Effect of the zwitterion structure on the thermo-responsive behaviour of poly(sulfobetaine methacrylates)

摘要: A series of new sulfobetaine methacrylates, including nitrogen-containing saturated heterocycles, was synthesised by systematically varying the substituents zwitterionic group. Radical polymerisation via RAFT (reversible addition–fragmentation chain transfer) method in trifluoroethanol proceeded smoothly and well controlled, yielding polymers with predictable molar masses. Molar mass analysis control end-group fidelity were facilitated labeling a fluorescent dye. The showed distinct thermo-responsive behaviour UCST (upper critical solution temperature) type an aqueous solution, which could not be simply correlated to their molecular structure incremental hydrophilic hydrophobic elements incorporated within them. Increasing spacer length separating ammonium sulfonate groups zwitterion moiety from three four carbons increased phase transition temperatures markedly, whereas increasing group carboxylate ester on backbone two provoked opposite effect. Moreover, analogous polyzwitterions decreased order dimethylammonio > morpholinio piperidinio alkanesulfonates. In addition basic effect polymers’ precise structure, concentration dependence studied. Furthermore, we investigated influence added low salts aqueous-phase for sodium chloride bromide as sulfate. strong effects evolved complex way salt concentration. strength these depended nature anion added, sulfate < bromide, thus following empirical Hofmeister series. contrast, no significant differences observed when changing cation, i.e. adding or