Diphenylacetylene having a trimethylsilyl group and two methoxy groups [p-(CH3)(3)SiC6H4C =CC6H4-m,p-(OCH3)(2)(la)] (1a)] polymerized with TaCl5/n-Bu4Sn catalyst to provide a high-molecular-weight polymer (2a). In contrast, monomers without trimethylsilyl group (lb) and having two t-butyldimethylsiloxy groups (1c) hardly polymerized because of poor solubility of the produced polymer 2b and steric hindrance of lc. Polymer 3a with high molecular weight was obtained by desilylation of 2a using CF3COOH. Membranes having p,m-dihydroxyphenyl groups to certain degrees (4a: 40%; 4b 90%) were synthesized by cleavage of methoxy groups in the membrane of 3a using AlCl3. Membrane 4a showed high CO2 permselectivity, while membrane 5a was too brittle. Polymers 2a and 3a totally dissolved in CHCl3 and THF, and their solutions turned into gels upon addition of metal chlorides such as TaCl5, AlCl3, etc. The gels returned to solutions by adding a small amount of methanol. This indicates that 2a and 3a form noncovalent intermolecular bonds through metal ligand interaction. (c) 2014 Elsevier Ltd. All rights reserved.