Showing papers in "Macromolecules in 2015"
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TL;DR: In this article, a cross-linked polymers constructed with dynamic-covalent boronic esters were synthesized via photoinitiated radical thiol-ene click chemistry.
Abstract: Cross-linked polymers constructed with dynamic-covalent boronic esters were synthesized via photoinitiated radical thiol–ene click chemistry. Because the reversibility of the boronic ester cross-links was readily accessible, the resulting materials were capable of undergoing bond exchange to covalently mend after failure. The reversible bonds of the boronic esters were shown to shift their exchange equilibrium at room temperature when exposed to water. Nevertheless, the materials were observed to be stable and hydrophobic and absorbed only minor amounts of water over extended periods of time when submerged in water or exposed to humid environments. The facile reversibility of the networks allowed intrinsic self-healing under ambient conditions. Highly efficient self-healing of these bulk materials was confirmed by mechanical testing, even after subjecting a single site to multiple cut–repair cycles. Several variables were considered for their effect on materials properties and healing, including cross-lin...
491 citations
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TL;DR: In this paper, the authors focus on recent advances that have been specifically designed to address many of these perceived limitations to reinforce the promise of reversible deactivation radical polymerization for the synthesis of complex macromolecules.
Abstract: Reversible deactivation radical polymerization (RDRP) has revolutionized modern polymer chemistry over the past two decades, thus laying the groundwork for the synthesis of complex macromolecules and enabling the preparation of previously inaccessible materials. Reversible addition-fragmentation chain transfer (RAFT) polymerization has emerged as one of the most promising techniques because of its functional group tolerance, applicability to a wide range of vinyl monomers, and its nondemanding experimental conditions. However, despite the promise and clearly demonstrated utility of RAFT, limitations of the method sometimes still exist, including the occasional need for extended polymerization times, limited access to high molecular weight polymers, low “livingness” due to unavoidable radical termination events, etc. This Perspective focuses on recent advances that have been specifically designed to address many of these perceived limitations to reinforce the promise of RAFT for the synthesis of complex an...
380 citations
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TL;DR: High refractive index polymers have been widely developed in recent years for their potential applications in advanced optoelectronic fabrications, such as high performance components for advanced display devices, encapsulants for light-emitting diode devices, microlens components for complementary metal oxide semiconductor image sensors, plastic lenses for eyeglasses, and camera, pick-up, and projector lenses as mentioned in this paper.
Abstract: High refractive index polymers have been widely developed in recent years for their potential applications in advanced optoelectronic fabrications, such as high performance components for advanced display devices, encapsulants for light-emitting diode devices, microlens components for complementary metal oxide semiconductor image sensors, plastic lenses for eyeglasses, and camera, pick-up, and projector lenses. This Perspective describes the recent progress in high refractive index (n) polymers over the past decade and focuses on the design concept to increase n values and Abbe’s number (ν) of polymers. After a brief introduction of the basic methodology for developing high-n polymers and important parameters, such as Abbe’s number and birefringence, applications of high-n polymers, such as antirefractive coatings, microlenses for CMOS image sensors, encapsulants for LEDs, and high-n thermoplastic lenses, are highlighted.
329 citations
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TL;DR: In this paper, the authors used time-domain flectance measurements of thermal conductivity along multiple directions of thin drop-cast PEDOT films to show that the thermal conductivities can be highly anisotropic (Λ∥ ≈ 1.0 W m −1 K −1 and Λ⊥ 0.3 W m−1 K−1 −1 for the in-plane and through-plane directions, respectively) when the electrical conductivity in the inplane direction is large (σ ≈ 500 S cm −1 ).
Abstract: Mixtures of poly(3,4-ethylenedioxythiophene) and polystyrenesulfonate (PEDOT:PSS) have high electrical conductivity when cast from aqueous suspensions in combination with a high boiling-point cosolvent dimethyl sulfoxide (DMSO). The electronic component of the thermal conductivity of these highly conducting polymers is of interest for evaluating their potential for thermoelectric cooling and power generation. We find, using time-domain thermore- flectance measurements of thermal conductivity along multiple directions of thick (>20 μm) drop-cast PEDOT films, that the thermal conductivity can be highly anisotropic (Λ∥ ≈ 1.0 W m −1 K −1 and Λ⊥ ≈ 0.3 W m −1 K −1 for the in-plane and through- plane directions, respectively) when the electrical conductivity in the in-plane direction is large (σ ≈ 500 S cm −1 ). We relate the increase in thermal conductivity to the estimated electronic component of the thermal conductivity using the Wiedemann−Franz law, and find that our data are consistent with conventional Sommerfeld value of the Lorenz number. We use measurements of the elastic constants (C11 ≈ 11 GPa and C44 ≈ 17 GPa) of spin-cast PEDOT films and through-plane thermal conductivity (Λ⊥ ≈ 0.3 W m −1 K −1 ) of drop-cast and spin-cast films to support our assumption that the phonon contribution to the thermal conductivity does not change significantly with DMSO composition.
253 citations
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TL;DR: In this paper, a triptycene-based ladder polymer (TPIM-1) exhibited very large selectivity gains outweighing permeability losses after 780 days, resulting in unprecedented performance for O2/N2 (P(O2) = 61 Barrer, α(O 2/N 2) = 86) and H2/H2/NB 2 (H2 2 ) = 1105 Barrer and α(H 2/NB 3 ) = 156) separations.
Abstract: Long-term physical aging and plasticization, two mobility-based phenomena that are counterintuitive in the context of “rigid” polymers of intrinsic microporosity (PIMs), were evaluated using pure- and mixed-gas permeation data for representative ladder and semiladder PIMs PIMs between 1 and 4 years old retained from 10- to 1000-fold higher H2 and O2 permeabilities than commercial membrane materials with similar or higher selectivities A triptycene-based ladder polymer (TPIM-1) exhibited very large selectivity gains outweighing permeability losses after 780 days, resulting in unprecedented performance for O2/N2 (P(O2) = 61 Barrer, α(O2/N2) = 86) and H2/N2 (P(H2) = 1105 Barrer, α(H2/N2) = 156) separations Interestingly, TPIM-1 aged more and faster than its more flexible counterpart, PIM-1, which exhibited P(O2) = 317 Barrer and α(O2/N2) = 50 at 1380 days Additionally, the more “rigid” TPIM-1 plasticized more significantly than PIM-1 (ie, TPIM-1 endured ∼93% increases in mixed-gas CH4 permeability ov
247 citations
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TL;DR: In this paper, the authors surveyed and analyzed the synthetic complexity of active-layer donor polymers used in single-junction polymer solar cells published through 2013 with power conversion efficiencies (PCEs) over 6%.
Abstract: Although organic photovoltaic technology offers many advantages, no consolidated commercial applications have been achieved after more than a decade of intensive research. Several challenges have yet to be overcome, including the scalability of the active material production, which is usually complex even at the laboratory scale. In this Perspective, this fundamental challenge is addressed by surveying and analyzing the synthetic complexity (SC) of active-layer donor polymers used in single-junction polymer solar cells published through 2013 with power conversion efficiencies (PCEs) over 6%. Five parameters are taken into account to evaluate the SC: (i) the number of synthetic steps, (ii) the yields of the monomers, (iii) the number of unit operations (in particular, (iv) of the column chromatographies) required for the purification of the monomers, and (v) the safety characteristics of the chemicals used for their preparation. Finally, the polymers are ranked according to a figure of merit based on SC an...
245 citations
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TL;DR: In this article, the photoactivation of trithiocarbonates (TTCs) by visible light (∼460 nm) is investigated, and the ability of TTCs to control radical polymerization under visible light in the complete absence of exogenous photoinitiators or catalysts is demonstrated for the first time.
Abstract: The application of external stimuli such as light to induce controlled radical polymerization reactions has important implications in the field of materials science. In this study, the photoactivation of trithiocarbonates (TTCs) (i.e., conventional RAFT agents) by visible light (∼460 nm) is investigated, and the ability of TTCs to control radical polymerization under visible light in the complete absence of exogenous photoinitiators or catalysts is demonstrated for the first time. By selectively exciting the spin-forbidden n → π* electronic transition, polyacrylates and polyacrylamides of low dispersity and high end group fidelity were obtained. In addition, this approach allows for the efficient synthesis of well-defined linear, (multi)block, and network (co)polymers. This study demonstrates the versatility of our strategy to generate polymers with controllable properties by visible light, which may be highly useful for applications such as surface patterning.
236 citations
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TL;DR: In this article, the authors investigated the transport properties of carbon dioxide in amorphous poly(ethylene furanoate) (PEF) using complementary pressuredecay sorption and permeation techniques.
Abstract: Transport properties of carbon dioxide in amorphous poly(ethylene furanoate) (PEF) were investigated using complementary pressure-decay sorption and permeation techniques. Detailed measurements for PEF at 35 °C indicate a significant, surprisingly large reduction in carbon dioxide permeability of 19× at 1 atm compared to poly(ethylene terephthalate) (PET), despite both an increase in free volume and carbon dioxide solubility of 1.6× for PEF vs PET. The solubility increase for PEF, which originates from greater interaction between carbon dioxide and the polar furan moiety, is offset by a substantial reduction in diffusivity of 31× compared to PET. Such diffusion reduction for PEF, which is 3× greater than the 9.7× reduction in oxygen diffusivity compared to PET, is thought to originate from a hindrance of polymer ring-flipping motions compared to PET. A possible mechanism for the surprising barrier improvement for carbon dioxide in PEF vs PET is explained herein along with a detailed comparison to oxygen a...
235 citations
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TL;DR: The first burst of research activity, challenging the boundaries of CuAAC in terms of attainable polymer constructs, resulted in a valuable toolbox of "click"-inspired conjugation methods as mentioned in this paper.
Abstract: This year, it has been a decade that the concept of “click” chemistry was pioneered in polymer and material science by the exploration of the synthetic scope of copper-catalyzed azide/alkyne cycloaddition (CuAAC), the “click” benchmark. The impact on the endeavors of polymer chemists has been substantial because the power of this concept, featuring modularity, orthogonality, and versatility for the design and synthesis of polymeric materials, was recognized very soon in macromolecular research groups worldwide. After this first burst of research activity, challenging the boundaries of CuAAC in terms of attainable polymer constructs, ongoing method development, and implementation, in response to the need for metal-free alternatives, resulted in a valuable toolbox of “click”-inspired conjugation methods. Because of the large diversity of employable reactions, applied in various polymeric systems, the first-time or occasional “click” user will be confronted with a burden of choice. Therefore, the principal a...
230 citations
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TL;DR: In this paper, a series of poly(phenylene oxide)s (PPOs) was tethered with cationic alkyl side chains of different lengths and configurations, and the polymers were configured with or without octyl extender chains pendant to the quaternary ammonium (QA) groups.
Abstract: In order to systematically improve the performance of anion-exchange membranes (AEMs) for alkaline fuel cells, a series of poly(phenylene oxide)s (PPOs) was tethered with cationic alkyl side chains of different lengths and configurations. PPO was first functionalized with bromomethyl and longer bromoalkyl side chains, respectively, before introducing quaternary ammonium (QA) groups via Menshutkin reactions involving trimethylamine and dimethyloctylamine, respectively. This resulted in samples with QA groups attached to PPO either directly in benzylic positions, or via flexible pentyl and heptyl spacer units, respectively. In addition, the polymers were configured with or without octyl extender chains pendant to the QA groups. All the cationic PPOs had an excellent solubility in, e.g., methanol and dimethyl sulfoxide, and flexible and mechanically robust AEMs with an ion exchange capacity of ∼1.4 mequiv g–1 were cast from solution. Analysis by small-angle X-ray scattering showed that the flexible spacer un...
229 citations
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TL;DR: In this paper, an alkali/urea hydrogen-bonded chitosan complex was used to successfully dissolve chitosa via freezing-thawing process, for the first time.
Abstract: Breaking the limitation of traditional acid dissolving methods for chitosan by creating an alkali/urea hydrogen-bonded chitosan complex, a new solvent (4.5 wt % LiOH/7 wt % KOH/8 wt % urea aqueous solution) was used to successfully dissolve chitosan via the freezing–thawing process, for the first time. Subsequently, high strength hydrogels with unique nanofibrous architecture were constructed from the chitosan alkaline solution. The results from 13C NMR, laser light scattering, atomic force microscopy, transmission electron microscopy, and scanning electron microscopy confirmed that chitosan easily aggregated in the solution and could self-assemble in parallel to form perfect regenerated nanofibers induced by heating. At elevated temperature and concentration, the regenerated chitosan nanofibers could entangle and cross-link with each other through hydrogen bonds to form hydrogels. The novel chitosan hydrogels exhibited homogeneous architecture and high strength as a result of the strong networks woven wi...
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TL;DR: FiberApp is introduced—a new tracking and analysis software based on a cascade of algorithms describing structural and topological features of objects characterized by a very high length-to-width aspect ratio, generally defined by carbon nanotubes.
Abstract: Biological semiflexible polymers and filaments such as collagen, fibronectin, actin, microtubules, coiled-coil proteins, DNA, siRNA, amyloid fibrils, etc., are ubiquitous in nature. In biology, these systems have a direct relation to critical processes ranging from the movement of actin or assembly of viruses at cellular interfaces to the growth of amyloid plaques in neurodegenerative diseases. In technology and applied sciences, synthetic macromolecules or fibrous objects such as carbon nanotubes are involved in countless applications. Accessing their intrinsic properties at the single molecule level, such as their molecular conformations or intrinsic stiffness, is central to the understanding of these systems, their properties, and the design of related applications. In this Perspective we introduce FiberApp—a new tracking and analysis software based on a cascade of algorithms describing structural and topological features of objects characterized by a very high length-to-width aspect ratio, generally d...
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TL;DR: Organic luminescent materials carrying no phenyl rings have attracted much interest from researchers due to their excellent biocompatibility and good biodegradability, which make them available for...
Abstract: Organic luminescent materials carrying no phenyl rings have attracted much interest from researchers due to their excellent biocompatibility and good biodegradability, which make them available for...
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TL;DR: In this paper, the authors highlight recent advances in organocatalyst design for isocyanate-based polyurethane synthesis with the aim of comparing the activity and selectivity of each of the new catalytic reactions to each other and the traditional metal-based catalysts.
Abstract: Organocatalysis has become an invaluable tool for polymer synthesis, and its utility has been demonstrated in ring-opening, anionic, zwitterionic, and group-transfer polymerizations. Despite this, the use of organocatalysis in other polymerization reactions such as step-growth polymerizations remains underexplored, relative to more traditional metal-based polymerizations. Recently, the use of organic bases such as guanidines, amidines, N-heterocyclic carbenes, and organic “strong or super-strong” Bronsted acids to catalyze the synthesis of metal-free polyurethanes has shown to be competitive to commercially widely used dibutyltin dilaurate and dibutyltin diacetate catalysts. This Perspective article highlights recent advances in organocatalyst design for isocyanate-based polyurethane synthesis with the aim of comparing the activity and selectivity of each of the new catalytic reactions to each other and the traditional metal-based catalysts. The article also draws attention to new trends in isocyanate-fre...
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TL;DR: In this paper, a commercial ethylene-propylene rubber grafted with maleic anhydride has been thermoreversibly cross-linked in two steps using a Diels-Alder coupling reaction.
Abstract: A proof of principle for the use of Diels–Alder chemistry as a thermoreversible cross-linking tool for rubber products is demonstrated. A commercial ethylene-propylene rubber grafted with maleic anhydride has been thermoreversibly cross-linked in two steps. The pending anhydride rings were first modified with furfurylamine to graft furan groups onto the rubber backbone. These pending furans were cross-linked with a bismaleimide via a Diels–Alder coupling reaction. The newly formed Diels–Alder cross-links break at elevated temperatures (>150 °C) and can be re-formed by thermal annealing (50–70 °C). Reversibility of the rubber network was proven with infrared spectroscopy and on the basis of the mechanical properties. Furthermore, reversibility was also shown in a practical way, i.e., by cutting the used material into pieces and pressing them into new samples displaying comparable mechanical properties (impossible for conventionally cross-linked rubbers). The physical properties of the resulting products ar...
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TL;DR: In this paper, the role of chemical interactions between the PTFE, the filler, and the metal countersurface has been investigated, and it has been shown that chemical changes are not an important part of the ultralow wear mechanism in these materials.
Abstract: The wear and friction behavior of ultralow wear polytetrafluoroethylene (PTFE)/α-alumina composites first described by Burris and Sawyer in 2006 has been heavily studied, but the mechanisms responsible for the 4 orders of magnitude improvement in wear over unfilled PTFE are still not fully understood. It has been shown that the formation of a polymeric transfer film is crucial to achieving ultralow wear on a metal countersurface. However, the detailed chemical mechanism of transfer film formation and its role in the exceptional wear performance has yet to be described. There has been much debate about the role of chemical interactions between the PTFE, the filler, and the metal countersurface, and some researchers have even concluded that chemical changes are not an important part of the ultralow wear mechanism in these materials. Here, a “stripe” test allowed detailed spectroscopic studies of PTFE/α-alumina transfer films in various stages of development, which led to a proposed mechanism which accounts ...
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TL;DR: In this article, a chemically stable and elastomeric triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-Polystyrene (SEBS), was functionalized with various benzyl- and alkyl-substituted quaternary ammonium (QA) groups for anion exchange membrane (AEM) fuel cell applications.
Abstract: A chemically stable and elastomeric triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), was functionalized with various benzyl- and alkyl-substituted quaternary ammonium (QA) groups for anion exchange membrane (AEM) fuel cell applications. Synthetic methods involving transition metal-catalyzed C–H borylation and Suzuki coupling were utilized to incorporate six different QA structures to the polystyrene units of SEBS. Changes in AEM properties as a result of different QA moieties and chemical stability under alkaline conditions were investigated. Anion exchange polymers bearing the trimethylammonium pendants, the smallest QA cation moiety, exhibited the most significant changes in water uptake and block copolymer domain spacing to offer the best ion transport properties. It was demonstrated that incorporating stable cation structures to a polymer backbone comprising solely C–H and C–C bonds resulted in AEM materials with improved long-term alkaline stability. After 4 weeks in...
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TL;DR: The proposed novel hopping model enables understanding the motion of large nanoparticles in polymeric nanocomposites and the transport of nano drug carriers in complex biological gels such as mucus.
Abstract: We propose a hopping mechanism for diffusion of large nonsticky nanoparticles subjected to topological constraints in both unentangled and entangled polymer solids (networks and gels) and entangled polymer liquids (melts and solutions). Probe particles with size larger than the mesh size ax of unentangled polymer networks or tube diameter ae of entangled polymer liquids are trapped by the network or entanglement cells. At long time scales, however, these particles can diffuse by overcoming free energy barrier between neighboring confinement cells. The terminal particle diffusion coefficient dominated by this hopping diffusion is appreciable for particles with size moderately larger than the network mesh size ax or tube diameter ae . Much larger particles in polymer solids will be permanently trapped by local network cells, whereas they can still move in polymer liquids by waiting for entanglement cells to rearrange on the relaxation time scales of these liquids. Hopping diffusion in entangled polymer liquids and networks has a weaker dependence on particle size than that in unentangled networks as entanglements can slide along chains under polymer deformation. The proposed novel hopping model enables understanding the motion of large nanoparticles in polymeric nanocomposites and the transport of nano drug carriers in complex biological gels such as mucus.
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TL;DR: In this paper, a series of poly(3-hexylthiophene)s (P3HTs) having a wide range of regioregularity (RR) from 64 to 98% were successfully produced.
Abstract: While the regioregularity (RR) of conjugated polymers is known to have a strong influence on their inherent properties, systematic study of the RR effect has been limited due to the lack of a synthetic methodology Herein, we successfully produced a series of poly(3-hexylthiophene)s (P3HTs) having a wide range of RR from 64 to 98% Incorporation of controlled amounts of head-to-head (H–H) coupled dimer in modified Grignard metathesis polymerization allows a facile tuning of the RR of the P3HTs with comparable molecular weight and low polydispersity Then, we investigated the effect of RR on structural, electrical, and mechanical properties of P3HTs in which a higher content of H–H regio-defects, namely lower RR, systematically lowered the degree of crystallinity Although high RR P3HT (98%) had higher charge carrier mobility (181 × 10–1 cm2 V–1 s–1), its strong crystallinity induced high brittleness and stiffness, resulting in device failure under a very small strain, as shown in tensile and bending test
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TL;DR: In this article, a series of Si-PAMAM dendrimers were synthesized by aza-Micheal reaction, and strong blue photoluminescence was observed even with the naked eye when these compounds were excited by a UV lamp.
Abstract: Poly(amidoamine) (PAMAM) dendrimers and hyperbranched poly(amidoamine)s are the first reported and most investigated luminescent polymers containing unconventional chromophores. The luminescence of these compounds is associated with the N-branched tertiary amine moiety, and the oxidation of the tertiary amine is assigned to the emitting source. However, in this paper, a series of novel siloxane–poly(amidoamine) (Si-PAMAM) dendrimers were synthesized by aza-Micheal reaction, and strong blue photoluminescence was observed even with the naked eye when these compounds were excited by a UV lamp. All of these compounds were not oxidated at all. Studies on the molecular structure showed that N → Si coordination bonds existed in these compounds, and those N → Si bonds caused the aggregation of carbonyl groups which show the strong luminescence.
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TL;DR: The triptycene-based hyper-cross-linked polymer sponge (THPS) as discussed by the authors may be ideal adsorbents for a wide range of large-scale applications in water purification and treatment.
Abstract: Cost-effective adsorbents for water treatment is easy available through one-pot Friedel–Crafts reaction of triptycene. With hierarchical porous structure, high surface area, high thermal stability, and excellent adsorption capacities for organic solvents and dyes, the triptycene-based hyper-cross-linked polymer sponge (THPS) may be ideal adsorbents for a wide range of large-scale applications in water purification and treatment.
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TL;DR: The monomer units of a polymer can be used to encode a message, and the genetic code is surely not the only type of code that can be “written” in a polymer, in principle, many other monomer-based codes could be developed.
Abstract: The monomer units of a polymer can be used to encode a message. This property is used, for instance, by nature to store genetic information in DNA macromolecules. Therefore, during the past decades, many researchers have aimed to recreate in vitro or in vivo the properties of nucleic acids. Peptide nucleic acids, or more generally speaking xeno-nucleic acids, are interesting examples of man-made genetic polymers. However, the genetic code is surely not the only type of code that can be “written” in a polymer. In principle, many other monomer-based codes could be developed. For example, a binary code can be potentially implemented in a synthetic macromolecule using two comonomers defined as 0 and 1 bit. This possibility is exciting because it would permit to develop a full new class of synthetic polymers, which contain sequence-coded information. Such polymers could be interesting for a variety of new applications, for example in the field of data storage and product identification. However, these tempting...
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TL;DR: In this article, a systematic investigation was carried out with three copper-amine catalysts ([CuIIL]2+, L = PMDETA, TPMA and Me6TREN] for aqueous atom transfer radical polymerization (ATRP) in water.
Abstract: Conducting an atom transfer radical polymerization (ATRP) in water provides several intriguing challenges. In order to attain a deeper understanding of the mechanism of aqueous ATRP, with particular attention to the reasons for the potential loss of control, a systematic investigation was carried out with three copper-amine catalysts ([CuIIL]2+, L = PMDETA, TPMA and Me6TREN). The association constants (KX) of [CuIIL]2+ and [CuIL]+ with X– and OH–, as well as the relative stabilities and redox properties of the complexes, were determined as a function of both [X–] and pH. In addition, rate constants and equilibrium constants of disproportionation for all three [CuIL]+ complexes were measured. Finally, ATRP equilibrium constants (KATRP) were estimated for all complexes, using 2-hydroxyethyl 2-bromoisobutyrate (HEBiB) as initiator. The primary factors affecting control in aqueous ATRP were identified as catalyst instability at both low and high pH, easy dissociation of deactivator (KX < 15), very high KATRP ...
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TL;DR: In this paper, the authors present measurements of the electrochemical transport properties of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in poly(ethylene oxide) (PEO) over a wide range of PEO molecular weights and salt concentrations.
Abstract: Transport of ions in polymer electrolytes is of significant practical interest, however, differences in the transport of anions and cations have not been comprehensively addressed. We present measurements of the electrochemical transport properties of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in poly(ethylene oxide) (PEO) over a wide range of PEO molecular weights and salt concentrations. Individual self-diffusion coefficients of the Li+ and TFSI– ions, D+ and D–, were measured using pulsed-field gradient nuclear magnetic resonance both in the dilute limit and at high salt concentrations. Conductivities calculated from the measured D+ and D– values based on the Nernst–Einstein equation were in agreement with experimental measurements reported in the literature, indicating that the salt is fully dissociated in these PEO/LiTFSI mixtures. This enables determination of the molecular weight dependence of the cation transference number in both dilute and concentrated solutions. We introduce a new para...
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TL;DR: In this article, a systematic study has been carried out to provide a better understanding of the ionic transport mechanism in polymerized ionic liquids (PolyILs) with different pendant groups.
Abstract: Polymerized ionic liquids (PolyILs) are promising candidates for energy storage and electrochemical devices applications. Understanding their ionic transport mechanism is the key for designing highly conductive PolyILs. By using broadband dielectric spectroscopy (BDS), rheology, and differential scanning calorimetry (DSC), a systematic study has been carried out to provide a better understanding of the ionic transport mechanism in PolyILs with different pendant groups. The variation of pendant groups results in different dielectric, mechanical, and thermal properties of these PolyILs. The Walden plot analysis shows that the data points for all these PolyILs fall above the ideal Walden line, and the deviation from the ideal line increases upon approaching the glass transition temperature (Tg). The conductivity for these PolyILs at their Tgs are much higher than the usually reported value ∼10–15 S/cm for polymer electrolytes, in which the ionic transport is closely coupled to the segmental dynamics. These r...
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TL;DR: In this article, seven naphthalimide derivatives with different substituents have been designed as versatile photoinitiators (PIs), and some of them when combined with an iodonium salt or an amine (and optionally chlorotriazine) are expected to exhibit an enhanced efficiency to initiate the epoxides and the free radical polymerization of acrylates under different irradiation sources.
Abstract: Seven naphthalimide derivatives (NDP1–NDP7) with different substituents have been designed as versatile photoinitiators (PIs), and some of them when combined with an iodonium salt (and optionally N-vinylcarbazole) or an amine (and optionally chlorotriazine) are expected to exhibit an enhanced efficiency to initiate the cationic polymerization of epoxides and the free radical polymerization of acrylates under different irradiation sources (i.e., the LED at 385, 395, 405, 455, or 470 nm or the polychromatic visible light from the halogen lamp). Remarkably, some studied naphthalimide derivative based photoinitiating systems (PIS) are even more efficient than the commercial type I photoinitiator bisacylphosphine oxide and the well-known camphorquinone-based systems for cationic or radical photopolymerization. A good efficiency upon a LED projector at 405 nm used in 3D printers is also found: a 3D object can be easily created through an additive process where the final object is constructed by coating down suc...
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TL;DR: In this paper, di- and multifunctional carboxylic acids found in fruit juices as well as other naturally available dicarboxyly acids were used to cross-link epoxidized sucrose soyate (ESS) without the use of extra catalyst or toxic compounds except for water.
Abstract: Naturally occurring carboxylic acids when used as cross-linkers with a highly functional bio-based epoxy resin result in thermosets having excellent physical and mechanical properties which are also degradable. Thermosets have many important applications (coatings, composites, adhesives, etc.), but they are typically made of nondegradable, nonrenewable materials. In this paper, di- and multifunctional carboxylic acids found in fruit juices as well as other naturally available dicarboxylic acids were used to cross-link epoxidized sucrose soyate (ESS) without the use of extra catalyst or toxic compounds except for water. For the sake of understanding the mechanism of the water-assisted curing reaction between ESS and the acids, the reactivity of the natural acids toward ESS and the curing process were investigated. Water enabled the natural acids with high water solubility and acidity to be dispersed well in ESS and led to rapid cross-linking with ESS. The thermosets possessed excellent thermal and mechanic...
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TL;DR: In this article, a cross-linked polybutadiene elastomer which could be thermally recycled like the plastic materials without the sacrifice of functional utility was reported. And the obtained polymer had good solvent resistance from ambient temperature to 100 °C.
Abstract: We reported a novel method of producing the cross-linked polybutadiene elastomer which could be thermally recycled like the plastic materials without the sacrifice of functional utility. The commercial polybutadiene was first attached with furan via thiol–ene reaction, and the cross-linked network was then built via Diels–Alder click reaction between the bismaleimide and attached furan groups from polybutadiene. The obtained polymer had good solvent resistance from ambient temperature to 100 °C. The mechanical properties of modified polybutadiene could be tailored by the amount of attached furan and the ratio of furan to bismaleimide. Furthermore, the dynamic cross-linked polybutadiene had good thermally remolded and self-healing behaviors. By this method, the dynamic cross-linked polybutadiene could be recycled to use in a sustainable way. Concerning all the raw materials were available in large quantities without tedious and multistep synthetic routes, this work demonstrated the high performance recycli...
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TL;DR: In this paper, the synthesis, self-assembly, conductivity, and rheological properties of ABA triblock brush polymers (BBCPs) with grafted polystyrene (A block, NPS = 21) and poly(ethylene oxide) (B block, NPEO = 45) side chains are reported.
Abstract: The synthesis, self-assembly, conductivity, and rheological properties of ABA triblock brush polymers (BBCPs) with grafted polystyrene (A block, NPS = 21) and poly(ethylene oxide) (B block, NPEO = 45) side chains are reported. Two backbone molecular weights (NA:NB:NA = 11:78:11 and 15:119:15) were investigated with lithium bis(trifluoromethane)sulfonimide (LiTFSI) doping ratios 2 ≤ [EO]:[Li+] ≤ 20. Blends with 2 ≤ [EO]:[Li+] ≤ 10 suppress PEO crystallization and self-assemble into hexagonally packed cylinders of the minority gPS component. Conductivity is on the order of 10–3 S/cm at 105 °C with a corresponding elastic modulus ca. 104 Pa. The optimum conductivity occurs at a blend ratio near 10:1 [EO]:[Li+], similar to that reported for linear block copolymer analogues.
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TL;DR: A major increase in the understanding of the structure and dynamics of Bombyx mori silk fibroin has been seen in the past 15 years as discussed by the authors, largely as a result of NMR studies.
Abstract: The past 15 years have seen a major increase in our understanding of the structure and dynamics of Bombyx mori silk fibroin, largely as a result of NMR studies. We now have a reasonably good idea of the structure before spinning (Silk I) and a good model for the crystalline regions after spinning (Silk II), though there are still some big outstanding questions. The details of the structures of Silk I and Silk II are the starting point for discussion of production of man-made silk fibroin, the origin of the strong silk fiber, and the mechanism of fiber formation in vivo.