Synthesis of Double Hydrophilic Block Copolymers Poly(2-oxazoline-b-ethylenimine) in a Two-Step Procedure

The synthesis of double hydrophilic block copolymers (DHBCs) containing a polyethylenimine (PEI) and a poly(2-alkyl-2-oxazoline) in two steps was investigated in this study. First, well-defined copolymers of poly(2-methyl-2-oxazoline)-b-poly(2-ethyl-2-oxazoline) (PMeOx-b-PEtOx) and poly(2-isopropyl-2-oxazoline)-b-poly(2-methyl-2-oxazoline) (PiPrOx-b-PMeOx) were synthesized. Then, their thermoresponsive properties were analyzed to obtain a selective hydrolysis of the PMeOx block. Concerning the PMeOx-b-PEtOx copolymers, no phase transiton was witnessed, and a selectivity appeared but was quite low regardless of the copolymer composition tested, while for the PiPrOx-b-PMeOx copolymers, a complete selective hydrolysis was achieved, allowing the synthesis of PiPrOx-b-PEI DHBCs due to micelles formations in the reactive media at high temperature. Thus, for different PiPrOx-b-PMeOx with varying composition, a MeOx unit hydrolysis degree higher than 90% was obtained with nearly no hydrolysis of the PiPrOx block, providing block copolymers suitable for gene transfer experiments. The reproducibility of the reaction was also demonstrated.