A facile approach to biodegradable poly(ε-caprolactone)-poly(ethylene glycol)-based polyurethanes containing pendant amino groups

A novel biodegradable poly(ε-caprolactone)-poly(ethylene glycol)-based polyurethanes (PCL-PEG-PU) with pendant amino groups was synthesized by direct coupling of PEG ester of NH₂-protected-(aspartic acid) (PEG-Asp-PEG diols) and poly(ε-caprolactone) (PCL) diols with hexamethylene dissocyanate (HDI) under mild reaction conditions and by subsequent deprotection of benzyloxycarbonyl (Cbz) groups. GPC, ¹H NMR, and ¹³C NMR studies confirmed the polymer structures and the complete deprotection. DSC and WXRD results indicated that the crystallinity of the copolymer was enhanced with increasing PCL diols in the copolymer. The content of amino group in the polymer could be adjusted by changing the molar ratio of PEG-Asp-PEG diols to PCL diols. Thus the results of this study provide a good way to prepare polyurethanes bearing hydrophilic PEG segments and reactive amino groups without complicated synthesis.