A thermo‐, photo‐ and chemoresponsive shape‐memory material is successfully prepared by introducing α‐cyclodextrin (αCD) and azobenzene (Azo) into a poly(acrylate acid)/alginate (PAA/Alg) network. The tri‐stimuli‐responsive formation/dissociation of αCD‐Azo acts as molecular switches freezing or increasing the molecular mobility. The resulting film herein can be processed into temporary shapes as needed and recovers its initial shape upon the application of light irradiation, heating, or chemical agent independently. Furthermore, the agar diffusion test suggests that the α‐CD‐Alg/Azo‐PAA has good biocompatibility for L929 fibroblast‐like cells.
In an effort to impart light gas (i.e., H2 and He) barrier to polymer substrates, thin films of polyethylenimine (PEI), poly(acrylic acid) (PAA), and montmorrilonite (MMT) clay are deposited via layer‐by‐layer (LbL) assembly. A five “quadlayer” (122 nm) coating deposited on 51 μm polystyrene is shown to lower both hydrogen and helium permeability three orders of magnitude against bare polystyrene, demonstrating better performance than thick‐laminated ethylene vinyl‐alcohol (EVOH) copolymer film and even metallized polyolefin/polyester film. These excellent barrier properties are attributed to a “nanobrick wall” structure. This highly flexible coating represents the first demonstration of an LbL deposited film with low hydrogen and helium permeability and is an ideal candidate for several packaging and protection applications.
Super gas barrier nanocoatings are recently demonstrated by combining polyelectrolytes and clay nanoplatelets with layer‐by‐layer deposition. These nanobrick wall thin films match or exceed the gas barrier of SiOx and metallized films, but they are relatively stiff and lose barrier with significant stretching (≥10% strain). In an effort to impart stretchability, hydrogen‐bonding polyglycidol (PGD) layers are added to an electrostatically bonded thin film assembly of polyethylenimine (PEI) and montmorillonite (MMT) clay. The oxygen transmission rate of a 125‐nm thick PEI‐MMT film increases more than 40x after being stretched 10%, while PGD‐PEI‐MMT trilayers of the same thickness maintain its gas barrier. This stretchable trilayer system has an OTR three times lower than the PEI‐MMT bilayer system after stretching. This report marks the first stretchable high gas barrier thin film, which is potentially useful for applications that require pressurized elastomers.
Polymeric nanosheets organized by molecular building blocks bearing specifically oriented reactive groups provide abundant and versatile strategies for tailoring structure and chemical functionality periodically over extended length scales that complement graphene. Here we report the bulk synthesis of free‐standing polymeric nanosheets via spatially confined polymerization from an elaborate 2D supramolecular system composed of two liquid‐crystalline lamellar bilayer membranes of a self‐assembled nonionic surfactant—dodecylglyceryl itaconate (DGI)—sandwiched by a water layer. By employing a covalent polymerization on the lamellar bilayer membranes, single‐bilayer‐thick (4.2 nm), and large area (greater than 100 μm2) polymeric nanosheets of bilayer membranes are achieved. The polymeric nanosheets could serve as a well‐defined 2D platform for post‐functionalization for producing advanced hybrid materials by introducing the reactions on the hydroxyl groups at the head of DGI on the outer surfaces.
A new molecular recognition motif between a water soluble pillar[10]arene ( WP10 ) and 1,10‐phenanthrolinium guest ( G ) in water is established. Mainly driven by the cooperativity of multiple electrostatic interactions, hydrophobic interactions, and π–π stacking interactions between WP10 and G , this host–guest complex exhibits a high association constant in water, which is about 17 times higher than that between WP10 and paraquat ( PQ ). Furthermore, this size selective host–guest complexation is employed to tune the lower critical solution temperature behavior of a random copolymer with PQ derivative pendants.
A triblock copolymer containing the complementary hydrogen bonding recognition pair ureidoguanosine–diaminonaphthyridine (UG–DAN) as pendant functional groups is synthesized using ring‐opening metathesis polymerization (ROMP). The norbornene‐based DAN monomer is shown to allow for a controlled polymerization when polymerized in the presence of a modified‐UG molecule that serves as a protecting group, subsequently allowing for the fabrication of functionalized triblock copolymers. The self‐assembly of the copolymers was characterized using dynamic light scattering and 1H NMR spectroscopy. It is demonstrated that the polymers self‐assemble via complementary hydrogen bonding motifs even at low dilutions, indicating intramolecular interactions.
The continuous photopolymerization of acrylate and methacrylate monomer miniemulsions (25% solids content) is investigated at room temperature in a compact helix minireactor. Using n‐butyl acrylate, the process yields 95% conversion after only 27 s residence time, and gel‐free high‐molecular‐weight products. Under optimized conditions, a 25‐fold increase in efficiency is obtained when compared to a batch photopolymerization. The reaction set‐up offers a frugal process because of moderate irradiance (2.6 mW cm?2), photoinitiator concentration (0.75 wt%), and low‐power UV‐A fluorescent lamp.
A series of (SiO2/MgO/MgCl2)?TiClx Ziegler‐Natta polyethylene catalysts have been synthesized using water‐soluble Mg‐compounds such as magnesium acetate as Mg‐source at different TiCl4 treating temperatures. The catalyst shows the highest activity of homopolymerization when preparation temperature is 120 °C with only 1.25 of optimal Al/Ti molar ratio, which is much lower than industrial value, resulting in much lower catalyst preparation and polyethylene production cost. The operation condition is relatively moderate and the synthesized catalysts exhibit rather high activity, good hydrogen response, and copolymerization ability with high 1‐hexene incorporation. The polymers obtained from these catalysts have high molecular weight and medium molecular weight distribution. Compared with the conventional industrial Ti/Mg Ziegler‐Natta catalysts using the relatively expensive, anhydrous and moisture‐sensitive Mg‐sources, the most unique feature of our novel catalysts is the capability of utilization of any soluble Mg‐compounds under mild conditions and can achieve rather high activity with only a small amount of cocatalyst, hence show great potential for application in polyethylene industry.
The combined effect of high pressure and electronic photo‐excitation has been proven to be very efficient in activating extremely selective polymerisations of small unsaturated hydrocarbons in diamond anvil cells (DAC). Here we report an ambient temperature, large volume synthesis of high density polyethylene based only on high pressure (0.4–0.5 GPa) and photo‐excitation (~350 nm), without any solvent, catalyst or radical initiator. The reaction conditions are accessible to the current industrial technology and the laboratory scale pilot reactor can be scaled up to much larger dimensions for practical applications. FTIR and Raman spectroscopy, and X‐ray diffraction, indicate that the synthesised material is of comparable quality with respect to the outstanding crystalline material obtained in the DAC. The polydispersity index is comparable to that of IV generation Ziegler‐Natta catalysts. Moreover the crystalline quality of the synthesised material can be further enhanced by a thermal annealing at 373 K and ambient pressure.
Tuning the chain‐end functionality of a short‐chain cationic homopolymer, owing to the nature of the initiator used in the atom transfer radical polymerization (ATRP) polymerization step, can be used to mediate the formation of a gel of this poly(electrolyte) in water. While a neutral end group gives a solution of low viscosity, a highly homogeneous gel is obtained with a phosphonate anionic moiety, as characterized by rheometry and diffusion nuclear magnetic resonance (NMR). This novel type of supramolecular control over poly(electrolytic) gel formation could find potential use in a variety of applications in the field of electro‐active materials.
A novel type of emulsion gel based on star‐polymer‐stabilized emulsions is highlighted, which contains discrete hydrophobic oil and hydrophilic aqueous solution domains. Well‐defined phenol‐functionalized core‐crosslinked star polymers are synthesized via reversible addition‐fragmentation chain transfer (RAFT)‐mediated dispersion polymerization and are used as stabilizers for oil‐in‐water emulsions. Horseradish‐peroxidase‐catalyzed polymerization of the phenol moieties in the presence of H2O2 enables rapid formation of crosslinked emulsion gels under mild conditions. The crosslinked emulsion gels exhibit enhanced mechanical strength, as well as widely tunable composition.
The host–guest complexation between a porphyrin‐based 3D tetragonal prism ( H ) and electron‐rich pyrene is investigated. This host–guest molecular recognition is further utilized to suppress the liquid‐crystalline behavior of a nematic molecule ( G ) containing cyanobiphenyl mesogens functionalized with a pyrenyl unit. Furthermore, coronene, with an increased number of π‐electrons, is used as a competitive guest to recover the liquid‐crystalline behavior of G . This supramolecular approach provides a glimpse of the new possibilities to modulate the structures of the mesophases.
A photocleavable terpolymer hydrogel cross‐linked with o‐nitrobenzyl derivative cross‐linker is shown to be capable of self‐shaping without losing its physical integrity and robustness due to spontaneous asymmetric swelling of network caused by UV‐light‐induced gradient cleavage of chemical cross‐linkages. The continuum model and finite element method are used to elucidate the curling mechanism underlying. Remarkably, based on the self‐changing principle, the photosensitive hydrogels can be developed as photoprinting soft and wet platforms onto which specific 3D characters and images are faithfully duplicated in macro/microscale without contact by UV light irradiation under the cover of customized photomasks. Importantly, a quick response (QR) code is accurately printed on the photoactive hydrogel for the first time. Scanning QR code with a smartphone can quickly connect to a web page. This photoactive hydrogel is promising to be a new printing or recording material.
Recent studies have shown that polymersomes templated by microfluidic double‐emulsion possess several advantages such as high monodispersity and encapsulation efficiency compared with those generated based on thin‐film rehydration and electroformation. Stabilizers, including bovine serum albumin (BSA) and polyvinyl alcohol (PVA), have been used to enhance the formation and stability of double emulsions that are used as templates for the generation of polymersomes. In this work, the effect of stabilizers on the mechanical response of double‐emulsion‐templated polymersomes using micropipette aspiration is investigated. It is demonstrated that the existence of stabilizers results in the inelastic response in polymersomes in the early stage of solvent removal. However, aged polymersomes that have little residual solvent show elastic behavior. Polymersomes prepared from PVA‐stabilized double emulsions have noticeably lower area expansion moduli than polymersomes prepared from stabilizer‐free and BSA‐stabilized double emulsions, suggesting that PVA is incorporated in the bilayer membrane of polymersomes.
Radial symmetry is essential for the conventional view of the polymer spherulite microstructure. Typically it is assumed that, in the course of the spherulite morphogenesis, the lamellar crystals grow radially. Using submicron X‐ray diffraction, it is shown that in banded spherulites of poly(propylene adipate) the crystals have the shape of a helix with flat‐on crystals winding around a virtual cylinder of about 6 µm in diameter. The helix angle of 30° implies that the crystal growth direction is tilted away from the spherulite radius by this angle. The implications of the helical crystal shape contradict the paradigm of the spherulitic microstructure. The radial growth rate of such spherulites does not correspond to the crystal growth rate, but to the propagation rate of the virtual cylinder the ribbons wind around.
The preparation of physically crosslinked hydrogels from quasi ABA‐triblock copolymers with a water‐soluble middle block and hydrophobic end groups is reported. The hydrophilic monomer N‐acryloylmorpholine is copolymerized with hydrophobic isobornyl acrylate via a one‐pot sequential monomer addition through reversible addition fragmentation chain‐transfer (RAFT) polymerization in an automated parallel synthesizer, allowing systematic variation of polymer chain length and hydrophobic–hydrophilic ratio. Hydrophobic interactions between the outer blocks cause them to phase‐separate into larger hydrophobic domains in water, forming physical crosslinks between the polymers. The resulting hydrogels are studied using rheology and their self‐healing ability after large strain damage is shown.
Rewritable optical storage has been obtained in a spiropyran doped liquid crystal polymer films. Pictures can be recorded on films upon irradiation with UV light passing through a grayscale mask and they can be rapidly erased using visible light. Films present improved photosensitivity and optical contrast, good resistance to photofatigue, and high spatial resolution. These photochromic films work as a multifunctional, dynamic photosensitive material with a real‐time image recording feature.
The molecular systems, modeling composite materials, are formed by the epoxy‐amine oligomers with covalently bound chromophore‐containing dendritic fragments ( EAD ) as a host and additional azo‐chromophores as guests. The relationship between the structure and quadratic nonlinear optical characteristics of the model systems is established by atomistic modeling and quantum chemistry. The effect of the chain length of the model systems and the choice of the dendron structure, in particular, the length of the groups tethering chromophores to the branching center, on the values of first hyperpolarizability is studied. Molecular dynamics, performed for the model systems at various temperatures, reveals chromophores local mobility at temperature close to 130 °C; the calculations being fulfilled with the force field MMFF94s modified in terms of the ESP partial charges estimate at B3LYP/6‐31G(d) level.
The chemical control of cell division has attracted much attention in the areas of single cell‐based biology and high‐throughput screening platforms. A mussel‐inspired cytocompatible encapsulation method for achieving a “cell‐division control” with cross‐linked layer‐by‐layer (LbL) shells is developed. Catechol‐grafted polyethyleneimine and hyaluronic acid are chosen as polyelectrolytes for the LbL process, and the cross‐linking of polyelectrolytes is performed at pH 8.5. Cell division is controlled by the number of the LbL nanolayers and cross‐linking reaction. We also suggest a new measuring unit, , for quantifying “cell‐division timing” based on microbial growth kinetics.
In this study, a new type of functional, self‐assembled nanostructure formed from porphyrins and polyamidoamine dendrimers based on hydrogen bonding in an aqueous solution is presented. As the aggregates formed are promising candidates for solar‐energy conversion, their photocatalytic activity is tested using the model reaction of methyl viologen reduction. The self‐assembled structures show significantly increased activity as compared to unassociated porphyrins. Details of interaction forces driving the supramolecular structure formation and regulating catalytic efficiency are fundamentally discussed.
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