Lipase-catalyzed synthesis of polyhydric alcohol-poly(ricinoleic acid) ester star polymers

Polyesters of poly(ricinoleic acid) and polyol acyl acceptors (trimethylolpropane, pentaerythritol, and dimer diol), examples of lipophilic star polymers, were synthesized via bulk polymerization at 70 degrees C in a 1 to 2-week period, using immobilized lipases from Candida antarctica B, CAL, and Rhizomucor miehei, RML (Novozyme and Lipozyme, respectively, from Novozymes North America, Franklinton, NC). In the screening of several synthesis procedures, the highest molecular weight and degree of conversion occurred when polyricinoleic acid, synthesized previously from ricinoleic acid using CAL as biocatalyst, was mixed with polyol and either CAL or RML. Such a procedure yielded pentaerythritol-poly(ricinoleic acid) tetraester with an average molecular weight of 4850 +/- 440 Da, according to H-1 NMR analysis. Seventy-eight percent of the polyol acyl acceptor's hydroxyl groups were esterified, with the average degree of polymerization for its poly(ricinoleyl) chains being 5.4 +/- 0.5. The product mixture contained 83% polyol ester and only 17 wt % nonesterified linear poly(ricinoleic acid). The rate-limiting step in the formation of poly(ricinoleic acid), propagation, was first-order with respect to monomer (ricinoleyl acyl groups); and, chain-transfer reactions were absent. The products formed possessed high viscosity and viscosity indices (155 for the pentaerythritol tetraester) and melting point temperatures below -7.5 degrees C, suggesting their use as environmentally-friendly lubricant materials. (c) 2006 Wiley Periodicals, Inc.