Lower Critical Solution Temperature Properties Research Articles

On-line temperature-responsive restricted access material of sample preparation technique coupling with liquid chromatography for detection of tetracycline residues in milk

Effort of sample preparation has been working towards the automation and improvement of accuracy. Development of on-line sample preparation coupled with liquid chromatography (LC) is a promising way. In this study, an on-line extraction-LC automated analysis was proposed based on a temperature-sensitive restricted access material (RAM) for the determination of tetracycline residues (TCs) in milk. The RAM was synthesized using silica as substrate by the two-step surface initiated-atom transfer polymerization (SI-ATRP), styrene (St), sodium 4-vinylbenzenesulfonate (Nass) and a lower critical solution temperature (LCST)-responsive n-vinylcaprolactam (VCl) were conjugated to fabricate multiple interaction-adsorption sites of P(St-co-Nass-co-VCl) on silica interior, while an upper critical solution temperature (UCST)-responsive sulfobetaine methacrylate (SBMA) was then block polymerized to form zwitterionic exclusion sites on exterior. Thereafter, the RAM was packed as extraction column to be fixed into LC ahead of C18 analytical column, establishing automatic analysis by rotation of switching valve. In conjunction with LCST and UCST dual-responsive properties to adjust the hydrophobic-hydrophilic transition of the grafted P(St-co-Nass-co-VCl)-b-PSBMA chains, the RAM column acquires the best extraction of TCs and meanwhile the furthest removal of proteins at about 30 ℃ of column temperature. And using the proposed automatic analysis for monitoring of TCs in milk, a wide linearity (20–900 ng mL−1), low limit of detection (1.0 ng mL−1) and limit of quantification (2.5 ng mL−1) as well as good inter-day (<3.9 % RSD) and intra-day precision (<4.8 % RSD) with satisfactory recoveries (97.2–101.9 %) show the superior efficiency. It is believed that the introduction of temperature-sensitive RAM to construct on-line extraction is a powerful tool for detecting trace substances in scientific analyses.

Host-guest assembly triggered lower critical solution temperature behavior with reversible photo-regulation

The less frequent lower critical solution temperature (LCST) phenomenon has attracted extensive attention due to the foresighted application in smart materials. Nevertheless, the existing LCST-type materials are mainly dominated by a few polymers with specific moieties due to the damped hydration at a higher temperature and the lack of reversible regulations of the corresponding temperature sensitivity. Herein, an unanticipated and reversibly photo-responsive LCST behavior was uncovered in the BSC4/Azo-4 assembly solution. Such behavior arose from the host-guest binding between BSC4 and Azo-4 in an aqueous solution since neither the guest nor host alone exhibited an LCST property. Ascribing to the distinct π-π stacking between the trans- and cis-isomers of Azo-4, a reversible regulation of LCST behavior was achieved by irradiating UV and blue light alternately. Our study demonstrated the complexity and possibility of supramolecular self-assembly, opening a new avenue in the fabrication and adjustment of LCST-type materials in the future.

Structure-Property Relationships of Elastin-like Polypeptides: A Review of Experimental and Computational Studies.

Elastin is a structural protein with outstanding mechanical properties (e.g., elasticity and resilience) and biologically relevant functions (e.g., triggering responses like cell adhesion or chemotaxis). It is formed from its precursor tropoelastin, a 60-72 kDa water-soluble and temperature-responsive protein that coacervates at physiological temperature, undergoing a phenomenon termed lower critical solution temperature (LCST). Inspired by this behavior, many scientists and engineers are developing recombinantly produced elastin-inspired biopolymers, usually termed elastin-like polypeptides (ELPs). These ELPs are generally comprised of repetitive motifs with the sequence VPGXG, which corresponds to repeats of a small part of the tropoelastin sequence, X being any amino acid except proline. ELPs display LCST and mechanical properties similar to tropoelastin, which renders them promising candidates for the development of elastic and stimuli-responsive protein-based materials. Unveiling the structure-property relationships of ELPs can aid in the development of these materials by establishing the connections between the ELP amino acid sequence and the macroscopic properties of the materials. Here we present a review of the structure-property relationships of ELPs and ELP-based materials, with a focus on LCST and mechanical properties and how experimental and computational studies have aided in their understanding.

Lower Critical Solution Temperature Phase Transition of Poly(PEGMA) Hydrogel Thin Films.

Surface-attached hydrogel films with well-controlled chemistry are a new approach of polymer thin layers and an actual alternative to polymer brushes and layer-by-layer assemblies. The advantage is that the thickness of hydrogel films can widely range from a few nanometers to several micrometers. Hydrogel films can also remarkably respond to stimuli such as temperature: (i) the thickness change is of great amplitude, fourfold and more, which could not be reached with the geometry of polymer brushes or layer-by-layer assemblies, (ii) the time response is very short (less than 1 s), and (iii) the swelling-to-collapse transition is narrow (a small temperature change of a few degrees may be enough). Poly(N-isopropylacrylamide) (PNIPAM) is the most temperature-responsive polymer investigated with a lower critical solution temperature (LCST) of around 32 °C. However, it is relevant to have the available polymers responding to various transition temperatures with the advantage of keeping the same chemistry. Poly[oligo(ethylene glycol) methacrylate] (PEGMA) meets these specifications since its transition temperature can be finely tuned with the number of oligo ethylene glycol units, while it attractively combines biocompatibility with PEG side chains. Here, we report the synthesis and the temperature-responsive properties of poly(PEGMA) hydrogel thin films. We used a simple, versatile, and well-controlled approach through thiol-ene click reaction, the so-called cross-linking and grafting, to synthesize surface-attached poly(PEGMA) hydrogel films with various thickness. We show that the transition temperature of poly(PEGMA) hydrogel films ranges from 15 to 60 °C if the number of PEG units is from 2 to 5. This transition temperature can also be finely adjusted for hydrogel films containing copolymers or mixing homopolymers of PEGMA with a suitable ratio. Moreover, the LCST properties, swelling-to-collapse amplitude and transition temperature, are not sensitive to salt. In particular, there is no effect on the LCST properties of surface-attached poly(PEGMA) hydrogel films in phosphate saline buffer, which is promising for applications in biology such as injectable hydrogels, drug delivery systems, hydrogel-based microfluidic valves, and flow switches for biotechnologies.

Reduction and temperature-responsive hydrogel composed of hydroxyethyl disulfide-bis-glycidyl ether-crosslinked poly(hydroxyethyl acrylate-co-methyl methacrylate)

Reduction and temperature-responsive gels were prepared by crosslinking poly(hydroxyethyl acrylate-co-methyl methacrylate) (poly(HEA-co-MMA)) using hydroxyethyl disulfide-bis-glycidyl ether(HEDSGE) as a disulfide cross-linker. Poly(HEA-co-MMA) exhibited lower critical solution temperature (LCST) behavior when MMA content was 7.4 and 8.3 mole %. Energy dispersive X-ray and Raman spectroscopy revealed that the copolymer chains of the gels were cross-linked by disulfide bond (i.e., HEDSGE). The gels released their content in proportion to the concentration of a reducing agent (i.e., dithiothreitol). In addition, the gels released their payloads in a temperature dependent manner, possibly due to the LCST property of the copolymer. Highlights Reduction and thermo-responsive gels were prepared by crosslinking poly(HEA-co-MMA) using HEDSGE. Poly(HEA-co-MMA) exhibited LCST behavior when MMA content was 7.4 mole % and 8.3 mole %. Gels released their content in proportion to dithiothreitol (a reducing agent) concentration. Gels released their payloads in a temperature dependent manner.

Aqueous Synthesis of Upper Critical Solution Temperature and Lower Critical Solution Temperature Copolymers through Combination of Hydrogen-Donors and Hydrogen-Acceptors.

The synthesis of thermo-responsive polymers from non-responsive and water-soluble monomers has great practical advantages but significant challenges. Herein, the authors report a novel aqueous copolymerization strategy to prepare polymers with tunable upper critical solution temperature (UCST) or lower critical solution temperature (LCST) from non-responsive monomers. Acrylic acid (AAc), N-vinylpyrrolidone (NVP), and acrylamide (AAm) are copolymerized in water, yielding copolymers with UCST behavior. Interestingly, by simply replacing AAm with its methylated homologue, dimethyl acrylamide (DMA), the thermo-responsiveness of the copolymers is converted into LCST-type. The cloud points of the copolymers can be tuned rationally with their monomer ratios and the condition of the solvent. The UCST property of the poly(AAc-NVP-AAm) comes from the AAc-AAm and AAc-NVP hydrogen-bonds, while the LCST property of poly(AAc-NVP-DMA) originates from the hydrophobic aggregation of AAc-NVP complex and DMA, as indicated by temperature-dependent 1 H NMR and dynamic light scattering.

Supramolecular host-guest complex of methylated β-cyclodextrin with polymerized ionic liquid ([vbim]TFSI)n as highly effective and energy-efficient thermo-regenerable draw solutes in forward osmosis

Supramolecular inclusion complexes with lower critical solution temperature (LCST) properties were investigated for the first time as forward osmosis (FO) draw solutes. Randomly methylated-β-cyclodextrin (Rm-β-CD) host molecules accommodate polymerized ionic liquids (([vbim]TFSI)n PILs) through their hydrophobic TFSI− anions as guests. LCST properties were tuned by varying the chain lengths of ([vbim]TFSI)n, from which, short-chain oligo([vbim]TFSI) was found most suitable. Draw solutions (DS) of Rm-β-CD/oligo([vbim]TFSI) complex have highly tunable cloud-point temperatures (Tc), fast LCST kinetics and sufficient osmotic properties for an efficient FO. Under PRO mode, 0.5 M Rm-β-CD/0.078 M oligo([vbim]TFSI) induced competitive FO water flux (Jv ~13.73 L m−2h−1) and negligible reverse solute flux (Js ~4.41 × 10−3 mol m−2h−1) against DI water feed. It successfully processed different saline feeds (0.034 M and 0.6 M NaCl) with reasonable FO performance and superior Js/JV ~0.001 mol m−2h−1, demonstrating its competence for FO desalination. When heated slightly above its Tc = 29 °C (TTP = 30 °C), thermal precipitation (TP) is ensued with the release of TFSI− anions in oligo([vbim]TFSI) from Rm-β-CD. Due to its hydrophobicity, oligo([vbim]TFSI) precipitates while entrapping the suspended Rm-β-CDs between its chains causing flocculation and sedimentation. Thus, with only +5 °C heating above FO temperature (25 °C), 95% of draw solutes are effectively recovered from the spent DS after settling. Residual (~5%) Rm-β-CD in the DS supernatant is subsequently removed via nanofiltration at 99.33% rejection, producing non-toxic water effluent based on in vitro cytotoxicity results. Energy consumption estimates reveal the feasibility of Rm-β-CD/oligo([vbim]TFSI) as it requires minimal heat energy for recovery. This study offers new insights on the potential of host-guest complexes as a new class of energy-efficient draw solutes for FO desalination technology.

Switchable Wettability of Poly(NIPAAm-co-HEMA-co-NMA) Coated PET Fabric for Moisture Management.

In this study, we synthesized a random poly[(N-isopropylacrylamide)-co-(2-hydroxyethylmethacrylate)-co-(N-methylolacrylamide)] [poly(NIPAAm-co-HEMA-co-NMA)] copolymer through free-radical polymerization. The NIPAAm, HEMA and NMA moieties were framed to provide thermoresponsiveness, water absorption and retention control, and chemical cross-linking to achieve stability in aqueous medium, respectively. The copolymer showed a significant change in optical transmittance with a variation in temperature due to the change in volume (i.e., hydrophilic/hydrophobic) between 25 °C and 40 °C, attributed to the lower critical solution temperature property of the NIPAAm moiety. The copolymers were wire-bar-coated onto polyethylene terephthalate (PET) fabric. Variation in the water contact angle affirmed the switchable wettability due to the change in temperature. We tested the coated fabrics for moisture absorption and release at different temperatures. The results at 20 °C and 37 °C indicated that the P2 copolymer had the highest moisture absorption and release capability. Therefore, the copolymers with tailored properties can be used as smart textiles for activity specific clothing.

High-throughput extracellular pH monitoring and antibiotics screening by polymeric fluorescent sensor with LCST property.

Monitoring extracellular pH (pHe) is important for biology understanding, since pHe and its homeostasis are closely relevant to cellular metabolism. Hydrogel-based pHe sensors have attracted significant attention and showed wide application, while they are tedious with significant time-cost operation and reproducibility variations for high-throughput application. Herein, we synthesized two polymers for pHe monitoring which are soluble in water at room temperature with easy operations and high reproducibility among various micro-plate wells for high-throughput analysis. P1 (P(OEGMA-co-MEO2MA-co-pHS)) and P2 (P(OEGMA-co-pHS)) were synthesized via the Reversible Addition Fragmentation Chain Transfer (RAFT) copolymerization of oligo(ethylene glycol) methacrylate (OEGMA), 2-(2'-methoxyethoxy) ethyl methacrylate (MEO2MA) and the pH sensitive fluorescence moiety N-fluoresceinyl methacrylamide (pHS). P1 is soluble in water at room temperature (25 °C) while insoluble at the temperature above 33 °C, indicating its feature of lower critical solution temperature (LCST) at 33 °C. Further P1 showed higher pH sensitivity and photostability than P2 (without LCST property) when used at physiological temperature (37 °C). Thus, P1 was chosen to in-situ monitor the micro-environmental acidification of E. coli, Hela and Ramos cells during their growth, and the metabolism inhibiting activity of a representative antibiotic, ampicillin. Cell concentration-dependent cellular acidification and drug concentration-dependent inhibition of cellular acidification were observed, demonstrating that the LCST polymer (P1) is suitable for real-time cellular acidification monitoring as well as for high-throughput drug screening. This study firstly demonstrated the use of a LCST polymeric sensor for high-throughput screening of antibiotics and investigation of cell metabolism.

Design of low temperature-responsive hydrogels used as a temperature indicator

Development of highly thermo-sensitive hydrogels, particularly at a low-temperature range, has promising applications in diverse fields. Herein we designed, synthesized, and characterized tri-copolymer poly(N-tert-butyl acrylamide-co-N-isopropyl acrylamide-co-acrylamide) p(NTBAM-co-NIPAM-co-AM) hydrogels using a facile one-pot method. The copolymerization of two thermo-responsive monomers of NTBAM and NIPAM with hydrophilic AM monomers aimed to tune the temperature range of lower critical solution temperature (LCST) between 8°C and 10 °C by varying the concentrations and molar ratios of NTBAM, NIPAM, and AM. At optimal conditions, p(NTBAM-co-NIPAM-co-AM) hydrogels showed a rapid and large deswelling by reducing their original sizes by 21% in 2 min as temperature was slightly changed from 8 °C to 10 °C. Such low-temperature-triggered de-swelling behavior and tunable LCST property are likely attributed to delicate interplay between different network components and their interactions with water. Due to high temperature sensitivity (∼2 °C), large volume deswelling ratio (90%), and low temperature-responsive range (8–10 °C), we further demonstrated a prototype hydrogel ball actuator as temperature indicator to monitor minor temperature-induced size changes. The design strategy for this p(NTBAM-co-NIPAM-co-AM) hydrogel could be generally applicable to other thermo-responsive hydrogels with different shapes and temperature-responsive ranges, which could be used as low-temperature indicator for many applications including vaccine storage and transportation.

Amphiphilic Carbazole-Containing Compounds with Lower Critical Solution Temperature Behavior for Supramolecular Self-Assembly and Solution-Processable Resistive Memories.

The self-organization and resistive memory performances of a series of newly synthesized water-soluble amphiphilic carbazole derivatives have been explored. Temperature-dependent UV/Vis absorption spectroscopy has been conducted to study the isodesmic self-assembly mechanism of the carbazole-containing compounds. This class of compounds also exhibits interesting lower critical solution temperature properties, which are sensitive to concentration and ionic additives. One of the compounds has been solution-processed and utilized as an active material in the engineering of resistive memory devices, exhibiting a switching voltage of about 3.9 V, a constant ON/OFF current ratio of 106 , and a long retention time of 104 s. The present work demonstrates the versatile potential applications of water-soluble amphiphilic carbazole-containing compounds in supramolecular chemistry and resistive memory devices.

Self‐assembly and lower critical solution temperature properties of supramolecular block copolymer/ionic liquid complexes depending on the alkyl chain length of imidazolium rings

ABSTRACTWe report the liquid crystalline (LC) assembly and lower critical solution temperature (LCST) properties of wedge‐shaped block copolymer (BCP)/1‐alkyl‐3‐methylimidazolium tetrafluoroborate ([CnMIM][BF4], n = 2, 4, 6) complexes (1–3) depending on the alkyl chain length of the ionic liquids (ILs). In contrast to the crystalline BCP, all of the ionic samples showed LC phases. 1 with [C2MIM][BF4] exhibited a hexagonal columnar phase, and 3 with [C6MIM][BF4] exhibited a gyroid phase. Interestingly, a temperature‐dependent transformation from columnar phase to gyroid phase was revealed for 2 with [C4MIM][BF4]. The phase difference may be explained by the supramolecular shape change that was dependent on the alkyl chain length of the ILs. The LCST behavior was characterized using the differential scanning calorimetry, turbidity observations, and the X‐ray diffraction techniques. Notably, the primary d‐spacing began to decrease at the clouding temperature (Tc). 3 showed the highest Tc at 130 °C, which is greater than the temperature of the order‐to‐disorder transition. The results demonstrate that the subtle variation in the IL structure affects the morphological and LCST properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3587–3596

Doxorubicin poly N-vinylpyrrolidone and poly N-isopropylacrylamide-co-N-vinylpyrrolidone coated magnetic nanoparticles

The project aims to improve the delivery of anti-cancer doxorubicin (DOX) drug by its encapsulation in two different polymer composites (the first polymer composite: the cross-linked methacrylic modified poly N-vinyl-pyrrolidone coated magnetic nanoparticle (PNVP@Fe3O4), and the second polymer composite: the cross-linked methacrylic modified poly N-isopropylacrylamide-co-N-vinylpyrrolidone coated magnetic nanoparticle [P(NIPAAM-co-NVP@Fe3O4)]). These two composites were synthesized by the radical copolymerization of the monomers without requiring any special conditions. Formations of these two composites were confirmed by FT-IR, UV, TGA–DTA, XRD, VSM and SEM. The results show the high drug loading and the low release time for the prepared composites. Furthermore, when N-isopropylacrylamide was used as a monomer, the composite showed a lower critical solution temperature property which can be beneficial in cancer drug delivery, since the temperature of cancer cells is higher than normal ones, and DOX can be released selectively in cancer cells.

New Cationic Linear Copolymers and Hydrogels of N-Vinyl Caprolactam and N-Acryloyl-N′-ethyl Piperazine: Synthesis, Reactivity, Influence of External Stimuli on the LCST and Swelling Properties

New cationic linear copolymers of N-vinyl caprolactam (VCL) and N-acryloyl-N′-ethyl piperazine (AcrNEP) were synthesized by thermal free-radical solution polymerization in dioxane at 75 °C. The chemical composition of the copolymers was determined by 1H NMR spectroscopy. The copolymers were water-soluble at all composition and exhibited lower critical solution temperature (LCST) behavior. The LCST was greatly influenced by the AcrNEP content, changes in pH, temperature, salt and surfactant concentration of the external medium. The copolymers were rich in AcrNEP content due to its higher reactivity over VCL. The reactivity of AcrNEP and VCL were determined by the extended Kelen–Tudos method to be r1AcrNEP = 0.41 and r2VCL = 0.13. The distribution of monomer sequence in the polymer chain was estimated using the terminal copolymerization model and the maximum tendency to alternation (∼70%) was at 45 mol % of AcrNEP in the feed. The effect of polymer concentration in the range 0.02 to 20 wt % on the LCST beha...

Surface Modification in Aqueous Dispersions with Thermo-Responsive Poly(methylvinylether) Copolymers in Combination with Ultrasonic Treatment

The process of surface modification of hyd- rophobic organic pigments (copper phthalocyanine (CuPc) and carbon black) as well as a hydrophilic inorganic pigment (titanium dioxide) in aqueous dispersions by employing tailor-made thermo-responsive copolymers, and the colloidal stability have been studied. The pigment surface modification is achieved by conventional adsor- ption and by (thermo)preci pitation of amphiphilic methyl vinyl ether (MVE) containing polyvinylether block and PMVE graft copolymers with poly(ethylene oxide) side chains exhibiting a lower critical solution temperature (LCST). The effect of mechanical treatment of the pigment dispersion by ultrasonic power alone or in combination with the LCST property was investigated. The course of the pigment surface coating process was followed by the Elec- trokinetic Sonic Amplitude (ESA) method. The tempera- ture-controlled sorption of PMVE-g-PEO graft copolymers on both inorganic and organic pigment surface was investigated. It was found that ultrasonic treatment together with LCST thermoprecipitation is a promising method for the surface modification of pigments with regard to dispersion stability.

Swelling and diffusion characteristics of modified poly (N-isopropylacrylamide) hydrogels

Thermo-responsive hydrogels are capable of swelling changes to external temperature. A series of modified poly (N-isopropylacrylamide) (PNIPA) hydrogels was synthesized by free radical polymerization in aqueous solution. Acrylamide (AAm) was used to increase the lower critical solution temperature (LCST), while sodium alginate (SA) was used to improve the swelling performance of the hydrogels. Experiments show that 5.5% mass ratio of AAm increased the LCST by about 9 °C above that of conventional PNIPA. Also, SA significantly improved the equilibrium swelling ratio associate with temperature change. Trypan blue diffusion revealed significant differences in the fluid release obtained from hydrogels with modified LCST and swelling properties. The implications of the modified fluid release and swelling characteristics are also discussed for the device design of thermo-sensitive hydrogels for localized drug delivery.

3-EthylatedN-Vinyl-2-pyrrolidone with LCST Properties in Water

The monomer 3-ethyl-1-vinyl-2-pyrrolidone (3) and the homopolymer poly(3-ethyl-1-vinyl-2-pyrrolidone) (5) have been synthesized. Polymer 5 is soluble in water and shows a critical temperature (T(c) ) of 27 °C. The presence of cyclodextrin causes a slight shift of the T(c) . The lower critical solution temperature (LCST) could be varied between 27 and 40 °C by copolymerization with N-vinyl-2-pyrrolidone. A linear correlation between the T(c) and the copolymer composition is observed.

Application of thermo-responsive poly(methyl vinyl ether) containing copolymers in combination with ultrasonic treatment for pigment surface modification in pigment dispersions

The process of surface modification of hydrophobic organic (copper phthalocyanine (CuPc)) as well as hydrophilic inorganic pigments (titanium dioxide) in aqueous dispersions by employing tailor-made thermo-responsive copolymers and the colloidal stability have been studied as a function of temperature. The pigment surface modification is achieved by conventional adsorption and by thermoprecipitation of amphiphilic methyl vinyl ether (MVE) containing block and graft copolymers, exhibiting a lower critical solution temperature (LCST), with poly(isobutyl vinyl ether) blocks and poly(ethylene oxide) side chains, respectively. The effect of mechanical treatment of the pigment dispersion by ultrasonic power alone or in combination with the LCST property was investigated. The course of the pigment surface coating process was followed by the electrokinetic sonic amplitude (ESA) method. The temperature-controlled sorption of PMVE- g-PEO graft copolymers on both inorganic and organic pigment surfaces was investigated. It was found that ultrasonic treatment together with LCST thermoprecipitation is a promising method for the surface modification of pigments with regard to dispersion stability.

Lower Critical Solution Temperature Properties of N‐Isopropylacrylamide‐Based Pseudopolyrotaxanes by Complexation with Cucurbituril[6

AbstractPseudopolyrotaxanes 4a and 5a are synthesized by two paths: a) directly from the pseudorotaxane, and b) by complexing with cucurbituril (CB[6]) in water at room temperature after the polymerization. Free radical copolymerization with CB[6] (un)complexed monomer and N‐isopropylacrylamide (NIPAAM) is carried out using a redox initiator in aqueous media at room temperature. The properties of pesudorotaxanes (4a and 5a) and polymers (4 and 5) are investigated by TGA, DSC, and turbidity measurements. The lower critical solution temperatures of the NIPAAM‐containing copolymers and CB[6] are significantly higher than those of pure NIPAAM copolymers. The pseudopolyrotaxanes 4a and 5a have a higher thermal stability, as a result of threading of the CB[6] rings onto the polymer side groups.magnified image

Mixed Block Copolymer Aggregates with Tunable Temperature Behavior

A block copolymer of propylene oxide (PO) and ethoxyethyl glycidyl ether (EEGE), (PO)(2)(EEGE)(6)(PO)(2), that has been found to possess lower critical solution temperature properties in water in the temperature range below 20 degrees C was mixed at 1:0.1, 1:1, and 1:10 weight ratios with commercially available Pluronic (L64 or P85) block copolymers. The cooperative association of the copolymers in aqueous solution was studied by dynamic light scattering over a wide temperature range (5-60 degrees C). At lower temperatures, the systems containing either L64 or P85 behave similarly irrespective of the composition: three species corresponding to (PO)(2)(EEGE)(6)(PO)(2) unimers, Pluronic-dominated mixed micelles, and large (50-60 nm in radius) composite (PO)(2)(EEGE)(6)(PO)(2)/Pluronic aggregates were identified. At a certain temperature, which is composition-dependent, the systems phase-separate [(PO)(2)(EEGE)(6)(PO)(2)/L64 1:0.1], enter an interval of instability [(PO)(2)(EEGE)(6)(PO)(2)/L64 1:1 and 1:10], or rearrange by dissociation of the large composite particles [(PO)(2)(EEGE)(6)(PO)(2)/P85]. The presence of a Pluronic micellar peak in the relaxation time distribution at lower temperatures, the dimensions of the composite particles, and the different behavior of the systems at elevated temperatures are discussed. A possible application of the thermosensitive mixtures in delivery/release of active substances is suggested.