In this study, the effect of the addition of metal particles on the gelation properties of poly[1-(3,4-dimethoxyphenyl)- 2-(4-trimethylsilylphenyl) acetylene] [poly(DMOTMSDPA)] and poly[1-phenyl-2(4-trimethylsilylphenyl) acetylene] [poly(TMSDPA)] was examined. The addition of TaCl5, NbCl5, and MoCl5 to poly(DMOTMSDPA) and poly(TMSDPA) solutions afforded gels. However, the addition of Ta(OCH3)(5) and Mo(OCH3)(5) did not induce gelation. Lewis acids such as TaCl5, NbCl5, and MoCl5 can coordinate with the pi-electrons from the polyacetylene backbone and lone pair of the methoxy groups. Mixed matrix membranes (MMMs) composed of poly(DMOTMSDPA) and these metal chlorides were fabricated by varying the amount of metal chloride. The metal chloride particles were uniformly dispersed in poly(DMOTMSDPA) because the polymer chains could interact with the metal chloride particles. The oxygen permeability of the MMMs composed of poly(DMOTMSDPA) was greater than that of pure poly(DMOTMSDPA). With the addition of 20 mol% of TaCl5, the oxygen permeability increased. In addition, the gas permeability of poly(TMSDPA) was increased by the addition of TaCl5. On the other hand, the gas selectivity values of MMMs were 1.8-3.1, suggesting that MMMs do not contain non-selective defects such as pinholes and interfacial voids in the matrix. (C) 2018 Elsevier Ltd. All rights reserved.