Gas Permeation Studies of Silylated Derivatives of Poly(methylphenylphosphazene)

Several silylated derivatives of poly(methylphenylphosphazene) [Me(Ph)PN] x [RMe 2 SiCH 2 (Ph)PN] y [R = CH 3, 3; (CH 2 ) 2 CH 3, 4; (CH 2 ) 2 CF 3, 5; and (CH 2 ) 2 (CF 2 ) 8 F, 6 ] were prepared via deprotonation of the methyl group of [Ph(Me)PN] n with n -BuLi followed by the treatment with chlorosilanes. Three new terpolymers, [Me(Ph)PN] x [Me 3 SiCH 2 (Ph)PN] y [RMe 2 SiCH 2 (Ph)PN] z [R = (CH 2 ) 2 (CF 2 ) 8 F; x = 0.44, y = 0.14, z = 0.42, 7; x = 0.46, y = 0.27, z = 0.27, 8; x = 0.33, y = 0.54, z = 0.13, 9 ], were also prepared via cosubstitution using varying ratios of Me 3 SiCl and RMe 2 SiCl. Structural characterization and purity of each of these polymers were established by 1 H and 31 P NMR spectroscopy, elemental analysis, and differential scanning calorimetry. The gas permeabilities of membranes of these polymers were determined at 35 °C and compared to that of the parent polymer [Me(Ph)PN] n, 1, for which permeabilities to N 2, O 2, CH 4, and CO 2 were 0.6 × 10 -10, 1.8 × 10 -10, 0.7 × 10 -10, and 6.5 × 10 -10 cm 3 (STP)·cm -1 ·cmHg -1 ·s -1, respectively. The incorporation of the silyl groups generally increased permeabilities relative to [Me(Ph)PN] n without significant changes in selectivity. Polymers from the cosubstitution reactions had as much as a 15-fold increase in gas permeabilities with selectivity ratios (e.g., α CO 2 /CH 4 = 8.9) similar to those of 1 . The trimethylsilyl groups also increased the T g values of the terpolymers 7 − 9 relative to the simple derivative 6 . The gas permeation properties of these polymers are discussed with respect to the lengths and concentration of the side groups.