Kan-ichi Hasegawa

Solvent and additive effects on the polymerization of phenylacetylenes

Abstract The effects of solvent and additive on the homopolymerization of phenylacetylenes using various catalyst systems, including either WCl 6 or MoCl 5 , were investigated. In general, the rates of polymerizations of p -methyl- and phenylacetylenes increased with decrease in the solvent polarity, in the order ethylene dichloride > benzene > carbon tetrachloride, whereas the opposite was true for p -chlorophenylacetylene. The addition of tetraphenyltin (TPT) to the system of phenylacetylene with WCl 6 enhanced the polymerization rate remarkably. The value of ϱ + was −0.47 for the copolymerization of phenylacetylene with ring-substituted phenylacetylene using WCl 6 · TPT and is equal to the ϱ + value for that using WCl 6 . This finding suggests that the propagation of the polymerization of phenylacetylene using WCl 6 proceeds by the same mechanism as that using WCl 6 · TPT. The propagation was proposed to proceed by [2 + 2] cycloaddition of phenylacetylene to giant ring poly(phenylacetylene) with subsequent cleavage of cyclobutene intermediate on the transition metal. The cis content in poly(phenylacetylene)s was enhanced by using MoCl 5 rather than WCl 6 and was higher in benzene than in ethylene dichloride. The microstructure of polymers was interpreted on the basis of Woodward-Hoffmann rules.

Polymerization of phenylpropynes

Abstract The polymerization of phenylpropynes was investigated. Cream-coloured powders, with M n between 3000 and 8500, were obtained from phenylpropynes using WCl6·tetraphenyltin; the rate was much smaller than that for the corresponding phenylacetylene. The magnitudes of the ring-substituent effects on the reactivity of phenylpropyne catalyzed by WCl6 were p+ = −0.96 towards a phenylacetylene propagating end and p+ = −2.19 towards a styryl end. These findings suggest that the former proceeds by metathesis and the latter polymerizes by a conventional cationic mechanism. Introduction of a β-methyl group on phenylacetylene decreased the reactivity by a factor of 1.5–1.8, towards a styryl cation. The polymerization mechanism of phenylpropyne is discussed on the basis of these data.