Synthesis of star-shaped polyzwitterions with adjustable UCST and fast responsiveness by a facile RAFT polymerization

Dual thermo- and pH-responsive star polymers with tunable upper critical solution temperatures (UCST) were synthesized by an "arm-first" RAFT polymerization approach. Crosslinking took place in a single step involving polymerization of 3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate (DMAPS) mediated by a macroRAFT agent containing carboxylic end-group and in the presence of crosslinker N,N-methylenebis(acrylamide) (MBA). Varied-temperature turbidity analysis, dynamic light scattering (DLS) and rheology analysis revealed that the star-shaped PDMAPS had a smaller hydrodynamic volume while retaining fast response properties, compared with linearly-shaped PDMAPS. Meanwhile, zeta-potential was used to determine that the range of UCST regulated by pH was greatly expanded and proportional to the number of end-groups that could be generally manipulated through RAFT polymerization. By changing the pH values from 3 to 10, the adjustable UCST range of the star polymer solution can reach over 36 °C. These results demonstrate that the topological structure and end-group effect are able to manipulate the phase transition behavior of polyzwitterions. These materials offer great potential as additives or drug delivery vehicles in biomedical applications.