Preparation of Temperature-Sensitive Core−Shell Poly(glycidol)/Poly(<i>N</i>-isopropylacrylamide) Nanohydrogels under Surfactant-Free Conditions

Abstract

A new method for synthesis of smart nanohydrogels under additives-free conditions and at high solid content is presented. The new core−shell nanohydrogels with cross-linked poly( N -isopropylacrylamide) (PNIPAAm) core and hydrophilic poly(glycidol) (PGl) shell were obtained by photo-cross-linking of PGl- b -PNIPAAm copolymers above their phase transition temperature ( T c ). As UV-active group, the chromophore 2-(dimethylmaleimido)- N -ethylacrylamide (DMIAAm) was synthesized and successfully incorporated in the PNIPAAm segment, while poly(glycidol) chains were responsible for stability of aggregates above T c . Photo-cross-linkable block copolymers with different PGl length (DP = 55 and 100), DMIAAm chromophore content, and PGl/PNIPAAm block ratio were synthesized for this investigation. It was found that the efficacy of cross-linking strongly depended on the length of PGl block in the copolymer. In the case of copolymers with shorter PGl chains formation of fully cross-linked nanohydrogels was observed already at 45 °C, while for copolymers with longer PGl chains monomodal nanohydrogels were formed at 55 °C. In contrast at given temperature, the rate of cross-linking was independent of chromophore content in copolymer and copolymer composition.