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

Abstract

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

Quantification of the scratch-healing efficiency for novel zwitterionic polymers

“…Although the materials often have hydrophilic characteristics due to their strong Coulomb interactions, in particular with high-ionic contents, polyzwitterions otherwise behave more like nonionic polymers rather than conventional polyelectrolytes 38,43 . One of the most common applications is zwitterionic hydrogels, which can be responsive to environmental conditions, such as the pH value, temperature or salt content [44][45][46] . It is also possible to combine different effects in one material, such as shape-memory and moisture sensitivity or even selfhealing 44,47,48 .…”

Forming Sticky Droplets from Slippery Polymer Zwitterions

“…Zwitterionic polymers are recognized widely for their water solubility and ability to reduce interactions with hydrophobes, oil, and proteins, and therefore find applications as low friction surfaces and antifouling coatings . However, tailoring the solubility of polymer zwitterions can actually promote attractive inter‐ and intramolecular dipole–dipole interactions that afford upper critical solution temperature (UCST) behavior in aqueous media . For example, the cloud point temperature of sulfobetaine methacrylamide polymers in water increased markedly, from ≈15 to ≈75 °C, by incremental increases in the number of methylene groups between the ammonium and the sulfonate groups .…”

Zwitterionic Polysulfamide Drug Nanogels with Microwave Augmented Tumor Accumulation and On‐Demand Drug Release for Enhanced Cancer Therapy

“…[ 15 ] Compared with the previous thermoresponsive zwitterionic systems, the introduction of hydrophobic benzsulfamide group in PMEDAPA nanogels may significantly enhance the self‐association effect between the positive charge and negative charge, which leads to the higher hyperthermia‐responsiveness of the PMEDAPA nanogels. [ 17 ] Since PMEDAPA‐54 nanogels exhibit the VPTT of 39.7 °C which is close to the physiological temperature, PMEDAPA‐54, abbreviated as PMEDAPA, is selected as the potential drug delivery system in the following in vitro and in vivo study.…”

“…[ 16 ] For example, zwitterionic sulfobetaine‐based polymers have been demonstrated to show collapsed conformations at low temperature whereas switched to stretched conformations at high temperature, exhibiting the upper critical solution temperature (UCST) type of thermoresponsiveness. [ 17 ] However, the currently reported thermoresponsive zwitterionic polymers mainly showed significant response to the temperature much lower than the physiological temperature, due to the superhydrophilicity of the zwitterionic polymers. [ 18 ] Therefore, it is reasonable to add an appropriate hydrophobic group to the zwitterionic structure, which could partly reduce the superhydrophilicity of the zwitterionic polymers and exhibit a higher thermoresponse.…”