ABSTRACT:Polystyrenes with isomeric p-oligodimethylsiloxanyl substituents were synthesized in order to elucidate the roles of these substituents on their film forming properties and oxygen permeation behavior. Branched chain oligodimethylsiloxanyl substituents gave polymers with higher glass transition temperatures than did straight chain substituents. It was indicated from the permeation experiments that trimethylsiloxyl groups in p-oligodimethylsiloxanyl substituents played essential roles in permeation by increasing the diffusion coefficient. The roles of the substituents are further discussed based on the spin-relaxation behavior of the polymers in the solid state.KEY WORDS p-Oligodimethylsiloxanylstyrene / Membrane / Glass Transition Temperature/ Oxygen Permeation/ Diffusion/ Spin-Relaxation/ It is generally admitted that the permeation of a gas through a homogeneous film at rubbery state is controlled by the diffusion and solubility coefficients of a gas in or through the film. P=DS (I)Where P, D, and Sare the permeability, the diffusion and the solubility coefficient, respectively.In our previous papers, we suggested that trimethylsiloxyl groups in p-substituents of poly(p-oligodimethylsiloxanylstyrene )s such as poly(p-pentamethyldisiloxanylstyrene) play essential roles to enhance the permeability of oxygen through increase in the diffusion coefficient. 1 -7 We also suggested that the frequency factor principally contributed to the increase in the diffusion coefficient. 3 In order to confirm further the importance of the role of trimethylsiloxyl groups in enhancing the diffusion coefficient in permeation, polystyrenes having various numbers of trimethylsiloxyl groups in isomeric p-substituents were synthesized and the oxygen permeation behavior through the polymer film was studied. EXPERIMENTAL GeneralColumn chromatography was performed on silica gel using n-hexane as the eluent. 1 H-NMR spectra were recorded on a JEOL 60 MHz spectrometer in CC1 4 , and the chemical shifts are given as b values in ppm from TMS as an internal standard. Spin-relaxation behavior of the polymers in the solid state was studied on a BRUKER 90 MHz spectrometer model CXP-90 at 90.13 MHz at 30°C and 65°C for proton, and on a JEOL 270 MHz CP MAS spectrometer model PX-270 at 25°C for carbon. Spin-lattice relaxation times (T 1 ) were determined by 180°-t-90° pulse method. The 685

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