Effect of the casting solvent on the free‐volume characteristics and gas permeability of poly[1‐(trimethylsilyl)‐1‐propyne] membranes

The effect of the casting solvent on the structure of poly[1‐(trimethylsilyl)‐1‐propyne] (PTMSP) membranes was investigated experimentally. The PTMSP membranes were cast from solutions of cyclohexane, toluene, and tetrahydrofuran; the membranes were characterized by the positron annihilation lifetime spectroscopy (PALS) technique and by gas‐permeation measurements of O 2 , N 2 , and CO 2 . The decay curves from the positron annihilation lifetime spectroscopy gave the best fit when two long‐life components (τ 3 and τ 4 , τ 3 < τ 4 ) were employed. This suggests that two types of free volume existed in the PTMSP membranes. The size and number density of τ 4 , which was characteristic for PTMSP, decreased in the following order of the casting solvents: cyclohexane > toluene > tetrahydrofuran. The order was consistent with the order of gas permeability. A good correlation was observed between the permeability and the structural parameter that denoted the free‐volume size and the number density of τ 4 . © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 497–501, 2003