(o‐Methylphenyl)acetylene polymerized with high yields in the presence of W and Mo catalysts. W catalysts were more active than the corresponding Mo catalysts. The weight‐average molecular weight of the polymer formed with W(CO)6–CCl4–hv reached 8 × 105, being higher than the maximum value (ca. 2 × 105) for poly(phenylacetylene). The polymer had the structure \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} [{\rm CH} \hbox{=\hskip-1pt=} {\rm C}(o - {\rm CH}_3 {\rm C}_6 {\rm H}_4 )\rlap{--} ]_n $\end{document}. The stereochemical structure of the main chain could be determined by 13C‐NMR; the cis content varied in a range of 41–61% depending on the polymerization conditions. The present polymer was thermally more stable than poly(phenylacetylene) according to thermogravimetric analysis. Interestingly, this polymer possessed deeper color than poly(phenylacetylene), and showed a fairly strong absorption in the visible region.

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ABSTRACT:(o-Alkylphenyl)acetylenes (alkyl: Et, n-Bu, n-C6 H 13 , n-C8 H 17 , and iso-Pr) polymerized in high yields with W and Mo catalysts. MoCl 5 -based catalysts, which are not very active to phenylacetylene (PA), exhibited high activity like the WCl6 counterparts. The weight-average molecular weights (Mw) of the polymers having o-n-alkyl groups were in the range 2 x 10 4 -55 x 104, being similar to or slightly higher than those of poly(PA), while the highest Mw value of poly(o-iso-Pr-phenylacetylene) [poly(iso-PrPA)] reached I x 10 6 • The formed polymers were dark red, and had the structure --fCH=C(C6 H4 -alkyl)k They were thermally more stable than poly(PA) according to the thermogravimetric analysis. The polymers with long o-n-alkyl groups were soluble in aliphatic solvents (e.g., hexane) unlike poly(PA), and their softening points were lower. Poly(o-iso-PrPA) was film-forming, and fairly gas-permeable (P02 27 barrers, P0 ,/PN, 2.2).KEY WORDS Substituted Acetylene/ ( o-Alkylphenyl)acetylene / TransitionMetal Catalyst / Metathesis Polymerization / Substituted Polyacetylene / Gas Permeability / In the polymerization of monosubstituted acetylenes by W and Mo catalysts, a general tendency has been observed that monomers with bulky substituents provide high molecular weight polymers. For instance, 1-hexyne, which is sterically not crowded, forms only oligomers whose weight-average molecular weights (M w) are a few thousand. 1 • 2 In contrast, tertbutylacetylene, which is very crowded, produces a polymer whose Mw exceeds 1 x 10 5 . t -4 The steric effect of phenylacetylene is moderate, and the M w of the polymer formed is usually 2 X 10 4 -3 X 10 4 . 1 • 5 W(C0) 6 -hv catalyst) and good thermal stability. 6 It has recently been found that phenylacetylenes with even bulkier ortho groups (e.g., CF 3 7 and Me 3 Si 8 • 9 ) yield polymers with very high molecular weight (Mw 1 x 10 6 and above).Thus it is interesting to examine how high the molecular weight of the polymer becomes when a substituent is introduced onto the ortho position of phenylacetylene to increase steric crowding. In fact, we studied the polymerization of(o-methylphenyl)acetylene (o-MePA) to find the formation of a polymer having high molecular weight (Mw up to 8 x 10 5 with * To whom correspondence should be addressed.The present study deals with the polymerization of (o-alkylphenyl)acetylenes, namely, phenylacetylenes having ethyl, n-butyl, n-hexyl, n-octyl, and iso-propyl groups at the ortho position

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