Thermosensitivity of optically active hydrogels constructed with N-(L)-(1-hydroxymethyl)propylmethacrylamide

We previously reported on the water soluble, optically active polymer, poly[N-(L)-(1-hydroxymethyl)propylmethacrylamide] (P(L-HMPMA)), which has lower critical solution temperatures of approximately 30 and 21 degrees C upon heating and cooling, respectively. The phase separation behavior of the P(L-HMPMA)-water binary system has a reversible and clear hysteresis during heating and cooling cycles. The present study describes the thermosensitive properties of the optically active polymer and its hydrogel. Circular dichroism and microcalorimetric measurements of the polymer in water supported the hypothesis that the soluble polymer chains might be compactly folded with an interaction between optically active side chains. In addition, these measurements showed the polymer chains in a state of relatively low hydration compared to that of P(D,L-HMPMA), which was free-radically synthesized from racemates of monomers. The solution properties reflected the swollen-shrunken behavior of corresponding hydrogels in response to temperature changes. The microscopic observation of aqueous polymer solutions and hydrogels also confirmed that the optically active properties of polymer chains affect their structure and thermosensitivity. SEM micrograph of the surfaces of the crosslinked P(L-HMPMA).     

Effects of crosslinker density on the polymer network structure in poly‐N,N‐dimethylacrylamide hydrogels

To investigate the effects of crosslinker density on the properties of hydrogels, compression tests, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Raman measurements were performed on poly‐N,N‐dimethylacrylamide hydrogels. The results of the compression tests showed that the Young's modulus increases as the crosslinker density increases. To understand the mechanism of the change in the mechanical properties, the structures of the polymer networks and water and the molecular vibrations were analyzed using SEM, DSC, and Raman methods. From the SEM images, it was found that the porosity estimated from the mesh size and cell density increases with increasing crosslinker density. In addition, the DSC and Raman results show that the thickness of the bound water increases as the porosity increases, although the density of the polymer chains in the porous wall remains nearly constant. The increase in the number density of polymer chains can be one of the mechanisms contributing to the increase in the mechanical strength of the hydrogels at lower crosslinker density below 5 mol %, as proposed by previous studies. At higher crosslinker density, however, the number density of polymer chains does not increase with increasing crosslinker density. The present results suggest that the bound water plays an important role in strengthening the hydrogel. The water structure may be one of the dominant factors governing the chemical and physical properties of hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1017–1027     

Solution of telechelic ionomers in water/AOT/oil (w/o) microemulsions: a static and dynamic light scattering study

Static and quasielastic light-scattering measurements of endsulfonated polyisoprene in a water in oil (w/o) microemulsions were used to characterize the structure and diffusion properties of this complex system. The hydrophilic end groups of the polymer stick to the surfactant covered oil/water interface, thus bridging the water droplets. This structure formation decreases the mobility of the aqueous nanodroplets and polymer molecules. At interdroplet distances larger than the end-to-end distance of the ionomer chain a decrease of the osmotic modulus is observed. It can be explained by a depletion force of free ionomer chains acting on the nanodroplets. With increasing polymer concentration structure formation of the microemulsion is observed at nanodroplet concentrations where the ionomer chains just fit the average separation of two nanodroplets.     

Spectroscopic studies of polymerized surfactants: 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine

Spectroscopic studies have been performed on aqueous dispersions of the surfactant 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine before and after polymerization with ul-traviolet light. Monomers of this lipid can, under certain conditions, convert from the expected spherical liposomal form to a unique phase consisting of hollow tubules. To determine the molecular conformation of these structures we have used Raman and infrared spectroscopies to probe the structure of the hydrocarbon chains and head groups of the lipids, and used absorption spectroscopy and resonance enhanced Raman scattering of the colored polymer to monitor the length and structure of the diacetylenic polymer backbone. Unusual C? H stretch-ing Raman bands imply that the hydrocarbon chain packing in the monomeric bilayers is different from that observed in other phosphatidylcholines, and that a distrubance in alkyl chain packing occurs on polymerization. Depending on irradiation conditions and the dispersal state of the lipid the polymer chains may be of at least three different colors, from which distinct resonance Raman spectra are obtained. The effective bond conjugation lengths range from quite short in the yellow polymer produced in sonicated vesicles to extremely long in a blue component seen in polymerized tubules.     

Spectroscopic characterization of polyaniline formed by using copper(II) in homogeneous and MCM-41 molecular sieve media

This work emphasizes the important role of the synthetic parameters in the structure of the polymeric material obtained in the aniline polymerization. The polymers formed by the oxidative polymerization of aniline by copper(II) ions in acidic aqueous solution, acetonitrile/water medium, and also copper(II) acetate complex encapsulated into MCM-41 molecular sieve were characterized by resonance Raman spectroscopy using three exciting laser lines and other techniques such as UV-vis, FTIR, and XANES (Nitrogen K edge). Additionally the products were investigated by thermogravimetric analysis and powder X-ray diffraction. When Cu(II) ions in acidic aqueous medium are used, emeraldine salt (ES-PANI) is formed through the usual head-to-tail polymerization mechanism, while in acetonitrile/water medium a polymer is observed having mainly phenazine-like rings, quinonediimine, and/or phenylenediamine segments in the chains, suggesting that a distinct mechanism is operating. The average molecular weights of the free polymers synthesized in water and in acetronile/water were, respectively, ca. 37 300 and 16 900 Da. The encapsulated polymer synthesized in Cu(II)-MCM-41 is a polymeric mixture of (i) ES-PANI and (ii) the polymer obtained when this metal cation was used as oxidant in acetonitrile/water medium. All the characterization data were compared to those ones obtained for standard free polyaniline and also for the encapsulated polymer into mesoporous MCM-41 formed by using persulfate in acidic aqueous medium as oxidant.     

SEM Morphologies of a Water-Soluble Terpolymer with Vinyl Biphenyl in Aqueous and Brine Solutions

A terpolymer PAAP, synthesized from acrylamide (AM), vinyl biphenyl (VP), and sodium 2-acrylamido-2-methylpropane sulfonate (NaAMPS), exhibits intermolecular hydrophobically associating behavior in water and aqueous brine solutions. A scanning electron microscope (SEM) was used to observe the conformations of polymer chains and morphologies of their associating microstructures in pure water and in brine solutions. This was done to reveal the relevant relationships between solution properties and associated microstructures for the PAAP polymer in pure water and brine solutions, and the mechanisms for the previously reported viscoelastic behavior of PAAP solutions. Continuous supermolecular associating network structures are formed via strong intermolecular hydrophobic association of biphenyl groups in an aqueous 0.1 g⋅dL⁻¹ PAAP solution, which leads to the excellent viscoelastic character of aqueous PAAP solutions. With increasing polymer concentration, the network structures of the polymer become much larger and more compact in aqueous solution, which results in the excellent thickening properties of their solutions. The SEM results reveal that the elongated conformations of molecular chains in aqueous PAAP solutions are favorable for intermolecular hydrophobic association. With the addition of NaCl, the associating network structures of PAAP are destroyed because of electrostatic shielding effects on the –SO₃^-\mathrm{SO}_{3}^{-} groups, and huge tree-like associated structures are formed. This results in a decrease in the solution viscosity and a loss of viscoelastic properties of PAAP solutions. However, with increasing NaCl concentration, the number and size of the aggregates increase, which results in the salt-thickening behavior of PAAP brine solutions.     

The influence of short strong hydrogen bonding on the structure and the physicochemical properties of alkyl-N-iminodiacetic acids in solid state and aqueous systems

Alkyl-N-iminodiacetic acids with varying alkyl chain lengths have been prepared and characterized with respect to structure, acidic properties, and ability to form aggregates in water. The alkyl-N-iminodiacetic acids are the group of ligands with the lowest molecule weight which can be characterized as chelating surfactants, compounds with surface chemical properties which at the same time have a high ability to bind metal ions. The solid alkyl-N-iminodiacetic acids have a unique structure with neutral zwitterionic units linked together to polymer chains through a short strong hydrogen bond, d(O(-H)...O) approximately 2.46 A, and where the nu(O-H) stretching vibration at ca. 720 cm(-1) supports the presence of such a hydrogen bond. The polymer chains are cross-linked together to bilayers through relatively strong hydrogen bonds between ammonium and carboxylate groups, and where the parallel alkyl groups are interdigitating each other; the bilayer surface consists of hydrophilic iminodiacetic acid groups. The acidic properties of monomeric alkyl-N-iminodiacetic acids in water are in the expected ranges with pK(a) values of about 1.7, 2.3, and 10.3. n-Octadecyl-N-iminodiacetic acid, present as aggregates in water, displays very acidic properties of the first proton, and a substantially weakened acidity of the second proton, pK(a2) = 5.5-7.5, depending on ionic strength, and pK(a3) = 9.5-10.5. This pattern of the acidic constants strongly indicates that the polymer structure with short strong hydrogen bonds is maintained in the aggregates and that such bonds can exist in aqueous systems if they are supported by a strong and rigid backbone structure, as the bilayers of well-organized long interdigitating alkyl chains in the studied systems. Hydrogenbis(methyl-N-iminodiacetic acid) perchlorate precipitates from perchloric acidic solutions of methyl-N-iminodiacetic acid. The structure is built up of dimers of zwitterionic methyl-N-iminodiacetic acid units linked together by an extra proton in a short strong hydrogen bond, d(O(-H)...O) approximately 2.456(6) A, and nu(O-H) = 789 cm(-1).     

Linear nano-templates of styrene and maleic anhydride alternating copolymers

Poly(styrene-alt-maleic anhydride) (SMA) self-assembles in aqueous solution to form nanotube structures. These can be used as templates to linearly guide the growth of a secondary polymeric or inorganic material. Templates are made starting from a basic SMA solution, followed by slow pH decrease by dialysis against deionized water, until a 50% degree of protonation is reached. The nanotube structure is composed of multiple polymer chains, associating sideways by π-stacking to form the nanotube walls. The SMA templates were used to grow linear composites, which shows the applicability of the template properties and also confirms the nanotube association mechanism. Linear polymer composites were formed using this SMA template: pyrrole was polymerized, silver nitrate was reduced to silver and silver cyanide nanowires were grown.     

Mixed solvent effect on lithium-coordination to poly(ethylene oxide)

This article presents a comparative study of the structure formation of poly (ethylene oxide) PEO/Li complexes in aqueous and acetonitrile solutions using small-angle neutron scattering (SANS). We demonstrate that in acetonitrile solutions, Li-cations coordinate to the ether–oxygen of the monomeric unit, and this results in charging and stretching of the polymer chains. This is found to be in contrast to aqueous solutions, where the ions remain free in solution. In particular, we demonstrate that the “binding” and “screening” regimes that were observed in case of PEO/K⁺ solutions in acetonitrile are also found in the respective PEO/Li⁺ solutions. The addition of water to solutions in acetonitrile increasingly diminishes the ion-coordination to the polymer, eventually resulting in neutral polymer chains at water contents above ϕ*_water = 30% (w/v). The preferential adsorption of water on PEO in mixtures of acetonitrile and water is evidenced by the pronounced stretching of polymer chains, in particular, at a water content of ϕ_water = 25% and 33.33% (w/v) where complete stretching of the chains is observed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3642–3650, 2006     

High water content clay–nanocomposite hydrogels incorporating guanidinium‐pendant methacrylamide: Tuning of mechanical and swelling properties by supramolecular approach

Novel clay–polymer composite hydrogels with high water content (up to 98 wt %) are developed, in which mechanical properties are reinforced by the formation of multiple ion‐pairs between the polymer chains and clay nanosheets (CNS). When a small amount of guanidinium‐pendant methacrylamide (0.1–0.2 wt %) is copolymerized with a neutral monomer (0.5–2.0 wt %) in an aqueous dispersion of CNS (1.0–3.0 wt %), a self‐standing hydrogel with satisfactory mechanical toughness and elasticity results, despite its high water content (95–98 wt %). The mechanical properties and swelling behaviors of the hydrogels can be tuned by the amount of the guanidinium‐pendant acrylamide. A systematic study indicates that the ion pairs, formed between the guanidinium groups in the polymer chains and the oxyanions on the surfaces of the CNS, serve as crosslinking points in the three‐dimensional network developed in these hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 839–847     

水溶性聚酯浓溶液的流变特性

研究了由对苯二甲酸二甲酯、间苯二甲酸、间苯二甲酸二甲酯 5 磺酸钠与乙二醇等共缩聚合成的PET型水溶性聚酯浓水溶液 (质量浓度 3 0 % )的流变特性 .研究表明 ,溶液的表观粘度随切变速率的变化规律呈现一定的切力增稠特征 ,流动指数范围为 1 0 4～ 1 2 0之间 ;其lgηa τ曲线呈线性 ,零切粘度值为 1 5 8～3 5 2cP ,随分子量、分子结构和温度而异 ,其中分子链中间苯二甲酸乙二醇酯 5 磺酸钠链节含量对溶液粘度影响较大 ;粘流活化能因分子结构和切变速率而变 ,其值范围为 1 2 0～ 2 3 9kJ/mol.     

Raman spectra of poly(ethylene glycols) in solution

Raman spectra have been obtained from poly(ethylene glycol) (PEG) in the solid and molten phases and in aqueous and chloroform solutions. Several new lines are observed or resolved in the Raman spectrum of the solid state as a result of using a high-power argon-ion laser as a source. The Raman spectra of the molten polymer and the chloroform solutions are indicative of a disordered structure, since additional Raman lines appear as a result of the additional rotational isomers. The Raman spectrum of the aqueous solution shows that considerably less structural change occurs upon dissolution in water.     

Water‐soluble conjugated polymers: Synthesis and optical properties

Two sets of water‐soluble poly(phenylene vinylene)s were synthesized and their optical properties were studied. The aqueous solubility of all these polymers is rendered by pendant sulfonate groups. One set of polymers (polymer I series) contains, in addition to the sulfonate pendants, dimethoxy substituents, while the other (polymer II series) contains oligo(ethylene oxide) side chains. Within each set, polymers containing lithium (Ia and IIa), sodium (Ib and IIb), and potassium (Ic and IIc) counter ions were prepared. The two sets of polymers showed different properties from physical appearance (fiber vs film) to thermal properties and to optical properties. It was found that set I polymers, with shorter side chains, exhibit stronger aggregation in aqueous solutions than set II polymers, which led to their lower fluorescence quantum yields and lower polymer‐to‐MV²⁺ quenching efficiencies. Within each set, the effect of counter ions on optical properties was noted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5123–5135, 2007     

Synthesis of poly-L-glutamic acid grafted silica nanoparticles and their assembly into macroporous structures

Polypeptide-coated silica nanoparticles represent an interesting class of organic-inorganic hybrids since the ordered secondary structure of the polypeptide grafts imparts functional properties to these nanoparticles. The synthesis of a poly-l-glutamic acid (PLGA) silica nanoparticle hybrid by employing N-carboxyanhydride (NCA) polymerization to synthesize the polypeptide chains and Cu catalyzed azide alkyne cycloaddition reaction to graft these chains onto the silica surface is reported. This methodology enables the synthesis of well-defined polypeptide chains that are attached onto the silica surface at high surface densities. The PLGA-silica conjugate particles are well dispersed in water, and have been thoroughly characterized using multinuclear ((13)C, (29)Si) solid state NMR, thermogravimetric analysis, Fourier transform infrared, dynamic light scattering, and transmission electron microscopy. The pH-dependent reversible aggregation of the PLGA-silica particles, driven by the change in PLGA structure, has also been studied. Preliminary results on the use of aqueous dispersions of silica-PLGA for the preparation of three-dimensional macroporous structures with oriented pores by ice templating methodology are also demonstrated. These macroporous materials, comprising a biocompatible polymer shell covalently attached to rigid inorganic cores, adopts an interesting lamellar structure with fishbone-type architecture.     

Heterophase Photocatalysts from Water‐Soluble Conjugated Polyelectrolytes: An Example of Self‐Initiation under Visible Light

We herein report a new design route to stable, heterophase photocatalysts, which function as highly dispersible conjugated polymer nanoparticles and porous monoliths under visible light in aqueous medium. They were constructed by attachment of the ionic‐liquid species 1‐alkyl‐3‐vinylimidazolium bromide onto the side chains of a photoactive polymer. The structure configuration allows not only photocatalysis in aqueous environment but also a unique self‐initiation radical cross‐linking process to transform the water‐soluble photoactive polymer into a heterophase system, either as nanoparticles or a porous monolith. High photocatalytic activity and reusability of the heterophase system were demonstrated in the degradation of organic dyes and reduction of Cr^VI into Cr^III in water under visible‐light irradiation.     

Polyelectrolyte properties of a plant and animal polysaccharide

The principal properties of polyelectrolytes in aqueous solution are reviewed; experimental data obtained about polysaccharides in our laboratory identify the main electrostatic interactions which occur between macromolecular chains, between ionic sites on isolated chains or between counterions and polyelectrolytes. Two examples are described. Hyaluronan, a linear alternated copolymer type with one anionic site per repeat unit, is very soluble in water, with a persistence length around 8 nm and a rheological behavior directly related to the molecular weight and polymer concentration in the presence of external monovalent electrolyte. The second example is that of pectin for which the influence of the charge density is studied. It exhibits an important ionic selectivity among divalent counterions in dilute solution with a dimer formation followed by aggregation and gelation.     

Effects of packing structure on the optoelectronic and charge transport properties in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)

Spin-coated poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) films of different molecular weights (Mn= 9-255 kg/mol), both in the pristine and annealed state, were studied in an effort to elucidate changes in the polymer packing structure and the effects this structure has on the optoelectronic and charge transport properties of these films. A model based on quantum chemical calculations, wide-angle X-ray scattering, atomic force microscopy, Raman spectroscopy, photoluminescence, and electron mobility measurements was developed to describe the restructuring of the polymer film as a function of polymer chain length and annealing. In pristine high molecular weight films, the polymer chains exhibit a significant torsion angle between the F8 and BT units, and the BT units in neighboring chains are close to one another. Annealing films to sufficiently high transition temperatures allows the polymers to adopt a lower energy configuration in which the BT units in one polymer chain are adjacent to F8 units in a neighboring chain ("alternating structure"), and the torsion angle between F8 and BT units is reduced. This restructuring, dictated by the strong dipole on the BT unit, subsequently affects the efficiencies of interchain electron transfer and exciton migration. Films exhibiting the alternating structure show significantly lower electron mobilities than those of the pristine high molecular weight films, due to a decrease in the efficiency of interchain electron transport in this structure. In addition, interchain exciton migration to low energy weakly emissive states is also reduced for these alternating structure films, as observed in their photoluminescence spectra and efficiencies.     

In-situ spectroscopic investigations of the redox behavior of poly(indole-5-carboxylic-acid) modified electrodes in acidic aqueous solutions

The oxidation of electrochemically grown poly(indole-5-carboxylic-acid) (P5CO2H) and its spectroscopic properties have been studied by in-situ spectroelectrochemical techniques. The purpose of this paper is to characterize the different modifications on the P5CO2H backbone, induced by the electrochemical oxidation in aqueous acidic solution. We have identified, on the basis of Raman spectra, the vibrational modes associated with neutral and oxidized segments of polymer. It was shown that at least three chemically and optically different species (perhaps other products too) are produced in different potential regimes upon oxidation of this polymer. The results obtained also indicate that the molecular properties of this conducting polymer are better revealed by in-situ resonant spectra than by ex-situ infrared and Raman studies.     

Thickening properties and emulsification mechanisms of new derivatives of polysaccharides in aqueous solution

The thickening properties of aqueous solutions of HHM-HEC (hydrophobically-hydrophilically modified hydroxyethylcellulose) and the emulsification mechanisms of HHM-HEC/water/oil systems were investigated. A dramatic increase in viscosity was observed with increased HHM-HEC concentration in water, caused by aggregation of hydrophobic alkyl chains. At higher concentrations of HHM-HEC (above 0.6 wt%) in water, it forms an elastic gel, which has good thixotropic properties and a high yield value. O/W (oil-in-water) type emulsions were obtained using HHM-HEC, which can emulsify various kinds of oil, including hydrocarbon, silicone, and perfluoropolymethylisopropyl ether. The viscosity of these emulsions depends only upon the oil volume fraction, not on the kind of oil. In addition, the oil particle size in the emulsions remained constant after a certain period because HHM-HEC formed a strong gel network structure and a protective layer, which prevented the emulsion from coalescing. Measurements of interfacial tension revealed that the alkyl chains in HHM-HEC did not significantly lower the interfacial tension at the water/oil interface when 0.5 wt% of HHM-HEC was added to water. Steady flow and oscillatory experimental results show that the rheological behavior of HHM-HEC/water/oil emulsions was similar to that of aqueous solutions of HHM-HEC. In the HHM-HEC/water/oil emulsion system, oil droplets were dispersed and kept stable in the strong gel structure of HHM-HEC. The aqueous solution of HHM-HEC showed salt resistance. It is thought to be due to sulfonic acid groups in HHM-HEC. The stability of the emulsion using HHM-HEC is based on both protective colloidal effects and associative thickening caused by alkyl chains in HHM-HEC.     

Improvement in semipermeable membrane performance of wholly aromatic polyamide through an additive processing strategy

A new concept for the method to provide semipermeability in ultrathin and single‐component wholly aromatic polyamide membranes has been developed for the first time. It was found that water molecules could permeate through the membrane prepared not from polyamides containing flexible ether, bulky binaphthyl, or fluorene rigid units, but one with carboxylic acid groups under a reverse osmosis mode. However, the enhancement of water transport properties by introducing the hydrophilic group of polyamide was not substantial. Therefore, polyamide membranes were prepared from the solution containing aqueous additives in order to weaken hydrogen bonds between polymer chains and thereby to suppress the aggregation of the polymer chains. As a result, water flux was dramatically improved with slightly improved NaCl rejection. Our analyses based on attenuated total reflectance Fourier transform infrared spectroscopy and solid‐state carbon polarization and magic angle spinning nuclear magnetic resonance (¹³C CPMAS NMR) spectroscopy confirmed that the aggregation of polymer chains due to the hydrogen bonds among the amide linkages was suppressed by the co‐ordination of the aqueous additives to the amide linkage. The state of water in the membranes analyzed by differential scanning calorimetry also supported the formation of pores. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1275–1281