST)') . The polymer obtained from the above monomers8) is expected to show novel functions as a gas-permeable material. This paper communicates properties of poly(BSMS) and gas permeability of poly(BSMS) membrane. Experimental partMaterials: 4-Bis(trimethylsilyl)methylstyrene (BSMS) was prepared as reported in our previous paper'). 2,2'-Azodiisobutyronitrile (AIBN) was purified by recrystallization from methanol. Commercial toluene was purified by conventional method9). Polymerization of 4-bis(trimethylsilyl)methylstyrene (BSMS):AIBN (9,4 mg; 0,057 mmol) and BSMS (3,O g; 11,4 mmol) were filled in a glass tube. After sealing off the tube under high vacuum, the mixture was allowed to react at 60°C for several hours, then the tube was opened. The polymer obtained was dissolved in THF and then poured into methanol. The precipitate was purified by successive reprecipitations (3 x ) from THF solution into methanol. The polymer sample collected was subjected to freeze-drying with benzene to remove solvents employed.Membrane preparation: A toluene solution containing 5 wt.-Yo of the polymer was cast on a polytetrafluoroethylene sheet, and the solvent was evaporated during 24 h. For measuring the gas permeability, the polymer membrane was dried in vacuo and cut into a circular piece of 22 mm diameter. The thickness of the membrane was in the range 100-150 hm.
Synthesis and gas permeation measurements of several types of polymers from methylstyrene derivatives containing mono-and bis(trialkylsily1) group(@ were carried out. Upon radical homoand co-polymerization of silicon-containing monomers high-molecular-weight polymers were obtained. Results from gas permeation measurements showed that these types of siliconcontaining polymers exhibit fairly high oxygen permselectivity (ratio of oxygen and nitrogen permeation coefficients Po,/PN2 = 3,l -4,6), keeping the oxygen permeation coefficient (PoJ in the range of between 1.4and 4 3lo-' cm3 (STP)cm . cm-' * s-' * cmHg -'. From time lag measurements, it was found that permeation coefficients are dependent on the solubility of gases in the membranes rather than on diffusivity. Actually, the oxygen solubility coefficients increase with increasing silicon content in the polymers. Permselectivity of oxygen against nitrogen is governed by polymer constitution rather than by silicon content.
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