Homogeneous Polymerization of Butadiene Catalyzed by Rhodium Salts

Abstract

A study has been made of the solution polymerization of butadiene, to predominantly trans 1, 4 polymer, catalysed by rhodium salts. The reaction is accelerated by protonic acids (including water) and by those reducing agents which in aqueous systems would be capable of reducing Rh^III to Rh^I. Ligands such as organic amines, and also bromide and iodide anions, tend to retard or even inhibit the reaction. The overall process appears to be a chain reaction, but is not free radical in character. The mechanism which best fits all the observations is one in which the active species is a π-allylic rhodium hydride, initiation occurring by hydride shift and propagation occurring by a ligand displacement process.