Self-oscillating soluble-insoluble changes of a polymer chain including an oxidizing agent induced by the Belousov-Zhabotinsky reaction

A new type of self-oscillating polymer was prepared by utilizing the Belousov-Zhabotinsky reaction. In this study, capture sites with a positive charge for an oxidizing agent as a counterion were incorporated into the copolymer of N-isopropylacrylamide and the ruthenium complex as a catalyst. Soluble-insoluble self-oscillation of the polymer was first achieved without adding an oxidizing agent. The effect of temperature on the self-oscillating behavior was investigated. It was clarified that the polymer had two advantageous characteristics because of the higher LCST; one is to enable self-oscillation around body temperature, and the other is to cause the oscillation for a longer time without intermolecular aggregation among the polymer chains in the reduced state. This achievement of self-oscillation of polymer chains including an oxidizing agent may lead to their practical use under oxidant-free conditions.     

Synthesis and solution properties of poly(vinyl ether)s with long alkyl chain,biphenyl, and cholesteryl pendants

The judicious choice of reaction conditions permitted living cationic polymerization of vinyl ethers with bulky and strongly interacting pendant groups, such as crystalline long alkyl chains and liquid crystalline mesogenic structures, using appropriate combinations of Lewis acids with added bases. Thus, well‐defined random and block copolymers with various pendants were also synthesized. Highly sensitive UCST‐type phase separation in various organic solvents was achieved employing crystallization of octadecyl pendants of homopolymers and random copolymers. This phase separation behavior is unusual for a polymer‐organic solvent system. Furthermore, thermally induced reversible physical gelation was conducted using this thermosensitive behavior. These specific pendants were very effective not only in organic media but also in water, in obtaining hydrogels with relatively low polymer concentrations. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4392–4406, 2008     

The remarkable role of hydrogen bond,halogen, and solvent effect on self-healing supramolecular gel

Self-healing supramolecular gels of low-molecular-weight (LMW) molecules are smart soft materials; however, the development of self-healing LMW gelator is still a challenging task because of the lack of in-depth studies about self-healing mechanisms of LMW gels and the solvent effect on gel properties. Therefore, herein a different perspective was used to study a family of D-gluconic acetal-based gelators with variable structural fragments in 14 different solvents, and a more detailed understanding of self-assembly and self-healing mechanism of supramolecular gels was attained. Based on the critical gelation concentration, phase transition temperature, and rheological data, A8 bearing an amide group in side chain and two chlorine atoms linked to benzene ring was found to be an outstanding gelator, which could form gels with good self-healing ability in a variety of solvents. Interestingly, A8 gel formed in n-BuOH demonstrates high transparency, good mechanical strength, self-supporting behavior, and great self-healing ability from mechanical damage. Based on the Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and theoretical calculation analysis, the self-assembly and self-healing mechanisms of A8 gel were proposed, indicating that a combination of hydrogen bonding and halogen effect was responsible for the efficient self-healing behavior of supramolecular gel. Furthermore, the analysis of solvent parameters indicated that the dispersion force of solvent favored gelators to self-assemble, hydrogen bonding donor ability of solvent mainly affected the formation of one-dimensional assembly, and hydrogen bonding receptor ability and polarity of solvent mainly influenced the supramolecular interactions among assemblies, significantly intervening the self-healing ability of gels. Overall, this study provides a new perspective to the understanding of gelator structure–property correlation in solvents and sheds light for future development of self-healing supramolecular gels.     

A semiempirical study on inhibition of catechol O-methyltransferase by substituted catechols

Catechol and endogenous catechol derivatives are readily methylated by catechol O-methyltransferase (COMT). In contrast, many catechol derivatives possessing electronegative substituents are potent COMT inhibitors. The X-ray structure of the active site of COMT suggests that the methylation involves a lysine as a general base. The lysine can activate one of the catecholic hydroxyl groups for a nucleophilic attack on the active methyl group of the coenzyme S-adenosyl-l-methionine (AdoMet). We studied the effect of dinitrosubstitution of the catecholic ring at the semiempirical PM3 level on the methylation reaction catalysed by COMT. The electronegative nitro groups make the ionized catechol hydroxyls less nucleophilic than the corresponding hydroxyl groups of the non-substituted catechol. As a consequence, dinitrocatechol is not methylated but is instead a potent COMT inhibitor. The implications of this mechanism to the design of COMT inhibitors are discussed.     

Influence of Material Properties on the Damage-Reporting and Self-Healing Performance of a Mechanically Active Dynamic Network Polymer in Coating Applications

We conducted a detailed investigation of the influence of the material properties of dynamic polymer network coatings on their self-healing and damage-reporting performance. A series of reversible polyacrylate urethane networks containing the damage-reporting diarylbibenzofuranone unit were synthesized, and their material properties (e.g., indentation modulus, hardness modulus, and glass-transition temperature) were measured conducting nanoindentation and differential scanning calorimetry experiments. The damage-reporting and self-healing performances of the dynamic polymer network coatings exhibited opposite tendencies with respect to the material properties of the polymer network coatings. Soft polymer network coatings with low glass-transition temperature (~10 °C) and indentation hardness (20 MPa) exhibited better self-healing performance (almost 100%) but two times worse damage-reporting properties than hard polymer network coatings with high glass-transition temperature (35~50 °C) and indentation hardness (150~200 MPa). These features of the dynamic polymer network coatings are unique; they are not observed in elastomers, films, and hydrogels, whereby the polymer networks are bound to the substrate surface. Evidence indicates that controlling the polymer’s physical properties is a key factor in designing high-performance self-healing and damage-reporting polymer coatings based on mechanophores.     

Aggregation-induced emission luminogens and tunable multicolor polymer networks modulated by dynamic covalent chemistry

Aggregation-induced emission(AIE) based luminescent materials are generating intensive interest due to their unique fluorescence in the aggregation state. Herein we report a strategy of dynamic covalent chemistry(DCC) controlled AIE luminogens for the regulation of multicolor emission in reversible covalent polymer networks. Tetraphenylethene derived ring-chain tautomers were prepared, and the emission was readily controlled through multimode, such as changing the solvent, adding the base, and d...     

聚丙烯腈溶液的凝胶化研究

聚丙烯腈是用途最广泛的聚合物之一,其溶于适当溶剂中形成的聚丙烯腈溶液是制备聚丙烯腈纤维、渗透膜等高分子材料的原料。聚丙烯腈溶液的物理化学性质对所制备材料的性能有很大的影响。本文对高分子溶液的凝胶化和高分子凝胶的特点做了简要介绍,并介绍了聚丙烯腈及其凝胶的特点。根据高分子浓溶液体系的特点提出用于表征聚丙烯腈溶液凝胶化的主要方法。从浓度和温度对聚丙烯腈溶液凝胶化行为的影响、熟化和非溶剂对聚丙烯腈溶液凝胶化行为的影响、聚丙烯腈溶液凝胶化的热可逆性、聚丙烯腈溶液凝胶化的分形特征以及聚丙烯腈凝胶的交联机理这几个方面对已有聚丙烯腈溶液的凝胶化研究成果和最新进展进行了综述。最后对聚丙烯腈溶液凝胶化和聚丙烯腈凝胶的研究前景做了展望。     

pH‐Responsive Supramolecular Polymerization in Aqueous Media Driven by Electrostatic Attraction‐Enhanced Crown Ether‐Based Molecular Recognition

All the previously reported supramolecular polymers based on crown ether‐based molecular recognition have been prepared in anhydrous organic solvents. This is mainly due to the weakness of crown ether‐based molecular recognition in the presence of water. Here we report a linear supramolecular polymer constructed from a heteroditopic monomer in an aqueous medium driven by crown ether‐based molecular recognition through the introduction of electrostatic attraction. In addition, the reversible transition between the linear supramolecular polymer and oligomers is achieved by adding acid and base. This study realizes the breakthrough of the solvent for supramolecular polymerization driven by crown ether‐based molecular recognition from anhydrous organic solvents to aqueous media. It is helpful for achieving supramolecular polymerization driven by crown ether‐based molecular recognition in a completely aqueous medium.     

Gelation characteristics and applications of poly(ethylene glycol) end capped with hydrophobic biodegradable dipeptides

Poly(ethylene glycol) (PEG) end capped with biodegradable hydrophobic dipeptides shows versatile gelation behavior in a wide range of aqueous and organic solvents. This gelation characteristic is attributed to the aggregation of polymer chains induced by dipeptide end groups. Both PEG molecular weight and molecular structure of end groups control this aggregation by striking a balance between two opposing molecular interactions: solubility of the PEG segment which tends to dissolve the polymer while hydrophobic and intermolecular noncovalent interactions between the end groups induce aggregation. Morphologically, this aggregated structure forms interpenetrating nano sheets with characteristic microstructural features. These gels are biodegradable and possess physicomechanical characteristics suitable for biomedical applications. Furthermore, proteins and hydrophobic model drugs can be encapsulated within the gels from aqueous and organic solvents, respectively, and can be released in a controlled fashion which indicates the applicability of the gels as drug delivery vehicles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1917–1928     

Thermal-responsive self-healing hydrogel based on hydrophobically modified chitosan and vesicle

High-performance polymer materials with stimulus-responsive, self-healing and controllable features are expected to have diverse applications. In this paper, we report a novel, thermal-switchable self-healing hydrogel which can be obtained simply by mixing the hydrophobically modified chitosan (hm-chitosan) with the thermal-responsive vesicle composed of 5-methyl salicylic acid (5mS) and dodecyltrimethylammonium bromide (DTAB). Temperature stimuli points to a sol–gel phase transition in the supramolecular hydrogel and such transition can be reversibly performed for several cycles. In particular, the gelation temperature can be easily controlled by varying the ratio of DTAB to 5mS. Aside from the temperature responsive ability, the original feature highlighted in this work is that such a vesicle-based hydrogel exhibits interesting self-healing feature in a matter of seconds through the autonomic reconstruction without the use of healing agent. Thus, hydrogels based on hm-chitosan and functional vesicle may have potential application in a wide range of areas.     

Dual cross-linked networks hydrogels with unique swelling behavior and high mechanical strength: based on silica nanoparticle and hydrophobic association

A series of physically cross-linked hydrogels composed poly(acrylic acid) and octylphenol polyoxyethylene acrylate with high mechanical strength are reported here with dual cross-linked networks that formed by silica nanoparticles (SNs) and hydrophobic association micro-domains (HAMDs). Acrylic acid (AA) and octylphenol polyoxyethylene acrylate with 10 ethoxyl units (OP-10-AC) as basic monomers in situ graft from the SNs surface to build poly(acrylic acid) hydrophilic backbone chains with randomly distributed OP-10-AC hydrophobic side chains. The entanglements among grafted backbone polymer chains and hydrophobic branch architecture lead to the SNs and HAMDs play the role of physical cross-links for the hydrogels network structure. The rheological behavior and polymer concentration for gelation process are measured to examine the critical gelation conditions. The correlation of the polymer dual cross-linked networks with hydrogels swelling behavior, gel-to-sol phase transition, and mechanical strength are addressed, and the results imply that the unique dual cross-linking networks contribute the hydrogels distinctive swelling behavior and excellent tensile strength. The effects of SNs content, molecular weight of polymer backbone, and temperature on hydrogels properties are studied, and the results indicate that the physical hydrogel network integrity is depended on the SNs and HAMDs concentration.     

Effect of solvent on the gelation properties of a metallo-organic polymer of [Fe(II) (4-octadecyl-1,2,4-triazole)3(ClO4)2]n

In this contribution we report on the preparation of thermally responsive supramolecular gels obtained through self-assembling of metallo-organic polymers of lipophilic Fe(II) complexes of 1,2,4-triazole functionalized with octadecyl chains ([Fe(II) (4-octadecyl-1,2,4-triazole)₃(ClO₄)₂]_n) in three organic solvents: toluene, cis-decalin and trans-decalin. A gel phase is formed in these solvents by cooling the homogeneous complex solutions below a well-defined temperature, the so-called gelation threshold. These gels are reversible as they form homogeneous solutions upon heating above the melting temperature. The systems have been characterized for their thermal and viscoelastic properties through differential scanning calorimetry and rheological experiments, respectively. The effect of the solvent type and concentration on the gelation behaviour of the metallo-organic polymer has been analysed. The results obtained point to structural differences and different gelation mechanisms for the gels prepared in different solvents and they also suggest the possibility to control the spin-crossover transition temperature associated to the sol-gel transition.     

Effects of added surfactants on thermoreversible gelation of associating polymer solutions

The influence of added surfactants on physical properties of associating polymer solutions was examined by a new statistical‐mechanical theory of associating polymer solutions with multiple junctions and by computer simulation. The sol–gel transition line, the spinodal line, and the number of elastically effective chains in the mixed networks were calculated as functions of the concentration of added surfactants. All of them exhibited nonmonotonic behavior as a result of the following two competing mechanisms. One was the formation of new mixed micelles by binding surfactants onto the polymer associative groups. These micelles serve as crosslink junctions and promote gelation. The other was the replacement of polymer associative groups in the already formed network junctions by added surfactants. Such replacement lowers connectivity of junctions and destroys networks. The critical micelle concentration was also calculated. The results are compared with the reported experimental data on poly(ethylene oxide)‐based associating polymers and hydrophobically modified cellulose derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 733–751, 2004     

Noncovalent Macromolecular Architectures of Oligo(p-phenylenevinylene)s (OPVs): Role of End Functional Groups on the Gelation of Organic Solvents

Summary: Self-assembly of a few OPV derivatives having different end functional groups to aggregates, fibrous networks and organogels are discussed. OPV1 and OPV2 functionalized with ester moieties form gels in nonpolar hydrocarbon solvents whereas OPV3 with carboxylic acid groups form gel from THF and dichloromethane. OPV4 with dicyano moieties form aggregates but could not gelate solvents. AFM and TEM studies revealed considerable difference in the morphology of the self-assembled structures of OPV1-4 . From the optical, morphological and gelation data it is concluded that the nature of the end functional groups strongly influences upon the self-assembly and gelation properties of OPVs.     

Reversible shear gelation of polymer–clay dispersions

Reversible, shear-induced gelation of semi-dilute aqueous colloidal dispersions consisting of monodisperse discoid particles (Laponite) and weakly adsorbing polymer (polyethylene oxide) is studied through a combination of small angle neutron scattering and oscillatory shear. When shaken the samples undergo a dramatic transition from a low viscosity fluid to a self-supporting, turbid gel. This complex non-linear behavior is found to occur over a narrow composition regime near a composition commensurate with saturation of the clay surface with polymer. Through a combination of SANS and rheology, shear gelation is found to occur through the deformation of large stable flocs that expose fresh surface area for the formation of new polymer bridges. At rest, the temporary shear-induced flocs slowly fractionate with time as the polymer desorbs from the clay surface. The shear-induced gelation is time reversible and strongly temperature-dependent suggesting that relaxation is an activated process. Samples showing shear induced gelation are also able to form stiff stable gels which are characteristically similar to pure clay dispersions.     

Mussel-mimicking sulfobetaine-based copolymer with metal tunable gelation,self-healing and antibacterial capability

In the present study, the sulfobetaine-based copolymer bearing a dopamine functionality showed gel formation adjusted by the application of metal salts for gelation and various values of pH. Normally, the liquid-like solution of the sulfobetaine-based copolymer and metal cross-linkers is transformed to a gel-like state upon increasing the pH values in the presence of Fe³⁺ and Ti³⁺. Metal-induced coordination is reversible by means of the application of EDTA as a chelating agent. In the case of Ag⁺ ions, the gel is formed through a redox process accompanied with the oxidative coupling of the dopamine moieties and Ag⁰ particle formation. Mussel-mimicking and metal-dependent viscoelastic properties were observed for Fe³⁺, Ti³⁺, and Ag⁺ cross-linking agents, with additionally enhanced self-healing behavior in comparison with the covalently cross-linked IO₄⁻ analogues. Antibacterial properties can be achieved both in solution and on the surface using the proper concentration of Ag⁺ ions used for gelation; thus, a tunable amount of the Ag⁰ particles are formed in the hydrogel. The cytotoxicity was elucidated by the both MTT assay on the NIH/3T3 fibroblast cell line and direct contact method using human dermal fibroblast cell (F121) and shows the non-toxic character of the synthesized copolymer.     

Self-assembly of carbazole-containing gelators: alignment of the chromophore in fibrous aggregates

Carbazole-containing gelators derived from l-isoleucine have been developed. They form elongated self-assembled fibers in common organic solvents and in liquid crystals, leading to the efficient gelation of these solvents. Spectroscopic studies indicate that the carbazolyl moieties are one-dimensionally stacked in the fibers. The stacking of the carbazolyl moieties is reversible by the association and dissociation of the hydrogen bonding. Moreover, anisotropically aligned fibers have been obtained in a homogeneously oriented smectic state of liquid crystals. This template behavior would serve as a versatile approach to the functionalization of self-assembled fibers.     

Structure-property relationship of a class of efficient organogelators and their multistimuli responsiveness

A new class of efficient low-molecular-weight gelators composed of a 2-substituted anthraquinone and a hydrazide subunit were synthesized, and the structure-property relationships with respect to their gelation abilities in organic solvents were investigated. The toluene gels showed exceptional thermal stability. Interestingly, it was also found that the ultrasound radiation could promote 1b-e to form a stable organogels instead of precipitates in polar solvent, and the ultrasound could remarkably induce changes of the morphology of the assembly in pyridine. Moreover, the reversible gel to sol phase transition could be achieved by adding TFA and TEA. The gelators 1b-e further showed selective gelation of aromatic solvents or chloroalkanes from their mixtures with water.     

水溶性高分子弱凝胶体系凝胶化过程的Monte Carlo模拟

为研究弱凝胶的形成过程,并把高分子弱凝胶用于三次采油,采用三维Monte Carlo模拟了高分子溶液凝胶化过程. 模拟预测了凝胶化开始的时间,得到了凝胶化过程中分子量分布的演化规律和胶团生长的三维图像. 发现生成溶胶与凝胶团的歧化过程,初始聚合物的浓度对能否形成凝胶至关重要,低于临界浓度不能形成凝胶. 模拟了凝胶化速度和聚合物浓度以及交联剂浓度的关系,并与粘度随凝胶化时间变化的实验结果进行比较, 结果表明, 聚合物浓度较高时,浓度对交联反应的影响减弱,这一趋势与实验结果相一致.     

Rheological and swelling behavior of semi‐interpenetrating networks of polyacrylamide and scleroglucan

Preparation and characterization of novel semi‐interpenetrating polymer network (semi‐IPN) hydrogels based on partially hydrolyzed polyacrylamide (HPAM) and scleroglucan solution crosslinked with chromium triacetate are described. Effects of scleroglucan concentration on the gelation process and swelling behavior of synthesized hydrogels in different media were investigated using dynamic rheometery and swelling tests, respectively. Oscillatory shear rheology showed that the limiting storage modulus of the semi‐IPN gels increased with increase in scleroglucan concentration. It was also found that the viscous energy dissipating properties of the semi‐IPN gels decreased with increase in the crosslinker concentration of the gelation system. In addition, the loss factor slightly decreased by increasing the scleroglucan content, indicating that the viscous properties of this gelling system decreased more than its elastic properties. The swelling tests showed that the equilibrium swelling ratio (ESR) of the semi‐IPN networks decreased with increase in scleroglucan content, due to the decrease of ionic groups of polyelectrolyte hydrogel. However, the semi‐IPN gels showed lower salt sensitivity in synthetic oil reservoir water as compared with HPAM gels. Therefore, these semi‐IPN hydrogels may be considered potentially good candidates for enhanced oil recovery (EOR) applications. Copyright © 2009 John Wiley & Sons, Ltd.