Side-chain Polymers Research Articles

Toward Efficient Charge Transport of Polymer-Based Organic Field-Effect Transistors: Molecular Design, Processing, and Functional Utilization

ConspectusPolymer-based organic field-effect transistors (OFETs) have attracted great attention owing to their significantly improved performance and the recently emerged prospects for broad applications. The charge carrier mobility of polymer-based OFETs has been improved from 10–5 to more than 10 cm2 V–1 s–1 over the past three decades. With the carrier mobility close to or higher than that of amorphous silicon, the application fields of polymer-based OFETs have been extended from sensing to logic or drive circuits. During OFET operation, the charge carriers are successively injected in and then transferred across the semiconducting channel under an external electric field. The behavior of the charge carriers is determined by both charge injection and charge transport. Well-matched frontier molecular orbital (FMO) energy levels and optimized hierarchical structures of semiconducting polymers are essential for the realization of high-performance polymer-based OFETs.In this Account, we mainly demonstrate our recent progress in molecular design strategies and fabrication processing methods for high-performance semiconducting polymers. Moreover, we provide some examples of integrated applications of polymer-based OFETs. The convenient FMO energy level modulation and excellent molecular designability of donor–acceptor (D–A) conjugated polymers facilitate studies on their performance enhancement in OFETs. Proper molecular design of the D–A polymer backbone and side chain can significantly contribute to charge injection enhancement, transport pathway establishment, and trap reduction, thereby resulting in efficient charge transport. Moreover, special fabrication processes of OFET devices can further enhance the charge transport by optimizing the hierarchical structures of semiconducting polymers, thereby enhancing their carrier mobility and stability. By employing high-performance semiconducting polymers as the semiconducting channel of OFETs, various applications can be implemented. These applications range from small-scale logic signal processing and periodic signal generation to complex visual perception systems, indicating broad application prospects in human life. The works on performance improvement and functional utilization of the semiconducting polymers in OFETs might provide insights for molecular design strategies and applications for future plastic electronics.

De Novo Design of Entropy-Driven Polymers Resistant to Bacterial Attachment via Multicomponent Reactions.

Nonbactericidal polymers that prevent bacterial attachment are important for public health, environmental protection, and avoiding the generation of superbugs. Here, inspired by the physical bactericidal process of carbon nanotubes and graphene derivatives, we develop nonbactericidal polymers resistant to bacterial attachment by using multicomponent reactions (MCRs) to introduce molecular "needles" (rigid aliphatic chains) and molecular "razors" (multicomponent structures) into polymer side chains. Computer simulation reveals the occurrence of spontaneous entropy-driven interactions between the bacterial bilayers and the "needles" and "razors" in polymer structures and provides guidance for the optimization of this type of polymers for enhanced resistibility to bacterial attachment. The blending of the optimized polymer with commercially available polyurethane produces a film with remarkably superior stability of the resistance to bacterial adhesion after wear compared with that of commercial mobile phone shells made by the Sharklet technology. This proof-of-concept study explores entropy-driven polymers resistant to bacterial attachment via a combination of MCRs, computer simulation, and polymer chemistry, paving the way for the de novo design of nonbactericidal polymers to prevent bacterial contamination.

Fluorination of the π-bridge in a polymer skeleton enables a significant improvement in photovoltaic performance

An easy and efficient approach for the synthesis of an important photoelectric intermediate 3-fluoro-2-iodithiophene is developed. Therefrom, a polymer J52FF, featuring fluorination of the π-bridges on the backbone and side chains of the classical polymer, J52, is synthesized. J52FF displays a coplanar molecular configuration with the dihedral angles smaller than 2° in skeleton, a low-lying HOMO energy level of −5.62 eV, which is nearly aligned with the acceptor IT-4F, and a broad absorption range from 300 nm to 650 nm. The J52FF:IT-4F (1:0.8) blend shows a strong and complementary spectral absorption, a uniform fibrillar textured morphology and high and balanced charge mobilities. The inverted device based on J52FF:IT-4F blend obtained an encouraging power conversion efficiency (PCE) of 14.83% with the open-circuit voltage (Voc) of 0.90 V, the short circuit current (Jsc) of 23.21 mA cm−2, and the fill factor (FF) of 0.71 under the optimal conditions, which is one of the best PCE value among the ever reported BDT-alt-BTz derivatives or IT-4F based non-fullerene organic solar cells (NF–OSCs). It demonstrates that fluorination of polymer in skeleton is an efficient strategy for obtaining high performance.

Carbazole-functionalized polyfluorenes: synthesis and conformational properties in chloroform solution and β-phase formation in copolyfluorene films

Novel copolyfluorenes (CPFs) containing 2.5 or 10 mol% of carbazole-2,7-diyl (2,7-Cz) or carbazole-3,6-diyl (3,6-Cz) derivatives in the backbone have been synthesized by means of palladium-catalyzed Suzuki polymerization under microwave irradiation. The structure of the CPF polymers was also modified by insertion of additional 2-ethylhexyl or carbazole, diaryloxadiazole, or triphenylamine units via 3,6-Cz or 2,7-Cz comonomer units in the side chains of polymers. The self-organization of molecules in chloroform solutions was investigated using light scattering and within a wide concentration interval. Analysis of the behavior of the CPFs showed that the synthesized copolymers have an increased equilibrium rigidity of molecules with a Kuhn segment length A = (10–15) nm. The A value decreases with the introduction of Cz-units into the macromolecule in the meta-position. It is shown that chemical structure of the CPFs and thermal treatment in the temperature range 60–150 °C have a dominant effect on the optoelectronic properties as well as on microstructures of their films.

Structure-based nomenclature for irregular linear, star, comb, and brush polymers (IUPAC Recommendations 2020)

Abstract The existing recommendations for the structure-based nomenclature of regular single-strand organic polymers are extrapolated to complex polymers. The key proposal is that polymeric moieties may be named substituents. The types of polymers covered include linear and branched polymers containing more than one block of a single type of constitutional repeating unit (CRU) and branched polymers containing a main chain from which one or more polymeric side chains emanate.

Acrylic Paints: An Atomistic View of Polymer Structure and Effects of Environmental Pollutants.

Most of the artwork and cultural heritage objects are stored in museums under conditions that are difficult to monitor. While advanced technologies aim to control and prevent the degradation of cultural heritage objects in line with preventive conservation measures, there is much to be learned in terms of the physical processes that lead to the degradation of the synthetic polymers that form the basis of acrylic paints largely used in contemporary art. In museums, stored objects are often exposed to temperature and relative humidity fluctuations as well as airborne pollutants such as volatile organic compounds (VOCs). The glass transition of acrylic paints is below room temperature; while low temperatures may cause cracking, at high temperatures the sticky surface of the paint becomes vulnerable to pollutants. Here we develop fully atomistic models to understand the structure of two types of acrylic copolymers and their interactions with VOCs and water. The structure and properties of acrylic copolymers are slighlty modified by incorporation of a monomer with a longer side chain. With favorable solvation free energies, once absorbed, VOCs and water interact with the polymer side chains to form hydrogen bonds. The cagelike structure of the polymers prevents the VOCs and water to diffuse freely below the glass transition temperature. In addition, our model forms the foundation for developing mesoscopic and continuum models that will allow us to access longer time and length scales to further our understanding of the degradation of artwork.

Azobenzene-containing side-chain ionic metathesis polymers: Facile synthesis, self-assembly and photoresponsive behavior

A series of well-defined azobenzene-functionalized ionomers were produced via ring-opening metathesis polymerization of norbornene-dicarboximide tethered to an ionic group further connected with an azobenzene unit in ionic liquid. The corresponding azobenzene-containing non-ionic polymers were also synthesized by the similar method. All the polymerizations were confirmed to be the characteristic of living based on the linear relationship between molecular weight and feed ratio. As expected, the distinct photoresponsive properties from azobenzene units in ionomers were observed under alternating irradiation of UV and visible light, which cannot be achieved by traditional azobenzene-containing non-ionic polymers. The ability and efficiency of trans−cis photoisomerization was depressed to some extent due to the presence of ionic groups nearby azobenzene units. Moreover, the sizes and morphologies of these ionomers can be modulated through changing the number of the methylene spacer to generate regular and uniform spherical nanostructures, ultimately leading to the unique photoisomerization behaviors. All these interesting results will not only provide a facile and efficient method for constructing photosensitive ionic metathesis polymers, but also expand the optical properties and application prospect of azobenzene-containing polymers.

Stable super-hydrophobic and comfort PDMS-coated polyester fabric

Abstract Super-hydrophobic fabrics have shown great potential during the last decade owing to their novel functions and enormous potential for diver’s applications. Surface textures and low surface energy coatings are the keys to high water repellency. However, the toxicity of nanomaterials, long perfluorinated side-chain polymers, and the fragile of micro/nano-texture lead to the super-hydrophobic surfaces are confined to small-scale uses. Thus, in this article, a stable polydimethylsiloxane (PDMS)-coated super-hydrophobic poly(ethylene terephthalate) (PET) fabric (PDMS-g-PET) is manufactured via dip-plasma crosslinking without changing the wearing comfort. Benefiting from the special wrinkled structure of PDMS film, the coating is durable enough against physical abrasion and repeated washing damage, which is suffered from 100 cycles of washing or 500 abrasion cycles, and the water contact angle is still above 150°. This study promotes the way for the development of environmentally friendly, safe, and cost-efficient for designing durable superhydrophobic coatings for various practical applications.

Supramolecular hydrogen bond enables Kapton nanofibers to reinforce liquid-crystalline polymers for light-fueled flight

We report fabrication of photoresponsive liquid-crystalline polymers reinforced with highly-oriented Kapton nanofibers with a supramolecular hydrogen bonding interface. To enhance the interfacial strength, hydroxyl groups are introduced into the side chain of azobenzene-containing liquid-crystalline polymers, forming hydrogen bonds with the Kapton nanofibers, directly imaged by nano-FTIR. Interestingly, the composite film exhibits the hierarchical structure of dragonfly wings, while demonstrating relatively high elastic modulus (1.64 GPa), reduced modulus (72.8 GPa), and nanohardness (4.5 GPa); 20–30 times higher than natural dragonfly wings. The enhanced mechanical performance and bilayer structure enables the composite film to exhibit rapid photoresponsive behaviors independent of the direction of illumination, due to an unconventional deformation mechanism arising from the interactions at the fiber-polymer interface. In addition, the flapping frequency and bending angle of the composite films can be continuously tuned for a single device (0.1–5 Hz, and 1.5–15.8°) by modifying the pulsed photoirradiation. The composite films are assembled into an artificial dragonfly device, and the light-driven flight aerodynamics are demonstrated in windy conditions. These not only provide a solution of micro-aircraft wings, but also offer a good bionic model for emulating dragonfly wings.

Study of the molecular orientation of steroidal side chains at polyimide surfaces using sum frequency generation vibrational spectroscopy.

The molecular orientation of steroidal side chains at rubbed polyimide (PI) surfaces is studied by sum frequency generation (SFG) vibrational spectroscopy. The main objective is to find a correlation between the molecular structure of the PI film and the liquid crystal alignment on the polymer. Analysis of the SFG spectra shows that rubbing of the polymer film appears to cause conformational changes in the methyl group of the polymer side chain near the steroidal structure. However, rubbing does not significantly influence the orientation of the isopropyl group at the end of the polymer side chain. This shows that the liquid crystal alignment is not correlated with the orientation of the isopropyl group.

Enhancing the healing ability and charge transport thermal stability of a diketopyrrolopyrrole based conjugated polymer by incorporating coumarin groups in the side chains

AbstractIn this paper, we present a new design strategy for healable polymeric semiconductors, which are demanding for the future flexible electronics, by incorporating coumarin groups in the polymer side chains. The selection of coumarin groups is based on the fact that photo‐dimerization can occur to coumarins upon UV light irradiation, thus side chains of conjugated polymers with coumarins can be cross‐linked. The photo‐crosslinking of side chains has negligible effect on the thin film morphology and interchain packing order for the DPP‐based conjugated polymer PDPP4T‐DCM with coumarins in the side chains. However, the photo‐crosslinking can facilitate the repair of the mechanically damaged thin film of PDPP4T‐DCM and the recovery of the semiconducting properties. Additionally, the photo‐crosslinking due to the coumarins in the side chains can lock thin film morphology and thus improve the thermal stability of charge transport.

Charge‐Reversal Polymer Nano‐modulators for Photodynamic Immunotherapy of Cancer

AbstractNanomedicine can regulate the balance between cytotoxic T lymphocytes (CTLs) and suppressive regulatory T lymphocytes (Tregs), which however has been rarely exploited for cancer immunotherapy. We report a charge‐reversal polymer nano‐modulator (SPDMCN) activated by tumor microenvironment (TME) for photodynamic immunotherapy of cancer. SPDMCN is constructed by conjugating an immunomodulator (demethylcantharidin, DMC) to the side chains of a photodynamic polymer via an acid‐liable linker. The negative charge of SPDMCN ensures its high stability in blood circulation and ideal tumor accumulation; exposure to acidic TME reverses its surface charge to positive, enhancing tumor penetration and locally releasing DMC. Upon near‐infrared photoirradiation, SPDMCN generates singlet oxygen to ablate tumors and promote maturation of dendritic cells. Released DMC inhibits protein phosphatase 2 (PP2A) activity and decreases Tregs differentiation. Such combinational action induces a sharp increase in CTL/Treg ratio in TME and effectively inhibits both primary and distant tumors in living mice.

Charge-Reversal Polymer Nano-modulators for Photodynamic Immunotherapy of Cancer.

Nanomedicine can regulate the balance between cytotoxic T lymphocytes (CTLs) and suppressive regulatory T lymphocytes (Tregs), which however has been rarely exploited for cancer immunotherapy. We report a charge-reversal polymer nano-modulator (SPDMC N) activated by tumor microenvironment (TME) for photodynamic immunotherapy of cancer. SPDMC N is constructed by conjugating an immunomodulator (demethylcantharidin, DMC) to the side chains of a photodynamic polymer via an acid-liable linker. The negative charge of SPDMC N ensures its high stability in blood circulation and ideal tumor accumulation; exposure to acidic TME reverses its surface charge to positive, enhancing tumor penetration and locally releasing DMC. Upon near-infrared photoirradiation, SPDMC N generates singlet oxygen to ablate tumors and promote maturation of dendritic cells. Released DMC inhibits protein phosphatase 2 (PP2A) activity and decreases Tregs differentiation. Such combinational action induces a sharp increase in CTL/Treg ratio in TME and effectively inhibits both primary and distant tumors in living mice.

Transfer, Amplification, Storage, and Complete Self‐Recovery of Supramolecular Chirality in an Achiral Polymer System

AbstractSupramolecular chirality and its complete self‐recovery ability are highly mystical in nature and biological systems, which remains a major challenge today. Herein, we demonstrate that partially cross‐linked azobenzene (Azo) units can be employed as the potential chiral trigger to fully heal the destroyed helical superstructure in achiral nematic polymer system. Combining the self‐assembly of Azo units and terminal hydroxyl groups in polymer side chains allows the vapor‐induced chiral nematic phase and covalent fixation of the superstructure via acetal reaction. The induced helical structure of Azo units can be stored by inter‐chain cross‐linking, even after removal of the chiral source. Most interestingly, the stored chiral information can trigger perfect chiral self‐recovery (CSR) behavior after being destroyed by UV light, heat, and solvents. The results pave a new way for producing novel chiroptical materials with reversible chirality from achiral sources.

Transfer, Amplification, Storage, and Complete Self-Recovery of Supramolecular Chirality in an Achiral Polymer System.

Supramolecular chirality and its complete self-recovery ability are highly mystical in nature and biological systems, which remains a major challenge today. Herein, we demonstrate that partially cross-linked azobenzene (Azo) units can be employed as the potential chiral trigger to fully heal the destroyed helical superstructure in achiral nematic polymer system. Combining the self-assembly of Azo units and terminal hydroxyl groups in polymer side chains allows the vapor-induced chiral nematic phase and covalent fixation of the superstructure via acetal reaction. The induced helical structure of Azo units can be stored by inter-chain cross-linking, even after removal of the chiral source. Most interestingly, the stored chiral information can trigger perfect chiral self-recovery (CSR) behavior after being destroyed by UV light, heat, and solvents. The results pave a new way for producing novel chiroptical materials with reversible chirality from achiral sources.

New Photoresponsive Poly(meth)acrylates Bearing Azobenzene Moieties Obtained via ATRP Polymerization Exhibiting Liquid-Crystalline Behavior.

Here, we report our studies on photoresponsive poly(meth)acrylates containing azobenzene groups connected to a polymer backbone via a short methylene linker. A series of side-chain azobenzene polymers was synthesized via the atom transfer radical polymerization (ATRP) technique using several catalytic systems. The polymers synthesized under the optimized conditions were characterized by a narrow polydispersity (Đ ≤ 1.35), and they underwent a reversible transformation of their structure under light illumination. The fabricated polymers can store and release energy accumulated during the UV-light illumination by the thermal cis-trans isomerization of the chromophore groups. The enthalpy of the process (determined from DSC) was relatively high and equaled 61.9 J∙g−1 (17 Wh∙kg−1), indicating a high potential of these materials in energy storage applications. The liquid-crystalline behavior of the synthesized poly(meth)acrylates was demonstrated by the birefringent optical textures as observed in thin-films and X-ray scattering studies.

Controllable construction and theoretical simulation of silica aerogel/polymer composites with electrostatic interaction interfaces

In our previous work, aerogel/polymer composites with electrostatic interaction interface were successfully constructed. Interesting experimental phenomena in heat and stress transfer had also been found. On the basis of these works, we had been thinking about how to control the characteristics of electrostatic interaction phase interface, and how these phase interface characteristics affected the properties of materials. In this paper, the electrostatic interaction phase interface characteristics of the composite were regulated from the aspects of polymer chain movement, charge amount and charge distribution. The effects of phase interface characteristics on stress and heat transfer behavior of the composites were analyzed from the aspects of experimental test characterizations and molecular dynamics simulation. The results showed that the action region of electrostatic attraction phase interface can be controlled by the properties of polymer side chain and charged monomer. The density, heat transfer characteristics and stress transfer behavior of the composites were affected. α-Methyl was beneficial to the thermal stability of the composites, and the thermal conductivity was about 0.012 W m−1K−1. When the alkyl side chain was long, the molecular chain arrangement was irregular, the reorientation ability of the molecular chain was poor, and the molecular chain breaks in the compression stage. In the theoretical simulation, it can be found that more charged groups in a single charged part of the molecule led to the increase of cationic density in the organic phase, which made it easier to form effective chemical bonds in the crosslinking process, and the final crosslinking degree was improved.

Photocurable selenophene/maleimide-based high-refractive-index copolymers obtained via radical copolymerization

Selenophene-containing copolymers with either alternating or random sequences and high refractive indices were synthesized via conventional free-radical copolymerization of 2-vinylselenophene (2VS). Copolymers with a moderate alternating tendency were obtained via radical copolymerization of electron-donating 2VS and electron-accepting maleimide derivatives, such as N-methyl maleimide (MMI), N-phenyl maleimide (PMI), and N-vinyl maleimide (VMI). Copolymerization of 2VS with glycidyl methacrylate (GMA) also afforded copolymers containing selenophene and reactive epoxy units in the side chains. The selenophene-containing poly(2VS) showed a high refractive index (1.6420 @ 589 nm) and a reasonable Abbe number (30.7). High refractive indices of 1.6138–1.5959 with corresponding Abbe numbers of ~30 were similarly achieved for the selenophene/maleimide copolymers. The introduction of the maleimide moiety into the polymer side chain improved its thermal stability (Td5 > 320 °C) and enhanced the glass transition temperature (Tg = 158–160 °C). Selenophene-containing copolymers with pendant N-vinyl units were obtained via copolymerization of 2VS and VMI, which was successfully employed as a precursor for obtaining a photoinduced crosslinked film via a thiol-ene reaction with 1,6-hexanedithiol in the presence of a photo-radical initiator under ultraviolet irradiation. Thus, for the first time, photocurable and high-refractive-index selenophene-based copolymers were developed through the combination of a selenophene-containing vinyl monomer and a maleimide derivative with a pendant N-vinyl group.

Side-Chain Selenium-Grafted Polymers Combining Antiangiogenesis Treatment with Photodynamic Therapy and Chemotherapy.

The abnormal tumor vasculature in solid tumors creates hypoxia and leads to compromising the delivery and anticancer efficiency of nanomedicine. Nanomaterials with intrinsic antiangiogenesis ability might normalize tumor vessels and improve the therapeutic effect of O2-related treatment like PDT. Herein, we designed and prepared ROS-responsive side-chain selenium-grafted polymers, which had potential antiangiogenic activity, as vehicles to load photodynamic therapeutic agent Ce6 and chemotherapeutic drug oridonin. Under NIR irradiation, the C-Se bonds on the side chain of polymers could be cleaved in the presence of 1O2 produced by Ce6 and further formed organic selenic acid through selenoxide elimination reaction. The generated seleninic acid could downregulate the expression of vascular endothelial growth factor (VEGF) and matrix metalloproteinase-2 (MMP-2) to inhibit angiogenesis and further relieve hypoxia. The released oridonin could significantly increase the intracellular ROS concentration. Both could modulate cancer cells' microenvironment to reinforce PDT. Therefore, these nanomedicines could be a good candidate for synergistic treatments of antiangiogenesis treatment, PDT, and chemotherapy.

Ultrathin Yet Robust Single Lithium-Ion Conducting Quasi-Solid-State Polymer-Brush Electrolytes Enable Ultralong-Life and Dendrite-Free Lithium-Metal Batteries.

Quasi-solid-state polymer electrolytes are one of the most promising candidates for long-life lithium-metal batteries. However, introduction of plasticizers for high ion conductivity at room temperature inevitably gives rise to poor mechanical strength and requires a very thick electrolyte membrane, which is detrimental to safety and energy density of the batteries. Herein, inspired by tube brushes coupling hardness with softness, a novel superstructured polymer bottlebrush BC-g-PLiSTFSI-b-PEGM (BC = bacterial cellulose; PLiSTFSI = poly(lithium 4-styrenesulfonyl-(trifluoromethylsulfonyl) imide); PEGM = poly(diethylene glycol monomethyl ether methacrylate)) with a hard nanofibril backbone and soft functional polymer side-chains is reported as an effective strategy to well balance the mechanical strength and ion conductivity of quasi-solid-state polymer electrolytes. The resulting single lithium-ion conducting quasi-solid-state polymer-brush electrolytes (SLIC-QSPBEs) integrate the features of the ultrathin membrane thickness (10µm), the nanofibril backbone-strengthened porous nanonetwork (Young's modulus = 1.9GPa), and the high-rate single lithium-ion conducting diblock copolymer brushes. As a result, the ultrathin yet robust SLIC-QSPBEs enable ultralong-term (over 3300 h) reversible and stable lithium plating/stripping in Li/Li symmetrical cell at a current density of 1mA cm-2 for lithium anode. This work affords a promising strategy to develop advanced electrolytes for solid-state lithium-metal batteries.