Interpolymer complex between poly(ethylene oxide) and poly(carboxylic acid)

An interpolymer complex was prepared by mixing aqueous solutions of poly(ethylene oxide) (PEO) and of a poly(carboxylic acid), i.e., poly(acrylic acid)(PAA), poly(methacrylic acid)(PMAA), or styrene-maleic acid copolymer(PSMA). The complexation mechanism was discussed on the basis of results of such experimental methods as viscosity, potentiometric titration, and turbidimetry. The hydrogen bond is primarily involved in these complexations, but the influence of hydrophobic interaction on complexation can not be ignored. If the degree of dissociation α of carboxylic acid or the degree of polymerization P_n of PEO was perceptibly changed, a stable complex was obtained at about α 0.1 or P_n (PEO) = 40 for PMAA, 200 for PAA. This fact indicates that more than a definite number of binding sites are necessary for a stable interpolymer complex to be formed and that cooperative interaction among active sites plays an important role in complex formation.     

Blood compatibility of surface-engineered poly(ethylene terephthalate) via o-carboxymethylchitosan

Poly(ethylene terephthalate) (PET) films were treated by argon plasma following by graft copolymerization with acrylic acid (AAc). The obtained PET-surface grafted PAA (PET-g-PAA) was coupled with chitosan (CS) and o-carboxymethylchitosan (OCMCS) molecules, respectively. Their surface physicochemical properties were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle and streaming potential measurements. The PET-g-PAA surface containing carboxylic acid, CS immobilized PET surface containing amino and OCMCS immobilized PET surface containing both carboxylic acid and amino groups, make the PET surface exhibited a hydrophilic character. The blood compatibility was evaluated by platelet contacting experiments and protein adsorption experiments in vitro. The results demonstrate that the PET surface coupling OCMCS shows much less platelet adhesive and fibrinogen adsorption compared to the other surface modified PET films. The anticoagulation of PET-OCMCS is ascribed to the suitable balance of hydrophobicity/hydrophilicity, surface zeta potential and the low adsorption of protein.     

Self-consistent-field analysis of the micellization of carboxy-modified poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers

The micellization properties of carboxy-modified Pluronics P85 (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers) are investigated by means of a molecularly realistic self-consistent-field theory. We consider the, so-called, carboxylic acid end-standing P85 (CAE-85) case where the carboxylic group is located at the end of both PEO parts and the carboxylic acid center-standing P85 (CAC-85) case where each of the carboxylic group presents between the PEO and PPO blocks. The micellization of these copolymers depends on the pH, the added electrolyte concentration phis, and the temperature. It is shown that the aggregation number (Nagg) decreases, whereas the critical micellization concentration (CMC) increases with pH. For the case of increasing phis, the Nagg increases and the CMC decreases. The critical micellization temperature (CMT) and cloud point temperature (CPT) increase with pH at low phis and decrease at increasing phis. The changing from CAE-85 to CAC-85 leads to increasing CMC and CMT, but lower CPT.     

Dynamic properties of poly(styrene)-poly(ethylene oxide) diblock copolymer films at the air-water interface

The complex dynamic elasticity of monolayers of the diblock copolymer poly(styrene)-poly(ethylene oxide) at the air-water interface in the pancake, quasi-brush, and brush regimes has been studied by means of three experimental techniques--the surface transverse and longitudinal waves and the oscillating barrier method. In the pancake regime the surface viscoelastic properties in the frequency range under investigation (0.01-520 Hz) prove to be indistinguishable from the surface properties of the homopolymer PEO. Transition to the quasi-brush regime is accompanied by rather abrupt changes in both components of the surface viscoelasticity. The surface viscosity in the brush regime exceeds significantly the results calculated from the theory of D. M. A. Buzza et al. (J. Chem. Phys.109, 5008 (1998)), which takes into account the dissipation arising from the flow of solvent through the brush phase. Possible reasons of this discrepancy are discussed.     

Microbial adhesion to poly(ethylene oxide) brushes: influence of polymer chain length and temperature

Glass surfaces were modified by end-grafting poly(ethylene oxide) (PEO) chains having molecular weights of 526, 2000, or 9800 Da. Characterization using water contact angles, ellipsometry, and X-ray photoelectron spectroscopy confirmed the presence of the PEO brushes on the surface with estimated lengths in water of 2.8-, 7.5-, and 23.7-nm, respectively. Adhesion of two bacterial (Staphylococcus epidermidis and Pseudomonas aeruginosa) and two yeast (Candida albicans and Candida tropicalis) strains to these brushes was studied and compared to their adhesion to bare glass. For the bacterium P. aeruginosa and the yeast C. tropicalis, adhesion to the 2.8-nm brush was comparable to their adhesion on bare glass, whereas adhesion to the 7.5- and 23.7-nm brushes was greatly reduced. For S. epidermidis, adhesion was only slightly higher to the 2.8-nm brush than that to the longer brushes. Adhesion of the yeast C. albicans to the PEO brushes was lower than that to glass, but no differences in adhesion were found between the three brush lengths. After passage of an air bubble, nearly all microorganisms adhering to a brush were removed, irrespective of brush length, whereas retention of the adhering organisms on glass was much higher. No significant differences were found in adhesion nor retention between experiments conducted at 20 and those conducted at 37 degrees C.     

Ionic strength-dependent pK shift in the helix-coil transition of grafted poly(L-glutamic acid) layers analyzed by electrokinetic and ellipsometric measurements

Surface-bound layers of poly(L-glutamic acid) prepared by a recently described "grafting-from" method were analyzed with respect to electrical charging and structural alterations upon variation of pH and concentration of the background electrolyte in aqueous solutions. The microslit electrokinetic setup (MES) was utilized for the combined determination of zeta potential and surface conductivity on the basis of streaming potential and streaming current measurements at polypeptide layers in contact with aqueous electrolyte solutions of varied composition. In situ ellipsometry was applied at similar samples immersed in identical aqueous solutions to investigate the influence of the solution pH on the structure of the polypeptide layers. Zeta potential and Dukhin number versus pH plots revealed the dissociation behavior of the surface-bound polypeptides indicating a significant shift of the pK of their acidic side chains correlating with the concentration of the background electrolyte potassium chloride and the related variation of the Debye screening length. Surface conductivity data pointed at a more expanded structure of the polypeptide layer in the fully dissociated state as an increased ion conductance in this part of the interface was determined. The occurrence of a strong increase of the thickness and a corresponding decrease of the refractive index for the coil state of the layer strongly supports the findings of the electrokinetic measurements. This fully reversible "switching" of the layer structure was attributed to helix-coil transitions within the grafted polypeptides induced by the dissociation of carboxylic acid functions of the polypeptide side chains. The shift of the "switching pH" of the surface-bound poly(L-glutamic acid) layers at varied concentrations of the background electrolyte was interpreted as a result of the pK shift of the carboxylic acid groups of the polypeptide side chains. The observed patterns prove that the electrostatic interactions causing this shift occur within but not between the grafted chains.     

Cellular responses to patterned poly(acrylic acid) brushes

We use patterned poly(acrylic acid) (PAA) polymer brushes to explore the effects of surface chemistry and topography on cell-surface interactions. Most past studies of surface topography effects on cell adhesion have focused on patterned feature sizes that are larger than the dimensions of a cell, and PAA brushes have been characterized as cell repellent. Here we report cell adhesion studies for RBL mast cells incubated on PAA brush surfaces patterned with a variety of different feature sizes. We find that when patterned at subcellular dimensions on silicon surfaces, PAA brushes that are 30 or 15 nm thick facilitate cell adhesion. This appears to be mediated by fibronectin, which is secreted by the cells, adsorbing to the brushes and then engaging cell-surface integrins. The result is detectable accumulation of plasma membrane within the brushes, and this involves cytoskeletal remodeling at the cell-surface interface. By decreasing brush thickness, we find that PAA can be 'tuned' to promote cell adhesion with down-modulated membrane accumulation. We exemplify the utility of patterned PAA brush arrays for spatially controlling the activation of cells by modifying brushes with ligands that specifically engage IgE bound to high-affinity receptors on mast cells.     

PH effects in the complex formation and blending of poly(acrylic acid) with poly(ethylene oxide)

The effect of pH on the complex formation between poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) has been studied in aqueous solutions by turbidimetric and fluorescent methods. It was shown that the formation of insoluble interpolymer complexes is observed below a certain critical pH of complexation (pH(crit1)). The formation of hydrophilic interpolymer associates is possible above pH(crit1) and below a certain pH(crit2). The effects of polymer concentrations in solution and PEO molecular weight as well as inorganic salt addition on these critical pH values were studied. The polymeric films based on blends of PAA and PEO were prepared by casting from aqueous solutions with different pHs. These films were characterized by light transmittance measurements and differential scanning calorimetry. The existence of the pH value above which the polymers form an immiscible blend was demonstrated. The transitions between the interpolymer complex, miscible blend, and immiscible blend caused by pH changes are discussed. The recommendations for preparation of homogeneous miscible films based on compositions of poly(carboxylic acids) and various nonionic water-soluble polymers are presented.     

Micellization phenomena of biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and poly(ethylene oxide)

This paper reports the studies on micelle formation of new biodegradable amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer with various PHB and PEO block lengths in aqueous solution. Transmission electron microscopy showed that the micelles took an approximately spherical shape with the surrounding diffuse outer shell formed by hydrophilic PEO blocks. The size distribution of the micelles formed by one triblock copolymer was demonstrated by dynamic light scattering technique. The critical micellization phenomena of the copolymers were extensively studied using the pyrene fluorescence dye absorption technique, and the (0,0) band changes of pyrene excitation spectra were used as a probe for the studies. For the copolymers studied in this report, the critical micelle concentrations ranged from 1.3 x 10(-5) to 1.1 x 10(-3) g/mL. For the same PEO block length of 5000, the critical micelle concentrations decreased with an increase in PHB block length, and the change was more significant in the short PHB range. It was found that the micelle formation of the biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and PEO was relatively temperature-insensitive, which is quite different from their counterparts consisting of poly(alpha-hydroxyalkanoic acid) and PEO.     

Highly ion conductive poly(ethylene oxide)-based solid polymer electrolytes from hydrogen bonding layer-by-layer assembly

We report the development of a solid polymer electrolyte film from hydrogen bonding layer-by-layer (LBL) assembly that outperforms previously reported LBL assembled films and approaches battery integration capability. Films were fabricated by alternating deposition of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) layers from aqueous solutions. Film quality benefits from increasing PEO molecular weight even into the 10(6) range due to the intrinsically low PEO/PAA cross-link density. Assembly is disrupted at pH near the PAA ionization onset, and a potential mechanism for modulating PEO:PAA ratio within assembled films by manipulating pH is discussed. Ionic conductivity of 5 x 10(-5) S/cm is achievable after short exposure to 100% relative humidity (RH) for plasticization. Adding free ions by exposing PEO/ PAA films to lithium salt solutions enhanced conductivity to greater than 10(-5) S/cm at only 52% RH and tentatively greater than 10(-4) S/cm at 100% RH. The excellent stability of PEO/PAA films even when exposed to 1.0 M salt solutions led to an exploration of LBL assembly with added electrolyte present in the adsorption step. Fortuitously, the modulation of PEO/PAA assembly by ionic strength is analogous to that of electrostatic LBL assembly and can be attributed to electrolyte interactions with PEO and PAA. Dry ionic conductivity was enhanced in films assembled in the presence of salt as compared to films that were merely exposed to salt after assembly, implying different morphologies. These results reveal clear directions for the evolution of these promising solid polymer electrolytes into elements appropriate for electrochemical power storage and generation applications.     

Iron hydroxide nanoparticles coated with poly(ethylene glycol)-poly(aspartic acid) block copolymer as novel magnetic resonance contrast agents for in vivo cancer imaging

PEG-coated β-FeOOH nanoparticles were prepared through electrostatic complex formation of iron oxide nanoparticles with poly(ethylene glycol)-poly(aspartic acid) block copolymer [PEG-P(Asp)] in distilled water. By dynamic light scattering (DLS) measurement, the nanopaticle size was determined to be 70 nm with narrow distribution. The FT-IR and zeta potential experimental results proved that PEG-PAsp molecules bound to the surface of the iron oxide nanoparticles via the coordination between the carboxylic acid residues in the PAsp segment of the block copolymer and the surface Fe of the β-FeOOH nanoparticles. The PEG-coated nanoparticles revealed excellent solubility and stability in aqueous solution as well as in physiological saline. In vivo MRI experiments on tumor-bearing mice demonstrated that the PEG-coated nanoparticles prepared by the current approach achieved an appreciable accumulation into solid tumor, suggesting their potential utility as tumor-selective MRI contrast agents.     

Synthesis and pH-sensitive micellization of doubly hydrophilic poly(acrylic acid)-b-poly(ethylene oxide)-b-poly(acrylic acid) triblock copolymer in aqueous solutions

A doubly hydrophilic triblock copolymer poly(acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) with M _w/M _n = 1.15 was synthesized by atom transfer radical polymerization of t-butyl acrylate (tBA), followed by acidolysis of the PtBA blocks. The pH-sensitive micellization of PAA-b-PEO-b-PAA in acidic solution was investigated by potentiometric titration, fluorescence spectrum, dynamic light scattering and zeta potential. The pK _a was 6.6 and 6.0 in deionized water and in 0.1 mol/L NaCl solution, respectively. The copolymer formed micelles composed of a weakly hydrophobic core of complexed PAA and PEO and a hydrophilic PEO shell in 1 mg/mL solution at pH < 5.5 due to hydrogen bonding. The critical micelle concentration was 0.168 mg/mL at pH 2.0. At pH < 4.5, steady and narrow distributed micelles were formed. Increasing pH to 5.0, unsteady and broad distributed micelles were observed. At pH > 5.5, the micelle was destroyed owing to the ionization of the PAA blocks.     

Iron hydroxide nanoparticles coated with poly(ethylene glycol)-poly(aspartic acid) block copolymer as novel magnetic resonance contrast agents for in vivo cancer imaging

PEG-coated β-FeOOH nanoparticles were prepared through electrostatic complex formation of iron oxide nanoparticles with poly(ethylene glycol)-poly(aspartic acid) block copolymer [PEG-P(Asp)] in distilled water. By dynamic light scattering (DLS) measurement, the nanopaticle size was determined to be 70 nm with narrow distribution. The FT-IR and zeta potential experimental results proved that PEG-PAsp molecules bound to the surface of the iron oxide nanoparticles via the coordination between the carboxylic acid residues in the PAsp segment of the block copolymer and the surface Fe of the β-FeOOH nanoparticles. The PEG-coated nanoparticles revealed excellent solubility and stability in aqueous solution as well as in physiological saline. In vivo MRI experiments on tumor-bearing mice demonstrated that the PEG-coated nanoparticles prepared by the current approach achieved an appreciable accumulation into solid tumor, suggesting their potential utility as tumor-selective MRI contrast agents.     

Molecular dynamics simulation study of the structure of poly(ethylene oxide) brushes on nonpolar surfaces in aqueous solution

The structure of poly(ethylene oxide) (PEO, M(w) = 526) brushes of various grafting density (sigma) on nonpolar graphite and hydrophobic (oily) surfaces in aqueous solution has been studied using atomistic molecular dynamics simulations. Additionally, the influence of PEO-surface interactions on the brush structure was investigated by systematically reducing the strength of the (dispersion) attraction between PEO and the surfaces. PEO chains were found to adsorb strongly to the graphite surface due primarily to the relative strength of dispersion interactions between PEO and the atomically dense graphite compared to those between water and graphite. For the oily surface, PEO-surface and water-surface dispersion interactions are much weaker, greatly reducing the energetic driving force for PEO adsorption. This reduction is mediated to some extent by a hydrophobic driving force for PEO adsorption on the oily surface. Reduction in the strength of PEO-surface attraction results in reduced adsorption of PEO for both surfaces, with the effect being much greater for the graphite surface where the strong PEO-surface dispersion interactions dominate. At high grafting density (sigma approximately 1/R(g)(2)), the PEO density profiles exhibited classical brush behavior and were largely independent of the strength of the PEO-surface interaction. With decreasing grafting density (sigma < 1/R(g)(2)), coverage of the surface by PEO requires an increasingly large fraction of PEO segments resulting in a strong dependence of the PEO density profile on the nature of the PEO-surface interaction.     

Glass bead grafting with poly(carboxylic acid) polymers and maleic anhydride copolymers

Glass beads were etched with acids and bases to increase the surface porosity and the number of silanol groups that could be used for grafting materials to the surfaces. The pretreated glass beads were functionalized using 3‐aminopropyltriethoxysilane (APS) coupling agent and then further chemically modified by reacting the carboxyl groups of carboxylic acid polymers with the amino groups of the pregrafted APS. Several carboxylic acid polymers and poly(maleic anhydride) copolymers, such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), poly(styrene‐alt‐maleic anhydride) (PSMA), and poly(ethylene‐alt‐maleic anhydride) (PEMA) were grafted onto the bead surface. The chemical modifications were investigated and characterized by FT‐IR spectroscopy, particle size analysis, and tensiometry for contact angle and porosity changes. The amount of APS and the different polymer grafted on the surface was determined from thermal gravimetric analysis and elemental analysis data. Spectroscopic studies and elemental analysis data showed that carboxylic acid polymers and maleic anhydride copolymers were chemically attached to the glass bead surface. The improved surface properties of surface modified glass beads were determined by measuring water and hexane penetration rates and contact angle. Contact angles increased and porosity decreased as the molecular weights of the polymer increased. The contact angles increased with the hydrophobicity of the attached polymer. The surface morphology was examined by scanning electron microscopy (SEM) and showed an increase in roughness for etched glass beads. Copyright © 2007 John Wiley & Sons, Ltd.     

Complexation of poly(acrylic acid)s with uranyl ion

The complexation of uranyl ion (UO₂²⁺) in aqueous solution with polymers containing carboxylic acid groups was studied potentiometrically. Overall formation constants of the uranyl complexes with poly(methacrylic acid) and crosslinked poly(acrylic acid) were much larger than those with the corresponding low molecular carboxylic acids. Decrease in the viscosity of the polymer solution on adding uranyl ion indicated that poly(acrylic acid) forms intra-polymer chelates with uranyl ion. The crosslinked poly(acrylic acid) adsorbed uranyl ions at higher efficiency than transition metal ions.     

Self-assembly of poly(ethylene oxide)-block-poly(acrylic acid) induced by CaCl2: mechanistic study

The interaction between CaCl 2 and double hydrophilic block copolymer, poly(ethylene oxide) 45- block-poly(acrylic acid) 70, PEO 45- b-PAA 70, was investigated. At a stoichiometric ratio of Ca2+:COO (-) = 0.5, Ca2+ ions were bound to COO (-) groups on PAA segments via electrostatic interaction. Small particles of 4-8 nm in diameter were observed, suggesting the formation of coil-like polymeric globule induced by charge neutralization. At Ca2+:COO (-) >or= 2.5, monodispersed aggregates of average hydrodynamic diameter of 52.0 +/- 7.4 nm were produced. The ISE, ITC, surface tension and fluorescence spectroscopic data confirmed that the formation of these aggregates is not the result of interaction between excess Ca2+ ions and the polymer, but rather it is due to changes in the water activity that triggers the structural rearrangement of Ca2+/PEO 45- b-PAA 70 complex.     

Comparison of the growth and degradation of poly(glycolic acid) and poly(ε‐caprolactone) brushes

The growth and degradation of poly(glycolic acid) (PGA) and poly(ε‐caprolactone) (PCL) brushes were compared. Using tin (octanoate) as the catalyst, optimal conditions were found for growth of each polyester brush from the hydroxy‐terminated silicon surface via ring‐opening polymerization. PCL brushes grew thicker at elevated temperatures but the thickest PGA brushes grew at room temperature. Unlike bulk polyesters that can degrade under both acidic and basic conditions, the confined surface polyester brushes only degraded under neutral or basic conditions. The degradation mechanism of grafted polyester brushes was probed through a blocking test. It was shown that the terminal hydroxy groups of these polyester brushes were essential to the degradation process indicating a preferential backbiting mechanism. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4643–4649     

Protein interaction with a Pluronic-modified poly(lactic acid) Langmuir monolayer

Interaction of bovine serum albumin (BSA) with poly(lactic acid) (PLA) layers mixed with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers (Pluronic) at air/solution interfaces was studied by the Langmuir balance technique. Wettability of the mixed PLA-Pluronic system was characterized in the form of a transferred one-layer Langmuir-Blodgett film, and considerable hydrophilization was obtained for all of the Pluronics (6400, 6800, 10500, and 12700) applied here. The density of PEO chains in the monolayer and hence the coverage of PLA was controlled by the composition and the compression of the mixed monolayers. Tensiometric investigations revealed that a significant reduction of BSA adsorption/penetration was achieved by applying the Pluronic 6800 and 12700 with long PEO blocks for hydrophilization of PLA. Interaction of BSA with the modified PLA monolayer depended on the density and length of the PEO chains. The surface morphological characteristics of the films determined by atomic force microscopy were in good correlation with the results of BSA interaction. The average roughness of the polymer LB layer was high due to BSA penetration into the PLA film, while smooth surfaces with small roughness were obtained when the PLA layer was modified by Pluronic 6800.     

XPS and wettability characterization of modified poly(lactic acid) and poly(lactic/glycolic acid) films

Poly(lactic acid) (PLA) and poly(lactic/glycolic acid) copolymers (PLGA) are biodegradable drug carriers of great importance, although successful pharmaceutical application requires adjustment of the surface properties of the polymeric drug delivery system to be compatible with the biological environment. For that reason, reduction of the original hydrophobicity of the PLA or PLGA surfaces was performed by applying a hydrophilic polymer poly(ethylene oxide) (PEO) with the aim to improve biocompatibility of the original polymer. PEO-containing surfaces were prepared by incorporation of block copolymeric surfactants, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic), into the hydrophobic surface. Films of polymer blends from PLA or PLGA (with lactic/glycolic acid ratios of 75/25 and 50/50) and from Pluronics (PE6800, PE6400, and PE6100) were obtained by the solvent casting method, applying the Pluronics at different concentrations between 1 and 9.1% w/w. Wettability was measured to monitor the change in surface hydrophobicity, while X-ray photoelectron spectroscopy (XPS) was applied to determine the composition and chemical structure of the polymer surface and its change with surface modification. Substantial reduction of surface hydrophobicity was achieved on both the PLA homopolymer and the PLGA copolymers by applying the Pluronics at various concentrations. In accordance with the wettability changes the accumulation of Pluronics in the surface layer was greatly affected by the initial hydrophobicity of the polymer, namely, by the lactide content of the copolymer. The extent of surface modification was also found to be dependent on the type of blended Pluronics. Surface activity of the modifying Pluronic component was interpreted by using the solubility parameters.