Synthesis of amphiphilic diblock copolymers derived from renewable dextran by nitroxide mediated polymerization: towards hierarchically structured honeycomb porous films

A dextran-based macroalkoxyamine was designed by a two step end functionalization of the initial polysaccharide. Nitroxide mediated polymerization of styrene (S) and methyl methacrylate (MMA) afforded both dextran-b-P(S-co-MMA) and dextran-b-PS amphiphilic linear diblock copolymers. We subsequently investigated their ability to generate honeycomb structured films using the “Breath Figure” (BF) technique, a method involving the condensation of water droplets during rapid evaporation of a polymer solution under humid conditions. The quality of pore ordering of resultant films was characterized by different microscopy techniques (optical, scanning electron (SEM) and atomic force (AFM) microscopy). While non-spherical pores were observed for dextran-b-P(S-co-MMA) copolymers, an organized pattern of spherical pores was produced with dextran-b-PS amphiphilic copolymers leading to ordered porous bio-hybrid films. The Flory–Huggins interaction parameter χ of the couple PS/dextran is sufficiently high to induce nanophase separation in between the pores, leading to a hierarchically structured honeycomb film based on a renewable dextran block.