Lipase-catalyzed synthesis of poly(ε-caprolactone) and characterization of its solid-state properties

Abstract

Ring-opening polymerization of ε-caprolactone has been successfully conducted using an immobilized form of Candida antarctica lipase B as catalyst. The effects of enzyme concentration, reaction medium, reaction temperature and time on monomer conversion and product molecular weight were investigated. Through optimization of reaction conditions, poly( ε -caprolactone) (PCL) was obtained with 99% monomer conversion and a number-average molecular weight ( M n ) of 18870 g/mol. The reaction system was then scaled up, and PCL was synthesized in 78% isolated yield, with M n and polydispersity index of 41540 g/mol and 1.69, respectively. The solid-state properties of this sample were systematically evaluated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). The product PCL showed excellent thermal stability, with degradation of the main chain in the temperature range of 280 -450 ° C. Remarkably, this high molecular weight PCL was a typical crystalline polymer with a high degree of crystallinity observed by DSC, WAXD and POM.

Enzymatic ring‐opening polymerization (ROP) of polylactones: roles of non‐aqueous solvents

“…In particular, the ROP reaction conducted in toluene (1:2 wt/vol, substrate/toluene ratio) at 70 °C for 4 h afforded 85% monomer conversion and M n 17 000 g mL ‐1 (PDI 1.8); the scaling up from 0.3 mL ϵ‐caprolactone to 10 mL even increased M n to 44 800 g mL ‐1 (PDI 1.7) while the isolated yield (86%) remained high. Similar results were reported by the Li group that more hydrophobic solvents (such as toluene, cyclohexane and n ‐hexane) led to high M n (up to ∼18 900 g mol ‐1 ) of poly(ϵ‐caprolactone) from the enzymatic ROP catalyzed by Novozym 435, while less hydrophobic ones (e.g. 1,4‐dioxane, acetone, THF, and chloroform) yielded lower molecular weights (2800–4200 g mol ‐1 ).…”

Recent Developments and Optimization of Lipase-Catalyzed Lactone Formation and Ring-Opening Polymerization

“…Sasi et al reported different results for cyclic and linear solvent molecules and cyclohexane resulted in better yields than linear n‐hexanes, even though the latter possesses higher log P value . Similar results were obtained by Yang et al for the polymerization of ε‐CL . Lactonizations showed higher yields in isooctane than in octane although their log P values are nearly the same .…”

“…In toluene, the highest molecular weights were obtained at 40 °C, which is in accordance with the findings of Yang et al where 45 °C reaction temperature yielded higher molecular weights than 60 °C. Increasing reaction time from 24 to 48 h led to a considerable decrease in molecular weight, probably due to more predominant hydrolysis and transesterification reactions after all cyclic monomers were consumed . When PEG was used as a macroinitiator in the eROP of ε‐CL in toluene, the temperature of 80 °C yielded significantly higher conversions and molecular weights than 60 °C.…”

“…For several types of monomers, condensation polymerization is not possible or it results in low molecular weight products, because the method is limited by the removal of the condensate. This often requires the use of vacuum or high temperatures, which is not ideal for thermally unstable monomers and oligomers . This is the case with polybutylene succinate (PBS), which almost tripled in molecular weight when an eROP strategy was employed …”

Candida antarctica Lipase B as Catalyst for Cyclic Esters Synthesis, Their Polymerization and Degradation of Aliphatic Polyesters

“…Almost all polymerization reactions were conducted in organic solvents, such as: toluene [40], 1,4-dioxane [41], isopropyl ether [42], isooctane [43], diphenyl ether [44], cyclohexane [45]. The reaction was also carried out in supercritical carbon dioxide [46,47], ionic liquids [48][49][50], and recently, in aqueous dispersion [51].…”