Showing papers in "Macromolecules in 2017"
TL;DR: The authors summarizes the features and limitations of reversible addition-fragmentation chain transfer (RAFT) polymerization, highlighting its strengths and weaknesses, as our understanding of the process from both a mechanistic and an application point of view has matured over the past 20 years.
Abstract: This Perspective summarizes the features and limitations of reversible addition–fragmentation chain transfer (RAFT) polymerization, highlighting its strengths and weaknesses, as our understanding of the process, from both a mechanistic and an application point of view, has matured over the past 20 years. It is aimed at both experts in the field and newcomers, including undergraduate and postgraduate students, as well as nonexperts in polymerization who are interested in developing their own polymeric structures by exploiting the simple setup of a RAFT polymerization.
828 citations
TL;DR: In this paper, the state of the art of membrane materials, including polymers and hybrid materials, as well as the current issues and barriers, and finally, future research directions in membrane science are outlined.
Abstract: Membrane gas separation is a mature and expanding technology. However, the availability of better membrane materials would promote faster growth. In this Perspective we analyze the state of the art of membrane materials, including polymers and hybrid materials, as well as the current issues and barriers, and finally, we outline future research directions in membrane science. Development of new membrane materials for large scale separations will rely on a multidisciplinary approach that embraces the broad fields of chemical and materials engineering, polymer science, and materials chemistry.
647 citations
TL;DR: In this article, the authors highlight five research topics, including the synthesis of renewable monomers and degradable polymers, the development of chemical recycling strategies, new classes of reprocessable thermosets, and the design of advanced catalysts.
Abstract: It is likely that a half-century ago even enthusiastic and optimistic proponents of the synthetic polymer industry (Mr. McGuire included) could not have predicted the massive scale on which synthetic polymers would be manufactured and used today. Ultimately, the future success of this industry will rely on the development of sustainable polymers—materials derived from renewable feedstocks that are safe in both production and use and that can be recycled or disposed of in ways that are environmentally innocuous. Meeting these criteria in an economical manner cannot be achieved without transformative basic research that is the hallmark of this journal. In this Perspective we highlight five research topics—the synthesis of renewable monomers and of degradable polymers, the development of chemical recycling strategies, new classes of reprocessable thermosets, and the design of advanced catalysts—that we believe will play a vital role in the development of sustainable polymers. We also offer our outlook on sev...
603 citations
TL;DR: In this article, the authors parse the vast literature to examine the forefront of the field of block polymers and identify exciting themes and challenging opportunities that portend a bracing future trajectory.
Abstract: Block polymers have undergone extraordinary evolution since their inception more than 60 years ago, maturing from simple surfactants to an expansive class of macromolecules encoded with exquisite attributes. Contemporary synthetic accessibility coupled with facile characterization and rigorous theoretical advances have conspired to continuously generate fundamental insights and enabling concepts that target applications spanning chemistry, biology, physics, and engineering. Here, we parse the vast literature to examine the forefront of the field and identify exciting themes and challenging opportunities that portend a bracing future trajectory. This Perspective celebrates the visionary role played by Macromolecules in advancing our understanding of this remarkable class of materials.
542 citations
TL;DR: The field of polymer nanocomposites has been at the forefront of research in the polymer community for the past few decades as mentioned in this paper, which has enabled many niche solutions such as filled rubbers, continuous fiber reinforced thermoset composites, membranes for gas separations, and dielectrics for capacitors and insulation.
Abstract: The field of polymer nanocomposites has been at the forefront of research in the polymer community for the past few decades. Foundational work published in Macromolecules during this time has emphasized the physics and chemistry of the inclusion of nanofillers; remarkable early developments suggested that these materials would create a revolution in the plastics industry. After 25 years of innovative and groundbreaking research, PNCs have enabled many niche solutions. To complement the extensive literature currently available, we focus this Perspective on four case studies of PNCs applications: (i) filled rubbers, (ii) continuous fiber reinforced thermoset composites, (iii) membranes for gas separations, and (iv) dielectrics for capacitors and insulation. After presenting synthetic developments we discuss the application of polymer nanocomposites to each of these topic areas; successes will be noted, and we will finish each section by highlighting the various technological bottlenecks that need to be over...
440 citations
TL;DR: In this paper, the use of brush surfaces in biology relevant applications is discussed and the effect of nanoscale patterning on brush surface properties and behavior is discussed. But, the authors focus on the application of brush surface modification.
Abstract: Polymer brushes have become a significant focus of polymer research with the need for straightforward and versatile surface modification. With the development of controlled radical polymerization from surfaces, new theoretical models, and sophisticated characterization tools, the resulting ability to control brush density and brush thickness gives unparalleled control over surface properties and functionality. By increasing brush density, a stretched brush conformation is formed as a result of constraining the cross-sectional area of that brush strand which thereby influences the interactions of molecules with the brush surface. The associated residual stress also gives polymer brushes properties distinct from an equivalent layer of coated polymer chains. Examples of uncharged and charged “grown from” polymer brushes, the effect of architecture on physical behavior, and the influence of nanoscale patterning will be described. The use of brush surfaces in biology relevant applications will be discussed and...
332 citations
TL;DR: In this paper, two bio-based epoxy monomers EP1 and EP2 were synthesized by one-pot reaction containing Schiff base formation and phosphorus-hydrogen addition between vanillin, diamines, and diethyl phosphite, followed by reacting with epichlorohydrin.
Abstract: Lignin derivative vanillin when coupled with diamines and diethyl phosphite followed by reaction with echichlorohydrin yields high-performance flame retardant epoxy resins. Biorenewable and environment-friendly flame retardant alternatives to bisphenol A epoxy resins (having plenty of applications such as coatings, adhesives, composites, etc.) have captured great attention due to their ecological and economic necessity. Vanillin, an industrial scale monoaromatic compound from lignin, is a promising sustainable candidate for high-performance polymers, while synthesis of diepoxies is challenging. Meanwhile, bio-based epoxy resins combining high performance and excellent fire resistance are more difficult to be achieved. In this paper, two novel bio-based epoxy monomers EP1 and EP2 were synthesized by one-pot reaction containing Schiff base formation and phosphorus–hydrogen addition between vanillin, diamines, and diethyl phosphite, followed by reacting with epichlorohydrin. Their reactivities are similar to...
311 citations
TL;DR: The translation of small molecule chemistries into efficient methodologies for polymer functionalization spans several decades, enabling critical advances in soft matter materials synthesis with tailored and adaptive property profiles.
Abstract: The translation of small molecule chemistries into efficient methodologies for polymer functionalization spans several decades, enabling critical advances in soft matter materials synthesis with tailored and adaptive property profiles. The present Perspective explores—based on selected examples—50 years of innovation in polymer functionalization chemistries. These span a diverse set of chemistries based on activated esters, thiol–ene/yne processes, nucleophilic systems based on isocyanates, reactions driven by the formation of imines and oximes, ring-opening processes, cycloadditions, and—in a recent renaissance—multicomponent reactions. In addition, a wide variety of chain types and architectures have been modified based on the above chemistries, often with exquisite chemical control, highlighted by key examples. We conclude our journey through polymer functionalization with the—in our view—most critically required advances that have the potential to move from “science fiction” to “science fact”.
295 citations
TL;DR: This Perspective presents the author's subjective summary of several conceptual advances and the remaining persistent challenges in the contexts of charge and size of polymers, structures in homogeneous solutions, thermodynamic instability and phase transitions, structural evolution with oppositely chargedpolymers, dynamics in polyelectrolyte solutions, kinetics of phase separation, mobility of charged macromolecules between compartments, and implications to biological systems.
Abstract: From the beginning of life with the information-containing polymers until the present era of a plethora of water-based materials in health care industry and biotechnology, polyelectrolytes are ubiquitous with a broad range of structural and functional properties. The main attribute of polyelectrolyte solutions is that all molecules are strongly correlated both topologically and electrostatically in their neutralizing background of charged ions in highly polarizable solvent. These strong correlations and the necessary use of numerous variables in experiments on polyelectrolytes have presented immense challenges toward fundamental understanding of the various behaviors of charged polymeric systems. This Perspective presents the author’s subjective summary of several conceptual advances and the remaining persistent challenges in the contexts of charge and size of polymers, structures in homogeneous solutions, thermodynamic instability and phase transitions, structural evolution with oppositely charged polyme...
290 citations
TL;DR: In this article, the authors outline recent advances concerning the formation and potential uses of block copolymer micelles, a class of soft-matter-based nanoparticles of growing importance, in terms of morphological diversity, structural complexity, control over micelle dimensions, scale-up, and applications in a range of areas from nanocomposites to nanomedicine.
Abstract: This Perspective outlines recent advances concerning the formation and potential uses of block copolymer micelles, a class of soft-matter-based nanoparticles of growing importance. As a result of rapidly expanding interest since the mid-1990s, substantial advances have been reported in terms of the development of morphological diversity, structural complexity, control over micelle dimensions, scale-up, and applications in a range of areas from nanocomposites to nanomedicine.
279 citations
TL;DR: In this article, the authors highlight innovative contributions in the synthesis of well-defined complex macromolecular architectures and emphasize the importance of these materials to polymer physical chemistry, physics, theory, and applications.
Abstract: The scope of this Perspective is to highlight innovative contributions in the synthesis of well-defined complex macromolecular architectures and to emphasize the importance of these materials to polymer physical chemistry, physics, theory, and applications. In addition, this Perspective tries to enlighten the past and show possible pathways for the future. Among the plethora of polymerization methods, we briefly report the impact of the truly living and controlled/living polymerization techniques focusing mainly on anionic polymerization, the mother of all living and controlled/living polymerizations. Through anionic polymerization well-defined model polymers with complex macromolecular architectures having the highest molecular weight, structural and compositional homogeneity can be achieved. The synthesized structures include star, comb/graft, cyclic, branched and hyberbranched, dendritic, and multiblock multicomponent polymers. In our opinion, in addition to the work needed on the synthesis, properties...
TL;DR: In this paper, a unique eugenol-derived epoxy (Eu-EP) is synthesized, and then vitrimeric materials are prepared by reacting EuEP with succinic anhydride (SA) at various ratios (1: 0.5, 1:0.75, and 1:1) in the presence of zinc-containing catalysts.
Abstract: Conventional epoxy polymers are constructed by petro-based resources that are toxic and nonrenewable, and their permanent cross-links make them difficult to be reprocessed, reshaped, and recycled. In this study, a unique eugenol-derived epoxy (Eu-EP) is synthesized, and then vitrimeric materials are prepared by reacting Eu-EP with succinic anhydride (SA) at various ratios (1:0.5, 1:0.75, and 1:1) in the presence of zinc-containing catalysts. All vitrimers exhibit excellent shape changing, crack healing, and shape memory properties. Although vitrimers with 1:0.75 and 1:1 ratios cannot be physically reprocessed, they can be well reprocessed by the chemical method of being simply decomposed in a benign ethanol solution without loading additional catalyst. The collected decomposed polymers can form vitrimers again after exposure at 190 °C for 3 h. This work combines the concepts of vitrimer preparation, chemical recycling, and biobased polymer together, which would bring a feasible way to satisfy the demands ...
TL;DR: A candid and critical overview of the current understanding of the relation between the structure and molecular architecture of polymer networks and their mechanical properties, restricting ourselves to soft networks made of flexible polymers and displaying entropic elasticity.
Abstract: Soft polymer networks have seen an explosion of recent developments motivated by new high tech applications in the biomedical field or in engineering. We present a candid and critical overview of the current understanding of the relation between the structure and molecular architecture of polymer networks and their mechanical properties, restricting ourselves to soft networks made of flexible polymers and displaying entropic elasticity. We specifically review and compare recent approaches to synthesize swollen hydrogels with enhanced toughness, resilient but tough unfilled elastomers and self-healing networks containing dynamic bonds. The purpose is less to draw a comprehensive catalogue of approaches than to identify and unify the underlying principles controlling toughening mechanisms and mechanical self-healing behavior and to point out remaining challenges.
TL;DR: It is demonstrated that naturally derived, cost-effective tannic acid (TA) can be an efficient gelation binder for the hydrogel formation with a series of commercially available water-soluble polymers.
Abstract: The development of facile and versatile strategies with low-cost for hydrogel construction is of tremendous scientific interest. Herein, we demonstrate that naturally derived, cost-effective tannic acid (TA) can be an efficient gelation binder for the hydrogel formation with a series of commercially available water-soluble polymers. With a five-polyphenol-arm structure, TA molecules are able to grasp polymer chains through either hydrogen or ionic bonds and cross-link them together by coordinate bonds in the presence of Fe(III) ions. These two interactions can be elegantly balanced by tuning the weight ratios of polymer/TA and TA/Fe3+, which is the key point for the construction of supramolecular hydrogels. The supramolecular hydrogels exhibit multiple functionalities including mechanical tenability, rapid self-healing, pH-stimuli responsiveness, and free radical scavenging abilities. TA as a dynamic and versatile catechol group modifier provides a simple path to the construction of multifunctional hydrog...
TL;DR: In this paper, the authors present the case that this concept has enabled the treatment of polymers as organic molecules, rather than impure mixtures of species, and allowed the translation of methods developed by synthetic organic chemists into ever more accessible living and/or controlled polymerization methods.
Abstract: The ideal of living polymerization has defined research in polymer chemistry over the past 50 years. In this Perspective, we present the case that this concept has enabled the treatment of polymers as organic molecules, rather than impure mixtures of species, and allowed the translation of methods developed by synthetic organic chemists into ever more accessible living and/or controlled polymerization methods. The concurrent development of rapid analytical methods for screening new polymerization methods for living characteristics, chiefly size exclusion chromatography, has greatly aided in the expansion of living polymerization methods.
TL;DR: The field of organic conducting polymers was ignited by the demonstration of metallic conductivity in polyacetylene as mentioned in this paper, and a retrospective view of this research area suggests some areas remain ripe for discovery/innovation.
Abstract: It has been about 40 years since the field of organic conducting polymers was ignited by the demonstration of metallic conductivity in polyacetylene. A retrospective view of this research area suggests some areas remain ripe for discovery/innovation. The breadth of activities is too large to be comprehensive; hence, selected seminal, as well as some personal, contributions will be used to illustrate concepts and anecdotal ways to think about conducting polymer systems. This Perspective can serve as a tutorial for newcomers to the field and will also remind experts about results from the past. It begins with some history and simple views of electronic structure, with selected examples. Segmented polymers containing isolated redox units will be discussed as well as how these materials can be made to have high conductivity. Key examples illustrating the matching of redox potentials are transition metal hybrid structures. Interchain interactions are emphasized along with their role in determining the nature o...
TL;DR: In this paper, the authors discuss the characteristics of each polarization and explain how to enhance the polarization using rational molecular designs without causing significant dielectric losses in multilayer polymers.
Abstract: High dielectric constant and low dielectric loss are desirable electrical properties for next-generation polymer dielectrics that show promise for applications in pulsed power, power electronics, and printable electronics. Unfortunately, the dielectric constant of polymers is often limited to 2–5, much lower than that of inorganic dielectrics, because of the nature of hydrocarbon covalent bonds for electronic and atomic polarizations. It is essential to understand the fundamental physics of different types of polarization and the associated loss mechanisms in polymers. In this Perspective, we discuss the characteristics of each polarization and explain how to enhance the polarization using rational molecular designs without causing significant dielectric losses. Among various approaches for high dielectric constant and low loss polymers, the multilayer film technology is of particular interest because a multilayer film is a unique one-dimensional system with tailored material choices, layer thicknesses, a...
TL;DR: In this article, the authors leverage the large accessible composition window of a newly synthesized single ion conducting polysulfone-poly(ethylene glycol) (PSf-co-PEG) miscible random copolymer to more completely understand the interrelationship of glass transition temperature, ion content, and the polymer's Li+ conductivity.
Abstract: Single-ion conducting polymer electrolytes have been proposed to significantly enhance lithium ion battery performance by eliminating concentration gradients within the cell. Such electrolytes have universally suffered from poor conductivity at low to moderate temperatures. In an attempt to improve conductivity, numerous studies have sought to better understand the fundamental interplay of ion content and segmental motion, with typical analyses relying on a fit of temperature-dependent conductivity data using the Vogel–Tammann–Fulcher (VTF) equation to assist in separating these effects. In this study, we leverage the large accessible composition window of a newly synthesized, single ion conducting polysulfone–poly(ethylene glycol) (PSf-co-PEG) miscible random copolymer to more completely understand the interrelationship of glass transition temperature, ion content, and the polymer’s Li+ conductivity. It is demonstrated here that choice of fitting procedure and Vogel temperature plays a crucial role in th...
TL;DR: The authors quantitatively compares the binding strengths between a selection of positive and negative polyelectrolytes by evaluating the extent to which ion pairs between them are broken by a common salt, KBr.
Abstract: Polyelectrolyte complexes, PECs, are spontaneously formed blends of polyelectrolytes bearing positive, Pol+, and negative, Pol–, repeat units. Many interesting PEC morphologies have been observed, ranging from dense precipitates to liquidlike coacervates to quasi-stable nanoparticles, depending on the identity of the polymers and the preparation conditions. While the number of polyelectrolytes available to synthesize these materials is large and increasing, the corresponding number of Pol+/Pol– combinations is vast. This work quantitatively compares the binding strengths between a selection of positive and negative polyelectrolytes by evaluating the extent to which ion pairs between them are broken by a common salt, KBr. Comparison of association constants or Gibbs free energies between different classes of ionic functionality reveals that more “hydrophilic” PECs are more weakly associated, small primary amines bind strongly, carboxylates bind weakly, and aromatic sulfonates interact more strongly than al...
TL;DR: By rationally introducing iodine into a novel naphthalimide-functionalized pillar[5]arene-based supramolecular polymer (PNA⊃GBP), the iodine could not only control the optical properties and self-assembly states of PNA ⊂GBP via electronic donor–acceptor effect but also control the molecular recognition properties by competitive redox reaction.
Abstract: A simple and efficient approach to endow the controllable multi-stimuli-responsive property for the supramolecular polymer was successfully developed by rationally introducing iodine into a novel naphthalimide-functionalized pillar[5]arene-based supramolecular polymer (PNA⊃GBP). Interestingly, by introducing iodine into the supramolecular polymer PNA⊃GBP, the iodine could not only control the optical properties and self-assembly states of PNA⊃GBP via electronic donor–acceptor effect but also control the molecular recognition properties by competitive redox reaction. Benefiting from these excellent iodine controlled multiresponse properties, the PNA⊃GBP showed selective fluorescent response for cyanide, cysteine, and mercury in supramolecular polymer gels, water solutions, and living cells with high sensitivities. The supramolecular polymer PNA⊃GBP could act as a novel smart material for selective detection CN–, Hg2+, and l-Cys.
TL;DR: In this article, a dibenzobarrelene-derived α-diimine nickel precatalysts for living copolymerization of ethylene and methyl 10-undecenoate were reported.
Abstract: Development of thermally stable nickel-based catalysts is highly desirable for industrial gas-phase olefin polymerizations. On the basis of the strategy of promoting the thermostability of nickel catalyst by the ligand backbone, we herein reported novel dibenzobarrelene-derived α-diimine nickel precatalysts for ethylene polymerization. Increasing the steric bulk on the ligand backbone was expected to inhibit the N-aryl rotation of the α-diimine ligands by the repulsive interactions, thus enhancing thermal stability (100 °C) and living fashion a temperatures up to 80 °C. Bulk ligand backbone also improved tolerance of nickel catalyst toward polar groups, and the α-diimine nickel catalyst containing a 2,6-tBu-dibenzobarrelene backbone catalyzed living copolymerization of ethylene and methyl 10-undecenoate.
TL;DR: In this paper, the impact of steric hindrance of N-alkyl substituents and network connectivity in poly(alkylurea-urethane) dynamic network films was investigated.
Abstract: Dynamic covalent networks are polymer networks that contain a dynamic covalent bond which allows them to be reprocessable, remoldable, and recyclable as well as exhibit crack healing or stress-relaxation properties. A key component of these materials is the nature of the dynamic covalent bond, which in addition to chemical composition and architecture can be used to dramatically alter the physical properties of these networks. The aim of this study is to understand the impact of steric hindrance of N-alkyl substituents and network connectivity in poly(alkylurea–urethane) dynamic network films. In these materials, the dynamic bond is the hindered alkyl urea moiety, whose dynamic behavior is dictated by the sterics of the alkyl substituent. Networks were prepared by the noncatalyzed curing reaction of aminoethanol compounds of varying substituents with a trifunctional isocyanate cross-linker and varying amounts of a monofunctional capping agent. Thermomechanical properties and FTIR studies show the impact o...
TL;DR: In this article, a simple way to prepare covalently cross-linked yet recyclable, robust, and macroscopically responsive elastomer vitrimers by engineering exchangeable bonds into rubber-carbon nanodot (CD) interphase using CD as high-functionality cross-linker is reported.
Abstract: Reinforcement, recycling, and functional applications are three important issues in elastomer science and engineering. It is of great importance, but rarely achievable, to integrate these properties into elastomers. Herein, we report a simple way to prepare covalently cross-linked yet recyclable, robust, and macroscopically responsive elastomer vitrimers by engineering exchangeable bonds into rubber–carbon nanodot (CD) interphase using CD as high-functionality cross-linker. The cross-linked rubbers can rearrange the network topology through transesterification reactions in the interphase, conferring the materials the ability to be recycled, reshaped, and welded. The relatively short chains bridging adjacent CD are highly stretched and preferentially rupture to dissipate energy under external force, resulting in remarkable improvements on the mechanical properties. Moreover, the malleable and welding properties allow the samples to access reconfigurable/multiple shape memory effects.
TL;DR: In this paper, a difunctional benzoxazine with o-trifluoroacetamide functionality has been synthesized via Mannich condensation, and the chemical structure of synthesized monomer has also been confirmed by 1H, 13C, and 19F nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FT-IR).
Abstract: A novel difunctional benzoxazine with o-trifluoroacetamide functionality has been synthesized via Mannich condensation. The chemical structure of synthesized monomer has also been confirmed by 1H, 13C, and 19F nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The ring-opening polymerization of the resin and the subsequent conversion of the freshly generated polybenzoxazine into polybenzoxazole are studied by FT-IR and differential scanning calorimetry (DSC). In addition to the advantage of low polymerization temperature as other reported o-amide benzoxazines, the o-trifluoroacetamide benzoxazine also exhibits an unexpected lower benzoxazole formation temperature. Furthermore, the resulting fluorinated polybenzoxazole derived from the benzoxazine monomer possesses the combined excellent properties of facile synthesis, easy processability, low dielectric constant, high thermal stability, and long shelf life, evidencing its potential applications in microelect...
TL;DR: In this paper, the authors demonstrate how block copolymer hydrophobicity allows control over aggregate morphology in water and leads to remarkable control over the length of polymeric nanoparticle worms.
Abstract: Hydrophobicity inherently affects a solutes behavior in water, yet how polymer chain hydrophobicity impacts aggregate morphology during solution self-assembly and reorganization is largely overlooked. As polymer and nanoparticle syntheses are easily achieved, the resultant nanoparticle architectures are usually attributed to chain topology and overall degree of polymerization, bypassing how the chains may interact with water during/after self-assembly to elicit morphology changes. Herein, we demonstrate how block copolymer hydrophobicity allows control over aggregate morphology in water and leads to remarkable control over the length of polymeric nanoparticle worms. Polymerization-induced self-assembly facilitated nanoparticle synthesis through simultaneous polymerization, self-assembly, and chain reorganization during a block copolymer chain extension from a hydrophilic poly(N,N-dimethylacrylamide) macro-chain-transfer agent with diacetone acrylamide and N,N-dimethylacrylamide. Slight variations in the m...
TL;DR: In this paper, the structure and morphology of crystalline polymers has been and remains a major challenge and individual contributions help build a body of knowledge that must cover length scales ranging from submolecular features to morphology and correlate them with bulk properties.
Abstract: Analyzing and understanding the structure and morphology of crystalline polymers has been and remains to be a major challenge. Some of the issues have resisted analyses for decades. The present account illustrates how individual contributions help build a body of knowledge that must cover length scales ranging from submolecular features to morphology and correlates them with bulk properties. Emphasis is put on structures and morphologies as formed spontaneously. Possible extension of the research area to connected fields is illustrated with a development on supramolecular crystals.
TL;DR: In this article, a series of elastic and highly conductive poly(2,6-dimethylphenylene oxide) (PPO)-based AEMs (x(QH)3QPPO) containing flexible, long-chain, multication cross-links are presented.
Abstract: Anion exchange membranes (AEMs) are a promising class of materials that enable non-noble metals to be used as catalysts in fuel cells. Compared to their acidic counterparts, typically Nafion and other perfluorosulfonate-based membranes, the low OH– conductivity in AEMs remains a concern as these materials are developed for practical applications. Cross-linked macromolecular structures are a popular way to optimize the trade-off between the ionic conductivity and the water swelling of AEMs with high ion exchange capacities (IECs). However, common cross-linked AEMs (e.g., x(QH)QPPO) that have high degrees of cross-linking with low molecular weight between cross-links are usually mechanically brittle. Moreover, the cross-links in AEMs can hinder the transport of OH–, leading to unsatisfactory conductivities. Here we report a series of elastic and highly conductive poly(2,6-dimethylphenylene oxide) (PPO)-based AEMs (x(QH)3QPPO) containing flexible, long-chain, multication cross-links. The strength and flexibi...
TL;DR: In this paper, the electrical conductivity of conjugated poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7, 8,8,8-tetracyanoquinodimethane (F4TCNQ) was investigated.
Abstract: Molecular p-doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is a widely studied model system. Underlying structure-property relationships are poorly understood because processing and doping are often carried out simultaneously. Here, we exploit doping from the vapor phase, which allows us to disentangle the influence of processing and doping. Through this approach, we are able to establish how the electrical conductivity varies with regard to a series of predefined structural parameters. We demonstrate that improving the degree of solid-state order, which we control through the choice of processing solvent and regioregularity, strongly increases the electrical conductivity. As a result, we achieve a value of up to 12.7 S cm-1 for P3HT:F4TCNQ. We determine the F4TCNQ anion concentration and find that the number of (bound + mobile) charge carriers of about 10-4 mol cm-3 is not influenced by the degree of solid-state order. Thus, the observed increase in electrical conductivity by almost 2 orders of magnitude can be attributed to an increase in charge-carrier mobility to more than 10-1 cm2 V-1 s-1. Surprisingly, in contrast to charge transport in undoped P3HT, we find that the molecular weight of the polymer does not strongly influence the electrical conductivity, which highlights the need for studies that elucidate structure-property relationships of strongly doped conjugated polymers.
TL;DR: In this article, the phenomenology of the glass transition and the associated behavior in near liquid and glassy states are detailed, including the cooling rate dependence of glass transition, Kovacs' three signatures of structural recovery, and enthalpy overshoots.
Abstract: The phenomenology of the glass transition and the associated behavior in the near liquid and glassy states are detailed, including the cooling rate dependence of the glass transition, Kovacs’ three signatures of structural recovery, and enthalpy overshoots. Dynamics in the liquid regime just above Tg and the associated temperature dependences are also covered since this behavior is important to understanding the glassy dynamics. The current models of structural recovery and their shortcomings are presented. A number of important unanswered questions are discussed, including how the relaxation time in the glassy state depends on structure, the relationship between the evolution of different properties, the resolution of the Kauzmann paradox, and the behavior of the equilibrium relaxation time below Tg. New experimental approaches are needed to make breakthroughs, such as two that are described: one involving 20 Ma amber to test whether the Vogel temperature dependence continues for the equilibrium state be...
TL;DR: In this article, a π-conjugated polymers with strong electron affinity, PNDTI-BBTs, consisting of naphtho[2,3-b:6,7-b′]dithiophenediimide (NDTI) and benzo[1,2-c:4,5-c′]bis[ 1,2,5]thiadiazole (BBT) units, were synthesized.
Abstract: New π-conjugated polymers with strong electron affinity, PNDTI-BBTs, consisting of naphtho[2,3-b:6,7-b′]dithiophenediimide (NDTI) and benzo[1,2-c:4,5-c′]bis[1,2,5]thiadiazole (BBT) units, were synthesized. PNDTI-BBTs have low-lying LUMO energy levels (∼−4.4 eV), which is sufficiently low for air-stable electron transport in organic field-effect transistors and for being readily doped by a well-known n-dopant, N,N-dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole (N-DMBI), affording doped polymer films with relatively high conductivities and Seebeck coefficients. Depending on the solubilizing alkyl groups (2-decyltetradecyl, PNDTI-BBT-DT, or 3-decylpentadecyl groups, PNDTI-BBT-DP), not only the electron mobility in the transistor devices with the pristine polymer thin films (PNDTI-BBT-DT: ∼0.096 cm2 V–1 s–1; PNDTI-BBT-DP: ∼0.31 cm2 V–1 s–1) but also the conductivity and power factor of the doped thins films (PNDTI-BBT-DT: ∼0.18 S cm–1 and ∼0.6 μW m–1 K–2; PNDTI-BBT-DP: ∼5.0 S cm–1 and ∼14 μW m–1 K–2) were dr...