Solventless Enantioelective Ring-Opening Polymerization of Substituted ε-Caprolactones by Enzymatic Catalysis

Abstract

Highly (S)-enriched substituted poly(ε-caprolactone)s were synthesized from 4-methyl-ε-caprolactone (4-MeCL) and 4-ethyl-ε-caprolactone (4-EtCL) by lipase Novozym-435 (from Candida antarctica) catalyzed ring-opening polymerizations. 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. Number-average molecular weights of the poly(4-EtCL) and poly(4-MeCL) were 4400 and 5400, respectively. The effect of reaction temperature on enzyme enantioselectivity, polymer molecular weight, and monomer conversion was also investigated at 45 and 60 °C. Contrary to many literature reports and conventional wisdom, the enantioselectivity of the lipase was greater at 60 °C, the higher reaction temperature. The solventless polymerization process appeared to be diffusion-controlled in which the monomer conversion and polymer molecular weight increased at higher reaction temperature.

Recent Developments in Lipase‐Catalyzed Synthesis of Polyesters

“…[90] Enantioselective ROP of methyl substituted e-CLs were carried out with Novozyme 435 catalyst. A benzyl alcohol initiated ROP of the monomers with the lipase catalyst at 45 8C showed (S)-selective for 3-MeCL, 4-MeCL, and 6-MeCL and (R)-selective for 5-MeCL.…”

Highly efficient enzymatic catalysis for cyclocarbonate polymerization

“…Through a rational design of ROP initiators, well-defined polymer architectures and specific functions can be readily realized. 5,11,12 In contrast, the control afforded by the polycondensation method is remarkably limited. Currently, the most frequently used catalysts for ROP are organometallic compounds.…”

Recyclable Tridentate Stable Palladium(II) PCP‐Type Catalysts Supported on Silica for the Selective Synthesis of Lactones

“…[15,16] One of the most interesting applications of the carbonylation reaction is for intramolecular cyclocarbonylation to give heterocyclic compounds such as five-, six-and seven-membered lactones in moderate to high yields. [11,12,14] Some of these products are pharmacologically active, or are used as intermediates to synthesize biologically active compounds [17] or polyesters, [18,19] and are often less readily accessible by conventional synthetic methods.…”