Hydrogenation of unsaturated polymers under the action of oligoallene complexes of transition metals

Abstract

The hydrogenation of isolated double bonds in cis-PB (96% cis units), trans-PB (84% trans units), and the statistical butadiene-styrene copolymer (63: 37) is performed under mild conditions (a temperature of 30–50°C and a constant hydrogen pressure of 70 kPa). Palladium, bimetallic palladium-nickel, and palladium-cobalt complexes containing oligodimethylallene ligands are used as catalysts. It is shown that the rate of hydrogenation decreases in the sequence cis-PB, trans-PB, butadiene-styrene copolymer. The highest degree of hydrogenation of cis-PB (98%) is attained in the presence of the bimetallic oligodimethylallene Pd-Ni complex ([Pd]: [Ni] = 0.8: 0.2). In the hydrogenation of the butadiene-styrene copolymer, the highest activity is exhibited by the Pd-Co catalyst (0.5: 0.5): For the butadiene component, the degree of hydrogenation is 98%, while for the styrene component, the degree of hydrogenation is 15%. The IR studies of the polymers indicate the exhaustive hydrogenation of double bonds for both polystyrene and polybutadiene components of the copolymer and the appearance of ordered sequences (-CH2-CH2-)n. As evidenced by DSC measurements and X-ray analysis, a crystalline phase forms during transformation of butadiene units into polyethylene chains.