Synthesis of poly (1-β-naphthyl-2-phenylacetylene) membranes through desilylation and their properties

The polymerization of 1-β-naphthyl-2-[(p-trimethylsilyl)phenyl]acetylene (8a) with TaCl₅-n-Bu₄Sn in cyclohexane provided a high molecular weight polymer (9a) (M_w = 3.4 × 10⁶). The corresponding monomers having p-dimethyl-t-butylsilyl and p-dimethyl(10-pinanyl)-silyl groups in place of p-trimethylsilyl group in 8a also polymerized in a similar way to give high molecular weight polymers (9b, 9c, respectively; M_w > 1 × 10⁶). All these polymers were soluble in many common solvents such as toluene and chloroform, and provided free-standing membranes by casting from toluene solution. The oxygen permeability coefficients (Po₂) of 9a at 25°C was as high as 3500 barrers. The membrane of poly(1-β-naphthyl-2-phenylacetylene) (10a) was prepared by desilylation of the membrane of 9a with trifluoroacetic acid. Polymer 10a was insoluble in any solvents, and showed high thermal stability (the onset temperature of weight loss in air ∼470°C). The Po₂ value of 10a reached 4300 barrers. Not only the membrane of 9c but also its desilylation product 10c exhibited large optical rotations ([α]_D = +2924 and +9800°, respectively) and strong CD signals. This indicates that the membrane of 10c maintains the helical main chain conformation of 9c with a large excess one-handed helix sense.