Dual-Stimuli-Responsive l-Serine-Based Zwitterionic UCST-Type Polymer with Tunable Thermosensitivity

Abstract

The synthesis of L-serine-based zwitterionic polymers, poly(L-serinyl acrylate)s (PSAs), of controllable molecular weights and low polydispersities via reversible addition−fragmentation chain transfer (RAFT) polymerization in water at 70°C is described. The obtained homopolymer PSA exhibits dual responsiveness toward pH and temperature in aqueous solution. The PSA exhibits an isoelectric point near pH 2.85 where the PSA molecules exist in its zwitterionic form. In the pH range of 2.3−3.5, the aqueous PSA solution appears as a two-phase system due to the formation of insoluble aggregates through the intra-and intermolecular electrostatic interaction between the pendent ammonium and carboxylate groups of the neighboring zwitterionic PSA molecules. Furthermore, in this pH range, the two-phase PSA solution becomes one-phase upon heating, exhibiting distinct reversible upper critical solution temperature (UCST)-type phase transition. The cloud point (T p ) is found to increase with increasing molecular weights of PSAs. It is also observed that the T p changes with changing the solution pH, exhibiting highest T p near the isoelectric point of PSA. Addition of an electrolyte such as brine solution also affects the T p of PSA solution following the antipolyelectrolyte effect. Finally, fluorescein isothiocyanate (FITC) tagged PSA with dual-responsiveness is prepared by the postmodification of pendent amino groups of PSA for futuristic applications in biosensors and bioimaging.

Tunable, concentration‐independent, sharp, hysteresis‐free UCST phase transition from poly(N‐acryloyl glycinamide‐acrylonitrile) system

“…In contrast, studies related to the polymers showing UCST type transitions in water are quite limited but increasing in the last years. Although, some of the zwitterionic polymers and polyelectrolytes show UCST‐type transitions in water, they are dominated by Coulomb interactions and the thermoresponsive behavior is highly dependent upon the molar mass, presence of salts, ionic strength and multivalent ions . In the last few years more and more attention has been given to the nonionic polymers with phase transitions dominated by hydrogen (H)‐bonding .…”

Chemical Tuning of Zwitterionic Ionic Liquids for Variable Thermophysical Behaviours, Nanostructured Aggregates and Dual‐Stimuli Responsiveness

“…Dynamic light scattering (DLS) data (Figure S42 in the Supporting Information) indeed revealed such aggregation of ZIL molecules by showing changes in D h s from approximately 2–3 to 2700–2800 nm when the pH values of the transparent solutions (1 wt %) were increased to anything above the soluble pH region. Such type of aggregate formation has already been reported for other zwitterionic macromolecular systems due to similar intra‐and/or intermolecular electrostatic interactions . Notably, the D h s of 1 wt % solutions of [BuImVa][Br], [BuImIBa][Br], [BuImAa][Br], [EtBzImAa][Br] and [VBzImAa][Br] remained at approximately 2–3 nm in the pH range 2–11 (Figure S42 in the Supporting Information), which supports the % T value of 0 in this pH range as mentioned above (Figure ) at 25 °C.…”

Amino Acid Functional Polymers: Biomimetic Polymer Design Enabling Catalysis, Chiral Materials, and Drug Delivery

“…[12] Recently, many zwitterionic amino acid functional polymers have been synthesized; however, their UCST response is rarely reported. [44] There exist good opportunities to explore more of the fundamental aspects of amino acid functional polymers and perhaps even their areas of application.…”

“…Reactive Site 2 -the carboxylic acid Amidation [12,13] Esterification [8,[14][15][16]19,22,24,32,42] Esterification [35] Acylation [25,30,43,44] For aspartic and glutamic acid Polar group Thermal response A Zwitterion…”

“…[17] behaviour, which may further the application of these materials. [62] Fujii et al investigated the synergistic interaction between the positive and negative charges of amino acid polyzwitterions by modifying the spacing between them. [17] By functionalizing the monomer from the a-carboxylic acid, they created a zwitterion with three carbon spacers between the positively charged protonated amine and the negatively charged deprotonated g-carboxyl group.…”