A new simple synthesis of soluble high molecular weight polyphenylenes by the cotrimerization of mono‐ and bifunctional terminal acetylenes

The monofunctional acetylenes, phenylacetylene and m‐ethynyltoluene, were each copolymerized with diethynylbenzene in a 1:1 mole ratio by using TiCl4/3AlEt2Cl as cyclotrimerization catalyst. The aromatic polymers which were produced were polydisperse with a molecular weight of ∼10,000. Variation of catalyst concentration had no effect on the molecular weight profile. An excess of bifunctional acetylene produced some insoluble gel but when some of the monofunctional acetylene was withheld and added only after an initial molecular weight build‐up by the excess bifunctional acetylene, soluble polymers with molecular weights of approximately 50,000 were obtained in high yield, provided the overall ratio of mono‐ to bifunctional acetylene was maintained at 1:1. The resulting polyphenylenes were highly soluble in benzene and chlorinated solvents but gave brittle films. This was attributed to a highly branched structure resulting from a lack of specificity by the catalyst. Thermogravimetric analysis showed the polymers to have high thermal stability.