Synthesis of silyl-disubstituted poly(p-phenylenevinylene) membranes and their gas permeability

p-Bis(bromomethyl)benzene with two silyl groups [SiMe2-n-C8H17, SiMe3 (1a), SiMe2-n-C8H17, SiEt3 (1b), SiMe2-n-C8H17, SiMe2-n-C8H17 (1c), SiMe2-n-C8H17, SiMe2-n-C18H37 (1d), SiMe2-n-C18H37, SiMe2-n-C18H37 (1e)] were polymerized by Gilch method to afford silyl-disubstituted poly(p-phenylenevinylene)s (2a–e). The polymers containing SiMe3 groups (2a) showed poor solubility and dissolved in only CHCl3. On the other hand, the other polymers (2b–e) exhibited good solubility in common organic solvents. According to thermogravimetric analysis (TGA), the silyl-disubstituted poly(p-phenylenevinylene)s showed high thermal stability (thermal decomposition temperature: Td ≥ 310 °C). Polymers 2a–e had relatively high molecular weight over 7.6 × 104, and gave free-standing membranes by solution casting method. Except 2e, the oxygen permeability coefficients (PO2) of membranes of the silyl-disubstituted poly(p-phenylenevinylene)s increased as increasing alkyl length of silyl groups (2a: 5.4, 2b: 6.0, 2c: 15.0, 2d: 20.4 barrers). The membrane of 2e having two dimethyl-n-octadecylsilyl groups in the repeating unit exhibited the lowest gas permeability among the present polymers, and its PO2 was 1.8 barrers. This is because polymers 2a–d were amorphous while 2e was crystalline. The PO2 values for amorphous poly(p-phenylenevinylene)s increase in direct proportion to the number of carbon in the side chains.