Neutral Copolymer Research Articles

Photo-reversible and selective Cu2+ complexation of a spiropyran-carrying sulfobetaine copolymer in saline solution

A sulfobetaine copolymer (1) carrying a photochromic spiropyran residue was synthesized, which reversibly isomerized between the closed and open forms in pure water and in saline by irradiation with visible light. The thermodynamic stability of the open form of the spiropyran methacrylate (SPMA) units of compound 1 was reduced upon increasing NaCl concentration. In addition, photo-reversible and selective Cu2+ complexation in saline solution ([NaCl] = 1.0 wt%) was achieved using compound 1 with metal ions (Cu2+, Zn2+, Ni2+, or Co2+). Covalently cross-linked compound 1 showed selective Cu2+ adsorption in pure water. In contrast, the other metal ions were increasingly adsorbed as NaCl concentration increased, resulting in lower selectivity of Cu2+ ion adsorption with 1, e.g., the ratios of adsorption of Cu2+, Zn2+, Ni2+, and Co2+ with 1 in 10 wt% saline were 73, 20, 10, and 3%, respectively, while only Cu2+ adsorption was observed in a solution of 1.0 wt% NaCl. Because the stability of the open form of the SPMA units and the metal complexation of 1 were influenced by NaCl concentration, the electrostatically cross-linked networks of the zwitterionic sulfobetaine units of 1 may be loosened by NaCl addition, resulting in easy entry of metal ions into the network. The order of metal complexation among the four metals corresponded to the Irving–Williams series. Hydrogen-bonded networks of water molecules also may contribute to the relatively ineffective selective adsorption of Cu2+ ions by 1 compared to the electrically neutral spiropyran-carrying copolymer of N-isopropylacrylamide, 2.

Morphological control on SBA-15 mesoporous silicas via a slow self-assembling rate

Pluronic 123-templated mesoporous SBA-15 silica rods with a length of ca. 3.0–4.0 μm were easily synthesized in a dilute silicate solution with a pH value of 2.0 at room temperature. Through a good control on the synthetic condition and the chemical components, a high homogeneity (>95%) of the hexagonal SBA-15 silica rods can be achieved. In addition, the effect of the synthetic conditions including acid source, weight ratio of the P123/sodium silicate, temperature, water content, pH value, and applying shearing flow were explored in detail to tailor the morphologies of the SBA-15 mesoporous silicas. In this paper, we also focused on the counterion effect on the synthesis of the SBA-15 mesoporous silicas. It was found that the SO4 2− counterion from H2SO4 has higher affinity to induce the formation of P123 rod-like micelles than that of Cl−, NO3 −. Meanwhile, we postulated that the self-assembly pathway of the silica species and the neutral tri-block copolymer micelles in a dilute solution with a pH value of 2.0 would occur through an S0···I0 rather than the S0X−…I+ one as previously discussed. We further employed the SAB-15 mesoporous silica rods as the templates to synthesize high-quality CMK-3 mesoporous carbon rods by using commercially available phenol–formaldehyde (PF) resin as the carbon source.

Temperature-Induced Swelling and Small Molecule Release with Hydrogen-Bonded Multilayers of Block Copolymer Micelles

We report on reversible temperature-triggered swelling transitions in hydrogen-bonded multilayer films of a polycarboxylic acid and stimuli-responsive block copolymer micelles (BCMs). A neutral hydrogen-bonding temperature-responsive diblock copolymer, poly(N-vinylpyrrolidone)-b-poly(N-isopropylacrylamide) (PVPON-b-PNIPAM), was synthesized by macromolecular design via the interchange of xanthates (MADIX). The block copolymer exhibited reversible micellization, forming PNIPAM-core micelles with PVPON coronae in 0.01 M buffer solutions at temperatures higher than 34 degrees C, or in solutions with high salt concentrations (C(NaCl) > 0.4 M) at 20 degrees C. The PVPON-b-PNIPAM BCMs were then assembled with poly(methacrylic acid) (PMAA) at acidic pH and higher temperature using the layer-by-layer (LbL) technique. Within the hydrogen-bonded multilayer, BCMs were stabilized through hydrogen bonding between PVPON and PMAA units and, unlike in solution, did not dissociate into unimers in low-salt solution at T < 34 degrees C. Instead, PVPON-b-PNIPAM BCMs reversibly swelled within film in response to temperature- or salt-concentration variations, reflecting collapse and dissolution of the BCM PNIPAM cores. The capacity of BCM/PMAA films to retain hydrophobic molecules was also dramatically dependent on temperature and/or ionic strength. The characteristic release time of pyrene from a [BCM/PMAA](10) film decreased from 80 to 10 min upon a decrease in temperature from 37 to 20 degrees C. In addition, at 20 degrees C, ionic strength was also capable of controlling the collapse of PNIPAM micellar cores and the subsequent film swelling and pyrene release rate. Incorporation of stimuli-responsive BCM micelles within LbL films opens new opportunities in designing nanoscale films capable of controlling molecular swelling, transport, and diffusion in response to environmental stimuli.

“Study of the effect of association between anionic surfactant and neutral copolymer on the corrosion behaviour of carbon steel in cyclohexane propionic acid”

The conductivity, weight loss and A.C. impedance studies were carried out to establish the influence the presence of neutral copolymer (Vinyl pyrrodlidone/Vinyl acetate copolymer) with anionic surfactant (Disodium laurethsulfosuccinate) in cyclohexane propionic acid (CHPA) on the corrosion behaviour of carbon steel. The protection efficiency ( P%) of AS in the absence and presence of polymer increases with increase in AS concentration until it reaches a maximum constant value near the CMC of AS and decreases with increase in solution temperature. The protective efficiency of AS can be enhanced and its critical micelle concentration shifts to low value by adding of 0.05 g/l of polymer. The critical micelle concentration of AS in the absence and presence of polymer increases with increase in temperature. The calculated thermodynamic parameters of micellization (Δ G mic), (Δ H mic) and (Δ S mic) in the presence of neutral copolymer molecules with AS show that these processes are spontaneous and exothermic in nature and indicate the association between AS and neutral copolymer molecules.

Protein adsorption and cell adhesion on cationic, neutral, and anionic 2-methacryloyloxyethyl phosphorylcholine copolymer surfaces

Protein adsorption and cell adhesion on cationic, neutral, and anionic water-soluble 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer surfaces were compared. These model MPC copolymers coated SiO 2 surfaces exhibited comparable surface ζ-potentials of 26.1 mV, near 0 mV, and −24.2 mV, respectively. X-ray photoelectron spectroscopy analyses indicated the similarities and the differences in the surface composition between the sample surfaces. Atomic force microscopy analyses revealed that the type of the charged moiety did not affect the surface roughness. Static contact angle measurements and dynamic contact angle analyses not only indicated that the surfaces were very hydrophilic in general, but also provided information on the surface mobility and the dominant role of MPC at the surface in aqueous conditions. Comparing with the SiO 2 substrates on which protein seriously adsorbed and cell heavily adhered, three MPC copolymers coated surfaces, despite their different charge properties, exhibited significantly low adsorbed amounts of different proteins having various electrical natures and totally no cell adhesion. This suggested that the incorporation of charged moieties in the MPC copolymers did not significantly inspire both the protein adsorption and cell adhesion. The MPC moieties were predominant at the surface when in contact with aqueous conditions and thereby dominated the bio-adsorptions, while the possible effect from electrostatic interactions would be too small and too limited to influence the overall situation. Therefore, these MPC copolymer surfaces can satisfy those biological applications requiring not only electrical but also non-biofouling properties.

Unprecedented microemulsion boosting effect induced by a charged diblock copolymer: bending modulus and curvature frustration of the surfactant film

Single-phase microemulsions made of comparable amounts of water and alkane cannot be stabilized unless a large proportion of surfactant is used. Typically 10 to 30% nonionic surfactants such as n-alkylpolyglycol ethers are required to form such phases. Over the past 15 years, several authors have shown that this proportion can be significantly reduced by adding minute amounts of neutral diblock copolymers. However, though the surfactant film elastic properties seem to play a role in this so-called efficiency boosting effect, there is no clear agreement about the influence of the copolymer on bending properties, and about the correlation between those properties and the boosting effect. We present in this paper an original experimental occurrence of the boosting effect by using charged diblock copolymers. Based on a combination of various experimental techniques, an unprecedented swelling is evidenced and discussed in terms of variations of bending modulus. In particular an expression of the microemulsion free energy density proposed by Andelman et al. is used to correlate successfully the surfactant film bending modulus to the boosting. A curvature “frustration” between surfactant and copolymer is also pointed out as a possible contribution to the boosting effect.

Tuning swelling pH and permeability of hydrogel multilayer capsules.

We report on tuning swelling pH transitions of hydrogel hollow capsules that were derived from hydrogen-bonded multilayers via chemical cross-linking. The capsules were either of a single component - a weak poly(carboxylic acid), such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(ethacrylic acid) (PEAA) - or contained two hydrogen-bonding polymers, such as in poly(carboxylic acid)/poly(N-vinylpyrrolidone-co-NH2) (PVPON-co-NH2) or in poly(carboxylic acid)/poly(N-vinylcaprolactam-co-NH2) (PVCL-co-NH2) systems. By varying the acidity of weak polyelectrolytes, the capsule swelling can be tuned over a wide pH range from 5 to 10. We show that differently from one-component capsules, the swelling amplitude of two-component capsules is limited by the number of cross-links provided by amino-containing units of a PVCL-co-NH2 copolymer. For two-component capsules with the same degree of cross-linking, permeability at the minimum swelling pH was decreased for PMAA-neutral copolymer capsules as compared to those of PAA-neutral copolymer. We also demonstrate that swelling pH of one-component capsules in the acidic region can be modulated via reversible association with a polycation. The fine control over the swelling pH transitions and permeability of hydrogel capsules enables their use in biomedical applications.

The electronic and optical properties of oligo(trans‐1,2‐di(2‐thienyl)‐1,3‐butadiene): A theoretical study

AbstractIn the present work we investigated the theoretical electronic structure of poly(trans‐1,4‐di(2‐thienyl)‐1,3‐butadiene) (PTB) and determined the optical properties of its neutral and doped oligomers. Geometrical optimizations were at the semiempirical level by using the Austin method 1 (AM1). The band structure of π electrons regarding to the neutral PTB polymer was obtained by using a tight‐binding Hamiltonian. The densities of electronic states (DOS) for neutral and doped copolymers were calculated by using the negative factor counting technique. The spatial charge distribution of the oligomeric chain was also analyzed. The energy of the electronic transitions and their associated oscillator strength values were calculated for the neutral, double, and single charged oligomers to determine the UV–vis absorption spectra. The calculations were performed using the intermediate neglect of differential overlap Hamiltonian in combination with the single configuration‐interaction technique in order to include correlation effects. The band gap obtained in the PTB was about 2.101 eV for the optics absorption and 1.73 eV for the DOS. The bipolaron states appear in the gap, about 0.57 eV and 0.48 eV below and above the conduction and valence bands, respectively. When the dopants concentration is increased the DOS showed that the energy gap tends to vanish, which may lead to semiconductor–metal transition. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Conformational Behavior of Comb-like Polyelectrolytes in Selective Solvent: Computer Simulation Study

In this work, we present molecular dynamics simulations of comb-like polyelectrolytes in selective solvent. The studied polymers have a neutral backbone and polyelectrolyte side chains. The solvent is poor for the backbone and the theta solvent for the side chains. The polymers are modeled on a coarse-grained level with implicit solvent. The simulations show that the comb-like polyelectrolytes tend to form intramolecular self-organized structures of the pearl necklace type. This type of conformational behavior has been predicted by Borisov and Zhulina (Borisov, O. V.; Zhulina, E. B. Macromolecules 2005, 38, 2506) for neutral comb-like copolymers in selective solvent. The present study shows that comb-like polyelectrolytes in selective solvent exhibit the same type of behavior; however, it can be controlled by one additional parameter, the degree of dissociation of the grafts. The local conformational characteristics are studied using the ensemble-averaged bond angle cosines as functions of monomer position in the chain, which reveal structural details invisible by other means.

Stoichiometry of Electrostatic Complexes Determined by Light Scattering

We report on the electrostatic complexation between oppositely charged polymers and inorganic nanoparticles investigated by static and dynamical light scattering. The nanoparticles put under scrutiny were citrate-coated nanocrystals of cerium oxide (CeO2, nanoceria), of iron oxide (γ-Fe2O3, maghemite), and of europium-doped yttrium vanadate (Eu:YVO4) with sizes in the 10 nm range. For the polymers, we have used cationic−neutral diblock copolymers (poly(trimethylammonium ethylacrylate)-b-poly(acrylamide), hereafter referred to as PTEA-b-PAM) with different molecular weights. For the three colloidal dispersions, we show that the electrostatic complexation gives rise to the formation of stable nanoparticle clusters in the 100 nm range. The complexation was monitored by systematic measurements of the scattering intensity vs X, the mixing ratio between nanoparticles and polymers. For five nanoparticle/polymer pairs, namely CeO2/PTEA5K-b-PAM30K, γ-Fe2O3/PTEA5K-b-PAM30K, γ-Fe2O3/PTEA11K-b-PAM30K, Eu:YVO4/PTEA2K-...

On the Stability of (Highly Aggregated) Polyelectrolyte Complexes Containing a Charged-block-Neutral Diblock Copolymer

Using light scattering and cryogenic transmission electron microscopy, we show that highly aggregated polyelectrolyte complexes (HAPECs) composed of poly([4-(2-aminoethylthio)butylene] hydrochloride)49-block-poly(ethylene oxide)212 and poly(acrylic acid) (PAA) of varying lengths (140, 160, and 2000 monomeric units) are metastable or unstable if the method of preparation is direct mixing of two solutions containing the oppositely charged components. The stability of the resulting HAPECs decreases with decreasing neutral-block content and with increasing deviation from 1:1 mixing (expressed in number of chargeable groups) of the oppositely charged polyelectrolytes, most probably for electrostatic reasons. The difference between the metastable and stable states, obtained with pH titrations, increases with increasing PAA length and increasing pH mismatch between the two solutions with the oppositely charged components.

Ordered phases of diblock copolymers in selective solvent

The authors propose a mean-field model to explore the equilibrium coupling between micelle aggregation and lattice choice in neutral copolymer and selective solvent mixtures. They find both thermotropic and lyotropic transitions from face-centered cubic to body-centered cubic ordered phases of spherical micelles, in agreement with experimental observations of these systems over a broad range of conditions. The stability of the nonclosed packed phase can be attributed to two physical mechanisms: the large entropy of lattice phonons near crystal melting and the preference of the intermicelle repulsions for the body-centered cubic structure when the lattice becomes sufficiently dense at higher solution concentrations. Both mechanisms are controlled by the decrease of micelle aggregation and subsequent increase of lattice density as solvent selectivity is reduced. These results shed new light on the relationship between micelle structure--"crewcut" or "hairy"--and long-range order in micelle solutions.

Hierarchical Self‐Assembly in Solutions Containing Metal Ions, Ligand, and Diblock Copolymer

Cores for thought: The combination of reversible self-assembly (polymerization through weak coordination) and micellization driven by electrostatic interactions has resulted in hierarchical self-assembly of a mixture of metal ions (green circles), bisligands, and a cationic–neutral diblock copolymer. This approach results in the formation of well-defined, stable, and equilibrated core–shell nanostructures (see picture, Rh=hydrodynamic radius).

Generalized Coating Route to Silica and Titania Films with Orthogonally Tilted Cylindrical Nanopore Arrays

We describe a simple, inexpensive coating method to produce thin silica and titania films with surfactant templated, orthogonally tilted cylindrical nanopore arrays. These films can be deposited onto any substrate because orientation of the 2D hexagonally close packed (HCP) mesophases out of the plane of the film is directed by a chemically neutral sacrificial copolymer layer. Orientation of the HCP mesophases through the entire thickness of films cured in open air is achieved by limiting the coating thickness. This generalizes the coating method by making it possible to deposit oriented films on substrates of any curvature and size. We find a critical thickness between 70 and 100 nm, below which the triblock copolymer surfactant-templated HCP phase aligns completely out of the plane of glass and silicon wafer substrates. Above this thickness, the effect of the chemically neutral bottom layer does not propagate across the entire film, and alignment of the HCP mesophases parallel to the (nonpolar) air interface produces a mixed orientation.

Synthesis and Characterization of Antibacterial and Temperature Responsive Methacrylamide Polymers

A new methacrylamide monomer (MAMP) containing a pyridine moiety was synthesized by reacting methacrylic anhydride and 3-(aminomethyl) pyridine. The monomer was homopolymerized in 1,4-dioxane and copolymerized with N-isopropyl acrylamide in DMF at two different compositions using AIBN as an initiator. The pyridine groups of the homopolymer and copolymers were reacted with various bromoalkanes containing 12, 14, and 16 carbon alkyl chains to obtain the polymers with pendant pyridinium groups. The monomer and polymers were characterized by elemental analysis, NMR, FTIR, SEC, TGA, and DSC. The neutral and quaternized copolymers with low MAMP content were water-soluble and showed temperature-responsive behavior in aqueous solutions. The lower critical solution temperatures (LCSTs) of these polymers varied between the temperatures of 25 and 42 °C. The LCST of quaternized copolymers were higher than that of the neutral copolymer because they were more hydrophilic. The LCST of the quaternized copolymers decreased with an increase in the alkyl chain length on the pyridinium group because the copolymers became more hydrophobic this way. The antibacterial activities of water-soluble copolymers were investigated against Staphylococcus aureus and Escherichia coli using the broth dilution and spread plate methods, whereas the water-insoluble polymers were tested for the antibacterial activity against the same types of bacteria using the shaking flask method. The quaternized water-soluble copolymers showed excellent antibacterial activities against both types of bacteria, whereas the neutral polymers and quaternized water-insoluble homopolymers and copolymers were not active.

Compressive Elastic Moduli of Poly(N‐Isopropylacrylamide) Hydrogels Crosslinked with Poly(Dimethyl Siloxane)

Hydrophobically modified and thermally reversible neutral and ionic copolymer hydrogels were prepared from N‐isopropylacrylamide (NIPAAm), vinyl terminated poly (dimethylsiloxane) (VTPDMS) and itaconic acid (IA) by free radical solution polymerization, and their properties such as swelling ratio and compression modulus were studied at the 25°C. The incorporation of VTPDMS as a hydrophobic macrocrosslinker into the structures of neutral NIPAAm hydrogels increased their mechanical strength around 10 times than those of the ones crosslinked with conventional tetra functional monomer, i.e., N,N′‐methylene bisacrylamide (BIS). Compression modulus decreased with an increase in IA content for ionic samples and increased with increasing molecular weight and content of VTPDMS for neutral samples. It was assumed that in the first case, electrostatic repulsive forces resulting from the ionized carboxyl groups of IA were responsible for decreasing mechanical strength, while in the second case, hydrophobic interactions between dimethylsiloxane units of VTPDMS chains enhanced the compression moduli. According to the results presented in this work, it can be said that the right balance of hydrophobic and hydrophilic constituents and adjustment of the number of ionized groups, as well as crosslinking degree, change the structure and physical properties of NIPPAAm hydrogels.

Synthesis and studies of semiconducting piperazine–aniline copolymer

Synthesis of piperazine–aniline copolymer has been studied by using various acids. The copolymer was characterized by spectral and physical techniques such as UV–Visible, FT-IR, fluorescence, viscosity, density and SEM studies. Conductivity of the copolymer was tested with various counter ions. The copolymer was found to have significant conductivity in the region of semiconductors. Morphological study reveals that the neutral copolymer forms into spongy and porous structure. Conductivity, density and viscosity are very much influenced by the nature of counter ions.

Mesopore size dependence of the ionic diffusivity in alumina based composite lithium ionic conductors

Ordered-mesoporous Al 2O 3 was synthesized by a sol–gel method using neutral copolymer surfactants as structure-directing agents. The pore size was controlled over the 3–15 nm range by the use of various surfactants. Composites composed of the synthesized mesoporous Al 2O 3 and a lithium ion conductor (LiI) were prepared. The maximum dc electrical conductivity, 2.6 × 10 − 4 S cm − 1 at 298 K, was observed for 50 LiI·50 Al 2O 3 composite with 4.2 nm average mesopore size, which was considerably higher than the previously reported LiI-alumina composites. A systematic dependence of conductivity upon pore size was observed, in which conductivity increased with decreasing pore size, except for samples with a pore size of 2.8 nm. The lithium ion diffusion coefficient determined by the 7Li pulsed field gradient nuclear magnetic resonance (PFG-NMR) showed excellent agreement with the measured conductivity calculated by the Nernst-Einstein equation. On the other hand, lithium migration activation energies obtained by quasielastic neutron scattering (QENS) and 7Li NMR spin-lattice relaxation time ( T 1) were considerably smaller than those obtained from electrical conductivity and PFG-NMR. This could be explained by the ion migration mechanism in heterogeneous composites and a possible enhancement of conductivity in mesoscopically confined spaces.

Physical Properties of Aqueous Solutions of a Thermo-Responsive Neutral Copolymer and an Anionic Surfactant: Turbidity and Small-Angle Neutron Scattering Studies

Aqueous mixtures of the anionic sodium dodecyl sulfate (SDS) surfactant and thermo-responsive poly(N-vinylcaprolactam) chains grafted with omega-methoxy poly(ethylene oxide) undecyl alpha-methacrylate (PVCL-g-C11EO42) have been characterized using turbidimetry and small-angle neutron scattering (SANS). Turbidity measurements show that the addition of SDS to a dilute aqueous copolymer solution (1.0 wt %) induces an increase of the cloud point (CP) value and a decrease of the turbidity at high temperatures. In parallel, SANS results show a decrease of both the average distance between chains and the global size of the objects in solution at high temperatures as the SDS concentration is increased. Combination of these findings reveals that the presence of SDS in the PVCL-g-C11EO42 solutions (1.0 wt %) promotes the formation of smaller aggregates and, consequently, leads to a more homogeneous distribution of the chains in solution upon heating of the mixtures. Moreover, the SANS data results show that the internal structure of the formed aggregates becomes more swollen as the SDS concentration increases. On the other hand, the addition of moderate amounts of SDS (up to 4 mm) to a semidilute copolymer solution (5.0 wt %) gives rise to a more pronounced aggregation as the temperature rises; turbidity and SANS studies reveal in this case a decrease of the CP value and an increase of the scattered intensity at low q. The overall picture that emerges from this study is that the degree of aggregation can be accurately tuned by varying parameters such as the temperature, level of surfactant addition, and polymer concentration.

Diblock Copolymer Micelles in a Dilute Solution

We performed theoretical and experimental investigations of dilute solutions of micelles of neutral amorphous diblock copolymers in selective solvents. The ranges of thermodynamic stability of spherical, cylindrical, and lamellar morphologies along with the equilibrium sizes and aggregation numbers of micelles are calculated and measured. For high molecular weight copolymers it is shown that the sphere-to-cylinder transition as well as precipitation of the micelles associated with cylinder-to-lamella transition occurs when aggregates have a crew-cut structure with the thickness of the corona smaller than the radius of the core. Similar to starlike micelles with corona larger than the core, the equilibrium parameters of crew-cut micelles are determined by the balance between the free energy of the corona and the surface energy of the core. The elastic free energy of the core remains small compared to the corona and surface free energies; however, it determines the transitions between different morphologies...