A New Family of Styrene/Diene Rubbers

The insertion of single styrene units into polyisoprene is demonstrated using borohydrido rare earth/dialkylmagnesium systems. This yields a new family of styrene/diene copolymers (SBR rubbers). The resulting poly[(1,4‐trans‐isoprene)‐co‐styrene] exhibits quite narrow molecular weight distributions, up to 30% inserted styrene, and a 96–98% 1,4‐trans‐microstructure. The presence of a bulky and electron‐rich ligand in the coordination sphere of the metal leads to an increase of the amount of styrene inserted and narrower chemical composition and molecular weight distributions. The presence of significant quantities of styrene in the medium does not alter the selectivity of the reaction, in contrast with cis‐specific polymerizations. magnified image