Metathesis polymerization of monomers containing two diphenylacetylene units: synthesis and properties of poly(diphenylacetylene)s bearing diphenylacetylene units on the side chain

The metathesis polymerization of monomers containing two diphenylacetylene units [Me3SiC6H4CCC6H4CCR; R = o-SiMe3C6H4 (1a), o,o-(SiMe3)2C6H3 (1b), o,o,p-(SiMe3)3C6H2 (1c), and o-CF3C6H4 (1d)] was performed using TaCl5/n-Bu4Sn. The polymerization of 1a–c containing SiMe3 group at the ortho position of a benzene ring afforded solvent-soluble products (2a–c) without crosslinking since the reaction of one acetylene was suppressed by steric hindrance. In contrast, the polymerization of 1d containing CF3 group afforded a solvent-insoluble product (2d). Polymers 2a–c exhibited similar thermal stability with a high decomposition temperature (T0 = 380 °C). Upon excitation with 400 nm light, 2a–c exhibited emissions (530 nm) at a longer wavelength than that of poly(diphenylacetylene) without a phenylacetylene on the side group. In addition, 2b and 2c exhibited intense fluorescence. The oxygen permeability coefficients of 2a–c were 54.3, 268, and 375 barrer, respectively. Gas diffusivity and solubility increased with increasing number of SiMe3 groups in the repeating unit.