Polymerization and polymer properties of (2-methyl-5-tert-butylphenyl)acetylene: steric effects of the ring substituents

Summary (2-Methyl-5-tert-butylphenyl)acetylene (2Me5tBuPA) polymerized in the presence of MoCl₅-n-Bu₄Sn catalyst in 1,4-dioxane to give a high molecular weight polymer . Not only MoCl₅- but also WCl₆-based catalysts were effective. The polymer obtained was a dark brown solid, soluble in organic solvents such as toluene and CHCl₃, and formed a freestanding film by solution casting. The onset temperature of weight loss of the polymer in air was 260 °C. Its oxygen permeability coefficient was 43 barrers, which is twice that of natural rubber. Differences from the results (usually lower molecular weight, not film-forming, and thermally less stable) of both poly(phenylacetylene) and polyo-methylphenyl)acetylene] are attributable to the synergistic steric effect of the o-methyl and m-tert-butyl groups.