Lower Critical Solution Temperature Phase Transition Research Articles

Ion‐Mediated Gelation of Thermo‐Responsive Cellulose Nanofibril/Poly(N‐isopropylacrylamide) Hybrid Hydrogels with Tunable De‐Swelling Kinetics

AbstractThe tunability of the lower critical solution temperature (LCST) of poly(N‐isopropylacrylamide) (PNIPAM) to lower or higher temperatures, as well as the ease of modulation of the LCST phase transition kinetics broadens the scope of application of PNIPAM‐based materials in biomedical fields. This work reports a facile approach to formulate a smart, injectable cellulose nanofibril (CNF)/PNIPAM hybrid gel. Hofmeister salts are used to induce ion‐mediated gelation of the nanofibrils and PNIPAM chains, resulting in an interpenetrating network (IPN) structure. From rheological measurements, the hybrid material displays excellent structural integrity at room temperature and tunable thermo‐stiffening around body temperature. De‐swelling kinetics can be modulated by varying the nature and concentration of the Hofmeister ion used. The successful realization of the IPN hybrid gel structure is dependent on the molecular weight of PNIPAM used. Moreover, the hybrid gels show good thermo‐reversibility during thermal cycling, as well as excellent injectability and remarkable self‐healing post‐injection, owing to shear‐thinning and thixotropic characters. Since rheology is a crucial technique in the analysis of soft matter and flow behavior is fundamental for the design and synthesis of application‐specific viscoelastic materials, the work reported herein provides a rheological basis for careful design and synthesis of smart gels.

Expeditious Discovery of Small-Molecule Thermoresponsive Ionic Liquid Materials: A Review.

Ionic liquids (ILs) are a class of low-melting molten salts (<100 °C) constituted entirely of ions, and their research has gained tremendous attention in line with their remarkably growing applications (>124,000 publications dated 30 August 2023 from the Web of ScienceTM). In this review, we first briefly discussed the recent developments and unique characteristics of ILs and zwitterionic liquids (ZILs). Compared to molecular solvents and other conventional organic compounds, (zwitter) ionic liquids carry negligible volatility and are potentially recyclable and reusable. For structures, both ILs and ZILs can be systematically tailor-designed and engineered and are synthetically fine-tunable. As such, ionic liquids, including chiral, supported, task-specific ILs, have been widely used as powerful ionic solvents as well as valuable additives and catalysts for many chemical reactions. Moreover, ILs have demonstrated their value for use as polymerase chain reaction (PCR) enhancers for DNA amplification, chemoselective artificial olfaction for targeted VOC analysis, and recognition-based affinity extraction. As the major focus of this review, we extensively discussed that small-molecule thermoresponsive ILs (TILs) and ZILs (zwitterionic TILs) are new types of smart materials and can be expeditiously discovered through the structure and phase separation (SPS) relationship study by the combinatorial approach. Using this SPS platform developed in our laboratory, we first depicted the rapid discovery of N,N-dialkylcycloammonium and 1,3,4-trialkyl-1,2,3-triazolium TILs that concomitantly exhibited LCST (lower critical solution temperature) phase transition in water and displayed biochemically attractive Tc values. Both smart IL materials were suited for applications to proteins and other biomolecules. Zwitterionic TILs are ZILs whose cations and anions are tethered together covalently and are thermoresponsive to temperature changes. These zwitterionic TIL materials can serve as excellent extraction solvents, through temperature change, for biomolecules such as proteins since they differ from the common TIL problems often associated with unwanted ion exchanges during extractions. These unique structural characteristics of zwitterionic TIL materials greatly reduce and may avoid the denaturation of proteins under physiological conditions. Lastly, we argued that both rational structural design and combinatorial library synthesis of small-molecule TIL materials should take into consideration the important issues of their cytotoxicity and biosafety to the ecosystem, potentially causing harm to the environment and directly endangering human health. Finally, we would concur that before precise prediction and quantitative simulation of TIL structures can be realized, combinatorial chemistry may be the most convenient and effective technology platform to discover TIL expeditiously. Through our rational TIL design and combinatorial library synthesis and screening, we have demonstrated its power to discover novel chemical structures of both TILs and zwitterionic TILs. Undoubtedly, we will continue developing new small-molecule TIL structures and studying their applications related to other thermoresponsive materials.

Thermally Reversible On‐Off Switching of Aggregation‐Induced Emission via LCST Phase Transition of Ionic Liquids in Water

AbstractA new phosphonium‐based ionic liquid is designed and synthesized using the 1,1,2,2‐tetraphenylethene‐derived anion ([P4444]4[TSPE]). Aqueous solutions of [P4444]4[TSPE] are obtained as transparent liquids (monophasic state), which suspended with increasing temperature. This behavior is found to exhibit a lower critical solution temperature (LCST) phase transition behavior. The LCST phase transition temperature can be controlled from 36 to 55 °C by changing the weight ratio between [P4444]4[TSPE] and water. When observing the LCST phase transition behavior of aqueous solutions of [P4444]4[TSPE] under excitation light with a wavelength of 365 nm, negligible photoluminescence in the monophasic state is observed at room temperature. Conversely, strong photoluminescence is observed in the suspended state when the temperature is above the LCST phase transition temperature. This strong photoluminescence is attributed to aggregation‐induced emission (AIE) that is induced by the restriction of the intramolecular rotations of the 4‐sulfophenyl groups against the ethylene core in the [TSPE] anion. This behavior is thermally reversible. This is the first example of on‐off switching of AIE achieved using the LCST behavior of ionic liquids.

Development of a novel micro-bead force spectroscopy approach to measure the ability of a thermo-active polymer to remove bacteria from a corneal model

Microbial keratitis occurs from the infection of the cornea by fungi and or bacteria. It remains one of the most common global causes of irreversible blindness accounting for 3.5% (36 million) of blind people as of 2015. This paper looks at the use of a bacteria binding polymer designed to bind Staphylococcus aureus and remove it from the corneal surface. Mechanical unbinding measurements were used to probe the interactions of a thermo-active bacteria-binding polymer, highly-branched poly(N-isopropyl acrylamide), functionalised with modified vancomycin end groups (HB-PNIPAM-Van) to bacteria placed on rabbit corneal surfaces studied ex-vivo. This was conducted during sequential temperature phase transitions of HB-PNIPAM-Van-S. aureus below, above and below the lower critical solution temperature (LCST) in 3 stages, in-vitro, using a novel micro-bead force spectroscopy (MBFS) approach via atomic force microscopy (AFM). The effect of temperature on the functionality of HB-PNIPAM-Van-S. aureus showed that the polymer-bacteria complex reduced the work done in removing bacterial aggregates at T > LCST (p < 0.05), exhibiting reversibility at T < LCST (p < 0.05). At T < LCST, the breaking force, number of unbinding events, percentage fitted segments in the short and long range, and the percentage of unbinding events occurring in the long range (> 2.5 µm) increased (p < 0.05). Furthermore, the LCST phase transition temperature showed 100 × more unbinding events in the long-range z-length (> 2.5 µm) compared to S. aureus aggregates only. Here, we present the first study using AFM to assess the reversible mechanical impact of a thermo-active polymer-binding bacteria on a natural corneal surface.

Preparation of Hierarchically Structured Amorphous Carbon Monoliths with Closed Spherical Mesopores via the Lower Critical Solution Temperature Phase Transition

AbstractSome polymer mixture systems become immiscible above a specific temperature, the so‐called lower critical solution temperature (LCST). In this work, the LCST behavior of a mixture of poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) triblock copolymers and phenolic resin oligomers is observed, and the corresponding phase transition is exploited to develop a facile route to hierarchically structured carbon monoliths. Whereas evaporation‐induced self‐assembly generates hexagonal channels in the monoliths, an additional phase transition at the LCST leads to an ordered arrangement of isolated pores. The fabrication method involves annealing the gel‐phased mixture with polymeric microbeads in a 3D‐structured mold at the LCST, followed by thermosetting and a carbonization process. The LCST phase transition behavior is observed experimentally by in situ small‐angle X‐ray scattering, optical transparency measurements, differential scanning calorimetry, and infrared spectroscopy. The fundamental mechanism of the LCST phase transition is further investigated by atomistic molecular dynamics simulations.

Multi-layer temperature-responsive hydrogel for forward-osmosis desalination with high permeable flux and fast water release

The development of forward-osmosis (FO) desalination is significantly restricted by the lack of suitable draw agents for both high permeable flux and fast release of water. To address this bottleneck, a multi-layer temperature-responsive hydrogel based on poly(N-isopropylacrylamide-co‑sodium acrylate) (P(NIPAAm-co-SA)) was developed. The drawing layer had a high concentration of SA for high osmotic pressure in the FO process. The releasing layer had no SA to preserve the lower critical solution temperature (LCST) of P-NIPAAm for fast water release. The multi-layer hydrogel yielded a high capacity of water absorption and high permeable flux due to the ionic drawing layer, which were comparable to that of the uniform P(NIPAAm-co-SA) hydrogels. Compared to the uniform hydrogels without LCST phase transition for the fast release of water, the releasing layer in our design preserved the LCST which facilitated the release of water as a result of inter-layer water transport from the drawing to the releasing layers. Such an effect allowed the further enhancement of water release by using the intermittent dewatering strategy and reduction of energy consumption. It was also found that reducing the gradient of SA concentration along the water transport path also improved the dewatering ratio as a result of promoting this inter-layer water transport.

A Computational Study on the LCST Phase Transition of a POEGMA Type Thermoresponsive Block Copolymer: Effect of Water Ordering and Individual Behavior of Blocks.

The atomistic origin underlying the lower critical solution temperature (LCST) behavior of thermoresponsive copolymers in water is still elusive. Here, we report all-atom molecular dynamics simulations of block copolymers of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA300) in water at various block ratios and at temperatures below and above the LCST values of each homopolymer block. Our single chain simulations showed that hydration water molecules accumulate particularly near the side chain carbon atoms by forming ordered cage-like structures via extensive hydrogen bonding between them. These water cage formations surround the entire surface of PMEO2MA- b-POEGMA300 and enable the copolymer to remain in water below the LCST. As the temperature increases, each block exhibits a separate coil-to-globule transition above its own LCST. A detailed analysis of the interactions between polymer-water and water-water revealed that this phase transition is mainly driven by the reduced local water ordering by the disruption of the water cages when the temperature is increased above the LCST. We found that the transition occurs differently in the copolymer than the POEGMA homopolymers due to the interaction of the blocks, especially around the joint of the blocks. Accordingly, the phase transition of a block acts as an additional disruptive effect on the other block's water cage structure, which reduces the LCST values of PMEO2MA and POEGMA300 in the copolymer, compared to their individual single chain homopolymers.

The role of hydrophobic hydration in the LCST behaviour of POEGMA300 by all-atom molecular dynamics simulations.

The solubility and lower critical solution temperature (LCST) behaviour of poly(oligo(ethylene glycol)methyl ether methacrylate) (POEGMA300) in water were comprehensively investigated by all-atom molecular dynamics (MD) simulations for 5-, 20-, 50- and 75-mer homopolymers. According to various structural and dynamic properties, the water-solubility of POEGMA300 below the LCST is mainly provided by hydrophobic hydration around the side chain carbon atoms, which is achieved by cage-like water formations. The LCST phase transition occurs when these cage-like structures are disrupted by increasing the temperature above the LCST. During this process, significant amounts of water molecules are released and the local water-ordering is reduced. Moreover, the number of hydrogen bonds and hydrogen bond lifetime results indicate that the hydrogen bonding between polymers and water molecules has relatively little effect on the phase transition. Also, the diffusion rates of 50- and 75-mer POEGMA300 decrease with increasing temperature, which may be due to the breakage of cage-like water structures when the polymer exceeds a certain chain length. Our atomistic level findings will enhance the understanding of the LCST phase transition of OEGMA based homopolymers and will be helpful to design homo- and co-polymers of OEGMAs with required properties.

Atomistic insights on the LCST behavior of PMEO2MA in water by molecular dynamics simulations

ABSTRACTFully atomistic molecular dynamics simulations of poly(2‐[2‐methoxyethoxy]ethyl methacrylate) (PMEO2MA) in water at temperatures below and above its lower critical solution temperature (LCST) were performed to improve the understanding of its LCST behavior. Atomic trajectories were used to calculate various structural and dynamic properties. Simulation results show that PMEO2MA undergo a distinct coil‐to‐globule transition above LCST. Detailed analyses of the number of first hydration shell water molecules around various atomic regions are revealed that the water solubility of PMEO2MA below LCST is mainly provided by the hydrophobic hydration around the side chain carbon atoms. This is achieved by the cage‐like water network formations which are disrupted when the temperature is increased above LCST, accompanied by significant amount of water molecule release and local water‐ordering reduction, which leads to the LCST phase transition. Furthermore, other analyses such as the number of hydrogen bonds and hydrogen bond lifetimes suggest that intermolecular hydrogen bondings between polymer and water molecules have little effect on the phase transition. Our results will contribute to a better understanding on the LCST phase transition of oligo(ethylene glycol) methyl ether methacrylate (OEGMA)‐based homopolymers at atomistic level that will be useful when designing homo‐ and co‐polymers of OEGMAs with desired properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 429–441

Hydrogels with a Memory: Dual-Responsive, Organometallic Poly(ionic liquid)s with Hysteretic Volume-Phase Transition.

We report on the synthesis and structure–property relations of a novel, dual-responsive organometallic poly(ionic liquid) (PIL), consisting of a poly(ferrocenylsilane) backbone of alternating redox-active, silane-bridged ferrocene units and tetraalkylphosphonium sulfonate moieties in the side groups. This PIL is redox responsive due to the presence of ferrocene in the backbone and also exhibits a lower critical solution temperature (LCST)-type thermal responsive behavior. The LCST phase transition originates from the interaction between water molecules and the ionic substituents and shows a concentration-dependent, tunable transition temperature in aqueous solution. The PIL’s LCST-type transition temperature can also be influenced by varying the redox state of ferrocene in the polymer main chain. As the polymer can be readily cross-linked and is easily converted into hydrogels, it represents a new dual-responsive materials platform. Interestingly, the as-formed hydrogels display an unusual, strongly hysteretic volume-phase transition indicating useful thermal memory properties. By employing the dispersing abilities of this cationic PIL, CNT-hydrogel composites were successfully prepared. These hybrid conductive composite hydrogels showed bi-stable states and tunable resistance in heating–cooling cycles.

From Macromolecular to Small‐Molecular Triggers: Facile Method toward Photoinduced LCST Phase Behavior of Thermoresponsive Polymers in Mixed Ionic Liquids Containing an Azobenzene Moiety

Instead of the reported photoinduced lower critical solution temperature (LCST) phase transition behavior in ionic liquids (ILs) achieved by photofunctional polymers, this study reports the facile photoinduced LCST phase behavior of nonfunctionalized polymers (poly(benzyl methacrylate) (PBnMA) and poly(2-phenylethyl methacrylate) (PPhEtMA)) in mixed ILs (1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)amide; [C1 mim][NTf2 ] and a newly designed functionalized IL containing an azobenzene moiety (1-butyl-3-(4-phenylazobenzyl)imidazolium bis(trifluoromethanesulfonyl)amide; [Azo][NTf2 ])) as a small-molecular photo trigger. Interestingly, the length of the alkyl spacer between the ester and aryl groups, which is the only structural difference between the two polymers, leads to two different photoresponsive LCST phase transition behaviors. On the basis of spectroscopic studies, the different phase transition behaviors of PBnMA and PPhEtMA may attribute to the different cooperative interactions between the polymers and [C1 mim][NTf2 ].

Effect of Methanol/Water Mixtures on the Lower Critical Solution Temperature of Poly(N-isopropylacrylamide)

ABSTRACTPoly(N-isopropylacrylamide) (PNIPAM) is a thermo-sensitive polymer that exhibits a lower critical solution temperature (LCST) around 305 K. Below the LCST, PNIPAM is soluble in water and above this temperature polymer chains collapse prior to aggregation. In the presence of methanol, electron paramagnetic resonance (EPR) spectroscopy suggests that, LCST of PNIPAM is depressed up to certain mole fraction of methanol (0.35 mole fraction) and it is speculated that addition of methanol affects the PNIPAM-water interactions. Above 0.35 mole fraction of methanol, LCST gets elevated to temperatures above ∼305 K (32°C) and cannot be detected up to 373 K (100 °C). The atomistic origin of this co-solvency effect on the LCST behavior is not completely understood. In the present study, we have used molecular dynamics (MD) simulations to investigate the effect of methanol-water mixtures on conformational transitions and the LCST of PNIPAM. We employ two different force fields i.e. polymer consistent force-field (PCFF) and CHARMM to study solvation dynamics and the PNIPAM LCST phase transition in various methanol-water mixture compositions (0.018, 0.09, 0.27, 0.5, and 0.98 mole fractions). Simulations are conducted at fully atomistic level for three different temperatures (260, 278, and 310 K) and radius of gyration (Rg) of PNIPAM chains was computed for determination of LCST behavior of PNIPAM.

A new thermo-responsive block copolymer with tunable upper critical solution temperature and lower critical solution temperature in the alcohol/water mixture

The multi-thermo-responsive block copolymer of poly[2-(2-methoxyethoxy)ethyl methacrylate]-block-poly[N-(4-vinylbenzyl)-N,N-diethylamine] (PMEO2MA-b-PVEA) displaying phase transition at both the lower critical solution temperature (LCST) and the upper critical solution temperature (UCST) in the alcohol/water mixture is synthesized by reversible addition-fragmentation chain transfer polymerization. The poly[2-(2-methoxyethoxy)ethyl methacrylate] (PMEO2MA) block exhibits the UCST phase transition in alcohol and the LCST phase transition in water, while the poly[N-(4-vinylbenzyl)-N,N-diethylamine] (PVEA) block shows the UCST phase transition in isopropanol and the LCST phase transition in the alcohol/water mixture. Both the polymer molecular weight and the co-solvent/nonsolvent exert great influence on the LCST or UCST of the block copolymer. By adjusting the solvent character including the water content and the temperature, the block copolymer undergoes multiphase transition at LCST or UCST, and various block copolymer morphologies including inverted micelles, core-corona micelles, and corona-collapsed micelles are prepared. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4399–4412

Hydration layer coupling and cooperativity in phase behavior of stimulus responsive peptide polymers.

It is shown that hydrophilic (backbone) and hydrophobic (side chain) hydration layers of elastin-like polypeptides (ELPs), a class of stimulus responsive peptide polymers that exhibit lower critical solution temperature (LCST) phase transition behavior, can exist in a coupled and decoupled state. The decoupled hydration state consists of hydrophobic and hydrophilic hydration layers that respond independently to temperature, while the coupled hydration state is characterized by a common, cooperative dehydration of both hydration layers. It is further shown that the primary sequence of an ELP can be tuned to exhibit either of the hydration layer coupling modes. Charged side chains lead to decoupling, while strongly hydrophobic side chains trigger stronger interaction between hydrophilic and hydrophobic hydration, leading to coupling of both layers. Further, for aprotic residues this coupling is fostered by decreasing bulkiness of hydrophobic side chains due to larger hydration numbers and water molecules mediating coupling between side chain and backbone hydration shells. For coupled hydration shells, the LCST phase transition characterized by spin probing continuous wave electron paramagnetic resonance spectroscopy is reminiscent of a first-order process even on nanoscopic length scales. In contrast, analogous synthetic polymers exhibit nanoscale phase transitions over a broad temperature range, indicating that their nanoscale phase behavior is not of first order. Hence, our results indicate that ELPs are the first identified class of polymers that exhibit a first-order inverse phase transition on nanoscopic length scales. These results may also provide insights into the role of hydration layers in governing the structure-function relationship of intrinsically disordered proteins.

Effect of Degree of Branching on the Thermoresponsive Phase Transition Behaviors of Hyperbranched Multiarm Copolymers: Comparison of Systems with LCST Transition Based on Coil-to-Globule Transition or Hydrophilic−Hydrophobic Balance

This work reports for the first time the influence of degree of branching (DB) on the thermoresponsive phase transition behaviors of hyperbranched multiarm copolymers. Two series of PEHO-star-PEOs (series A) and PEHO-star-PDMAEMAs (series B) with the hydrophobic DB-variable PEHO core and different kinds of linear arms (PEO arms or PDMAEMA arms) were synthesized. It was found these two series demonstrate thermoresponsive phase transitions with the lower critical solution temperature (LCST). The studies on the LCST transition mechanism indicate that series A belongs to the thermoresponsive polymer system with LCST transition based on hydrophilic-hydrophobic balance, while series B belongs to the thermoresponsive polymer system with LCST transition based on coil-to-globule transition. Correspondingly, there is a big difference in the DB dependence of LCST transition between series A and series B. For series A, the LCST phase transition is highly dependent on the DB of the PEHO core in copolymers. For series B, the LCST phase transition is independent of the DB but dependent on solution pH. Such results may extend the knowledge on the structure-activity relationship of thermoresponsive highly branched polymers.

Synthesis and characterization of new biodegradable thermosensitive polyphosphazenes with lactic acid ester and methoxyethoxyethoxy side groups

Two novel biodegradable thermosensitive polyphosphazenes with lactic acid ester and methoxyethoxyethoxy side groups were synthesized via the macromolecular substitution reactions of poly(dichlorophosphazene) with the sodium salt of lactic acid ester and sodium methoxyethoxyethoxide. Their structures were confirmed by 31P NMR, 1H NMR, 13C NMR, IR, DSC, and elemental analysis. The lower critical solution temperature (LCST) behavior in water and in vitro degradation property of the polymers was investigated. The results indicated that two polymers showed LCST phase transition over a range of concentrations from 0.13 to 15 wt% and pH-sensitive degradation properties.

Allosteric Actuation of Inverse Phase Transition of a Stimulus-Responsive Fusion Polypeptide by Ligand Binding

We report herein a biopolymer actuator with a modular design that allosterically transduces ligand binding into an aqueous demixing phase transition. The biopolymer actuator consists of two modular domains: a ligand binding protein domain, calmodulin (CaM), that is fused to a transducer domain, a stimulus-responsive elastin-like polypeptide (ELP) that exhibits a reversible lower critical solution temperature (LCST) phase transition. We demonstrate that binding of calcium to CaM spontaneously triggers the phase transition of the attached ELP, leading to formation of meso-microscale particles depending on the chain length of the ELP. This behavior is reversible as chelation of the bound calcium results in dissolution of the assembled particles, is selective for calcium as opposed to magnesium, and is abolished by the binding of a peptide ligand that is specific to calcium-bound CaM. These results are, to our knowledge, the first demonstration of biomolecular recognition-triggered, allosteric regulation of the LCST phase transition of a polymer and are significant because they expand the available triggers of the LCST transition of stimulus-responsive polymers to biochemical ligand binding. The ability to allosterically trigger the LCST transition of ELPs by biomolecular recognition will be useful for developing "smart" polymer actuators that capitalize upon the myriad ligand-protein pairs that are available from biology and for application in the design of selective pull-down assays in proteomics, drug delivery, and nanoscale biomolecular devices.

Synthesis of thermoresponsive poly(N-isopropylmethacrylamide) and poly(acrylic acid) block copolymers via post-functionalization of poly(N-methacryloxysuccinimide)

Polymers exhibiting a thermoresponsive, lower critical solution temperature (LCST) phase transition have proven to be useful for many applications as “smart” or “intelligent” materials. A series of poly(N-isopropylmethacrylamide) (PNIPMAM) polymer, poly(N-isopropylmethacrylamide)-b-poly(acrylic acid) (PNIPMAM-b-PAA) diblock, and poly(acrylic acid)-b-poly(N-isopropylmethacrylamide)-b-poly(acrylic acid) (PAA-b-PNIPMAM-b-AA) triblock copolymer samples were synthesized via ATRP. A facile post-functionalization route was developed that uses an activated ester functionality to convert poly(N-methacryloxysuccinimide) (PMASI) blocks to LCST capable polyacrylamide, while poly(t-butyl acrylate) (PtBA) blocks were converted to water-soluble poly(acrylic acid) (PAA). The post-functionalization was monitored via 1H NMR and ATR-FTIR. The aqueous solution properties were explored and the PNIPMAM polymers were shown to have a LCST phase transition varying from 35 to 60°C. The ability to synthesize block copolymers that are thermoresponsive and water-soluble will be of great benefit for broader applications in drug delivery, bioengineering, and nanotechnology.

Color Change ofN-Isopropylacrylamide Copolymer Bearing Reichardts Dye as Optical Sensor for Lower Critical Solution Temperature and for Host−Guest Interaction with β-Cyclodextrin

With a simple reaction pathway, a polymerizable solvatochromic dye monomer was synthesized. Copolymerization of this dye monomer with NiPAAM leads to formation of a solvatochromic copolymer with lower critical solution temperature (LCST) behavior. This resulting copolymer visualizes via a red-orange color change (a) the LCST phase transition and (b) the host−guest interaction of cyclodextrin with this copolymer simply by the naked eye. Actually, these effects are completely reversible.