Enzyme-catalyzed quantitative chain-end functionalization of poly(ethylene glycol)s under solventless conditions

This is the first report of quantitative vinyl chain-end functionalization of poly(ethylene glycol)s (PEGs) with reduced environmental effects and renewable catalysis. Divinyl adipate (DVA) was transesterified using Candida antarctica lipase B (CALB) supported on an acrylic resin at 50 degrees C under dry nitrogen and solventless conditions. After the reactions CALB was removed by filtration and excess DVA was recovered by hexane extraction followed by distillation for reuse. H-1 and C-13 NMR spectroscopy and MALDI-ToF mass spectrometry was used to analyze the structure and purity of the products. The effects of DVA excess and PEG chain length were investigated. Model experiments with tetra(ethylene glycol) (TEG) led to polycondensation. At DVA/TEG 20/1 molar ratio similar to 82% of the product was Vinyl-TEG-Vinyl, together with vinyl-telechelic dimers and trimers. When reacting monomethoxy MeO-PEG-OH of M-n = 1100 g mol(-1) under the same conditions, pure MeO-PEG-Vinyl was obtained with no coupling. MeO-PEG-OH with M-n = 2000 g mol(-1) gave pure MeO-PEG-Vinyl at 5 molar excess of DVA. With HO-PEG-OH1000 of M-n = 1000 g mol(-1) at DVA/PEG 20/1 molar ratio no polycondensation and only 2% coupled product was found, while HO-PEG-OH with M-n = 2000 g mol(-1) under the same conditions gave pure telechelic Vinyl-PEG-Vinyl.