Hydrogenation of ring-opening metathesis polymer with ruthenium catalysts

Abstract

A ring-opening metathesis polymer (ROMP) of 8-methyl-8-methoxycarbonyltetracyclo[4.4.0.12,5.1 7,10]dodec-3-ene (poly-1) was hydrogenated with homogeneous catalysts. Monohydrido or dihydrido ruthenium(II) complexes achieved high hydrogenation degree which gave thermally stable saturated ROMP of 1 (poly-1-H2). The kinetics of hydrogenation reactions in the presence of carbonylchlorohydridotris(triphenylphosphine)ruthenium. RuHCl(CO)(Ph3)3, (2) were studied in detail and found to follow first-order kinetics to the concentration of double bonds. Apparent activation energy for the overall hydrogenation reaction determined in the temperature range of 155-180 °C was smaller than that observed for the hydrogenation of acrylonitrile butadiene copolymer by rhodium catalyst. The stirring rate did not affect hydrogenation reaction rate, although slower stirring lead to lower conversion at the very beginning of the reaction, indicating diffusion of hydrogen into the reaction media can be neglected if stirring is efficient. The concentration of 2 also affected the reaction rate. The reaction rate leveled off at around 3 × 10-2mM reaching more than 4300 of turnover number. Applying 100 kg cm-2 of hydrogen at 160°C in m-xylene, high hydrogenation degrees were achieved at ruthenium concentration as low as 20ppm to the polymer.