Hydrogen-bonded Polymer Complexes Research Articles

Hydrogen bonded polymer complex thin films for highly stretchable gas barriers

Highly flexible buffer-cured hydrogen bonded polymer complex coating demonstrates high oxygen barrier up to 50% strain.

Stabilize and Reinforce Hydrogen-Bonded Polymer Complex Elastic Fiber by Catechol Chemistry and Coordination

Stabilize and Reinforce Hydrogen-Bonded Polymer Complex Elastic Fiber by Catechol Chemistry and Coordination

Photo-responsive Behaviors of Hydrogen-Bonded Polymer Complex Fibers Containing Azobenzene Functional Groups

Photo-responsive Behaviors of Hydrogen-Bonded Polymer Complex Fibers Containing Azobenzene Functional Groups

Transparent and mechanically strong hydrogen-bonded polymer complex elastomers with improved self-healability under ambient conditions

A major challenge in designing self-healing polymeric materials is to combine robust mechanical properties and high healing efficiency. Herein, we report a kind of transparent, hydrogen-bonded polymer complex elastomers with both good mechanical strength and rapid self-healing capability under ambient conditions. Such elastomers were simply fabricated by in situ photoinitiated random copolymerization of acrylic acid (AA) and N-acryloyl-6-aminocaproic acid (A6ACA), in the presence of a linear polyethylene oxide (PEO). By evaporating water molecules from the samples via free drying, the dynamical hydrogen bonding between PEO and poly(A6ACA-co-AA) were substantially formed, which endowed the polymer chains to form physically crosslinked three-dimensional polymer network, as well as the topological chain entanglements. The resulting optically transparent elastomers exhibited both good mechanical strengths (at break) as high as 1.73 MPa, and excellent stretchability that could be stretched up to 24 times their initial length, respectively. Comparing with the elastomers based on PEO and PAA homopolymer without the A6ACA comonomer, the introduction of A6ACA as a comonomer afforded complex elastomers with comparable mechanical strength and, more importantly, significantly improved self-healing efficiency even under ambient conditions, probably due to the significantly decreased glass transition temperature that facilitated chain mobility and reformation of hydrogen bonds. It is therefore believed that the copolymerization strategy offers a practical method to tune the compositions and to tailor the properties of hydrogen-bonded polymer complexes for engineering elastomers with balanced mechanical and self-healing performance under ambient environment for various applications.

Functionalization-Directed Stabilization of Hydrogen-Bonded Polymer Complex Fibers: Elasticity and Conductivity

Elastic, repairable and conductive fibers are desirable in the newly emerging field of soft electronic and wearable devices. Here, we design a multifunctional fiber by incorporation of different components to optimize its performance. The combination of the poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) through hydrogen bonding endows the fiber with high elasticity and repairability. Polydopamine (PDA) significantly increases the stability of the fiber, thus the fiber will not dissolve in alkaline solutions and still keep the repairable ability. The fiber shows a reversible swelling-shrinking property as pH values go up and down. Further, the conductive component, carbon nanotube, is adsorbed at the swelling state and then is fastened with fiber shrinking.

Hydrogen-bonded thin films of cellulose ethers and poly(acrylic acid)

Etherification of cellulose can get a series of water soluble derivatives, which can form hydrogen-bonded polymer complex with poly(acrylic acid) (PAA). Three cellulose ethers hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC) and methyl cellulose (MC) are LbL assembled with PAA to fabricate thin films. The hydrogen bonding of the films is characterized with FT-IR. The film growth behaviors are monitored by a quartz crystal microbalance (QCM) and a spectroscopic interferometer, which shows a different growth rate for different system and a strong dependence on pH values. The stability of the films can be increased by heat treatment. Once the cross-linked structure is formed, and the dissolution of film can be prevented even in the high pH value. In addition, the films show good water adsorption ability from environment. Owing to pH responsive behavior and good water adsorption, CE/PAA films can be explored for various applications, especially for biomedical application.

Nanofiltration membrane constructed by tuning the chain interactions of polymer complexation

The complete hydrolysis of poly(2-ethyl-2-oxazoline) (PEOX) produces poly(ethylene imide) (PEI). While PEOX and poly(acrylic acid) (PAA) can form hydrogen-bonded polymer complexes that are precipitated from solution at low pH values, PEI and PAA can form polyelectrolyte complexes in the solutions with neutral pH values. In this work, partially hydrolyzed PEOX (PEOX-EI, hydrolysis degree 60%) and PAA are selected to prepare nanofiltration (NF) membranes. In order to obtain homogenous mixed solutions that are suitable for the membrane preparation, alkaline (NaOH) is precisely added into the system to tune the hydrogen bonding and electrostatic force between the PEOX-EI and PAA chains. FT-IR spectroscopy is applied to investigate the interactions between the PEOX-EI and PAA chains. The rheological behaviors of the homogenous mixed solutions of PEOX-EI and PAA are studied in order to optimize the membrane casting conditions. By taking the advantage of the reaction between the imine groups in PEI chains and terephthaloyl chloride, the cast membranes are further cross-linked to enhance the membrane stability. The NF performance of the complex membrane is then evaluated using methyl blue (MYB) solutions, resulting in a MYB rejection rate of 99.2% and a flux of 55.8 L/m2·h under the pressure of 6 bar.

Dewetting Behavior of Hydrogen Bonded Polymer Complex Film under Hydrothermal Condition

Hydrogen-bonded polymer complex films with the thickness ranging from 50 nm to 2400 nm were prepared by layer-by-layer (LbL) assembly of poly(2-ethyl-2-oxazoline) (PEOX) and poly(acrylic acid) (PAA). The dewetting behavior of PEOX/PAA films under hydrothermal condition was investigated. It was found that the dewetting occurred at solid-liquid interface, and the typical morphologies such as holes, irregular cellular structure, and droplets were observed. Atomic force microscopy (AFM) revealed the initial rupture of the film. Microscopic Raman and infrared (IR) imaging demonstrated that the PEOX and PAA chains remained association during the dewetting process.

Chain diffusion and exchange during build-up of hydrogen-bonded polymer complex film

Poly(vinylpyrrolidone) (PVPON) and poly(acrylic acid) (PAA) were layer-by-layer (LbL) assembled to prepare thin film based on hydrogen bonding. A series of simple experiments were designed to investigate polymer chain diffusion and exchange behaviors of hydrogen-bonded PVPON/PAA film. PAA was labeled with fluorescence dye, fluorescein amine (FAM). The prepared (PVPON/PAA)20 films were immersed into PAA solution, PVPON solution and PAA-FAM solution separately, for a period that was much longer than the assembly time, and the thickness, the composition and the characteristic absorbance of the film were monitored. The experiment results indicated that polymers not only diffused into the thin film from the assembly solution but also diffused out from the thin film into the assembly solution, i.e. there existed a polymer chain exchange. The growth of hydrogen-bonded PVPON/PAA film was related with polymer chain diffusion and exchange at a certain time scale.

Rheological behavior and self-healing of hydrogen-bonded complexes of a triblock Pluronic® copolymer with a weak polyacid

Hydrogen-bonded polymer complexes (HBPCs) form upon association of macromolecules via multiple intermolecular hydrogen bonds. The transient nature of their hydrogen bonding enables their responsiveness to external stimuli such as pH, temperature, and solvents or external fields. Here, hydrogen-bonded assemblies were obtained via the complexation of a triblock copolymer Pluronic® F127, with poly(methacrylic acid) (PMAA). Various rheological material functions of PMAA/F127 complexes, including dynamic properties, relaxation modulus, and shear viscosity, were characterized using steady torsional, oscillatory shear, step strain, compressive squeeze, and capillary flows. The structure of the HBPCs involves agglomerates of the hydrogen-bonded complexes, i.e. nanoclusters, connected by hydrogen bonding interactions. The strengths of the hydrogen bonds in the HBPCs could be manipulated via the exposure of these complexes to aqueous solutions at different pH levels and/or cosolvent concentrations, resulting in changes in the elasticity and viscosity of the HBPCs. Especially the ionization degree, the resultant ratio of the polyacid to F127, and the development of micro- and nanoscale porosity played significant roles in the manipulation of the rheological behavior of the HBPCs. Under low pH conditions, the PMAA/F127 HBPCs could be extruded from capillary dies with relatively small diameters (800–1500 μm) and high length over diameter ratios (40–60). Upon exit from capillary dies, the extrudates preserved their shape, albeit exhibiting flow instabilities and the associated bulk distortions at high shear rates. Under low pH conditions, the generalized Maxwell model described the relaxation modulus in the linear regime, and the Kaye-Bernstein, Kearsley and Zapas model was effective in the prediction of the shear viscosity of the HBPC. The self-healing behavior of PMAA/F127 complexes was demonstrated and linked to the pH-controllable hydrogen-bonding interactions between PMAA and F127.

Hydrogen-Bonded Polymer Complex Thin Film of Poly(2-oxazoline) and Poly(acrylic acid).

The hydrogen-bonded polymer complex thin film of poly(2-ethyl-2-oxazoline) (PEOX) and poly(acrylic acid) (PAA) was fabricated with layer-by-layer (LbL) assembly. The film shows exponential growth at early stage and transfers to linear growth after 10 assembling cycles, and the stable thickness increment per assembling cycle in the linear region could be higher than 100 nm. The film growth should be related with polymer chain diffusion during LbL assembly. The effects of assembling time, rinsing time, temperature, pH value, concentration and molecular weight on the thin film growth were investigated. Increasing the assembly time, the temperature and the concentration is favorable to produce the thick film. Prolonging rinsing time is good for preparing smooth film. The film can be constructed below pH 4.5 while the prepared film will not completely dissolve until pH value elevates to 7.0. Molecular weight has a subtle effect on the PEOX/PAA film growth. The PEOX-PAA pair that has a big molecular weight contrast shows fast film growth in the linear region.

Highly Elastic Fibers Made from Hydrogen-Bonded Polymer Complex

In this letter, we put forward an approach to prepare hydrogen-bonded complex fibers. First, a spinnable fluid is obtained by restricting hydrogen bonds, and then it is extruded through a spinneret into a coagulation bath where hydrogen bonds are built to induce fiber formation. The hydrogen-bonded poly(acrylic acid)/poly(ethylene oxide) (PAA/PEO) complex was prepared into fibers. PAA/PEO fiber shows excellent elastic behavior and can be drawn to more than 12× its original length without breaking, which is much higher than Spandex fiber or natural rubber fiber. In the fiber, PAA and PEO are miscible in the molecular level. Dynamic hydrogen bonding between PAA and PEO restricts the crystallization of PEO, retains flexibility of polymer chains, and also provides recovery forces when removing stress.

Hydrogen-bonded polymer complexes and nanocages of weak polyacids templated by a Pluronic® block copolymer.

We investigate the phase behavior, morphology, and temperature response of hydrogen-bonded assemblies formed by a triblock copolymer Pluronic® F127 (F127) and polycarboxylic acids of varied hydrophobicity and chain lengths. As confirmed by FTIR, the complexes of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) with F127 at acidic pH were stabilized by multiple hydrogen bonding between carboxylic acid groups of polyacids and ether groups of F127. The colloidal stability of the polyacid/F127 complexes (their occurrence as stable dispersions, slowly coagulating dispersions or precipitates) was dependent on the composition of complexes, polyacid molecular weight and hydrophobicity, as well as temperature. For both polyacids, complexes could not be solubilized in excess of polyacids, but excess of F127 resulted in the formation of colloidally stable nanostructured clusters whose size could be controlled from tens to hundreds of nanometers by the polyacid-to-F127 ratio, temperature, and the polyacid molecular weight. Hydrophobicity of polyacids had a dramatic effect on the temperature response of Pluronic®-enriched assemblies. While PMAA suppressed the LCST behavior of F127 due to binding within the temperature-responsive PPO core of F127, more hydrophilic PAA allowed F127 micellization and supported reversible, temperature-induced re-structuring of PAA-F127 clusters. At temperatures above the LCST of Pluronic®, low-molecular-weight PAA formed nanosized dispersed complexes, in which the polyacid chains were wrapped around individual F127 micelles. Chemical crosslinking of PAA in the shells of these complexes followed by removal of the templating F127 cores resulted in easy-to-prepare monodisperse pH-responsive polymer nanocages with controllable size and swelling amplitude.

Hydrogen-Bonded Polymers with Bent-Shaped Side Chains and Poly(4-vinylpridine) Backbone: Phase Behavior and Thin Film Morphologies

We investigate the self-assembly behavior of a series of supramolecular hydrogen bonded polymer complexes P4VP(nCBP)x in which bent-shaped molecules (nCBP, n = 10,12,14) are attached to a poly(4-vinylpridine) (P4VP) backbone via hydrogen bond interaction in both bulk and thin films. The formation of lamellar and hexagonal columnar (ΦH) phases are dependent on the blending ratio of nCBP per vinylpridine unit (x), aliphatic tail length (n), and temperature. When increasing the grafting density x, the phase structure of polymer complexes transform from lamellar to ΦH phase. A nonreversible lamellar to ΦH phase transition appears in the heating process for P4VP(10CBP)x with x ≥ 0.4, P4VP(12CBP)x with x ≥ 0.3, and P4VP(14CBP)x with x ≥ 0.2. The lamellar and ΦH phase are oriented parallel to the substrate in the thin film as verified by both GISAXS and AFM.

Hydrogen bond detachment in polymer complexes

The hydrogen bonded polymer complex bulk and thin film was prepared by solution mixing and layer-by-layer assembly, respectively. Poly(vinylpyrrolidone) (PVPON) and poly(ethylene oxide) (PEO) were hydrogen bonding acceptor polymers while poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) were hydrogen bonding donor polymers. The detachment of hydrogen bond between the chains in polymer complexes was investigated during the dissolution in alkaline solution, ionic liquid and tertiary amine N-oxide. We compared the dissolution process of the polymer complex bulk with the polymer complex thin film, and discussed the polymer chain length, chain entanglement degree and temperature effect on hydrogen bond detachment and dissolution of polymer complexes.

Chain Dynamics of Water-Saturated Hydrogen-Bonded Polymer Complexes and Multilayers

The chain mobility of a series of hydrogen-bonded polymer complexes and multilayers were compared by variable temperature wide-line deuterium NMR spectroscopy. Poly(methacrylic acid), deuterated at the methyl group, PMAA-d3, was complexed with five different hydrogen bond acceptor polymers—poly(ethylene oxide) (PEO), poly(acrylamide) (PAAM), poly(vinyl methyl ether) (PVME), poly(vinylpyrrolidone) (PVPon), and poly(vinylcaprolactam) (PVCL)—as well as with chitosan, where the interaction should be primarily ion pairing. The overall chain mobility of PMAA in its water-saturated complexes was observed to increase in the following order: PVCL < PVPon < chitosan < PVME < PAAM < PEO. For these polymer pairs, the same trend in chain mobility was also confirmed for the first few layers deposited on colloidal silica. The observed chain dynamics correlate well with the reported variation of the critical pH, bilayer thickness, and the permeability for multilayer films of the same polymers. In addition, the extent of ...

Hydrogen-bonded polymer complexes of macrocycles containing a pyridyl moiety and carboxyl-functionalized polystyrenes

Copolystyrenes complexed with macrocyclic compounds through hydrogen bonding have been synthesized by the copolymerization of styrene with the complex of 4-vinylbenzoic acid and crown ethers containing a 2,6-pyridyl moiety. The glass transition temperatures of the copolymeric complexes are significantly lower than that of the simple copolymer, which shows that the carboxylic acid groups in the polymer backbone do not intermolecularly dimerize. The UV absorption spectra of polymeric complexes suggest that they have complex structures similar to that of the low-molecular-weight complexes of 4-ethylbenzoic acid and the crown ethers.

Hydrogen-bonded polymer complexes

Hydrogen-bonded polymer complexes formed from poly(4-hydroxystyrene) and poly( N, N-dimethyl-acrylamide) were studied by cross-polarization/magic angle spinning 13C nuclear magnetic resonance spectroscopy. Evidence for specific interaction was provided by a shift of ∼3 ppm in the phenolic carbon resonance peak. The proton spin-lattice relaxation times are shorter than the values predicted by a linear model. On the other hand, the rotating frame spin lattice relaxation times, T 1 ϱ , of the complexes agree with the predictions. The scale of homogeneity is estimated from the T 1 ϱ data to be ∼2.5 nm.