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

Abstract

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.