Synthesis of poly( L ‐lysine)‐graft‐polyesters through Michael addition and their self‐assemblies in aqueous solutions

A series of poly(L‐lysine)s grafted with aliphatic polyesters, poly(L‐lysine)‐graft‐poly(L‐lactide) (PLy‐g‐PLLA) and poly(L‐lysine)‐graft‐poly(ϵ‐caprolactone) (PLy‐ g‐PCL), were synthesized through the Michael addition of poly(L‐lysine) and maleimido‐terminated poly(L‐lactide) or poly(ϵ‐caprolactone). The graft density of the polyesters could be adjusted by the variation of the feed ratio of poly(L‐lysine) to the maleimido‐terminated polyesters. IR spectra of PLy‐g‐PCL showed that the graft copolymers adopted an α‐helix conformation in the solid state. Differential scanning calorimetry measurements of the two kinds of graft copolymers indicated that the glass transition temperature of PLy‐g‐PLLA and the melting temperature of PLy‐g‐PCL increased with the increasing graft density of the polyesters on the backbone of poly(L‐lysine). Circular dichroism analysis of PLy‐g‐PCL in water demonstrated that the graft copolymer existed in a random‐coil conformation at pH 6 and as an α‐helix at pH 9. In addition, PLy‐g‐PCL was found to form micelles to vesicles in an aqueous medium with the increasing graft density of poly(ϵ‐caprolactone).