Zwitterionic poly(sulfobetaine methacrylate)s in water: from upper critical solution temperature (UCST) to lower critical solution temperature (LCST) with increasing length of one alkyl substituent on the nitrogen atom

Increasing the alkyl length on nitrogen of the polymer changes behaviour from UCST, to soluble, LCST, and insoluble.

Influence of additives on thermoresponsive polymers in aqueous media: a case study of poly(N-isopropylacrylamide)

Thermoresponsive polymers (TRPs) in different solvent media have been studied over a long period and are important from both scientific and technical points of view.

Forming Sticky Droplets from Slippery Polymer Zwitterions

Polymer zwitterions are generally regarded as hydrophilic and repellant or "slippery" materials. Here, a case is described in which the polymer zwitterion structure is tailored to decrease water solubility, stabilize emulsion droplets, and promote interdroplet adhesion. Harnessing the upper critical solution temperature of sulfonium- and ammonium-based polymer zwitterions in water, adhesive droplets are prepared by adding organic solvent to an aqueous polymer solution at elevated temperature, followed by agitation to induce emulsification. Droplet aggregation is observed as the mixture cools. Variation of salt concentration, temperature, polymer concentration, and polymer structure modulates these interdroplet interactions, resulting in distinct changes in emulsion stability and fluidity. Under attractive conditions, emulsions encapsulating 50-75% oil undergo gelation. By contrast, emulsions prepared under conditions where droplets are nonadhesive remain fluid and, for oil fractions exceeding 0.6, coalescence is observed. The uniquely reactive nature of the selected zwitterions allows their in situ modification and affords a route to chemically trigger deaggregation and droplet dispersion. Finally, experiments performed in a microfluidic device, in which droplets are formed under conditions that either promote or suppress adhesion, confirm the salt-responsive character of these emulsions and the persistence of adhesive interdroplet interactions under flow.

UCST-Type Thermosensitive Hairy Nanogels Synthesized by RAFT Polymerization-Induced Self-Assembly

While lower critical solution temperature (LCST)-type thermosensitive nanogels have been intensively studied, the upper critical solution temperature (UCST)-type versions are much less explored. This communication reports a method for the synthesis of zwitterionic UCST nanogels by reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly in water-organic solvent mixtures. The nanogels were prepared by RAFT polymerization of 3-dimethyl(methacryloyloxyethyl)ammonium propanesulfonate, whose polymer is known to exhibit UCST behavior in water, conducted in ethanol-water mixtures at 70 °C using poly(poly(ethylene glycol) methyl ether methacrylate) as a macro-chain transfer agent (CTA) and a difunctional monomer as cross-linker. At a sufficiently high ethanol content in reaction media, spherical hairy nanogels with a single size distribution were obtained. These nanogels exhibited reversible heating-induced swelling and cooling-induced shrinking, consistent with the expected UCST behavior. The hydrodynamic size, volume changing ratio, and transition temperature of nanogels can be tuned by varying ethanol content in solvent mixtures, molar ratio of monomer-to-macro-CTA, and amount of cross-linker. Hairy nanogels were also successfully synthesized using a water-THF mixture as medium. The use of water-organic solvent mixtures as reaction media allowed for facile incorporation of a hydrophobic fluorescent monomer to make functional UCST nanogels.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.

From LCST to UCST: the phase separation behaviour of thermo-responsive polysiloxanes with the solubility parameters of solvents

Thermo-responsive polysiloxanes with tunable LCST- and UCST-type phase separation in mixed solvents were synthesised via a facile, highly efficient, catalyst-free aza-Michael addition of poly(aminopropylmethylsiloxane) to N-isopropylacrylamide.

A stimuli-responsive methionine-based zwitterionic methacryloyl sulfonium sulfonate monomer and the corresponding antifouling polymer with tunable thermosensitivity

This report describes a dual pH- and thermo-responsive methionine-based zwitterionic methacryloyl sulfonium sulfonate monomer and the corresponding zwitterionic antifouling polymer with ion-induced tunable thermosensitivity.

CO2-Triggered UCST transition of amphiphilic triblock copolymers and their self-assemblies

Self-assembled vesicles presenting morphological transformations (vesicles–micelles–unimers) upon external stimuli due to their CO₂ adjustable UCST behavior in aqueous solution.

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

Modulating the thermo-responsive behaviour of poly(sulfobetaine methacrylates) whereby small structural changes cause big effects but show little logic.

Modulating the solubility of zwitterionic poly((3-methacrylamidopropyl)ammonioalkane sulfonate)s in water and aqueous salt solutions via the spacer group separating the cationic and the anionic moieties

Even small variations of the spacer group between the anionic and the cationic moieties of poly(sulfobetaine)s strongly affect their aqueous phase behaviour.

Thermoreversible physically crosslinked hydrogels from UCST-type thermosensitive ABA linear triblock copolymers

Moderately concentrated aqueous solutions of UCST-type thermosensitive ABA linear triblock copolymers undergo cooling-induced, reversible sol–gel transitions.

Triply responsive soft matter nanoparticles based on poly[oligo(ethylene glycol) methyl ether methacrylate-block-3-phenylpropyl methacrylate] copolymers

The stimulus-responsive properties of nanoparticles based on poly[oligo(ethylene glycol) methyl ether methacrylate-b-3-phenylpropyl methacrylate] (p(OEGMA-b-PPMA)) copolymers in alcohols are described.

Preparation and study of multi-responsive polyampholyte copolymers of N-(3-aminopropyl)methacrylamide hydrochloride and acrylic acid

Multi-responsive polyampholytes show LCST and UCST behaviour at different pH values, based on electrostatic and hydrogen bonding interactions.

Understanding the UCST-type transition of P(AAm-co-AN) in H2O and D2O: dramatic effects of solvent isotopes

The UCST-type transition of poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) (molar fraction of AN: 13.3%; PDI = 3.2) in H2O and D2O is explored and compared by applying turbidity, DLS as well as FTIR measurements. The transition temperature of P(AAm-co-AN) in D2O is observed to be almost 10 °C higher than that in H2O at the same concentration, demonstrating a dramatic solvent isotope effect. Such a phenomenon could be rooted from a stronger interaction among polymer chains in D2O than in H2O, as indicated from DLS results. It is also observed in second-derivative analysis of FTIR spectra in the ν(C=O) region, where all C=O groups participate in the formation of inter-/intra-chain hydrogen bonds (C=O···H-N) in D2O while there is still part of relatively "free" C=O groups in H2O. Moreover, we find in the temperature-dependent FTIR spectra that C≡N groups exhibit hydrating behavior while C=O groups present increased inter-/intra-molecular hydrogen bonding interaction (C=O···H-N) upon cooling, revealing the later process to be the driving force of the UCST-type transition.