| Abstract
| - We report the ring-opening polymerization reaction of ε-caprolactone in supercritical carbondioxide (scCO2) using an enzyme catalyst, Lipase B from Candida antarctica supported on macroporousbeads (Novozym-435). Ring-opening polymerization of lactones is more commonly performed in organicsolvents or in bulk using a Lewis acid catalyst. Recently there has been much interest in the replacementof such catalysts by enzymes. We demonstrate that the enzymatic route is viable in scCO2, yielding poly(ε-caprolactone) (Mn = 12 000−37 000 g mol-1) with molecular weights very similar to those obtainedfrom the same enzyme catalysts in organic solvents, but with lower polydispersities (typical PDI = 1.4−1.6) and higher yields of polymer product (typically 95−98%). In the same process the unique “gaslike”mass transfer properties of scCO2 can also be exploited to remove quantitatively any unconverted monomerand low molecular weight oligomers by scCO2 extraction. It is also shown that the enzyme catalyst canbe cleaned and recycled using scCO2, while still producing high molecular weight polymer (Mn = 35 000−37 000 g mol-1). Thus, a combination of enzyme catalyst and scCO2 can be used repeatedly to preparebiodegradable poly(ε-caprolactone) (PCL) in the complete absence of potentially toxic organic solvents ormetal catalysts.
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