Self‐Healing,Expansion–Contraction,and Shape‐Memory Properties of a Preorganized Supramolecular Hydrogel through Host–Guest Interactions

Supramolecular materials cross‐linked between polymer chains by noncovalent bonds have the potential to provide dynamic functions that are not produced by covalently cross‐linked polymeric materials. We focused on the formation of supramolecular polymeric materials through host–guest interactions: a powerful method for the creation of nonconventional materials. We employed two different kinds of host–guest inclusion complexes of β‐cyclodextrin (βCD) with adamantane (Ad) and ferrocene (Fc) to bind polymers together to form a supramolecular hydrogel (βCD‐Ad‐Fc gel). The βCD‐Ad‐Fc gel showed self‐healing ability when damaged and responded to redox stimuli by expansion or contraction. Moreover, the βCD‐Ad‐Fc gel showed a redox‐responsive shape‐morphing effect. We thus succeeded in deriving three functions from the introduction of two kinds of functional units into a supramolecular material.     

Self‐Healing,Expansion–Contraction,and Shape‐Memory Properties of a Preorganized Supramolecular Hydrogel through Host–Guest Interactions

Supramolecular materials cross‐linked between polymer chains by noncovalent bonds have the potential to provide dynamic functions that are not produced by covalently cross‐linked polymeric materials. We focused on the formation of supramolecular polymeric materials through host–guest interactions: a powerful method for the creation of nonconventional materials. We employed two different kinds of host–guest inclusion complexes of β‐cyclodextrin (βCD) with adamantane (Ad) and ferrocene (Fc) to bind polymers together to form a supramolecular hydrogel (βCD‐Ad‐Fc gel). The βCD‐Ad‐Fc gel showed self‐healing ability when damaged and responded to redox stimuli by expansion or contraction. Moreover, the βCD‐Ad‐Fc gel showed a redox‐responsive shape‐morphing effect. We thus succeeded in deriving three functions from the introduction of two kinds of functional units into a supramolecular material.     

An H‐shaped polymer bonding β‐cyclodextrin at branch points: Synthesis and influences of attached β‐cyclodextrins on physical properties

We report on the synthesis of an H‐shaped polymer bonding β‐cyclodextrin (β‐CD) at branch points and influences of attached β‐CD on physical properties. First, a poly(ethylene glycol)(PEG)‐based functional macroinitiator bearing two azidos and four chlorines at chain‐ends (PEG‐2N₃(‐4Cl)) was prepared via terminal modification reactions. Then, PEG‐2N₃(‐4Cl) was applied to initiate the atom transfer radical polymerization of N‐isopropylacrylamide, leading to the synthesis of an H‐shaped block polymer with PEG as the central chain and poly(N‐isopropylacrylamide) (PNIPAM) as side‐arms (PEG‐2N₃(‐4PNIPAM)). Azido groups were at the branch points of the polymer. Finally, the click reaction between PEG‐2N₃(‐4PNIPAM) and alkynyl monosubstituted β‐cyclodextrin (β‐CD) afforded another H‐shaped polymer with two β‐CDs bonding at the polymer branch points (PEG‐2CD(‐4PNIPAM)). The glass transition temperature (T_g) and lower critical solution temperature (LCST) of the H‐shaped polymer increased after the attachment of β‐CD. The self‐assembly and thermal responsive behaviors, as well as the encapsulation behaviors of PEG‐2CD(‐4PNIPAM) were also altered. When temperature was below the LCSTs, PEG‐2N₃(‐2PNIPAM) dissolved in water molecularly, whereas PEG‐2CD(‐4PNIPAM) could self‐assemble into nano‐sized micelles. After the LCST transitions, PEG‐2N₃(‐4PNIPAM) aggregated into micron‐sized unstable particles, whereas PEG‐2CD(‐4PNIPAM) transformed into PNIPAM‐cored nanomicelles. Besides, PEG‐2CD(‐4PNIPAM) can encapsulate doxorubicin below its LCST due to the formation of micelles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Heat‐Induced Supramolecular Organogels Composed of α‐Cyclodextrin and “Jellyfish‐Like” β‐Cyclodextrin–Poly(ε‐caprolactone)

In general, the complexation and gelation behavior between biocompatible poly(ε‐caprolactone) (PCL) derivatives and α‐cyclodextrin (α‐CD) is extensively studied in water, but not in organic solvents. In this article, the complexation and gelation behavior between α‐CD and multi‐arm polymer β‐cyclodextrin‐PCL (β‐CD‐PCL) with a unique “jellyfish‐like” structure are thoroughly investigated in organic solvent N,N‐dimethylformamide and a new heat‐induced organogel is obtained. However, PCL linear polymers cannot form organogels under the same condition. The complexation is characterized by rheological measurements, DSC, XRD, and SEM. The SEM images reveal that the complexes between β‐CD‐PCL and α‐CD present a novel topological helix porous structure which is distinctly different from the lamellar structure formed by PCL linear polymers and α‐CD, suggesting the unique “jellyfish‐like” structure of β‐CD‐PCL is crucial for the formation of the organogels. This research may provide insight into constructing new supramolecular organogels and potential for designing new functional biomaterials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1598–1606     

Redox‐ and Glucose‐Induced Shape‐Memory Polymers

A novel redox‐induced shape‐memory polymer (SMP) is prepared by crosslinking β‐cyclodextrin modified chitosan (β‐CD‐CS) and ferrocene modified branched ethylene imine polymer (Fc‐PEI). The resulting β‐CD‐CS/Fc‐PEI contains two crosslinks: reversible redox‐sensitive β‐CD‐Fc inclusion complexes serving as reversible phases, and covalent crosslinks serving as fixing phases. It is shown that this material can be processed into temporary shapes as needed in the reduced state and recovers its initial shape after oxidation. The recovery ratio and the fixity ratio are both above 70%. Furthermore, after entrapping glucose oxidase (GOD) in the system, the material shows a shape memory effect in response to glucose. The recovery ratio and the fixity ratio are also above 70%.

     

pH‐ and β‐cyclodextrin‐responsive micelles based on polyaspartamide derivatives as drug carrier

A novel kind of graft polymer poly(aspartic acid)‐ethanediamine‐g‐adamantane/methyloxy polyethylene glycol (Pasp‐EDA‐g‐Ad/mPEG) was designed and synthesized for drug delivery in this study. The chemical structure of the prepared polymer was confirmed by proton NMR. The obtained polymer can self‐assemble into micelles which were stable under a physiological environment and displayed pH‐ and β‐cyclodextrin (β‐CD)‐responsive behaviors because of the acid‐labile benzoic imine linkage and hydrophobic adamantine groups in the side chains of the polymer. The doxorubicin (Dox)‐loaded micelles showed a slow release under physiological conditions and a rapid release after exposure to weakly acidic or β‐CD environment. The in vitro cytotoxicity results suggested that the polymer was good at biocompatibility and could remain Dox biologically active. Hence, the Pasp‐EDA‐g‐Ad/mPEG micelles may be applied as promising controlled drug delivery system for hydrophobic antitumor drugs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1387–1395     

Noncovalently connected micelles based on a β‐cyclodextrin‐containing polymer and adamantane end‐capped poly(ε‐caprolactone) via host–guest interactions

New random copolymers, poly(N‐vinyl‐2‐pyrrolidone‐co‐mono‐6‐deoxy‐6‐methacrylate ethylamino‐β‐cyclodextrin) (PnvpCD) bearing pendent β‐cyclodextrin (CD) groups were synthesized. PnvpCD formed soluble graft‐like polymer complex with adamantane (AD) end‐capped poly(ε‐caprolactone) (PclAD) in their common solvent N‐methyl‐2‐pyrrolidone driven by the inclusion interactions between the CD and AD groups. The formation of the graft complex has been confirmed by viscometry, dynamic light scattering (DLS), and isothermal titration calorimeter. The graft complex self‐assembled further into noncovalently connected micelles in water, which is a selective solvent for the main chain PnvpCD. Transmission electron microscopy, DLS, and atomic force microscopy have been used to investigate the structure and morphology of the resultant micelles. A unique “multicore” structure of the micelles, in which small PclAD domains scattered within the micelles, was obtained under nonequilibrium conditions in the preparation. However, the micelles prepared in a condition close to equilibrium possess an ordinary core‐shell structure. In both cases, the core and shell are believed to be connected by the AD‐CD inclusion complexation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4267–4278, 2009     

Ultrasound‐Driven Secondary Self‐Assembly of Amphiphilic β‐Cyclodextrin Dimers

The controlled secondary self‐assembly of amphiphilic molecules in solution is theoretically and practically significant in amphiphilic molecular applications. An amphiphilic β‐cyclodextrin (β‐CD) dimer, namely LA‐(CD)₂, has been synthesized, wherein one lithocholic acid (LA) unit is hydrophobic and two β‐CD units are hydrophilic. In an aqueous solution at room temperature, LA‐(CD)₂ self‐assembles into spherical micelles without ultrasonication. The primary micelles dissociates and then secondarily form self‐assemblies with branched structures under ultrasonication. The branched aggregates revert to primary micelles at high temperature. The ultrasound‐driven secondary self‐assembly is confirmed by transmission electron microscopy, dynamic light scattering, ¹H NMR spectroscopy, and Cu²⁺‐responsive experiments. Furthermore, 2D NOESY NMR and UV/Vis spectroscopy results indicate that the formation of the primary micelles is driven by hydrophilic–hydrophobic interactions, whereas host–guest interactions promote the formation of the secondary assemblies. Additionally, ultrasonication is shown to be able to effectively destroy the primary hydrophilic–hydrophobic balances while enhancing the host–guest interaction between the LA and β‐CD moieties at room temperature.     

Preparation and sorption properties of a β‐cyclodextrin‐linked chitosan derivative

β‐Cyclodextrin (β‐CD) was coupled to chitosan by the intermediate of its monochlorotriazinyl derivative, called βW7MCT, so that a chitosan derivative bearing cyclodextrin was obtained. Because the average degree of substitution of the cyclodextrin derivative was 2.8, the reaction yielded crosslinked insoluble products. The structure of these materials has been investigated by high‐resolution magic‐angle spinning (HRMAS) with gradients. For the first time, HRMAS spectra of chitosan polymers containing β‐CD were obtained. This NMR technique produced one‐ and two‐dimensional well‐resolved solid‐state spectra. These data confirm the proposed structure. Decontamination of waters containing textile dyes were carried out with the crosslinked derivatives. These tests showed that the new chitosan derivatives are characterized by a rate of sorption and a global efficiency superior to that of the parent chitosan polymer and of the well‐known cyclodextrin‐epichlorohydrin gels. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 169–176, 2001     

Supramolecular Assembly of β‐Cyclodextrin‐Capped Gold Nanoparticles on Ferrocene‐Functionalized ITO Surface for Enhanced Voltammetric Analysis of Ascorbic Acid

A supramolecular recognition functionalized electrode (βCD‐nanoAu/Fc‐ITO) which exhibits redox‐activity was prepared through supramolecular assembly of β‐cyclodextrin (βCD) capped gold nanoparticles (βCD‐nanoAu) on the ITO previously coated with a monolayer of ferrocene residues (Fc‐ITO). The immobilization of βCD‐nanoAu on Fc‐ITO was confirmed by atomic force microscopy (AFM), and the supramolecular nature of the immobilization approach was also confirmed by cyclic voltammetry. On the other hand, the electrocatalytic activity of βCD‐nanoAu/Fc‐ITO electrode was also studied. The electrocatalytic activity toward ascorbic acid (AA) was enhanced compared with that at the Fc‐ITO electrode, and a linear relationship existed between the anodic peak and the concentration of AA in the range of 5.3×10^?5 to 3.0×10^?3 M with a detection limit (S/N=3) of 4.1×10^?6 M.     

Redox‐Responsive Macroscopic Gel Assembly Based on Discrete Dual Interactions

The macroscopic self‐assembly of polymeric hydrogels modified with β‐cyclodextrin (βCD gel), ferrocene (Fc gel), and styrenesulfonic acid sodium salt (SSNa gel) was investigated. Under reductive conditions, the Fc gel selectively adhered to the βCD gel through a host–guest interaction. On the other hand, the oxidized ferrocenium (Fc⁺) gel selectively adhered to the SSNa gel through an ionic interaction under oxidative conditions. The adhesion strength was estimated by a tensile test. We finally succeeded in forming an ABC‐type macroscopic assembly of all three gels through two discrete noncovalent interactions.     

Biobased poly(2,5‐furandimethylene succinate‐co‐butylene succinate) crosslinked by reversible Diels–Alder reaction

We synthesized biobased poly(2,5‐furandimethylene succinate‐co‐butylene succinate) [P(FS‐co‐BS)] copolymers by polycondensation of 2,5‐bis(hydroxymethyl)furan, 1,4‐butanediol, and succinic acid. These copolymers could be crosslinked to form network polymers by means of a reversible Diels–Alder reaction with bis‐maleimide. The thermal properties, mechanical properties, and healing abilities of the P(FS‐co‐BS)s and the network polymers were investigated. The mechanical properties of the network polymers depended on the comonomer composition of the P(FS‐co‐BS)s and the maleimide/furan ratio in the network polymers. Some of the copolymers exhibited healing ability at room temperature, and their healing efficiency was enhanced by solvent or heat. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 216–222     

Polymerization and characterization of self‐assembled β‐cyclodextrin‐threaded chiral monomers

A helical inclusion complex polymer was fabricated through the polymerization of β‐cyclodextrin‐threaded chiral monomers. The photo induced polymerization of inclusion complex clusters caused shrinkage of the polymer and decreased the pitches, leading to the disappearance of spring‐like construction under TEM. From the results of circular dichroism of the inclusion complex polymer, the helical construction was confirmed, and an entanglement of the polymer chains is proposed. After removal of the β‐cyclodextrins from the pendant groups of the inclusion complex polymer, the helical structure was found to be maintained. The highly ordered molecular arrangement of β‐cyclodextrins removed from the inclusion complex polymer was confirmed using POM. Here we demonstrate the fabrication of helical polymer fibers composed of entangled polymers through self‐assembled β‐cyclodextrin‐threaded chiral monomers. The helical polymer construction was maintained by the entwisted polymer chains even after the removal of β‐cyclodextrins from the pendant groups of the inclusion complex polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2975–2981, 2010     

Redox‐Switchable Supramolecular Graft Polymer Formation via Ferrocene–Cyclodextrin Assembly

The redox switchable formation of very well‐defined supramolecular graft polymers in aqueous solution driven by host–guest interactions between ferrocene (Fc) and cyclodextrin (CD) is presented. The Fc‐containing acrylic backbone copolymer (PDMA‐stat‐Fc) is prepared via reversible addition–fragmentation chain transfer (RAFT) copolymerization of N,N‐dimethyl­acrylamide (DMA) and the novel monomer N‐(ferrocenoylmethyl)acrylamide (NFMA). Via the RAFT process, copolymers containing variable Fc ratios (5‐10 mol%) are prepared, affording polymers of molecular masses of close to 11 000 g mol⁻¹ and molar mass dispersities (Đ) of 1.2. The β‐cyclodextrin (β‐CD) containing building block is synthesized via RAFT‐polymerization, too, in order to afford a polymer with well‐defined molecular mass and low dispersity ( = 10 300 g mol⁻¹, Đ = 1.1), employing a propargyl‐functionalized chain transfer agent for the polymerization of N,N‐diethylacrylamide (DEA). The polymerization product is subsequently terminated with β‐CD via the regiospecific copper (I)‐catalyzed 1,3‐cycloaddition (PDEA‐βCD). Host–guest interactions between Fc and CD lead to the formation of supramolecular graft‐polymers, verified via nuclear Overhauser enhancement spectroscopy (NOESY). Importantly, their redox‐responsive character is clearly confirmed via cyclic voltammetry (CV). The self‐assembly of the statistical Fc‐containing lateral polymer chain in aqueous solution leads to mono‐ and multi‐core micelle‐aggregates evidenced via TEM. Only diffused cloud‐like, non‐spherical nanostructures are observed after addition of PDEA‐βCD (TEM).

     

β‐Cyclodextrin polymer brushes based on hyperbranched polycarbosilane: Synthesis and characterization

In this article, our main goal is to combine hyperbranched polymer with β‐cyclodextrin (β‐CD) to establish a novel functional polymer species with core‐shell structure and supramolecular system for further application in inclusion technologies and the complex drugs delivery system. Therefore, two β‐CD polymer brushes based on hyperbranched polycarbosilane (HBP) as a hydrophobic core and poly(N,N‐dimethylaminoethyl methacrylate) (PDMA) carrying β‐CD units as a hydrophilic shell were synthesized. Hyperbranched polycarbosilane macroinitiator carrying ? Cl groups (HBP‐Cl) was also prepared by using 1,1,3,3‐tetrmethyldisiloxane, allyl alcohol, and chloroacetyl chloride as reagents. The molecular structures of HBP‐Cl macroinitiator and β‐CD polymer brushes were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance (¹H NMR), ¹³C nuclear magnetic resonance (¹³C NMR) spectroscopies, size exclusion chromatography/multi‐angle laser light scattering (SEC/MALLS) and laser particle size analyzer. The results indicate that the grafted chain length of two β‐CD polymer brushes can be controlled by changing the feed ratio. Differential scanning calorimetry (DSC) results show that two β‐CD polymer brushes have two glass transition temperatures (T_gs) from a hydrophobic core part and a hydrophilic shell part, respectively, and the T_g from PDMA is higher than that of HBP‐g‐PDMA. Thermalgravimetric analyzer (TGA) analysis indicates that the thermostability of two β‐CD polymer brushes is higher than that of HBP, but is lower than that of HBP‐g‐PDMA. Using phenolphthalein (PP) as a guest molecule, molecular inclusion behaviors for two β‐CD polymer brushes were studied. It reveals that two β‐CD polymer brushes possess molecular inclusion capability in PP buffer solution with a fixed concentration. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5036–5052, 2008     

Synthesis of ferrocene‐modified poly(glycidyl methacrylate) and its burning rate catalytic property

A series of ferrocene‐modified poly(glycidyl methacrylate) (PGMA‐Fc) compounds were synthesized and applied as burning rate catalysts in simulative solid propellant to overcome migration problems. ¹H NMR and Fourier transform infrared spectroscopies and gel permeation chromatography were used to characterize the synthesized polymers. Their electrochemical behavior was evaluated using cyclic voltammetry. Their catalytic performance for the decomposition of ammonium perchlorate (AP) was investigated using thermogravimetric analysis. Anti‐migration studies were conducted in migration tubes under 50°C. The results show that PGMA‐Fc has a good catalytic effect on lowering the thermal decomposition temperature of AP. Anti‐migration studies show that PGMA‐Fc has better anti‐migration performance than ferrocene and catocene.     

Asymmetric cyclopolymerization of N‐tert‐butyl‐N‐allylacrylamide in the presence of β‐cyclodextrin

The radical polymerization of N‐tert‐butyl‐N‐allylacrylamide (t‐BAA) was carried out in a dimethyl sulfoxide/H₂O mixture in the presence of β‐cyclodextrin (β‐CD). The polymerization proceeded with the complete cyclization of the t‐BAA unit and yielded optically active poly(t‐BAA). The IR spectrum of the obtained polymer showed that the cyclic structure in the polymer was a five‐membered ring. The optical activity of poly(t‐BAA) increased with an increasing molar ratio of β‐CD to the t‐BAA monomer. The interaction of β‐CD with t‐BAA was confirmed by ¹H NMR and ¹³C NMR analyses of the polymerization system. It is suggested that interaction of the t‐BAA monomer with the hydrophobic cavity of β‐CD plays an important role in the asymmetric cyclopolymerization of t‐BAA. The radical copolymerization of t‐BAA with styrene (St), methyl methacrylate, ethyl methacrylate, or benzyl methacrylate (BMA) also produced optically active copolymers with a cyclic structure from the t‐BAA unit. St and BMA carrying a phenyl group were predicted to compete with t‐BAA for interaction with β‐CD in the copolymerization system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2098–2105, 2000     

Catalytic Au Electrodes Based on SAMs of per(6‐deoxy‐6‐thio‐2,3‐di‐O‐methyl)‐β‐cyclodextrin

A three‐step sequential self‐assembly procedure was applied in preparing gold electrodes modified in a stable and controlled way by a monolayer of thiolated β‐cyclodextrin (β‐CD), with methylene blue (MB) included in its cavity as the active component of the monolayer, and octanethiol as the nonelectroactive spacer blocking the electrode surface not occupied by β‐CD. MB acted as a mediator of electrons with respect to a solution soluble analyte, H₂O₂, and provided electrical contact between the electrode and solution resident enzyme, laccase, catalyzing reduction of oxygen to water.     

Self‐healing of poly(propylene oxide)‐polybenzoxazine thermosets by photoinduced coumarine dimerization

In this work, a self‐healing strategy for poly(propylene oxide)s bearing coumarine‐benzoxazine units (PPO‐CouBenz)s based on light induced coumarine dimerization reactions is described. Four different types of poly(propylene oxide) amines with molecular weights ranging from 440 to 5000 Da were reacted with formaldehyde and 4‐methyl‐7‐hydroxycoumarin to yield desired (PPO‐CouBenz)s. The crosslinked polymer films were prepared by solvent casting of various compositions of PPO‐CouBenzs in chloroform followed by thermal ring opening reaction of benzoxazine groups at 210–240 °C. Thermal curing and thermal stability of the initial PPOs and final products were investigated. Using allyl benzoxazine in the formulation, it was demonstrated that the toughness of the films was improved. Photoinduced healing of coumarin‐based cured PPO‐CouBenz polymer films was investigated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2911–2918     

A Rapidly Self‐Healing Supramolecular Polymer Hydrogel with Photostimulated Room‐Temperature Phosphorescence Responsiveness

Development of self‐healing and photostimulated luminescent supramolecular polymeric materials is important for artificial soft materials. A supramolecular polymeric hydrogel is reported based on the host–guest recognition between a β‐cyclodextrin (β‐CD) host polymer (poly‐β‐CD) and an α‐bromonaphthalene (α‐BrNp) polymer (poly‐BrNp) without any additional gelator, which can self‐heal within only about one minute under ambient atmosphere without any additive. This supramolecular polymer system can be excited to engender room‐temperature phosphorescence (RTP) signals based on the fact that the inclusion of β‐CD macrocycle with α‐BrNp moiety is able to induce RTP emission (CD‐RTP). The RTP signal can be adjusted reversibly by competitive complexation of β‐CD with azobenzene moiety under specific irradiation by introducing another azobenzene guest polymer (poly‐Azo).