title: Candida antartica lipase B catalyzed polycaprolactone synthesis: effects of organic media and temperature.
abstract: Engineering of the reaction medium and study of an expanded range of reaction temperatures were carried out in an effort to positively influence the outcome of Novozyme-435 (immobilized Lipase B from Candida antarctica) catalyzed epsilon-CL polymerizations. A series of solvents including acetonitrile, dioxane, tetrahydrofuran, chloroform, butyl ether, isopropyl ether, isooctane, and toluene (log P from -1.1 to 4.5) were evaluated at 70 degrees C. Statistically (ANOVA), two significant regions were observed. Solvents having log P values from -1.1 to 0.49 showed low propagation rates (< or = 30% epsilon-CL conversion in 4 h) and gave products of short chain length (Mn < or = 5200 g/mol). In contrast, solvents with log P values from 1.9 to 4.5 showed enhanced propagation rates and afforded polymers of higher molecular weight (Mn = 11,500-17,000 g/mol). Toluene, a preferred solvent for this work, was studied at epsilon-CL to toluene (wt/vol) ratios from 1:1 to 10:1. The ratio 1:2 was selected since, for polymerizations at 70 degrees C, 0.3 mL of epsilon-CL and 4 h, gave high monomer conversions and Mn values (approximately 85% and approximately 17,000 g/mol, respectively). Increasing the scale of the reaction from 0.3 to 10 mL of CL resulted in a similar isolated product yield, but the Mn increased from 17,200 to 44,800 g/mol. Toluene appeared to help stabilize Novozyme-435 so that lipase-catalyzed polymerizations could be conducted effectively at 90 degrees C. For example, within only 2 h at 90 degrees C (toluene-d8 to epsilon-CL, 5:1, approximately 1% protein), the % monomer conversion reached approximately 90%. Also, the controlled character of these polymerizations as a function of reaction temperature was evaluated.
authors.affiliation: NSF Center for Biocatalysis and Bioprocessing of Macromolecules, Polytechnic University, Department of Chemistry and Chemical Engineering, Six Metrotech Center, Brooklyn, New York 11201, USA. Kumar@poly.edu, rgross@poly.edu
authors.forename: A
authors.initials: A
authors.lastname: Kumar
authors.forename: R A
authors.initials: RA
authors.lastname: Gross
mesh_terms: D002175:Candida / Q000201:enzymology*; D002208:Caproates / Q000737:chemistry; D003470:Culture Media; D007700:Kinetics; D007783:Lactones / Q000737:chemistry; D008049:Lipase / Q000737:chemistry*; D008970:Molecular Weight; D011091:Polyesters / Q000138:chemical synthesis*; D012997:Solvents; D013696:Temperature
chemical_list: D002208:Caproates; D003470:Culture Media; D007783:Lactones; D011091:Polyesters; D012997:Solvents; C016240:polycaprolactone; C121056:caprolactone; D008049:Lipase