Water-soluble hyperbranched poly(ester urethane)s based on D,L-alanine: isocyanate-free synthesis, post-functionalization and application

The green synthesis of a novel hyperbranched poly(ester urethane) (HBPEU) has been reported via an isocyanate-free method based on D, L-alanine and a lower-toxic cyclic carbonate monomer, glycerol carbonate. Benefiting from the efficient reaction between the amine and five-membered cyclic carbonate, an AB(2)-type monomer bearing urethane linkages has been quantitatively formed without using a toxic isocyanate species. Subsequent bulk polyesterification was carried out to give water-soluble HBPEUs with moderate molecular weights and a degree of branching (DB) in the range of 0.44-0.52. Furthermore, the polycaprolactone arms were grafted to the HBPEU core via ring-opening polymerization of epsilon-caprolactone initiated by the peripheral hydroxyl groups around HBPEU, forming biodegradable and biocompatible amphiphilic star copolymers, which acts as an "unimolecular reverse micelle" in CHCl3. Two water soluble dyes, methyl orange and bromophenol blue, were successfully transported from water to the insoluble chloroform phase by the core-shell star polymers, indicating the great potential of the micelles as nanocarriers. The arm lengths and core sizes of the star polymers greatly influenced the dye-loading capacity of the nanocarrier.