Polyarylene Networks via Bergman Cyclopolymerization of Bis‐ortho‐diynyl Arenes

Bis‐ortho‐diynylarene (BODA) monomers, prepared from common bisphenols in three high yielding steps, undergo free‐radical‐mediated thermal polymerization via an initial Bergman cyclo‐rearrangement. Polymerization is carried out at 210 °C in solution or neat with large pre‐vitrification melt windows (4–5 h) to form branched oligomers containing reactive pendant and terminal aryldiynes. Melt‐ and solution‐processable oligomers with weight‐average molecular weight M_w = 3000–24 000 g mol^–1 can be coated as a thin film or molded using soft lithography techniques. Subsequent curing to 450 °C affords network polymers with no detectable glass transition temperatures below 400 °C and thermal stability ranging from 0.5–1.5 % h^–1 isothermal weight loss measured at 450 °C under nitrogen. Heating to 900–1000 °C gives semiconductive glassy carbon in high yield. BODA monomer synthesis, network characterization and kinetics, processability, thin‐film photoluminescence, and thermal properties are described.     

High‐Strain Shape‐Memory Polymers

Shape‐memory polymers (SMPs) are self‐adjusting, smart materials in which shape changes can be accurately controlled at specific, tailored temperatures. In this study, the glass transition temperature (T_g) is adjusted between 28 and 55 °C through synthesis of copolymers of methyl acrylate (MA), methyl methacrylate (MMA), and isobornyl acrylate (IBoA). Acrylate compositions with both crosslinker densities and photoinitiator concentrations optimized at fractions of a mole percent demonstrate fully recoverable strains at 807% for a T_g of 28 °C, at 663% for a T_g of 37 °C, and at 553% for a T_g of 55 °C. A new compound, 4,4′‐di(acryloyloxy)benzil (referred to hereafter as Xini) in which both polymerizable and initiating functionalities are incorporated in the same molecule, was synthesized and polymerized into acrylate shape‐memory polymers, which were thermomechanically characterized yielding fully recoverable strains above 500%. The materials synthesized in this work were compared to an industry standard thermoplastic SMP, Mitsubishi's MM5510, which showed failure strains of similar magnitude, but without full shape recovery: residual strain after a single shape‐memory cycle caused large‐scale disfiguration. The materials in this study are intended to enable future applications where both recoverable high‐strain capacity and the ability to accurately and independently position T_g are required.     

Temperature‐Memory Effect of Copolyesterurethanes and their Application Potential in Minimally Invasive Medical Technologies

Minimally invasive surgery often requires devices that can change their geometry or shape when placed inside the body. Here, the potential of thermoplastic temperature‐memory polymers (TMP) for the design of intelligent devices, which can be programmed by the clinician to individually adapt their shifting geometry and their response temperature T_sw to the patient's needs, is explored. Poly(ω‐pentadecalactone) as hard segments and poly(?‐caprolactone) segments acting as crystallizable controlling units for the temperature‐memory effect (TME) are chosen to form multiblock copolymers PDLCL. These components are selected according to their thermal properties and their good biocompatibility. Response temperatures obtained under stress‐free and constant strain recovery can be systematically adjusted by variation of the deformation temperature in a temperature range from 32 °C to 65 °C, which is the relevant temperature range for medical applications. The working principle of TMP based instruments for minimally invasive surgical procedures is successfully demonstrated using three temperature‐memory catheter concepts: individually programmable TM‐catheter, an in‐situ programmable TM‐catheter, and an intelligent drainage catheter for gastroenterology.     

Highly Oriented Nanofibrils of Regioregular Poly(3‐hexylthiophene) Formed via Block Copolymer Self‐Assembly in Liquid Crystals

A novel method making use of block copolymer self‐assembly in nematic liquid crystals (LCs) is described for preparing macroscopically oriented nanofibrils of π‐conjugated semiconducting polymers. Upon cooling, a diblock copolymer composed of regioregular poly(3‐hexylthiophene) (P3HT) and a liquid crystalline polymer (LCP) in a block‐selective LC solvent can self‐assemble into oriented nanofibrils exhibiting highly anisotropic absorption and polarized photoluminescence emission. An unusual feature of the nanofibrils is that P3HT chains are oriented along the fibrils' long axis. This general method makes it possible to use LCs as an anisotropic medium to grow oriented nanofibrils of many semiconducting polymers insoluble in LCs.     

Strong,Tailored, Biocompatible Shape‐Memory Polymer Networks

Shape‐memory polymers are a class of smart materials that have recently been used in intelligent biomedical devices and industrial applications for their ability to change shape under a predetermined stimulus. In this study, photopolymerized thermoset shape‐memory networks with tailored thermomechanics are evaluated to link polymer structure to recovery behavior. Methyl methacrylate (MMA) and poly(ethylene glycol) dimethacrylate (PEGDMA) are copolymerized to create networks with independently adjusted glass transition temperatures (T_g) and rubbery modulus values ranging from 56 to 92 °C and 9.3 to 23.0 MPa, respectively. Free‐strain recovery under isothermal and transient temperature conditions is highly influenced by the T_g of the networks, while the rubbery moduli of the networks has a negligible effect on this response. The magnitude of stress generation of fixed‐strain recovery correlates with network rubbery moduli, while fixed‐strain recovery under isothermal conditions shows a complex evolution for varying T_g. The results are intended to help aid in future shape‐memory device design and the MMA‐co‐PEGDMA network is presented as a possible high strength shape‐memory biomaterial.     

Toward the Prediction and Control of Glass Transition Temperature for Donor–Acceptor Polymers

Semiconducting donor–acceptor (D–A) polymers have attracted considerable attention toward the application of organic electronic and optoelectronic devices. However, a rational design rule for making semiconducting polymers with desired thermal and mechanical properties is currently lacking, which greatly limits the development of new polymers for advanced applications. Here, polydiketopyrrolopyrrole (PDPP)‐based D–A polymers with varied alkyl side‐chain lengths and backbone moieties are systematically designed, followed by investigating their thermal and thin film mechanical responses. The experimental results show a reduction in both elastic modulus and glass transition temperature (T_g) with increasing side‐chain length, which is further verified through coarse‐grained molecular dynamics simulations. Informed from experimental results, a mass‐per‐flexible bond model is developed to capture such observation through a linear correlation between T_g and polymer chain flexibility. Using this model, a wide range of backbone T_g over 80 °C and elastic modulus over 400 MPa can be predicted for PDPP‐based polymers. This study highlights the important role of side‐chain structure in influencing the thermomechanical performance of conjugated polymers, and provides an effective strategy to design and predict T_g and elastic modulus of future new D–A polymers.     

Crystallinity Control of a Nanostructured LiNi0.5Mn1.5O4 Spinel via Polymer‐Assisted Synthesis: A Method for Improving Its Rate Capability and Performance in 5 V Lithium Batteries

Li–Ni–Mn spinels of nominal composition LiNi_0.5Mn_1.5O₄, which are functional materials for electrodes in high‐voltage lithium batteries, are prepared by thermal decomposition of mixed nanocrystalline oxalates obtained by grinding hydrated salts and oxalic acid in the presence of polyethyleneglycol 400. Their structure, microstructure, and texture are established from combined X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction, transmission electron microscopy (TEM), IR spectroscopy, and N₂ absorption measurements. The polymer tailors the shape of particles, which adopt a nanorodlike morphology at low temperatures (400 °C). In fact, the nanorods consist of highly distorted oriented nanocrystals connected by a polymer‐based film as inferred from IR and XPS spectra. The electrochemical properties of spinels in this peculiar form are quite poor, mainly as a result of the high microstrain content of their nanocrystals. Raising the temperature up to 800 °C partially destroys the nanorods, which become highly crystalline nanoparticles approximately 80 nm in size. At this temperature, the polymer facilitates crystal growth; this leads to highly crystalline polyhedral nanoparticles as revealed from TEM images and microstrain data. Following functionalization as a cathode in lithium cells, this material exhibits a very good rate capability, coulombic efficiency, and capacity retention even upon cycling at voltages as high as 5 V. Moreover, it withstands fast‐charge–slow‐discharge processes, which is an important cycle‐life‐related property for commercial batteries.     

Benzobisthiazole as Weak Donor for Improved Photovoltaic Performance: Microwave Conductivity Technique Assisted Molecular Engineering

New donor–acceptor‐type copolymers comprised of benzobisthiazole (BBTz) as a weak donor rather than acceptor are proposed. This approach can simultaneously lead to deepening the HOMO and LUMO of the polymers with moderate energy offset against fullerene derivatives in bulk heterojunction organic photovoltaics. As a proof‐of‐concept, BBTz‐based random copolymers conjugated with typical electron acceptors: thienopyrroledione (TPD) and benzothiadiazole (BT) based on density functional theory calculations are synthesized. Laser‐flash and Xe‐flash time‐resolved microwave conductivity (TRMC) evaluations of polymer:[6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM) blends are conducted to screen the feasibility of the copolymers, leading to optimization of processing conditions for photovoltaic device application. According to the TMRC results, alternating BBTz‐BT copolymers are designed, exhibiting extended photoabsorption up to ca. 750 nm, deep HOMO (–5.5 to –5.7 eV), good miscibility with PCBM, and inherent crystalline nature. Moreover, the maximized PCE of 3.8%, the top‐class among BBTz‐based polymers reported so far, is realized in an inverted cell using TiO_x and MoO_x as the buffer layers. This study opens up opportunities to create low‐bandgap polymers with deep HOMO, and shows how the device‐less TRMC evaluation is of help for decision‐making on judicious molecular design.     

Acylhydrazones as Reversible Covalent Crosslinkers for Self‐Healing Polymers

The utilization of dynamic covalent and noncovalent bonds in polymeric materials offers the possibility to regenerate mechanical damage, inflicted on the material, and is therefore of great interest in the field of self‐healing materials. For the design of a new class of self‐healing materials, methacrylate containing copolymers with acylhydrazones as reversible covalent crosslinkers are utilized. The self‐healing polymer networks are obtained by a bulk polymerization of an acylhydrazone crosslinker and commercially available methacrylates as comonomers to fine‐tune the T_g of the systems. The influence of the amount of acylhydrazone crosslinker and the self‐healing behavior of the polymers is studied in detail. Furthermore, the basic healing mechanism and the corresponding mechanical properties are analyzed.     

Rational Design of Supramolecular Conjugated Polymers Displaying Unusual Colorimetric Stability upon Thermal Stress

The colorimetric stability upon thermal stress of a series of conjugated polymer supramolecules prepared from 10,12‐docosadiyndioic acid (DCDDA)‐derived diacetylene monomers has been explored. Polydiacetylenes obtained from DCDDA‐bis‐mBzA 3 , containing m‐carboxyphenylanilido groups at the both ends of the monomer, were observed to be highly colorimetrically stable upon thermal stimulation. The blue color of a solution containing these polydiacetylene vesicles remains unchanged even when the vesicles were subjected to boiling water. The unusual colorimetric stability is further demonstrated by the observation that blue color persists until vesicles in ethylene glycol are heated to 140 °C. The nature of this unusual thermal stability was elucidated by using polydiacetylene supramolecules, prepared from analogs of DCDDA‐bis‐mBzA 3 . The presence of internal amide groups as well as aromatic interactions was found to be essential for the high colorimetric stability of the polydiacetylene supramolecules.     

Polymer‐Stabilized Chromonic Liquid‐Crystalline Polarizer

Robust coatable polarizer is fabricated by the self‐assembly of lyotropic chromonic liquid crystals and subsequent photo‐polymerizing processes. Their molecular packing structures and optical behaviors are investigated by the combined techniques of microscopy, scattering and spectroscopy. To stabilize the oriented Sunset Yellow FCF (H‐SY) films and to minimize the possible defects generated during and after the coating, acrylic acid (AA) is added to the H‐SY/H₂O solution and photo‐polymerized. Utilizing cross‐polarized optical microscopy, phase behaviors of the H‐SY/H₂O/AA solution are monitored by varying the compositions and temperatures of the solution. Based on the experimental results of two‐dimensional wide angle X‐ray diffraction and selected area electron diffraction, the H‐SY crystalline unit cell is determined to be a monoclinic structure with the dimensions of a = 1.70 nm, b = 1.78 nm, c = 0.68 nm, α = β = 90.0° and γ = 84.5°. The molecular arrangements in the oriented H‐SY films were further confirmed by polarized Fourier‐transform infrared spectroscopy. The polymer‐stabilized H‐SY films show good mechanical and chemical stabilities with a high polarizability. Additionally, patterned polarizers are fabricated by applying a photo‐mask during the photo‐polymerization of AA, which may open new doors for practical applications in electro‐optic devices.     

Multiresponsive PEDOT–Ionic Liquid Materials for the Design of Surfaces with Switchable Wettability

Among the different types of stimuli‐responsive polymers, conjugated polymers reveal unique multiresponsive behavior. In this work, the synthesis and characterization of new functional poly(3,4‐ethylenedioxythiophenes) (PEDOT) bearing imidazolium ionic‐liquid moieties (PEDOT‐Im) is reported. PEDOT‐Im polymers show multiresponsive properties to a variety of stimuli, such as temperature, pH, oxidative doping, and presence of anions. These stimuli provoke different changes in PEDOT‐Im, such as changes in color, oxidation state, and, wetting behavior. In all cases, a reversible effect is observed, and the polymers reveal responsive properties in solution as well as in the form of thin films. Whereas sensitiveness to pH and oxidative doping are known phenomena for other PEDOT derivatives, responsiveness to temperature and to anions is a unique property of PEDOT‐Im. The anion exchange is further investigated by means of the Quartz Crystal Microbalance with dissipation. Anion exchanges induce fast, adjustable, and reversible contact angle changes between 24° and 107°. As a potential application, surfaces with switchable wettability triggered by anion solutions are prepared by spin‐coating PEDOT‐Im films onto different substrates.     

Paper‐Based Electrochromic Devices Enabled by Nanocellulose‐Coated Substrates

As environmental considerations for both the processing and disposal of electronic devices become increasingly important, the ability to replace plastic and glass substrates with bioderived and biodegradable materials remains a major technological goal. Here, the use of cellulose nanofiber‐coated paper is explored as an environmentally benign substrate for preparing low‐resistance (460 Ω sq^?1), colorless (a* = ?2.3, b* = ?2.7) printed poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrodes. The PEDOT:PSS/paper electrodes support the reversible oxidation of three electrochromic polymers (ECPs) (cyan, magenta, and yellow), affording the possibility for fully printed, color displays on paper. Lateral electrochromic devices (ECDs) incorporating an ion gel electrolyte are demonstrated where a magenta‐to‐colorless device achieves a color contrast (ΔE*) of 56 owing to a highly color‐neutral bleached state of the ECP (a* = ?0.5, b* = 2.9). Black‐to‐colorless devices achieve ΔE* = 29 and are able to retain 86% of their color contrast after 9000 switches. The switching times of these lateral devices are quantified through colorimetric image analysis which shows comparable performance for devices constructed on paper as devices using ITO/glass electrodes (10 Ω sq^?1). The paper ECDs are then combusted in air leaving 3% of the initial mass at 600 °C, highlighting this approach as a promising route toward disposable displays.     

Poly(arylene piperidinium) Hydroxide Ion Exchange Membranes: Synthesis,Alkaline Stability,and Conductivity

A series of poly(arylene piperidinium)s (PAPipQs) devoid of any alkali‐sensitive aryl ether bonds or benzylic sites are prepared and studied as anion exchange membranes (AEMs) for alkaline fuel cells. First, the excellent alkaline stability of the model compound 4,4‐diarylpiperidinium is confirmed. Medium molecular weight poly(arylene piperidine)s are then synthesized in polycondensations of N‐methyl‐4‐piperidone and either bi‐ or terphenyl via superelectrophilic activation in triflic acid. Film‐forming PAPipQs are subsequently prepared in Menshutkin reactions with methyl, butyl, hexyl, and octyl halides, respectively. AEMs based on poly(terphenyl dimethylpiperidinium) show the best performance with no structural degradation detectable by ¹H NMR spectroscopy after storage in 2 m aq. NaOH at 60 °C after 15 d, and a mere 5% ionic loss at 90 °C. In the fully hydrated state these AEMs reach an OH^? conductivity of 89 mS cm^?1 at 80 °C. The presence of longer pendant N‐alkyl chains (butyl to octyl) is found to significantly promote Hofmann ring‐opening elimination reactions and the degradation rate increases with increasing alkyl chain length. The results of the present study demonstrate that PAPipQs are efficiently prepared from readily available monomers and show excellent alkaline stability and OH^? conductivity when devoid of pendant N‐alkyl chains.     

Photocrosslinkable Nanocomposite Multilayers for Responsive 1D Photonic Crystals

A straightforward method to increase the refractive index of photocrosslinkable polymers by incorporation of high index inorganic nanoparticles is demonstrated and shown to enhance the reflection efficiency of thermochromic 1D photonic multilayers. The refractive index of spin‐coated and UV‐crosslinked films based on poly(para‐methyl styrene) (PpMS) copolymers is increased from 1.57 for the copolymer alone to as high as 1.67 for nanocomposite samples with a volume fraction of 0.38 of ZrO₂ nanoparticles. Thermochromic photonic multilayers consisting of alternating films of PpMS–ZrO₂ with poly(N‐isopropylacrylamide) (PNIPAM) copolymers shows the increases in reflectance as large as 2.5‐fold compared to PpMS/PNIPAM multilayers lacking particles. In addition, ZrO₂ nanoparticles are used to increase the refractive index of PNIPAM‐based films up to 1.68 with a volume fraction of 0.49 of nanoparticles, enabling the fabrication of alternating PNIPAM–ZrO₂/PNIPAM multilayers with a well‐defined Bragg peak that shifts from 635 nm at 6 °C to 410 nm at 48 °C, and reflectance intensities as high as ≈0.30.     

Preparation of Oriented Aluminum Nitride Thin Films on Polyimide Films and Piezoelectric Response with High Thermal Stability and Flexibility

c‐Axis oriented aluminum nitride (AlN) thin films are successfully prepared on amorphous polyimide films by radiofrequency magnetron reactive sputtering at room temperature. Structural analysis shows that the AlN films have a wurtzite structure and consist of c‐axis oriented columnar grains about 100 nm wide. The full width at half maximum of the X‐ray diffraction rocking curves and piezoelectric coefficient d₃₃ of the AlN films are 8.3° and 0.56 pC N^–1, respectively. The AlN films exhibit a piezoelectric response over a wide temperature range, from –196 to 300 °C, and can measure pressure within a wide range, from pulse waves of hundreds of pascals to 40 MPa. Moreover, the sensitivity of the AlN films increases with the number of times it was folded, suggesting that we can control the sensitivity of the AlN films by changing the geometric form. These results were achieved by a combination of preparing the oriented AlN thin films on polyimide films, and sandwiching the AlN and polymer films between top and bottom electrodes, such as Pt/AlN/polyimide/Pt. They are thin (less than 10 μm), self powered, adaptable to complex contours, and available in a variety of configurations. Although AlN is a piezoelectric ceramic, the AlN films are flexible and excellent in mechanical shock resistance.     

Temperature‐Switchable Assembly of Supramolecular Virus–Polymer Complexes

Here a method is presented for the temperature‐switchable assembly of viral particles into large hierarchical complexes. Dual‐functional diblock copolymers consisting of poly(diethyleneglycol methyl ether methacry­late) (poly(DEGMA)) and poly((2‐dimethylamino)ethyl methacrylate) (poly(DMAEMA)) blocks self‐assemble electrostatically with cowpea chlorotic mottle virus (CCMV) particles into micrometer‐sized objects as a function of temperature. The poly(DMAEMA) block carries a positive charge, which can interact electrostatically with the negatively charged outer surface of the CCMV capsid. When the solution temperature is increased above 40 °C, to cross the cloud point temperature (T_cp) of the DEGMA block, the polymer chains collapse on the surface of the virus particle, which makes them partially hydrophobic, and consequently causes the formation of large hierarchical assemblies. Disassembly of the virus–polymer complexes can be induced by reducing the solution temperature below the T_cp, which allows the poly(DEGMA) blocks to rehydrate and free virus particles to be released. The assembly process is fully reversible and can sustain several heating–cooling cycles. Importantly, this method relies on reversible supramolecular interactions and therefore avoids the irreversible covalent modification of the particle surface. This study illustrates the potential of temperature‐responsive polymers for controlled binding and releasing of virus particles.     

Thermo‐Switchable Charge Transport and Electrocatalysis Using Metal‐Ion‐Modified pNIPAM‐Functionalized Electrodes

Metal ions (Ag⁺, Cu²⁺, Hg²⁺) are incorporated into an electropolymerized, poly(N‐isopropyl acrylamide), pNIPAM, thermosensitive polymer associated with an electrode using the “breathing‐in” method. The ion‐functionalized pNIPAM matrices reveal ion‐dependent gel‐to‐solid phase‐transition temperatures (28 ± 1 °C, 25 ± 1 °C, 40 ± 1 °C for the Ag⁺, Cu²⁺, and Hg²⁺‐modified pNIPAM, respectively). Furthermore, the ion‐functionalized polymers exhibit quasi‐reversible redox properties, and the ions are reduced to the respective Ag⁰, Cu⁰, and Hg⁰ nanocluster‐modified polymers. The metal‐nanocluster‐functionalized pNIPAM matrices enhance the electron transfer (they exhibit lower electron‐transfer resistances) in the compacted states. The electron‐transfer resistances of the metal‐nanocluster‐modified pNIPAM can be cycled between low and high values by temperature‐induced switching of the polymer between its contracted solid and expanded gel states, respectively. The enhanced electron‐transfer properties of the metal nanocluster‐functionalized polymer are attributed to the contacting of the metal nanoclusters in the contracted state of the polymers. This temperature‐switchable electron transfer across a Ag⁰‐modified pNIPAM was implemented to design a thermo‐switchable electrocatalytic process (the temperature‐switchable electrocatalyzed reduction of H₂O₂ by Ag⁰‐pNIPAM).     

Off/On Fluorescent Nanoparticles for Tunable High‐Temperature Threshold Sensing

Herein, a versatile threshold temperature sensor based on the glass transition temperature‐triggered fluorescence activation of a dye/developer duo, encapsulated in polymeric nanoparticles is reported. The emission enhancement, detectable even by unaided eye is completed within a narrow temperature range and activates at adjustable threshold temperatures up to 200 °C. Fluorescence is chosen as sensing probe due to its high detection sensitivity together with an advanced spatial and temporal resolution. The strategy is based on nanoparticles prepared from standard thermoplastic polymers, a fluorescence developer, and the commercially available Rhodamine B base dye, a well‐known and widely used fluorescent molecule. By making nanoparticles of different thermoplastic polymers, fast, abrupt, and irreversible disaggregation induced fluorescence enhancement, with tunable threshold temperature depending on the nanoparticles polymer glass transition is achieved. As a proof‐of‐concept for the versatility of this novel family of NPs, their use for sensing the thermal history of environments and surfaces exposed to the threshold temperature is showed.     

Thermally Stable Hole‐Transporting Materials Based upon a Fluorene Core

We report a new class of diamine hole‐transporting materials (HTMs) based upon a fluorene core. Using a fluorene core, rather than a biphenyl group, leads to enhanced thermal stability, as evidenced by glass‐transition (T_g) temperatures as high as 161 °C for N,N′‐iminostilbenyl‐4,4′‐fluorene (ISF). The fluorene‐based HTMs have lower ionization potentials (I_p) than their biphenyl analogs, which leads to more efficient injection of holes from the indium tin oxide (ITO) anode, and higher quantum efficiencies. Devices prepared with fluorene‐based HTMs were operated under thermal stress. The failure of an organic light‐emitting diode (OLED) under thermal stress has a direct correlation with the thermal stability of the HTM that is in contact with the ITO anode. OLEDs based on ISF are stable to over 140 °C.