Lower Critical Solubility Temperature Research Articles

Electrostatic potential gap at the interface between triethylamine and water phases studied by molecular dynamics simulation

Molecular dynamics calculations were carried out in order to investigate the interfacial properties of the two-phase coexistence state of the triethylamine (TEA) and water mixture, which is known to have a lower critical soluble temperature. Two kinds of initial configuration were adopted. One was a two-phase coexistence state and the other was a random mixed state of TEA and water molecules. After an equilibration calculation of several nanoseconds, the density profiles converged to the same equilibrated two-phase coexistence state. In the equilibrated state, anisotropic orientations were observed for both molecules, which makes an electrostatic potential gap between these phases.

Synthesis and characterization of poly(N-isopropylacrylamide) films by photopolymerization

A novel method used for the preparation of poly(N-isopropylacrylamide) (PNIPAAm) films of varying crosslink density under homogeneous/heterogeneous conditions is described in this paper. Photopolymerization of the N-isopropylacrylamide (NIPAAm) monomer in water (homogeneous at ∼7°C and heterogeneous at ∼40°C) or a mixture of water/ethanol (50:50, heterogeneous at ∼7°C) was carried out using 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (hydrophilic) or 2-hydroxy-2-methyl propiophenone (hydrophobic) photo-initiator. In order to investigate the effect of temperature and crosslink density, polymerization was carried out at ∼7°C [below lower critical soluble temperature (LCST)] and ∼40°C (above LCST) using varying amounts of N,N′-methylene bisacrylamide (BIS) ranging from 1–4 wt%. Degree of swelling (determined by optical microscopy), phase transition temperature [determined by differential scanning calorimetry (DSC)] as well as morphology (scanning electron microscopy) were found to be dependent on solvent system (homogeneous/heterogeneous), temperature of polymerization and crosslink density. Hydrogels prepared at ∼7°C using hydrophobic photo-initiator and water/ethanol (50:50) as solvent, showed much higher degree of swelling at all levels of crosslink density as compared to hydrogel prepared at ∼7°C using hydrophilic photo-initiator and water as solvent. Hydrogels were used for patterning which may find applications in microfluidic devices. Copyright © 2006 John Wiley & Sons, Ltd.

Thermosensitive Nanospheres with a Gold Layer Revealed as Low-Cytotoxic Drug Vehicles

In this paper, the positive effect of a gold layer on cell viability is demonstrated by examining the results given by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfop henyl)-2H-tetrazolium (MTS) assay and two-color cell fluorescence viability (TCCV) assay. These cytotoxicity tests were performed with human cervical adenocarcinoma cells (HeLa cell line) and transformed African green monkey kidney fibroblast cells (Cos-7 cell line). To fabricate the nanostructures as drug vehicles, first, poly(l,l-lactide-co-ethylene glycol) (PLLA-PEG) and poly(N-isopropylacrylamide-co-D,D-lactide) (PNIPAAm-PDLA) were synthesized, and then two kinds of thermosensitive nanospheres comprising "shell-in-shell" structures without a gold layer (PLLA-PEG@PNIPAAm-PDLA) and with a gold layer (Au@PLLA-PEG@PNIPAAm-PDLA) were constructed by a modified double-emulsion method (MDEM). Both of them displayed a unique thermosensitive character exhibiting the lower critical solubility temperature (LCST) at 36.7 degrees C which was confirmed by UV-vis spectroscopy and differential scanning calorimetry (DSC). The release profiles of entrapped bovine serum albumin (BSA) were monitored at 22 and 37 degrees C, respectively, to reveal the thermal dependence on the release rate. In cell viability tests, both PLLA-PEG@PNIPAAm-PDLA and Au@PLLA-PEG@PNIPAAm-PDLA showed excellent cell viability, and furthermore, Au@PLLA-PEG@PNIPAAm-PDLA, particularly at high doses, exhibited more enhanced cell viability than PLLA-PEG@PNIPAAm-PDLA. This effect is mainly attributed to the gold layer which binds the protein molecules first and consequently facilitates transmembrane uptake of essential nutrients in the cell media, resulting in favorable cell proliferation.

Investigation of the self‐association behavior of a thermosensitive copolymer with lower critical solubility temperature near human heat by dynamic laser light scattering

AbstractThe special thermosensitive copolymer with lower critical solubility temperature near human heat of 37°C in aqueous solution has been prepared successfully by copolymerizing N‐isopropylacrylamide (NIPAM) and N‐isopropylmethacrylamide (NIPMAM) randomly at an appropriate monomer ratio. The self‐association behavior of the poly[NIPAM‐ran‐NIPMAM] copolymer has been studied by dynamic laser light scattering (DLLS) at a concentration higher than the critical concentration of the self‐association calculated from viscosity data according to cluster theory. The effect of the concentration and temperature on the self‐association behavior in water has been discussed respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 583–588, 2005

Modifying stainless steel surfaces with responsive polymers: effect of PS-PAA and PNIPAAM on cell adhesion and oil removal

The treatment of stainless steel surfaces with responsive polymers was investigated using X-ray photoelectron spectroscopy and scanning electron microscopy. Poly(N-isopropylacrylamide) (PNIPAAM) is a temperature-sensitive polymer which is soluble in water below 32°C (Lower Critical Solubility Temperature (LCST)) but collapses and aggregates above 32°C. This polymer was adsorbed at 50°C from solutions at different concentrations, followed by rinsing and different drying procedures. Thereby, a large variety of surface structures could be obtained, from smooth films to surfaces showing marked relief features due to residues of PNIPAAM aggregates. Two poly(styrene)-b-poly(acrylic acid), PS-PAA, with different block lengths, were spin-coated on stainless steel and showed preferential exposure of PS blocks at the outermost surface. PNIPAAM-conditioning was shown to strongly reduce yeast cell adhesion and to facilitate the removal of oil soil due to its high water affinity and chain mobility below the LCST. PS-PAA coatings also reduced yeast cell adhesion; this may partly be due to a reorganization of the surface, leading to exposure of PAA chains in contact with water and thus to electrostatic repulsion of the yeast cells.

Synchronous delivery systems composed of Au nanoparticles and stimuli-sensitive diblock terpolymer

A method to construct synchronous delivery systems via direct self-assembly of Au nanoparticles on the poly[(N-isopropylacrylamide-r-acrylamide)-b-L-lactic acid] (PNAL) nanospheres has been presented in this paper. To achieve amphiphilic diblock terpolymer, hydrophobic poly (L-lactic acid) (PLLA) block was added to poly(N-isopropylacrylamide- r-acrylamide) (PNA) block via Michel-type addition reaction. Lower critical solubility temperature (LCST) was modulated at 35.6 degrees C which is close to the body temperature, but higher than poly(N-isopropylacrylamide) (PNIPAAm) homopolymer by controlling the ratio between isopropylacrylamide (IPAAm) monomers and acrylamide (AAm) monomers. Using this amphiphilic diblock terpolymer, PNAL nanospheres were fabricated by emulsion/evaporation technique followed by direct self-assembly of Au nanoparticles on the PNAL nanospheres due to the high affinity of amino groups donated from PNA block. The 'core' site of Au@PNAL nanospheres can load various lyphophilic drugs. Moreover, Au nanoparticles in the 'shell' domain of PNAL nanospheres give optimal environment to conjugate various biomolecules. Therefore, it is expected that Au@PNAL hybrid nanospheres can be utilized in synchronous delivery of both biomolecules in the 'shell' domain and various therapeutic drugs in the 'core' domain.

A Novel Thermosensitive Composite Fabricated with Au Nanoparticles, Poly(Lactide), and Poly(N-Isopropylacrylamide)

A novel approach to load a hydrophilic bovine serum albumin (BSA) into the drug carriers was proposed in terms of thermosensitive dual-shell structures which were fabricated with poly(N-isopropylacrylamide), poly(lactide) and Au nanoparticles. Spherically well-defined dualshell structures were constructed by a modified-double-emulsion method (MDEM). The lower critical solubility temperature of the structures was shifted to 36.4 °C which was confirmed by UVVis spectroscopy.

Adsorption of poly(N-isopropylacrylamide) on glass substrata.

The adsorption of poly(N-isopropylacrylamide) (PNIPAAM), a well known thermosensitive polymer, on glass was investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The polymer was dissolved in water at low (0.02 g/L) and high (2 g/L) concentration and the tested temperatures were below (25 degrees C) and above (50 degrees C) the lower critical solubility temperature (LCST). Whatever the conditions, a smooth layer of adsorbed molecules spread along the surface was observed. The thickness was about twice higher for high concentration compared to low concentration. The cohesion in the adsorbed layer, as revealed by scraping tests performed by AFM, was higher above the LCST than below the LCST. On top of this adsorbed layer, single-chain coils, globules, or aggregates were present, depending on concentration and temperature. The observation of these additional adsorbed entities was poorly reproducible, presumably due to the lack of shear control upon rinsing. These results emphasize the importance of the characterization of surface morphology to interpret amounts of adsorbed polymers.

Effects of sodium dodecyl sulfate on poly( N -isopropylacrylamide) adsorption at the air-water interface above the lower critical solubility temperature

The behavior of poly (N-isopropylacrylamide) (PNIPAM) at the air–water interface above the lower critical solubility temperature and the effects of sodium dodecyl sulfate (SDS) have been studied by neutron reflectivity. In the absence of SDS, PNIPAM adsorbs at the air–water interface and forms a thick and dense multilayer which can be characterized by two regions: a first region made up of pure polymer, and a second containing the same volume fraction of polymer as in the bulk precipitate. In the presence of SDS, polymer adsorption is decreased, and the structure of the adsorbed polymer can be described as a layer of colloidal particles of collapsed PNIPAM stabilized by SDS molecules. At higher SDS concentrations where the PNIPAM is completely resolubilized into charged chains, most, but not all, of the polymer is displaced from the surface, and the remaining adsorbed polymer forms a thin and dilute layer.

Improved method for the isolation and purification of water‐soluble polyphosphazenes

We report in this article an improved procedure to isolate and purify representative water-soluble polyphosphazenes that dramatically reduces the time and equipment involved, while maintaining or exceeding the yields and purity reported in the literature for these polymers obtained using dialysis methods. This technique takes advantage of the phase transition behavior exhibited by some hydrophilic polymers, namely that associated with the lower critical solubility temperature (LCST). The polymers used in this study were poly[bis-(2-(2-methoxyethoxy)ethoxy)phosphazene], MEEP (1), and two new water-soluble polymers. These polymers are similar to MEEP, yet they contain a small percentage of a crosslinkable pendant group; either 2-hydroxyethyl allyl ether (2), or o-allyl phenol (3). The observed behavior was quite different for these two polymers than that found for MEEP, and is a direct consequence of the pendant group substitution patterns. Although the homopolymer MEEP yielded a single sharp LCST point, the two heteropolymers exhibited this phase transition over a broader temperature range. Further, fractionation of polymer 3, based on pendant group speciation, was possible due to the more hydrophobic nature of the phenol. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1092–1099, 2000

Improved method for the isolation and purification of water-soluble polyphosphazenes

We report in this article an improved procedure to isolate and purify representative water-soluble polyphosphazenes that dramatically reduces the time and equipment involved, while maintaining or exceeding the yields and purity reported in the literature for these polymers obtained using dialysis methods. This technique takes advantage of the phase transition behavior exhibited by some hydrophilic polymers, namely that associated with the lower critical solubility temperature (LCST). The polymers used in this study were poly[bis-(2-(2-methoxyethoxy)ethoxy)phosphazene], MEEP (1), and two new water-soluble polymers. These polymers are similar to MEEP, yet they contain a small percentage of a crosslinkable pendant group; either 2-hydroxyethyl allyl ether (2), or o-allyl phenol (3). The observed behavior was quite different for these two polymers than that found for MEEP, and is a direct consequence of the pendant group substitution patterns. Although the homopolymer MEEP yielded a single sharp LCST point, the two heteropolymers exhibited this phase transition over a broader temperature range. Further, fractionation of polymer 3, based on pendant group speciation, was possible due to the more hydrophobic nature of the phenol. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1092–1099, 2000

Lower critical solubility temperature materials as biofouling release agents

Poly(N-isopropylacrylamide) (PNIPAAM) exhibits a lower critical solubility temperature (LCST) of 32°C. Using thin films of this compound as a model system, the potential of ‘smart polymers’ as biofouling-release agents was examined. PNIPAAM-coated glass slides were incubated in artificial sea water containing the marine bacterium Halomonas marina or in natural bay water at a temperature above the LCST. Upon rinsing of the biofouled samples with artificial sea water below the LCST, the dissolution of the coating released over 90% of the attached fouling material, a significant increase over the release obtained for glass controls. These experiments demonstrate the potential of PNIPAAM and similar polymers as possible fouling-release agents, and suggest that tethered PNIPAAM (or similar polymers) may be useful as regenerable fouling-release surfaces.

Application of thermosensitive polymers as a new embolic material for intravascular neurosurgery.

Application of thermosensitive polymers as an embolic material for intravascular neurosurgery was investigated. We intended to use thermosensitive polymers to occlude vessels by precipitation in response to body temperature. Copolymers of N-isopropylacrylamide (NIPAM) and N-n-propylacrylamide (NPAM) were selected as thermosensitive polymers. To determine the optimal lower critical soluble temperature (LCST) for the embolic material, we developed an in vitro flow model. In this study the copolymers with an LCST of 24-26 degrees C showed appropriate precipitation. To prove the occlusion of vessels in vivo, we injected the copolymers into a rabbit kidney through a microcatheter. The extent of embolization was judged by angiography and histological examination. An acute toxicity test of the copolymer of NIPAM and NPAM was performed in comparison with that of the NIPAM monomer. The copolymer used in this paper showed no acute toxicity in mice. Water solubility, non-adhesiveness, and non-toxicity are the advantages of the use of thermosensitive polymers as an embolic material. By changing the LCST, various embolic materials can be designed. Based on our results, we believe that the application of thermosensitive polymers as a new embolic material is very promising.

Temperature- and pH- Sensitive Hydrogels for Controlled Release of Antithrombotic Agents

AbstractPolymeric hydrogels capable of reversible swelling with changes in environmental temperature and pH were synthesized and studied as matrix systems capable of controlled release of antithrombotic drugs to the site of a blood clot. Monomers N-isopropylacrylamide (NIPAAm) and methacrylic acid (MAA) were chosen for the temperature- and pHdependent swelling characteristics of their polymers, respectively. Equilibrium swelling studies were performed as functions of pH and of temperature, and kinetic swelling studies were performed on the thermally responsive gels as a function of time after the gel was subjected to a step-change in temperature. Experimental results indicate that P(NIPAAmco- MAA) hydrogels can be synthesized so that they are either pH- or temperaturesensitive, depending upon the composition of the network. The pure PNIPAAm gels showed a lower critical solubility temperature (LCST) of around 32°C, below which the gel was in its swollen state, and above which the gel collapsed. As the amount of methacrylic acid in the gels was increased, the degree of swelling in deionized water decreased and the temperature sensitivity was lost. The hydrogels containing MAA displayed a transition in swelling behavior between pH 4 and 6. The mesh sizes of the hydrogel networks were calculated from the results of the swelling studies by Flory-Rehner theory. A kinetic experiment on the temperature-sensitive pure PNIPAAm hydrogel showed that the polymer network collapsed rapidly upon temperature changes across the LCST.

Thermodynamic properties of polyolefin solutions at high temperature: 2. Lower critical solubility temperatures for polybutene-1, polypentene-1 and poly(4-methylpentene-1) in hydrocarbon solvents and determination of the polymer-solvent interaction parameter for PB1 and one ethylene-propylene copolymer

Lower critical solubility temperature ( LCST) for 3 polyolefins, polybutene-1 (PB1), polypentene-1 (PP1) and poly(4-methylpentene-1) (P4MP1), and the x interaction parameter in concentrated solutions for PB1 and the 33% ethylene ethylene-propylene copolymer have been measured in linear, branched, cyclic alkanes and some other solvents. Effects on x of the equation of state term, of correlations of molecular orientations ( CMO) and of the solvent steric hindrance were investigated. The solvent density d s is found to be a good empirical parameter to characterize the equation of state term and to correlate the LCST. The parameter d s d p (where d p is the polymer density) affords an excellent correlation for the LCST of all polyolefins in normal and branched alkanes (polyethylene (PE) excepted). In dilute solution (at the LCST) the effect of CMO and solvent steric hindrance could not be distinguished from equation of state effects. However, values of x, found to be higher in branched than in linear alkanes in solutions of the linear polymer (PE) but not with the branched PB1 and the copolymer, are indicative of the importance in concentrated solutions of CMO even at high temperatures (100°–135°C). Furthermore, the lowering of x from linear PE to the branched PE and to the ethylene-propylene copolymers, following the expected diminution of CMO in the corresponding melts, is another indication of the persistance of CMO at high temperature. Solvent steric hindrance is seen to lower x (measured here by gas-liquid chromatography).

Intrinsic viscosities of four homopolymers and one copolymer in nonpolar solvents. II. Effect of solvent steric hindrance

AbstractIntrinsic viscosities at 25°C of an ethylene‐propylene copolymer containing 81% ethylene (81% E) of polypentenamer (PPmer), polyisobutylene (PIB), polypentene‐1 (PP‐1), and polydimethylsiloxane (PDMS) have been measured in n‐C9 and three branched nonanes and n‐C7 and five branched heptanes. The effect of the solvent steric hindrance on the free energy, i.e., on the χ parameter was investigated. The highly sterically hindered, cruciform molecules 3,3‐dimethylpentane and 3,3‐diethylpentane are the best solvents for four of the five polymers. The enhancement of solvent quality due to the steric hindrance diminishes when the polymer free volume increases. The difference in [η] between 2,4‐dimethylpentane and 2,3‐dimethylpentane is −50%, −35%, −2% for PPmer, PIB, PDMS, and can be correlated to a measure of the polymer free volume, i.e., the lower critical solubility temperature. The χ, χH, and χS are calculated from [η] using the Stockmayer‐Fixman relation and from h, the heat of mixing at infinite dilution of the polymer, obtained previously. With each polymer, a good correlation is found between h and [η] obtained with the six heptanes and four nonanes. The correlation points to the same effect being at the origin of χH and χS but of different magnitude. In cases showing the steric hindrance effect, a negative contribution occurs in h (or χH) which is larger in magnitude than the corresponding negative entropic contribution leaving a net negative effect in χ itself. Probably due to their very compact shape and fewer degrees of freedom, the cruciform solvents lose less entropy than the chain solvents in mixing.

A high hydroxyl group content found in high molecular weight fractions of poly(oxyethylene glycol)

AbstractThe results of a fractionation of high molecular weight poly(oxyethylene glycol) with the mixture benzene—isooctane are presented. The fractions are characterized by gel permeation chromatography (GPC), infrared spectroscopy, viscometry, and dialysis. A high hydroxyl content was found for the higher fractions, which is not compatible with a linear polyoxyethylene glycol molecule with hydroxyl endgroups. The presence of hydroxyl groups on the chain is improbable. The dialysis of the higher fractions in CCl4 and toluene shows that a surprising amount passes through the dialysis bag. The possibility of degradation of the polymer is considered. However, GPC analysis of the products of the dialysis suggest that the high molecular weight is made up of aggregates of middle‐sized molecules and low molecular weight ones, held together by hydrogen bonding between hydroxyl and ether groups. Some results of a fractionation in water with the lower critical solubility temperature at 99°C. are given.

Segregation of fish oils with liquid propane and butane.

F ISH OIL REFINING has been studied for a long time because of the characteristics of the raw material which limit its utilization. The oil consists of a complex mixture of triglyeerides with a variety of saturated and unsaturated compounds. The high iodine value (170-200) suggests the possibility of obtaining an appropriate drying oil that could compete with those of vegetable origin. Compared with the latter, fish oils contain higher percentages of saturated (2535%) and monounsaturated (23-30%) fat ty acids. It is thus important to eliminate all or part of these components which will not allow an appropriate drying of the coating. In addition, fat ty acids are present with more than 22 carbons and up to six double bonds which oxidize easily, impairing the odor and color of the product. Fractional crystallization, remodelling, and extraction with solvents can be used for modifying the oil composition. Solvent extraction is widely applied in the petroleum industry for segregating and purifying lubricants. Among the solvents used for selective fractionation are liquid hydrocarbons, furfural, and methyl ethyl ketone. With liquid propane, the solubility of triglycerides decreases with temperature. A lower critical solubility temperature (CST) exists, above which there are two phases in equilibrium. The solubility of the components is determined by the degree of unsaturation and chain length. Hixson and others (1,2) have studied the solubility of pure triglycerides and fatty acids in liquid propane by using vegetable oils. They determined CST for different components and studied the separation of such systems as propane-abietic acidsunflower oil. Commercial separation of fish oils with liquid propane has been applied in South Africa to obtain Vitamin A concentrates (3). This study reports on the possibility of using liquid propane near its critical temperature for separating fish oils in two fractions of different iodine value. Fractionation studies were performed in a Magne-