Amphiphilic–zwitterionic block polymers

Abstract

Amphiphilic block copolymers have broad research interest and demonstrated applications due to their self-assembly over a range of different conditions. Polyzwitterions have attracted attention due to their higher hydrophilicity, charge sensitivity and anti-fouling properties making them a popular material in the field of stimuli responsive soft materials, e.g., self-healing hydrogels, water transport membranes, etc. An array of novel amphiphilic–zwitterionic block copolymers was designed where the hydrophilic segment is a polyzwitterion along with a low T_g hydrophobic block. As a first step, a parent block copolymer precursor of poly (dimethyl amino ethyl methacrylate)-b-poly (n-butyl acrylate-ran-allyl methacrylate) with different copolymer volume fractions was synthesized using RAFT polymerization. The advantage of using this technique is the ability to synthesize polymers with predetermined molecular weight, well-defined chemical composition, and a narrow dispersity. Variation of the content of the zwitterionic sulfobetaine was investigated through post-polymerization modification of the poly (dimethyl amino ethyl methacrylate) block using nucleophilic ring-opening reactions with varying amounts of 1,3-propane sultone. NMR spectroscopy and GPC data were analyzed to calculate the degree of polymerization and molecular weight in parent neutral block copolymers and its modified amphiphilic–zwitterionic counterpart. Thermal analysis of these zwitterionic systems was investigated by using TGA and DSC showing high thermal stability and also to determine the T_g. This study creates a platform to synthesize novel amphiphilic zwitterionic block polymer systems with well-defined molecular weight, copolymer composition and tunable zwitterionic moiety using a two-step strategy. Combining higher hydrophilicity of zwitterionic polymers with self-assembly of amphiphilic block copolymers, these materials will open an opportunity for future fundamental structure–property studies.