Biocatalytic Synthesis of Ricinoleic Acid Star Polymers: 'Green' Manufacturing of Potentially Valuable Lubricant Additives and Drug Delivery Materials

摘要

Bulk-phase polymerization catalyzed by lipases has been employed to synthesize oligomers of ricinoleic acid, a renewable material derived from castor oil, and to covalentlyattach the oligomeric chains to polyols such as pentaerythritol, producing novel star polymers possessing desirable physical properties for bio-based lubricants. For instance, pentaerythritol-tetra[poly(ricinoleic acid)], produced at 87% purity, possessed a value of the number-averaged molecular weight, Mn, of 4.8 kDa, a high viscosity index (155), and a low melting point temperature (< -15°C). A targeted viscosity value can be readily achieved by controlling the product's Mn, since viscosity versus Mnfor star polymers is a linear relationship. Lipase-catalyzed polymerization provides an environmentally-friendly processing alternative to chemical synthesis since the former employs mild temperatures and pressures, the absence of solvents, and frequently requires little or no downstream purification. This chapter consists of an assessment of poly(hydroxy acids) and their derivatives as biolubricants and a review of the enzymatic synthesis and modification of poly(hydroxyl acids), including star polymer formation. Recent results on the lipase-catalyzed synthesis of ricinoleic acid copolymers in the author's laboratory are presented.