Polymerization of substituted acetylenes by various rhodium catalysts: Comparison of catalyst activity and effect of additives

This research deals with comparison of the activity of various Rh catalysts in the polymerization of monosubstituted acetylenes and the effect of various amines used in conjunction with [Rh(nbd)Cl] 2 in the polymerization of phenylacetylene. A zwitterionic Rh complex, Rh + (nbd)[( η 6 ‐C 6 H 5 )B − (C 6 H 5 ) 3 ] ( 3 ), was able to polymerize phenylacetylene ( 5a ), t ‐butylacetylene ( 5b ), N ‐propargylhexanamide ( 5c ) and n ‐hexyl propiolate ( 5d ), and displayed higher activity than the other catalysts examined, that is [Rh(nbd)Cl] 2 ( 1 ), [Rh(cod)( O ‐ o ‐cresol)] 2 ( 2 ), and Rh‐vinyl complex ( 4 ). Monomers 5a and 5c polymerized virtually quantitatively or in fair yields with all these catalysts, while monomer 5b was polymerizable only with catalyts 3 and 4 . Monomer 5d did not polymerize in high yields with these Rh complexes. The catalytic activity tended to decrease in the order of 3 > 4 > 2 > 1 . Although polymerization of 5a did not proceed at all in toluene with [Rh(nbd)Cl] 2 alone, it smoothly polymerized in the presence of various amines as cocatalysts. The polymerization rate as well as the molecular weight of polymer depended on the basicity and steric bulkiness of amines.