Controlling the Thermoelectric Properties of Organometallic Coordination Polymers via Ligand Design

Organometallic coordination polymers (OMCPs) are a promising class of thermoelectric materials with high electrical conductivities and thermal resistivities. The design criteria for these materials, however, remain elusive and so far material modifications have been focused primarily on the nature of the metal cation to tune the thermoelectric properties. Herein, an alternative approach is described by synthesizing new organic ligands for OMCPs, allowing modulation of the thermoelectric properties of the novel OMCP materials over several orders of magnitude, as well as controlling the polarity of the Seebeck coefficient. Extensive material purification combined with spectroscopy experiments and calculations furthermore reveal the charge‐neutral character of the polymer backbones. In the absence of counter‐cations, the OMCP backbones are composed of air‐stable, ligand‐centered radicals. The findings open up new synthetic possibilities for OMCPs by removing structural constraints and putting significant emphasis on the molecular structure of the organic ligands in OMCP materials to tune their thermoelectric properties.     

Intrinsic Surface Dipoles Control the Energy Levels of Conjugated Polymers

Conjugated polymers are an important class of materials for organic electronics applications. There, the relative alignment of the electronic energy levels at ubiquitous organic/(in)organic interfaces is known to crucially impact device performance. On the prototypical example of poly(3‐hexylthiophene) and a fluorinated derivative, the energies of the ionization and affinity levels of π‐conjugated polymers are revealed to critically depend on the orientation of the polymer backbones with respect to such interfaces. Based on extensive first‐principles calculations, an intuitive electrostatic model is developed that quantitatively traces these observations back to intrinsic intramolecular surface dipoles arising from the π‐electron system and intramolecular polar bonds. The results shed new light on the working principles of organic electronic devices and suggest novel strategies for materials design.     

Electrochemically Nanostructured Polyvinylferrocene/Polypyrrole Hybrids with Synergy for Energy Storage

Unconjugated redox polymers, such as polyvinylferrocene (PVF), have rarely been used for energy storage due to their low intrinsic conductivity. Conducting polymers with conjugated backbones, though conductive, may suffer from insufficient exposure to the electrolyte due to the often formed nonporous structures. The present work overcomes this limitation via simultaneous electropolymerization of pyrrole and electroprecipitation of PVF on electrode surfaces. This synthesis method relies on the π–π stacking interactions between the aromatic pyrrole monomers and the metallocene moieties of PVF. This fabrication process results in a highly porous polymer film, which enhances the ion accessibility to polypyrrole (PPy). PPy serves as a “molecular wire,” improving the electronic conductivity of the hybrid and the utilization efficiency of ferrocene. The PVF/PPy hybrid exhibited a specific capacitance of 514.1 F g^?1 _, which significantly exceeds those of PPy (27.3 F g^?1) and PVF (79.0 F g^?1), respectively. This approach offers an alternative to nanocarbon materials for improving the electronic conductivity of polymer hybrids, and suggests a new strategy for fabricating nanostructured polymer hybrids. This strategy can potentially be applied to various polymers with π‐conjugated backbones and redox polymers with metallocene moieties for applications such as energy storage, sensing, and catalysis.     

Constructing High-Efficiency Orange-Red Thermally Activated Delayed Fluorescence Polymers by Excited State Energy Levels Regulation via Backbone Engineering

Thermally activated delayed fluorescence (TADF) materials have attracted extensive attention because of their 100% theoretical exciton utilization. Solution-processable orange-red TADF polymers are one of indispensable participants. Herein, a series of orange-red TADF polymers with dibenzothiophene (DBT) and carbazole (Cz) units as joint backbones are synthesized. Their performance can be successfully optimized by regulating the connection positions of DBT units through backbone engineering. It is found that the pNAI37 series with DBT units embedded in the polymeric backbones at the 3, 7 sites display a better performance than those connected at the 2, 8 sites. The optimal polymer, pNAI3705, exhibits a better excited state nature, leading to the photoluminescence quantum yield of 60%. Consequently, pNAI3705 based organic light-emitting diodes reach a maximum external quantum efficiency of 20.16%, and maintain 10.61% at 500 cd m⁻², which is in first tier among orange-red polymers. These results unambiguously suggest the potential application of the combined DBT and Cz backbones in TADF polymers. This design strategy may provide a versatile approach for optimizing the properties of TADF polymers through backbone engineering.     

Highly Fluorinated Comb‐Shaped Copolymers as Proton Exchange Membranes (PEMs): Improving PEM Properties Through Rational Design

A new class of comb‐shaped polymers for use as a proton conducting membrane is presented. The polymer is designed to combine the beneficial physical, chemical, and structural attributes of fluorinated Nafion‐like materials with higher‐temperature, polyaromatic‐based polymer backbones. The comb‐shaped polymer unites a rigid, polyaromatic, hydrophobic backbone with lengthy hydrophilic polymer side chains; this combination affords direct control over the polymer nanostructure within the membrane and results in distinct microphase separation between the opposing domains. The microphase separation serves to compartmentalize water into the hydrophilic polymer side chain domains, resulting in effective membrane water management and excellent proton conductivities.     

Molecular Origin of Strain-Induced Chain Alignment in PDPP-Based Semiconducting Polymeric Thin Films

Donor–acceptor (D–A) type semiconducting polymers have shown great potential for the application of deformable and stretchable electronics in recent decades. However, due to their heterogeneous structure with rigid backbones and long solubilizing side chains, the fundamental understanding of their molecular picture upon mechanical deformation still lacks investigation. Here, the molecular orientation of diketopyrrolopyrrole (DPP)-based D–A polymer thin films is probed under tensile deformation via both experimental measurements and molecular modeling. The detailed morphological analysis demonstrates highly aligned polymer crystallites upon deformation, while the degree of backbone alignment is limited within the crystalline domain. Besides, the aromatic ring on polymer backbones rotates parallel to the strain direction despite the relatively low overall chain anisotropy. The effect of side-chain length on the DPP chain alignment is observed to be less noticeable. These observations are distinct from traditional linear-chain semicrystalline polymers like polyethylene due to distinct characteristics of backbone/side-chain combination and the crystallographic characteristics in DPP polymers. Furthermore, a stable and isotropic charge carrier mobility is obtained from fabricated organic field-effect transistors. This study deconvolutes the alignment of different components within the thin-film microstructure and highlights that crystallite rotation and chain slippage are the primary deformation mechanisms for semiconducting polymers.     

Systematic Investigation of Side‐Chain Branching Position Effect on Electron Carrier Mobility in Conjugated Polymers

Recently, polymer field‐effect transistors have gone through rapid development. Nevertheless, charge transport mechanism and structure‐property relationship are less understood. Here we use strong electron‐deficient benzodifurandione‐based poly(p‐phenylene vinylene) ( BDPPV ) as polymer backbone and develop six BDPPV ‐based polymers ( BDPPV‐C1 to C6 ) with various side‐chain branching positions to systematically study the side‐chain effect on device performance. All the polymers exhibited ambient‐stable n‐type transporting behaviors with the highest electron mobility of up to 1.40 cm² V^?1 s^?1. The film morphologies and microstructures of all the six polymers were systematically investigated. Our results demonstrate that the interchain π–π stacking distance decreases as moving the branching position away from polymer backbones, and an unprecedentedly close π–π stacking distance down to 3.38 Å is obtained for BDPPV‐C4 to C6 . Nonetheless, closer π–π stacking distance does not always correlate with higher electron mobility. Polymer crystallinity, thin film disorder, and polymer packing conformation, which all influenced by side‐chain branching position, are proved to show significant influence on device performance. Our study not only reveals that π–π stacking distance is not the decisive factor on carrier mobility in conjugated polymers but also demonstrates that side‐chain branching position engineering is a powerful strategy to modulate and balance these factors in conjugated polymers.     

Crystallinity and Orientation Manipulation of Anthracene Diimide Polymers for All-Polymer Solar Cells

Electron-carrying polymers are highly desired for various optoelectronic applications but are still scarce. Herein, two anthracene diimide (ADI) polymers with thiophene and bithiophene as comonomer, respectively, are reported as electron acceptor materials in all-polymer solar cells (all-PSCs) for the first time. Effects of crystallinity and orientation of two polymer films as well as their blends with different donor polymers on photovoltaic properties are elaborately investigated by grazing-incidence X-ray diffraction and photo-induced force microscopy. It is found that molecular crystallinity and orientation determine the blend film morphology, and the similar high crystallinity and the same face-on orientation of donor and acceptor polymers are favorable for obtaining excellent photovoltaic performances. With this principle, a suitable donor polymer is singled out to match with the ADI acceptor polymer, offering an impressive efficiency of ≈7% for all-PSCs. This work demonstrates that ADI polymers are promising as acceptor materials and provides guidelines for screening donor and acceptor polymer combinations for all-PSCs.     

Cover Picture: Hierarchically Organized Superstructure Emerging from the Exquisite Association of Inorganic Crystals,Organic Polymers,and Dyes: A Model Approach Towards Suprabiomineral Materials (Adv. Funct. Mater. 9/2005)

Suprabiomineral materials possessing hierarchically organized superstructures are investigated by Imai and Oaki on p. 1407. Inorganic crystals, organic polymers, and functional dyes have assembled via a simple biomimetic route into a superstructure that contains six different tiers, from the macroscale to the nanoscale. The hierarchy originates from the strong interaction between crystals and polymers and the diffusion‐controlled conditions. The versatile role of the polymer is found to be essential for the construction of a superstructure. This approach promises to generate novel types of functional materials with controllable structures and properties. We report a novel hierarchically organized superstructure emerging from an exquisite association of inorganic crystals, organic polymers, and dyes. The resultant K₂SO₄/poly(acrylic acid) composite includes five different tiers from the nanoscopic to the macroscopic. An additional new tier leading to functionality is formed by the incorporation of organic dyes that are organized in a nanospace. The emergent superstructure and properties are designed through changes in polymer concentration. The multiple roles of the polymer realize the generation of the architecture at each size scale. This model approach should be widely applicable to other systems, allowing for the preparation of innovative materials by an appropriate combination of crystals, polymers, and functional molecules.     

ε‐Branched Flexible Side Chain Substituted Diketopyrrolopyrrole‐Containing Polymers Designed for High Hole and Electron Mobilities

Based on the integrated consideration and engineering of both conjugated backbones and flexible side chains, solution‐processable polymeric semiconductors consisting of a diketopyrrolopyrrole (DPP) backbone and a finely modulated branching side chain (ε‐branched chain) are reported. The subtle change in the branching point from the backbone alters the π?π stacking and the lamellar distances between polymer backbones, which has a significant influence on the charge‐transport properties and in turn the performances of field‐effect transistors (FETs). In addition to their excellent electron mobilities (up to 2.25 cm² V^?1 s^?1), ultra‐high hole mobilities (up to 12.25 cm² V^?1 s^?1) with an on/off ratio (I_on/I_off) of at least 10⁶ are achieved in the FETs fabricated using the polymers. The developed polymers exhibit extraordinarily high electrical performance with both hole and electron mobilities superior to that of unipolar amorphous silicon.     

Oriented Poly(dialkylstannane)s

The inorganic (or ‘organometallic’) polymers poly(dibutylstannane), poly(dioctylstannane), and poly(didodecylstannane) have been oriented by shear forces, the tensile drawing of blends with polyethylene, and deposition from solution onto glass slides coated with an oriented, friction‐deposited poly(tetrafluoroethylene) (PTFE) layer. Orientation of the polystannanes has been examined by polarization microscopy, UV‐vis spectroscopy with polarized light, and X‐ray diffraction and their direction is found to depend on the length of the alkyl side groups and the method of orientation. Remarkably, in some cases the polystannane backbones are oriented parallel and in other instances perpendicular to the direction of the external orientation stimuli. The latter structural arrangement is most conspicuous for polymers substituted with dodecyl side groups, which are found to align parallel to the applied orientation direction, which forces the polymer backbone into a perpendicular position. Finally, UV‐vis spectra indicate that changes in the backbone conformation of certain polystannanes might be induced by applying mechanical stress.     

A Tailorable Family of Elastomeric‐to‐Rigid, 3D Printable,Interbonding Polymer Networks

Soft materials with widely tailorable mechanical properties throughout the material's volume can shape the future of soft robotics and wearable electronics, impacting both consumer and defense sectors. Herein, a platform of 3D printable soft polymer networks with unprecedented tunability of stiffness of nearly three orders of magnitude (MPa to GPa) and an inherent capability to interbond is reported. The materials are based on dynamic covalent polymer networks with variable density of crosslinkers attached to prepolymer backbones via a temperature‐reversible Diels–Alder (DA) reaction. Inherent flexibility of the prepolymer chains and controllable crosslinking density enable 3D printed networks with glass transition temperatures ranging from just a few degrees to several tens of degrees Celsius. Materials with an elastomeric network demonstrate a fast and spontaneous self‐healing behavior at room temperature both in air and under water—a behavior difficult to achieve with other crosslinked materials. Reversible dissociation of DA networks at temperatures exceeding ≈120 °C allows for reprintability, while control of the stereochemistry of DA attachments enables reprogrammable shape memory behavior. The introduced platform addresses current major challenges including control of polymer interbonding, enhanced mechanical performance of printed parts, and reprocessability of 3D‐printed crosslinked materials in the absence of solvent.     

Micro and nano structures of carbonised polymer through pyrolytic transformation from polymer structures

Micro and nano structures of carbonised polymers resulting from the pyrolytic transformation of polymer structures are presented. Polymers have become increasingly popular as materials for micro/nano electromechanical systems (MEMS/NEMS), especially for chemical or biological application. Focus is on the transformation of polymer structures into carbonised structures using a pyrolysis process. Combination of this pyrolysis process with conventional MEMS/NEMS fabrication technology could provide various fine structures of carbonised polymer. Carbonised polymers have advantages over conventional carbon materials, with respect to compatibility with MEMS, because they can be transformed directly from a polymer structure. Three-dimensional micro and nano free-standing structures of carbonised polymer as typical MEMS/NEMS structures are reported. Micro molding process is used to demonstrate a unique polymer structure to be pyrolysed. Furthermore, EB lithography technology is employed for the patterning of polymers in addition to UV photolithography which is used by previous researches. A 100 nm wide bridge structure is designed as nano structures. In addition, the presented structures of carbonised polymer are expected to be applied to micro and nano functional devices such as electrochemical sensors by making the best use of their carbon-like features     

Thieno[3,2‐b]thiophene Flanked Isoindigo Polymers for High Performance Ambipolar OFET Applications

The synthesis of a new thieno[3,2‐b]thiophene isoindigo (iITT) based monomer unit, and its subsequent incorporation into a series of alternating copolymers is reported. Copolymerisation with benzothiadiazole, bithiophene and thiophene comonomer units by palladium catalysed cross coupling gives three new narrow band gap semiconducting polymers for OFET applications. Extending the fused nature of the isoindigo core serves to further enhance molecular orbital overlap along the polymer backbones and facilitate good charge transport characteristics thus demonstrating the potential of extending the fused ring system that is attached to the isoindigo core. When used as the semiconducting channel in top‐gate/bottom‐contact OFET devices, good ambipolar properties are observed, with hole and electron mobilities up to 0.4 cm²/Vs and 0.7 cm²/Vs respectively. The three new polymers show good stability, with high temperature annealing showing an increase in the crystallinity of the polymers which corresponds directly to charge carrier mobility improvement as shown by X‐ray diffraction, atomic force microscopy and photothermal deflection spectroscopy.     

功能高分子材料在伪装防护中的应用

基于材料的光、电物理特性,介绍了导电高分子材料、电致变色高分子材料、光致变色高分子材料和高分子纳米复合材料,论述了几种功能高分子材料作为新型吸波材料、智能化隐身材料、热抑制/电热膜层材料、低发射率/高反射率膜层材料的研究进展情况,最后简要总结了功能高分子材料在伪装防护领域的发展方向.     

微波多模腔体对水性聚氨酯涂膜加热仿真分析

水性聚氨酯为水与高分子聚酯材料的混合材料,工业上采用热风和红外干燥方式对水性聚氨酯材料进行干燥存在干燥效率低同时时间长等问题。为解决在传统干燥过程中存在的问题,本文通过使用有限元方法对水性聚氨酯涂膜在多模微波腔体内进行建模,通过测试并拟合水性高分子聚氨酯乳液介电常数随温度的变化曲线;仿真了微波干燥方式下涂膜的温度分布,获得了涂膜整体平均温度随微波功率的变化仿真结果,确定了在相同的时间内有利于水性聚氨酯涂膜干燥的微波功率,仿真了在该微波功率下涂膜整体温度随时间的动态变化过程。     

掺杂聚合物的激光微烧蚀推进性能研究现状

基于激光微烧蚀聚合物产生微冲量这一原理,研究10^-5 N·s至10^-7N．s量级冲量的激光微推力器是当前一个研究热点。聚合物对入射激光的吸收率往往很低,掺杂是提高聚合物的激光微烧蚀性能的一个重要途径。回顾了掺杂聚合物的推进性能实验,分析了不同掺杂下推进性能的实验结果,认为以碳、红外染料或者含能材料作为掺杂剂可以获得较好的推进性能参数,含能聚合物是较好的备选靶材。为国内掺杂聚合物激光微推进性能的研究提供了有益参考。     

Porous Structures: In situ Porous Structures: A Unique Polymer Erosion Mechanism in Biodegradable Dipeptide‐Based Polyphosphazene and Polyester Blends Producing Matrices for Regenerative Engineering (Adv. Funct. Mater. 17/2010)

Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in‐growth in regenerative medicine. To allow tissue in‐growth and nutrient transport, traditional three‐dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here we demonstrated for the first time a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure. This polymer system was developed on the highly versatile platform of polyphosphazene‐polyester blends. Co‐substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4‐phenylphenoxy group generated a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permitted the formation of 3D void space filled with self‐assembled polyphosphazene spheres. Characterization of such self‐assembled porous structures revealed macropores (10–100 μm) between spheres as well as micro‐ and nanopores on the sphere surface. A similar degradation pattern was confirmed in vivo using a rat subcutaneous implantation model. 12 weeks of implantation resulted in an interconnected porous structure with 82–87% porosity. Cell infiltration and collagen tissue in‐growth between microspheres observed by histology confirmed the formation of an in situ 3D interconnected porous structure. It was determined that the in situ porous structure resulted from unique hydrogen bonding in the blend promoting a three‐stage degradation mechanism. The robust tissue in‐growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation.     

Recent Progress in Applications of the Cold Sintering Process for Ceramic–Polymer Composites

Ceramic–polymer composites are of interest for designing enhanced and unique properties. However, the processing temperature windows of sintering ceramics are much higher than that of compaction, extrusion, or sintering of polymers, and thus traditionally there has been an inability to cosinter ceramic–polymer composites in a single step with high amounts of ceramics. The cold sintering process is a low‐temperature sintering technology recently developed for ceramics and ceramic‐based composites. A wide variety of ceramic materials have now been demonstrated to be densified under the cold sintering process and therefore can be all cosintered with polymers from room temperature to 300 °C. Here, the status, understanding, and application of cold cosintering, with different examples of ceramics and polymers, are discussed. One has to note that these types of cold sintering processes are yet new, and a full understanding will only emerge after more ceramic–polymer examples emerge and different research groups build upon these early observations. The general processing, property designs, and an outlook on cold sintering composites are outlined. Ultimately, the cold sintering process could open up a new multimaterial design space and impact the field of ceramic–polymer composites.     

Rational Design of High‐Mobility Semicrystalline Conjugated Polymers with Tunable Charge Polarity: Beyond Benzobisthiadiazole‐Based Polymers

High‐mobility semiconducting polymers composed of arylene vinylene and dithiophene‐thiadiazolobenzotriazole (SN) units are developed by three powerful design strategies, namely, backbone engineering, heteroatom substitution, and side‐chain engineering. First, starting from the quaterthiophene‐SN copolymer, a vinylene spacer is inserted into the quaterthiophene unit for constructing highly‐planar backbones. Second, heteroatoms (O and N atoms) are incorporated into the thienylene vinylene moieties to tune the electronic properties and intermolecular interactions. Third, the alkyl side chains are optimized to tune the solubility and self‐assembly properties. As a consequence, a remarkable thin film transistor performance is obtained. The very high hole mobility of 3.22 cm² V^?1 s^?1 is achieved for the p‐type polymer, PSNVT‐DTC8, which is the highest value ever reported for the polymers based on the benzobisthiadiazole and its analogs. Moreover, heteroatom substitution efficiently varies the charge polarity of the polymers as in the case of the N atom substituted PSNVT_z‐DTC16 displaying n‐type dominant ambipolar properties with the electron mobility of 0.16 cm² V^?1 s^?1. Further studies using grazing‐incidence wide‐angle X‐ray scattering and atomic force microscopy have revealed the high crystallinities of the polymer thin films with strong π–π interactions and suitable polymer packing orientations.