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

Abstract

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 °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. ¹H and ¹³C 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 ∼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.