Polymerization of 1‐(trimethylsilyl)‐1‐propyne homologs containing two silicon atoms by tantalum‐ and niobium‐based catalysts

Abstract

AbstractPolymerization of new 1‐(trimethylsilyl)‐1‐propyne homologs containing two silicon atoms [CH3CCSi(CH3)2CH2Si(CH3)3 and CH3CCSi(CH3)2CH2CH2Si(CH3)3] was investigated by use of Ta and Nb catalysts. CH3CCSi(CH3)2CH2Si(CH3)3 was polymerized quantitatively by TaCl5 alone to provide a polymer having molecular weight over 106. CH3CCSi(CH3)2CH2CH2Si(CH3)3 was polymerized in good yield by an equimolar mixture of TaCl5 with an appropriate organometallic cocatalyst such as Ph4Sn to give a polymer with molecular weight of ca. 4 X 105. Nb catalysts were less active toward these monomers than the corresponding Ta catalysts. These two kinds of polymers had alternating double bonds along the main chain according to IR and 13C‐NMR spectra. Both polymers were white solids completely soluble in low‐polarity solvents like toluene, and solution casting afforded uniform, tough films. These polymers were thermally fairly stable, and their softening points were above 350°C. Films of these polymers showed smaller oxygen permeability coefficients [P = 4 × 10−9 – 8 × 10−9 cm3(STP) · cm/(cm2·sec·cmHg)] but larger separation factors [(P/P) = 3.4 – 3.6] than a poly[1‐(trimethylsilyl)‐1‐propyne] film.