Oxidation state and proton doping level in copolymers of 2-aminobenzoic acid and 2-methoxyaniline

UV-vis spectra of homopolymers and copolymers of 2-aminobenzoic acid (OAB) and 2-methoxyaniline (OMA) were analyzed in order to obtain information about the oxidation state and proton doping level of these polymers. Dimethyl sulfoxide (DMSO) was used as a solvent in which protonated forms of polyanilines are preserved and a mixture of N-methyl-2-pyrrolidone and triethylamine (0.5 %) as a solvent (NMP/TEA) in which polyanilines are assumed to be non-protonated. Polymers were prepared in the emeraldine salt form, externally doped with HCl. It was found that only external doping is eliminated in NMP/TEA while internal doping by carboxylate groups bound in OAB units remains operative. Since doped quinoid units do not contribute to the quinoid band (Q-band at 630 nm), the intensity ratio of the Q-band and benzenoid band (B-band at 320 nm) cannot be simply correlated with the oxidation state of poly(OMA-co-OAB) copolymers in contrast to poly(OMA) and polyaniline. Spectra of copolymers with less than 60 % of OMA units as well as those of poly(OAB) in DMSO and NMP/TEA are almost identical due to internal doping, which is proposed to lead to structures in which main-chain protons are coulombically bound with immobile carboxylate anions. In the spectra of copolymers with less than 60 % of OMA units, a well-resolved band occurs at 500 nm, which can be ascribed to alternating or close-to-alternating sequences of OMA and OAB units.     

Photophysical and Electrochemical Investigations on Photoconducting Poly(6-tert-butyl-3,4-dihydro-2H-1,3-benzoxazine)

Poly(6-tert-butyl-3,4-dihydro-2H-1,3-benzoxazine) was synthesized by thermally activated cationic ring opening polymerization. The structure of the polymer was confirmed by spectral and thermal studies. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were estimated using cyclic voltammetry and optical absorption. Modulated photocurrent measurement technique was employed to study the spectral and field dependence of photocurrent. Photocurrent of the order of 1.5 µA/m² was obtained for polymer at a biasing electric field of 40 V/µm.     

Versatile functionalization of polyester hydrogels with electroactive aniline oligomers

Functionalizing aliphatic polyester hydrogels with an aniline oligomer is a means of achieving electrically conductive and degradable hydrogels. To lower the aniline oligomer content while maintaining a high conductivity and to overcome the acidic degradation product from polylactide reported in our previous work, a series of electroactive and degradable hydrogels based on polycaprolactone (PCL) hydrogels and carboxyl‐capped aniline pentamer (CCAP) were synthesized by a simple coupling reaction at room temperature. The reaction was carried out between the hydroxyl groups of hydroxyethylmethacrylate in a photopolymerized glycidyl methacrylate (GMA)‐functionalized PCL‐poly(ethylene glycol)‐PCL degradable network and carboxyl group of CCAP, using 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide as water‐condensing agent and 4‐dimethylaminopyridine as catalyst. The electroactivity of the hydrogels was verified by cyclic voltammetry, which showed three pairs of redox peaks. The electrical conductivities and swelling ratios of these hydrogels were controlled by the CCAP content, the poly(ethylene glycol) molecular weight in the macromer, and the crosslinking density of the hydrogels. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

3‐D Interdigitated electrodes for uniform stimulation of electro‐responsive hydrogels for biomedical applications

Stimuli‐responsive hydrogels are continuing to increase in demand in biomedical applications. Occluding a blood vessel is one possible application which is ideal for a hydrogel because of their ability to expand in a fluid environment. However, typically stimuli‐responsive hydrogels focus on bending instead of radial uniform expansion, which is required for an occlusion application. This article focuses on using an interdigitated electrode device to stimulate an electro‐responsive hydrogel in order to demonstrate a uniform swelling/deswelling of the hydrogel. A Pluronic‐bismethacrylate (PF127‐BMA) hydrogel modified with hydrolyzed methacrylic acid, in order to make it electrically responsive, is used in this article. An interdigitated electrode device was manufactured containing Platinum electrodes. The results in this paper show that the electrically biased hydrogels deswelled 230% more than the non‐biased samples on average. The hydrogels deswelled uniformly and showed no visual deformations due to the electrical bias. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1523–1528     

Novel Macrocycles. Part 6. Synthesis, Structures and Cation Binding from Optical Spectroscopy of 9,10-Anthraquinone-crown Ethers

The 9,10-anthraquinone-[12]crown-4, [15]crown-5 and [18]crown-6 derivatives were synthesized from 1,2-dihydroxy-9,10-anthraquinone and 1,8-dihydroxy-9,10-anthraquinone which were condensed with dihalides or ditosylates of polyethylene glycols in alkali carbonate/DMSO. The 9,10-anthraquinone derived polyoxacyclo-alkanes were characterized with IR, mass spectrometry, ¹H, ¹³C spectroscopy and elemental analysis. The cation binding properties were studied with UV-vis spectroscopy. The association constants found in acetonitrile were selectively dependent on the cation radius and macrocycle size as well as the molecular structures. The observed results from UV-vis studies, however, showed the stronger complexing role of 1,2-derived macrocycles compared to those of 1,8-derivatives. The theoretical conformational analysis and the energy optimisations of the 9,10-anthraquinone-macrocycles carried out with MM+ method explained the binding results.     

Elucidation of the chemical and morphological structure of double-network (DN) hydrogels by high-resolution magic angle spinning (HRMAS) NMR spectroscopy

(1)H HRMAS NMR spectroscopy is applied to gain insight into the chemical and morphological structure of double-network (DN) hydrogels, prepared from poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) and poly(acrylamide) (PAAm). The method enables one to obtain detailed information at the molecular level about the formation of covalent bonds between the two polymer networks through non-reacted double bonds of the cross-linker N,N'-methylene bis(acrylamide) (MBAA). Evidence to the existence of strong hydrogen-bond interactions based on the N-H group of the PAMPS as a hydrogen-bond donor and the C=O group of the PAAm as a hydrogen-bond acceptor is also provided. These findings clarify the origin of the toughening mechanism and the exceptionally strong mechanical properties of DN gels, further supported by microhardness data.     

Conductive Hydrogels: Mechanically Robust Hybrids for Use as Biomaterials

A hybrid system for producing conducting polymers within a doping hydrogel mesh is presented. These conductive hydrogels demonstrate comparable electroactivity to conventional conducting polymers without requiring the need for mobile doping ions which are typically used in literature. These hybrids have superior mechanical stability and a modulus significantly closer to neural tissue than materials which are commonly used for medical electrodes. Additionally they are shown to support the attachment and differentiation of neural like cells, with improved interaction when compared to homogeneous hydrogels. The system provides flexibility such that biologic incorporation can be tailored for application.

     

Synthesis and Photophysical Properties of Some PEG Substitued Titanyl Phthalocyanine Derivatives

Summary: Polyethylene glycol substituted titanyl phthalocyanine was prepared in two steps starting from phthalonitrile and characterized by FT-IR, UV-vis spectrophotometry, and fluorescence spectrophotometry. The titanyl phthocyanine derivatives (TiOPcs) showed high solubility in common organic solvents, such as, CH₃Cl and DMF. These compounds decreased in absorbance intensity with increase of molecular weight of polyethylene glycol at maxima wavelength of visible range. The fluorescence spectra showed a fluorescence emission near 690 nm with a quantum yield of 0.05–0.32 (λ_ex = 625 nm).     

Highly efficient quenching of nanoparticles for the detection of electron‐deficient nitroaromatics

Reported herein is the highly efficient quenching of fluorescent organic nanoparticles by 2,4‐dinitrotoluene and 2,4,6‐trinitrotoluene. These fluorescent nanoparticles are formed from the hydrophobic collapse of fluorescent polymer chains and display quenching efficiencies that are in line with the highest reported literature values. Moreover, the fluorescent quenching occurs only for the fluorescent nanoparticles, and not for the precursor polymer solutions, which display marked insensitivity to the presence of nitroaromatics. This aggregation‐dependent fluorescent quenching has numerous applications for the detection of small‐molecule electron‐deficient analytes. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4150–4155     

Novel poly(amido-amine)-based hydrogels as scaffolds for tissue engineering

Biodegradable and biocompatible amphoteric poly(amido-amine) (PAA)-based hydrogels, containing carboxyl groups along with amino groups in their repeating unit, were considered as scaffolds for tissue engineering applications. These hydrogels were obtained by co-polymerising 2,2-bisacrylamidoacetic acid with 2-methylpiperazine with or without the addition of different mono-acrylamides as modifiers, and in the presence of primary bis-amines as crosslinking agents. Hybrid PAA/albumin hydrogels were also prepared. The polymerisation reaction was a Michael-type polyaddition carried out in aqueous media. The PAA hydrogels were soft and swellable materials. Cytotoxicity tests were carried out by the direct contact method with fibroblast cell lines on the hydrogels both in their native state (that is, as free bases) and as salts with acids of different strength, namely hydrochloric, sulfuric, acetic and lactic acid. This was done in order to ascertain whether counterion-specific differences in cytotoxicity existed. It was found that all the amphoteric PAA hydrogels considered were cytobiocompatible both as free bases and salts. Selected hydrogels samples underwent degradation tests under controlled conditions simulating biological environments, i.e. Dulbecco medium at pH 7.4 and 37 degrees C. All samples degraded completely and dissolved within 10 d, with the exception of hybrid PAA/albumin hydrogels that did not dissolve even after eight months. The degradation products of all samples turned to be non-cytotoxic. All these results led us to conclude that PAA-based hydrogels have a definite potential as degradable matrices for biomedical applications.     

Electrochemical characterization of hydrogels for biomimetic applications

Hydrogels are increasingly being recognized as having potential in bio‐compatible applications. In previous work, we investigated the feasibility of poly(ethylene glycol)‐dimethacrylate (PEG‐1000‐DMA) and poly(ethylene glycol)‐diacrylate (PEG‐400‐DA) polymerized using either a chemical initiator (C) or a photoinitiator (P) to encapsulate and stabilize biomimetic membranes for novel separation technologies or biosensor applications. In this paper, we have investigated the electrochemical properties of the hydrogels used for membrane encapsulation. Specifically, we studied the crosslinked hydrogels by using electrochemical impedance spectroscopy (EIS), and we demonstrated that chemically crosslinked hydrogels had lower values for the effective electrical resistance and higher values for the electrical capacitance compared with hydrogels with photoinitiated crosslinking. Transport numbers were obtained using electromotive force measurements and demonstrated that at low salt concentrations, both PEG‐400‐DA‐C and PEG‐400‐DA‐P hydrogels presented an electropositive character whereas PEG‐1000‐DMA‐P was approximately neutral and PEG‐1000‐DMA‐C showed electronegative character. Sodium transport numbers approached the bulk NaCl electrolyte value at high salt concentrations for all hydrogels, indicating screening of fixed charges in the hydrogels. The average salt diffusional permeability 〈P_s〉 and water permeability 〈P_w〉 were found to correlate with EIS results. Both PEG‐1000‐DMA‐C and PEG‐400‐DA‐C had higher 〈P_s〉 and 〈P_w〉 values than PEG‐1000‐DMA‐P and PEG‐400‐DA‐P hydrogels. In conclusion, our results show that hydrogel electrochemical properties can be controlled by the choice of polymer and type of crosslinking used and that their water and salt permeability properties are congruent with the use of hydrogels for biomimetic membrane encapsulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Self-Standing Hydrogels Composed of Conducting Polymers for All-Hydrogel-State Supercapacitors

Conducting polymer hydrogels that are capable of contacting with electrolytes at the molecular level, represent an important electrode material. However, the fabrication of self-standing hydrogels merely composed of conducting polymers is still challenging owing to the absence of reliable methods. Herein, a novel and facile macromolecular interaction assisted route is reported to fabricate self-standing hydrogels consisting of polyaniline (PANi: providing high electrochemical activity) and poly(3,4-ethylenedioxythiophene) (PEDOT: enabling high electronic conductivity). Owing to the synergistic effect between them, the self-standing hydrogels possess good mechanical properties and electronic/electrochemical performances, making them an excellent potential electrode for solid-state energy storage devices. A proof-of-concept all-hydrogel-state supercapacitor is fabricated, which exhibits a high areal capacitance of 808.2 mF cm⁻², and a high energy density of 0.63 mWh cm⁻³ at high power density of 28.42 mW cm⁻³, superior to many recently reported conducting polymer hydrogels based supercapacitors. This study demonstrates a novel promising strategy to fabricate self-standing conducting polymer hydrogels.     

对二甲氨基苯甲酸的阴离子识别应用研究

采用紫外分光光度法和荧光分光光度法研究了主体分子对二甲氨基苯甲酸与HPO42-、SO42-、H2PO4-、ClO4-、HSO4-、NO3-、BF4-、PF6-、F-、Cl-和Br-等11种阴离子客体的识别作用.发现在乙腈溶液中,该主体分子对二价阴离子HPO42-和SO42-表现了强亲和力和高选择性;并对一价阴离子F-和H2PO4- 具有一定的响应能力;而与一价阴离子ClO4-、HSO4-、NO3-、BF4-、PF6-、Cl-和Br-几乎没有作用.结果表明主客体分子本身的酸碱性和阴离子的负电荷数目是影响主体分子对阴离子识别性能的主要因素.     

Novel UV‐induced photografting process for preparing poly(tetrafluoroethylene)‐based proton‐conducting membranes

A novel process comprising the UV‐induced photografting of styrene into poly(tetrafluoroethylene) (PTFE) films and subsequent sulfonation has been developed for preparing proton‐conducting membranes. Although under UV irradiation the initial radicals were mainly generated on the surface of the PTFE films by the action of photosensitizers such as xanthone and benzoyl peroxide, the graft chains were readily propagated into the PTFE films. The sulfonation of the grafted films was performed in a chlorosulfonic acid solution. Fourier transform infrared and scanning electron microscopy were used to characterize the grafted and sulfonated membranes. With a view to use in fuel cells, the proton conductivity, water uptake, and mechanical properties of the prepared membranes were measured. Even through the degree of grafting was lower than 10%, the proton conductivity in the thickness direction of the newly prepared membranes could reach a value similar to that of a Nafion membrane. In comparison with γ‐ray radiation grafting, UV‐induced photografting is very simple and safe and is less damaging to the membranes because significant degradation of the PTFE main chains can be avoided. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2624–2637, 2007     

Preparation,characterization, and binding profile of molecularly imprinted hydrogels for the peptide hepcidin

Molecularly imprinted hydrogels for the capture of the peptide hormone hepcidin were prepared by water‐in‐oil (w/o) suspension polymerization under mild conditions. Spherical and relatively uniformly sized gel beads were routinely obtained after optimization of the synthetic methodology. The polymers were analyzed by Fourier transform infrared spectroscopy, optical microscopy, and scanning electron microscopy. Although the imprinted materials exhibited higher affinity towards the epitope template (hepcidin N‐terminus) than their corresponding blank polymers, the full‐length target peptide was found strongly bound to all the hydrogels tested. However, by using whole fluorescent hepcidin as the print species, the imprinting effect was more pronounced. Moreover, bovine serum albumin did not bind to the poly N‐isopropylacrylamide (PNIPAm)‐based polymers. Thus, polymeric “sponges” for biomacromolecules with size‐exclusion effect were developed, useful for peptide concentration, immobilization and/or purification from serum samples. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1721–1731, 2010     

Fast synthesis of temperature-sensitive PNIPAAm hydrogels by microwave irradiation

A novel method, microwave irradiation synthesis, is proposed for the preparation of thermo-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels. The PNIPAAm hydrogels were separately synthesized by using microwave irradiation method and water-bath heating method. Chemical groups, lower critical solution temperature (LCST) and surface morphology of these PNIPAAm hydrogels were characterized by FT-IR, DSC and SEM. Swelling ratios of the gels were measured gravimetrically in the temperature range from 10.0 to 60.0 °C. Results showed that (1) the use of microwave irradiation can greatly shorten the reaction time required for PNIPAAm hydrogel synthesis from several hours to several minutes in comparison with water-bath heating method, and obviously improve the yields of the PNIPAAm gels, which were up to 99% after a short reaction time; (2) SEM micrographs and textural measurement revealed that the gels synthesized using microwave irradiation had more porous structure, and their average pore sizes and specific surface areas were larger than those of the gels synthesized using water-bath heating method; and (3) the PNIPAAm hydrogels synthesized using microwave irradiation had much higher swelling ratios at 10.0 °C below the LCST, and had lower swelling ratio at 60.0 °C above the LCST compared to the hydrogels synthesized by water-bath method.     

UV-photocrosslinking of inulin derivatives to produce hydrogels for drug delivery application

In this work, INU, a natural polysaccharide, has been chemically modified in order to obtain new photocrosslinkable derivatives. To reach this goal, INU has been derivatized with MA thus obtaining four samples (INU-MA derivatives) as a function of the temperature and time of reaction. An aqueous solution of the derivative INU-MA1 was irradiated by using a UV lamp with an emission range from 250 to 364 nm and without using photoinitiators. The obtained hydrogel showed a remarkable water affinity but it underwent a partial degradation in simulated gastric fluid. To overcome this drawback, INU-MA1 was derivatized with SA thus obtaining the INU-MA1-SA derivative designed to produce a hydrogel showing a low swelling and an increased chemical stability in acidic medium. Ibuprofen, as a model drug, was loaded by soaking into INU-MA1 and INU-MA1-SA hydrogels and its release from these matrices was evaluated in simulated gastrointestinal fluids. INU-MA1 hydrogel showed the ability to quickly release the entrapped drug thus indicating its potential as a matrix for an oral formulation. INU-MA1-SA hydrogel showed a pH-responsive drug delivery. Therefore it is a promising candidate for controlled drug release in the intestinal tract.     

PHEMA hydrogels obtained by a novel low-heat curing procedure with a potential for in situ preparation

In this work, we report on poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels obtained by a low heat curing reaction. These materials are suitable for in situ preparation and therefore endowed with a potential for several biomedical applications. The novel procedure adopted involves as the first step the synthesis of a soluble oligomeric PHEMA precursor containing polymerizable functions as side substituents. As the second step, the precursor is dissolved in equal amounts of 2-hydroxyethyl methacrylate (HEMA) and water, to form a viscous but still injectable syrup. A low temperature water soluble initiator is then added. The curing reaction starts promptly and is completed within few minutes. During the entire process the internal temperature never rises above 40 degrees C. Preliminary mechanical characterizations performed on the hydrogels in their water-swollen state and diffusion tests in absorption/desorption experiments clearly indicated that on all respects the novel hydrogels are comparable with conventional PHEMA hydrogels obtained according to literature from HEMA in the presence of divinyl crosslinkers. However, the much shorter curing time combined with the far lower curing temperature endow the new hydrogels with a higher potential in view of specific surgical requirements, and particularly for in situ preparation.     

Ion-Dependent Hydration and Transparency of the Corneal Stroma,a Polyelectrolyte Biogel

The cornea is the clear outer window of the eye, composed primarily of dense regular connective tissue called the stroma. The tissue is composed of 70% water and parallel collagen fibrils surrounded by proteoglycans containing high concentrations of acidic and neutral glycosaminoglycans (GAGs) and contains ∼2 – 10% cells by volume. When the surface membranes covering the stroma are damaged by injury or disease, the stroma swells due to the hydrophilic nature of the polysaccharides. At the same time, swelling spreads the collagen fibrils apart and the tissue loses transparency. We investigated the role of different salts in modifying swelling behavior and transparency loss. In saline (148 mM NaCl) solution, hydration increases as a multi exponential function of time: Initially the stroma gains hydration at a fast rate, then slows down. In the presence of divalent cations, swelling behavior significantly decreased, and the effect was weakly anion-dependent. Under imposed stromal swelling pressures, Ca⁺⁺ and Mg⁺⁺ inhibited hydration equally, and their effects were additive, indicating that they work by similar mechanisms. They were also concentration-dependent, with no apparent ceiling to the effect within normal biological ionic strengths. As stated above, Mg⁺⁺ and Ca⁺⁺ both dehydrate stromas and decrease swelling rates compared to saline, and as a stroma hydrates, it loses transparency: visible spectrophotometry of stromas bathed in NaCl lose transparency faster than those bathed in MgSO₄, because MgSO₄ solutions hydrate stromas slower. Stromas bathed in Ca⁺⁺ hydrated slower than those bathed in NaCl, but interestingly, high (49 – 148 mM) concentrations of Ca⁺⁺ caused transparency loss almost instantly. In hyaluronin (a collagen fibril-free polyanionic biogel), when similar concentrations of Ca⁺⁺ were added, transparency also decreased. Our conclusion is that the dehydrating effects of Mg⁺⁺ and low concentrations of Ca⁺⁺ are due to shielding of electrostatic repulsion between anionic GAGs. The higher concentrations of Ca⁺⁺ dehydrate by a combination of covalent binding to (precipitating) GAGs and/or shielding their electrostatic repulsions, and scatter light by precipitating GAGs and disrupting collagen fibril order. These techniques and ionic probes are useful for studying the structure and function of polyionic hydrogels and may be useful for modifying the materials properties of biological and synthetic gels.     

偶氮苯为探针的液晶聚合物聚集形态研究

利用紫外-可见光谱,对比研究了尾挂侧链液晶聚合物和腰挂侧链液晶聚合物在结晶相和液晶相转变过程中的液晶基元取向情况.研究表明,石英基材表面倾向于诱导偶氮液晶基元垂直于基材排列;观察到了在液晶态尾挂侧链液晶聚合物和腰挂侧链液晶聚合物的不同取向行为.在室温下重新结晶数天后,腰挂液晶聚合物的紫外可见光谱缓慢回复.