Synthesis and properties of halogen- or methyl-containing poly(diphenylacetylene) membranes

Abstract

Novel diphenylacetylenes with both trimethylsilyl groups and other substituents (R 2C 6H 3C CC 6H 4- p-SiMe 3, R = m, p-Cl,Cl, m, m-Cl,Cl, m, p-Br,Br, m, m-Br,Br, m, p-Me,Me, m, m-Me,Me, 1a– f, respectively) were polymerized with TaCl 5– n-Bu 4Sn to produce solvent-soluble polymers ( 2a– f). Most polymers ( 2a– e) had high molecular weight over 1 × 10 6, and gave free-standing membranes by the solution casting method. Desilylation of these Si-containing polymer membranes was carried out with trifluoroacetic acid (TFA), which afforded solvent-insoluble desilylated polymer membranes ( 3a– e). According to thermogravimetric analysis (TGA), both Si-containing and desilylated polymers showed high thermal stability ( T 0 ≥ 420 °C). The fractional free volume (FFV) of both Si-containing and desilylated polymer membranes ( 2a– d, 3a– d) were fairly large (ca. 0.27–0.32), while the FFVs of membranes ( 2e, 3e) were rather small (0.28 and 0.24). The oxygen permeability coefficients ( P O 2 ) of 2a was as high as 5400 barrers, which is the largest among all the poly(diphenylacetylene) derivatives. Polymers 2b– d also exhibited high oxygen permeability, and their desilylated ones 3b– d retained similar high oxygen permeability. On the other hand, the P O 2 values of 2e and 3e were 1200 and 530 barrers, respectively, which are smaller than those of the halogen-containing polymers ( 2a– d and 3a– d).