Healable supramolecular polymer solids

The reversible nature of non-covalent interactions between constituting building blocks permits one to temporarily disassemble supramolecular polymers through the application of an appropriate external stimulus “on command”. This framework has recently emerged as a general design strategy for the development of healable polymer systems. The approach exploits that the temporary disassembly decreases the molecular weight and in the case of cross-linked polymers the cross-link density, and thereby causes an increase of the chain mobility and a reduction of the viscosity of the material. The transformation thus enables the disassembled material to flow and fill defects, before the original supramolecular polymer is re-assembled. Focusing on recent progress in the area of healable supramolecular polymer solids based on hydrogen-bonding, metal-ligand and π–π interactions, as well as supramolecular nanocomposites, this review article summarizes the development and current state of the field.     

A self-assembled supramolecular solid for catalytic application

A 1,8-naphthalenecarboxylic anhydride-4,5-dicarboxylate (L) bridged copper(II) dimeric molecular module [Cu₂L₂(DMF)₂(H₂O)₂] (1) can self-organize into a solid-state supramolecular architecture. The combination of the multitopic contact sites of hydrogen bonds coupled with two bulky aromatic cores promoted the molecule to self-link into a solid-state supramolecular architecture, which was almost insoluble in water and common organic solvents. Solid 1 can heterogeneously catalyze the cross-coupling of arylboronic acids with imidazole in the absence of a base or additive to generate the corresponding coupling products in excellent yields in methanol at 50 °C, which can be recovered and recycled by a simple filtration and was used for six consecutive cycles with consistent activity.     

Large macro-dipoles generated in a supramolecular polymer of N,N′,N″-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide in n-decane

A supramolecular polymer formed by N,N′,N″-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide (DO₃B) in n-decane (C₁₀) possesses large macro-dipoles naturally generated by three-fold inter-molecular hydrogen bonding aligned along its helical columnar structure connected by defective portions, which are DO₃B molecules containing failure in the hydrogen bond formation, in the order of head to tail arrangement without dipole inversion like type-A polymers.     

Macromolecular and supramolecular chirality: a twist in the polymer tales

Significant advances have been made recently in generating chiral polymer surfaces and materials using a range of methods such as block copolymer self‐assembly, layer‐by‐layer assembly and surface functionalization by polymer brushes. This paves the way for novel chiral materials that can harness and tailor chiral interactions for specific functionalities and properties in a range of biomedical and bioanalytical applications. This paper reviews these advances and speculates on the future of chiral surfaces. © 2013 Society of Chemical Industry     

Fabrication of polymer antireflective coatings by self-assembly of supramolecular block copolymer

We demonstrated a method of fabricating antireflective coatings based on the self-assembly of supramolecular block copolymer formed by polystyrene terminated with carboxyl (PS-COOH) and poly(methyl methacrylate) terminated with amine (PMMA-NH₂) via hydrogen bonding. Different porous films were generated by selectively removing PS-COOH from the spin-coated films with a selective solvent, cyclohexane, under different conditions. The refractive index of such porous film can be tuned from 1.49 down to 1.26 by controlling the thickness of the porous film. For the porous layer with n ˜ 1.26, the light transmittance of the glass about 97.93% was achieved in the visible range (λ ˜ 574 nm). By varying the solution concentration and exposing time in cyclohexane, inhomogeneous three-layered porous films were generated: top and bottom layers with high porosities and the middle layers with lower porosities, respectively. The light transmittance of the glass coated with this inhomogeneous film was about 98.00% in the near-infrared region corresponding to wavelength between 800 and 1400 nm. The wavelength region of the broadband antireflective films with high transmittance more than 99.00% can be fine tuned to 1200-2000 nm with increasing the film thickness.     

Effect of self-complementary motifs on phase compatibility and material properties in blends of supramolecular polymers

Applicability of supramolecular polymers blending in preparation of materials with tunable properties is reported. The effect of strongly dimerising 2-ureido-4[1H]-pyrimidinone (UPy) end groups on phase compatibility in binary polymer blends was studied. A low molecular weight poly(tetrahydrofuran) diol was functionalized with UPy moieties (PTHF(UPy)₂, a soft material) and mixed with varying amounts of low molecular weight UPy functionalized polycaprolactone di- and triol (PCL(UPy)₂ and PCL(UPy)₃, both relatively strong and stiff materials). Thermal studies showed that T_g of the homopolymers shifted to intermediate temperatures. AFM observation suggested that the phase domain decreased significantly after UPy functionalization of diols. Also the mechanical properties improved at a higher rate than those predicted by the rule of mixtures. These findings indicate that blend components are placed in intimate contact as a result of the UPy-UPy interactions. The reversible crosslinking by PCL(UPy)₃ gave better control still over the mechanical properties of the supramolecular polymer blends.     

Photoregulated complexation,redox behavior,and photoluminescence of a supramolecular polymer solution

Reported in this paper is a new finding based on a spectroscopic and electrochemical study of a supramolecular polymer in dilute solution. Dissolved in a mixture of dichloromethane and acetonitrile, zinc‐tetraphenylporphyrin (ZnTPP) can complex with a polymethacrylate bearing an azopyridine moiety (AzPy) through the axial coordination between the metal and pyridyl group. The self‐assembled polymer (PAzPy–ZnTPP) displays different photoluminescence and redox behaviors compared with those of noncomplexed ZnTPP. Moreover, the reversible trans–cis‐photoisomerization of azopyridine upon UV and visible light irradiation was found to alter the equilibrium of the axial coordination between azopyridine and ZnTPP in solution, resulting in photoregulable redox potentials and fluorescence emission of the metalloporphyrin. The results suggest that supramolecular polymer solutions could enhance the mechanism of photoinduced change in the degree of complexation, which gives rise to a phenomenon of photoregulation of the electrochemical and optical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 744–750, 2006     

Functionalization of 3D covalent organic frameworks using monofunctional boronic acids

Co-crystallizing a monomer capable of forming a three-dimensional covalent organic framework (3D COF) with a truncated analog represents a robust strategy to functionalize the pores of these crystalline polymer networks. Here we elaborate this approach by demonstrating that monofunctional arylboronic acids serve as effective truncation/functionalization agents for COF-102, a boroxine-linked 3D network derived from the dehydration of a tetrahedral tetrakis(boronic acid) monomer. The COF-102 network forms under typical solvothermal conditions, even in the presence of a large excess of 4-tolylboronic acid, which is incorporated into the polymer's boroxine linkages up to a maximum loading level of ca. 33 mol%. This finding indicates the maximum truncation level for the COF-102 network and suggests that framework crystallization is irreversible. At high feed ratios of the monofunctional boronic acid, the isolated COF-102-tolyl powders are initially contaminated by significant amounts of tris(4-tolyl)boroxine, which is removed through a solution-based activation process to provide COF-102-tolyl samples with high functionalization density, long-range order, and permanent porosity. We also demonstrate the generality of this truncation study by evaluating several other readily available arylboronic acids, each of which are incorporated into the COF similarly. Together these findings demonstrate the simplicity and generality of this truncation/functionalization approach, as well as its fundamental limits.     

Prediction of methane storage in covalent organic frameworks using big-data-mining approach

A combination of computational materials screening and machine learning (ML) technique is being adopted as a popular approach to study various materials toward application of interest. In this work, we began with high-throughput molecular simulations to calculate the methane storage (6.5 MPa) and deliverable (6.5-0.58 MPa) capacities of 404,460 covalent organic frameworks (COFs) at 298 K. Then, the full data sets with 23 features were randomly split into training and test sets in a ratio of 20:80, which were applied to evaluate the prediction abilities of several ML algorithms, including gradient boosting decision tree (GBDT), neural network (NN), support vector machine (SVM), random forest (RF) and decision tree (DT). The results indicate that the RF model has the highest prediction accuracy, which was further employed to reduce the dimension of features space and quantitatively analyze the relative importance of each feature value. The binary classification predictors built using the features with the highest influence weight can give a successful identification of top-performing candidates from the test set containing 323,168 COFs with an accuracy exceeding 96%. The deliverable capacities of the identified COFs were found to outperform those reported so far for various adsorbents. The findings may provide a useful guidance for the design and synthesis of new high-performance materials for methane storage application.     

Reducing active layer thickness of polyamide composite membranes using a covalent organic framework interlayer in interfacial polymerization

Polyamide(PA)-based thin-film composite membranes exhibit enormous potential in water purification, owing to their facile fabrication, decent performance and desirable stability. However, the thick PA active layer with high transport resistance from the conventional interfacial polymerization hampers their applications. The controllable fabrication of a thin PA active layer is essential for high separation efficiency but still challenging. Herein,a covalent organic framework TpPa-1 interlayer was firstly deposited on a polyethersulfone(PES) substrate to reduce the thickness of PA active layer in interfacial polymerization. The abundant pores of TpPa-1 increase the local concentration of amine monomers by adsorbing piperazine molecules, while hydrogen bonds between hydrophilic groups of TpPa-1 and piperazine molecules slow down their diffusion rate. Arising from those synergetic effects, the PA active layer is effectively reduced from 200 nm to 120 nm. By optimizing TpPa-1 interlayer and PA active layer, the water flux of resultant membranes can reach 171.35 L·m~(-2)·h~(-1)·MPa~(-1), which increased by 125.4% compared with PA/PES membranes, while the rejection rates of sodium sulfate and dyes solution remained more than 90% and 99%, respectively. Our strategy may stimulate rational design of ultrathin PA-based nanofiltration membranes with high performances.     

Connectivity and spacing effects in hydrogen-bonding polymer solutions and blends

In recent experimental work, it was found that the number of hydrogen bonds in polymer mixtures is strongly influenced by chain-connectivity effects and the spacing of functional groups along the chain. In this article, the relationships between the equilibrium constants used to describe the number of hydrogen bonds in mixtures of various types (blends, solutions, random copolymers, etc.) is elucidated and described. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1273–1281, 1998     

Multielectronic redox and electrocatalytic supramolecular films based on a tetraruthenated iron porphyrin

Layer-by-layer electrostatic assembled Fe-3TRPyP/CuTSPc supramolecular films constituted by homogeneously dispersed electrochemically active columnar structures, about 15 nm high, were obtained and characterized. They are redox conductors acting as rectifiers in the presence of redox species in solution, providing an excellent electrocatalyst for both oxidation and reduction of nitrite and sulfite. The spectroelectrochemical characterization of the supermolecular porphyrin in solution (−2.6 to 2.3 V) revealed 11 redox processes involving up to 26 electrons, allowing further applications of the thin films as multi electron-transfer catalysts and active materials for molecular devices.     

Phenylboronate-diol crosslinked polymer gels with reversible sol-gel transition

Covalent dynamic gels based on reversible phenylboronic acid-diol ester bonds were prepared by crosslinking of N,N-dimethylacrylamide-4-((4-vinylbenzyloxy)carbonyl)phenylboronic acid copolymer, poly(VPB-co-DMA), and poly(2,2-bis(hydroxymethyl)butyl acrylate) (PHBA) in several organic solvents at ambient temperature. These gels formed rapidly and revealed typical properties of chemical gels. Analysis of the composition-property relationships of these polymer gels, specifically considering the effects of pH, molar ratio of HBA to VPB units, and gelator concentrations on dynamic rheological properties, were performed. Additionally, the polymer gels can be switched into their starting polymer solutions by adjusting pH of the system. The reversible sol-gel phase transition can be performed for several cycles in a similar way of supramolecular gel. Moreover, the gel revealed interesting self-healing property which occurred autonomously without any outside intervention. Employing this dynamic character, it is possible to regenerate the used gel, and thus has the potential to perform in a range of dynamic or bioresponsive applications.     

Ternary hydrogen-bonded polymer solutions

Ternary-phase diagrams have been experimentally determined at 100°C for systems containing a series of poly(n-alkyl methacrylates), poly(ethylene oxide) (PEO), and a solvent [4-ethyl phenol (EPh)]. A totally miscible phase diagram is experimentally determined for the poly(methyl methacrylate)/PEO/EPh system, while a closed-loop diagram is observed for the analogous system containing poly(ethyl methacrylate). The corresponding phase diagrams of analogous mixtures containing poly(n-propyl methacrylate) or poly(n-butyl methacrylate) exhibit large heterogeneous areas. Theoretically predicted phase diagrams calculated using an association model developed in our laboratory are in general accord with these observations for ternary hydrogen-bonded polymer/polymer solutions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1265–1271, 1998     

Transforming covalent organic framework into thin-film composite membranes for hydrocarbon recovery

We, for the first time, employed chemically stable covalent organic framework (COF) (TpPa-1) as a transport-active phase within the polymer (styrene-butadiene rubber; SBR) matrix to make TpPa-1@SBR thin-film composite (TFC) membranes. Three composite membranes, viz., TpPa-1(30)@SBR, TpPa-1(50)@SBR, and TpPa-1(70)@SBR have been prepared with varying COF content. These membranes were characterized for gas permeance and results were compared with the pristine SBR-based TFC membrane. The fully organic nature of chemically stable COF offered good compatibility with the host polymer matrix (SBR) and resulted into flexible TFC membranes even at 70% of COF loading; compared to the other porous material (MOFs or Inorganic fillers), it is appreciable.     

Water-selective hybrid membranes with improved interfacial compatibility from mussel-inspired dopamine-modified alginate and covalent organic frameworks

Hybrid membranes combining the merits of both polymer matrices and fillers have drawn extensive attention. The rational design of polymer–filler interface in hybrid membranes is vitally important for reducing the occurrence of void defects. Herein, imine-type covalent organic frameworks(COFs) were selected as the fillers due to their totally organic nature and multi-functionalities. Mussel-inspired dopamine-modified sodium alginate(Alg DA) was synthesized as the polymer matrix. The dopamine modification significantly improves the Alg DA–COF compatibility,which enhances the COF content up to 50 wt% in the hybrid membranes. The improved interfacial compatibility enhances the membrane separation selectivity. Accordingly, when utilized for dehydration of ethanol/water mixed solution(water concentration of 10 wt%), the hybrid membrane reveals high water concentration of ～98.7 wt% in permeate, and stable permeation flux larger than 1500 g·m~(-2)·h~(-1). This work might afford useful insights for fabricating hybrid membranes with high separation selectivity by optimizing the polymer–filler interface.     

国内有机高分子絮凝剂的开发及应用

介绍了我国有机高分子絮凝剂研究开发的历史与现状及其在水处理中的应用，内容涉及合成有机高分子絮凝剂，化学改性天然高分子絮凝剂和微生物絮凝剂；介绍了我国有机高分子絮凝剂的产业现状，生产技术水平及国内外差距，同时指出，随着水资源短缺日趋严重和环保法规的日益强化，有机高分子絮凝剂在水处理中的应用将迅速增加。     

基于超分子化学方法制备自愈合聚合物材料的研究进展

本文综述了超分子化学方法制备自愈合聚合物材料的研究进展,着重介绍了利用氢键、π-π键、离子键等非共价键主-客体相互作用来制备自愈合聚合物材料的研究现状。     

有机高分子絮凝剂的研究进展

简单总结了有机高分子絮凝剂的发展概况,介绍了人工合成有机高分子絮凝剂和天然改性有机高分子絮凝剂的合成方法和在水处理领域的应用,并对其发展前景进行了展望。     

Synthesis and rheological properties of an associative star polymer in aqueous solutions

Rheological properties of aqueous solutions and hydrogels formed by an amphiphilic star block copolymer, poly(acrylic acid)-block-polystyrene (PAA₅₄-b-PS₆)₄, were investigated as a function of the polymer concentration (C_p), temperature, and added salt concentration. The water-soluble polymer synthesised by atom transfer radical polymerization (ATRP) was found to form hydrogels at room temperature at polymer concentrations, C_p, over 22 g/L due to the interpolymer hydrophobic association of the PS blocks. Increasing C_p leads to stronger elastic networks at room temperature that show a gel-to-solution transition with increasing temperature. Increase of ionic strength decreases the moduli compared with the pure hydrogel but did not affect the gel-sol transition temperature significantly. Small-angle X-ray experiments showed two distinct scattering correlation peaks for samples above the gelling C_p, which indicates the aggregates formed due to hydrophobic association. Upon heating the intensity of the scattering correlation peaks was found to decrease indicating the loss of the network structure due to thermal motion.