Alternating Copolymerization of Butadiene and Propylene

An alternating copolymer of propylene and butadiene is prepared with vanadium or titanium compounds and alkylaluminum compounds as the polymerization catalyst. The catalyst should be prepared at extremely low temperature as −70° C and halogen atom is essential to the catalyst activity. Carbonyl compounds such as ketone, acid, ester, acid anhydride, and acid peroxide are very effective additives to the catalyst for enhancement of the molecular weight of the polymer. Potentiometric titration and the ESR studies suggest that a divalent vanadium compound associated to form the dimer through a chloride bridge is a precursor of the active species. An anionic copolymerization mechanism involving the alternating coordination of monomers is proposed. The copolymer is always of a 1:1 composition irrespective of the composition of monomer feed and the alternating structure of trans-1,4-poly (butadiene co propylene) is estimated from IR and NMR data. The copolymer seems to be a new versatile synthetic rubber having excellent low temperature properties, high rebound, good compatibility with conventional rubbers, and high resistance toward aging.