Enantioenriched Substituted Polycaprolactones by Enzyme Catalysis

Abstract

The kinetic resolution of racemic seven-membered lactones substituted either at the 4- or the 6-position is achieved in bulk (solvent free) conditions, by lipase-catalysed butanolysis. Novozym-435 lipase (from Candida antarctica) induced (S)-selective butanololysis, and (R)-lactones were recovered unreacted with >97% enantiomeric excess (e.e.). The (S)-selective Novozyme-435 catalysis is also employed for the ring opening polymerization of 4-methyl-ε-caprolactone (4-MeCL) and 4-ethyl-ε-caprolactone (4-EtCL) to obtain highly (S)-enriched substituted poly ε-caprolactones. The polymerizations were performed in bulk, thus eliminating the need for solvents in the polymerization process. Poly (4-EtCL) and poly (4-MeCL) having >95% enantiomeric purity (eep) have been prepared. The effect of reaction temperature on enzyme enantioselectivity, polymer molecular weight, and monomer conversion was also investigated at 45 and 60 °C. The optically enriched (R)- 4-MeCL and 4-EtCL obtained were mixed with rac-4-MeCL and 4-EtCL to prepare mixtures of variable enantiopurities and the mixtures were subjected to chemical polymerization initiated by Sn(Oct)2 to obtain poly (4-EtCL) and poly (4-MeCL) of variable enantiopurities. The effects of optical purity of the polymers glassy state were evaluated by DSC.