1H‐NMR and UV studies of Rh complexes as a stereoregular polymerization catalysts for phenylacetylenes: Effects of ligands and solvents on its catalyst activity

Phenylacetylene and its homologues bearing methoxy or chloro groups in the para position of the phenyl ring were stereoregularly polymerized by Rh complex catalysts, e.g., [Rh (norbornadiene) Cl]2, in the presence of various solvents. The 1H‐NMR and UV study of the Rh complex showed that the activity of the Rh catalysts greatly depends upon not only the ligand in the Rh catalyst but also on the solvent used, e.g., polyphenylacetylene with a highly cis‐transoidal content was quantitatively obtained when norbornadiene was coordinated as the ligand, and triethylamine (TEA) was used as solvent, whereas tetrahydrofuran (THF) and benzene reduced the cis content. It was also found that the Rh catalyst as a dimer complex dissociates into the monomeric species not only when TEA was used but also when alcohol, benzene, and THF were used. The resulting monomeric species was considered as the important propagation species in this polymerization. The sharp line width observed in the 1H‐NMR spectrum of polyphenylacetylene and its homologues which were prepared in ethanol or TEA was interpreted by the narrow chemical shift distribution arising from the high cis content.