The 50 most-cited articles in Macromolecules, 2020

We present a brief overview of current developments in the field of polymer electrolytes, with the focus on single-ion conducting polymers. The latter have significant advantages relative to electrolytes with dual-ion conductivity for use in energy storage devices. First we discuss various mechanisms of ionic conductivity in polymers and fundamental limitations imposed by these mechanisms. We also emphasize the role of ion–ion correlations in conductivity that are not negligible in concentrated and semidilute ionic systems. Next we discuss several classes of polymer electrolytes (gels, block copolymers, and composites) that are already employed or have good potential to be employed in current battery technologies. At the end we discuss perspectives for the design of dry single-ion conducting polymer electrolytes with required room temperature conductivity.

It is of great importance to develop epoxy vitrimers with the combination of high performance and versatile recyclability. Herein, two imine-containing hardeners were synthesized from bio-based vanillin and petroleum-based p -hydroxy benzaldehyde. The epoxy resins cured by these two hardeners show high T g (>120 °C), tensile strength (>60 MPa), Young’s modulus (>2500 MPa), and good solvent resistance. Owing to the incorporation of imine dynamic covalent bond, the cured epoxy resins are reprocessable and degradable. Notably, the chemical degradation products can be reused to prepare new epoxy resins, thus achieving a closed-loop recycling process. Both the reprocessed and chemically recycled epoxy resins exhibit high-percentage retention of thermal and mechanical properties. Finally, this study demonstrates that the epoxy resin cured by the vanillin-based hardener shows comparable thermal, mechanical, and recycling properties compared with the epoxy resin cured by the petroleum-based counterpart.

Since the birth of synthetic hydrogel 60 years ago, hydrogels possessing various useful properties and functions have been developed. The research directions of hydrogels have expanded to diverse application fields as well. However, in contrast to natural hydrogels found in biological soft tissues, which have elaborate structures from molecular to macroscopic scales and sophisticated functions, synthetic hydrogels only have very simple structures and naive functions. We have great opportunities to develop hydrogel materials through learning from nature. This Perspective discusses the opportunities and challenges in the fabrication of hydrogels with excellent physical functions by mimicking biological structures at different length scales.

The existence of a “memory” of the previous crystalline state, which survives melting and enhances recrystallization kinetics by a self-nucleation process, is well-known in polymer crystallization studies. Despite being extensively investigated, since the early days of polymer crystallization studies, a complete understanding of melt memory effects is still lacking. In particular, the exact constitution of self-nuclei is still under debate. In this Perspective, we provide a comprehensive and critical overview of melt memory effects in polymer crystallization. After the phenomenology of the process and some key concepts are introduced, the main experimental results of the past decades are summarized. Analogies and discrepancies of the melt memory characteristics of different polymeric systems are highlighted. Based on this background, the most significant interpretations and theories of melt memory effects are described, underlining that different interpretations may apply to various specific cases. Recent insights into self-nucleation, gained thanks to a multitechnique approach…

Abstract Vitrimers, in stringent contrast to dissociative networks, involve associative covalent exchanges and remain fully cross-linked at all temperatures. However, we have previously reported on poly(1,2,3-triazolium) dynamic networks that exhibit linear rheological characterization indistinguishable from vitrimers although being based on a dissociative covalent exchange process, i.e., de-N-alkylation and re-N-alkylation reactions. Herein, we highlight the main features of dissociative and associative covalent adaptable networks (CANs) and discuss their respective linear rheological behaviors. After giving a detailed overview of the extent and potential of dynamic polymer networks having 1,2,3-triazolium cross-links in particular and CANs involving trans-N-alkylation exchanges in general, we perform a detailed rheological comparative characterization of previously described aliphatic 1,2,3-triazolium-based dynamic networks and a new bicomponent thermosetting system issued from the mixing of linear polystyrene chains having complementary benzyl iodide and 1,2,3-triazole pendent…

A family of biobased polyimine elastomeric vitrimers was synthesized by reactions between di- and trifunctional polyetheramines and a furan-based dialdehyde. By varying the triamine to diamine ratio and the molar mass of the diamine, a set of cross-linked networks with similar chemical structures but different cross-link densities was obtained. All these materials exhibit a vitrimeric behavior because of the dynamic nature of the imine bonds. This fundamental study clearly reveals that the cross-link density has a drastic effect on the relaxation properties of the vitrimers. For instance, the relaxation times and the activation energies reduced when the cross-link density of the vitrimer networks decreased. This shows that the relaxation properties of vitrimers can be controlled by the sole modification of the network physical properties without the introduction of a catalyst, a change in chemical structure, or the introduction of additional chemical groups. In addition, a fast dual relaxation process has been clearly evidenced during stress relaxation experiments, which could…

Compared with liquid electrolytes, the solid polymer electrolyte (SPE), which possesses improved thermal and mechanical stability, is believed the broadest potential application for satisfying the safety needs of advanced electrochemical devices. However, some breakable SPEs could lead to catastrophic failure of batteries that triggered by a short circuit. In the present contribution, a new class of SPE containing disulfide bonds and urea groups is reported. The hydrogen bonding between the urea groups and disulfide metathesis reaction endows the SPE with a high level of self-healing without external stimuli at room temperature as well as ultrafast self-healing at elevated temperatures. The completely healed SPE with extreme damage shows a high self-healing efficiency and no changes in the ionic conductivity and cycling performance of the solid-state lithium-metal/LiFePO 4 cell compared to the pristine one.

Early epoxy vitrimers in the literature rely on an inequivalent epoxy/anhydride stoichiometry and a large amount of catalyst to achieve a decent transesterification rate within the crosslinked network. This design approach raises a number of concerns such as poor miscibility of the catalyst with other ingredients, poor mechanical properties owing to insufficient crosslinking, the toxicity of the catalyst, etc. In this study, a hydroxyl-amine compound, triethanolamine (TEOA), is incorporated as a catalytic co-curing agent to a typical BPA epoxy–cyclic anhydride curing system to give a TEOA-mediated covalent adaptable network system. The hydroxyl groups and tertiary amine of TEOA catalyze the curing process, and the tertiary amine and the regenerated hydroxyls in the crosslinked network accelerate dynamic transesterification. The resulting epoxy vitrimer exhibits a high glass transition temperature (∼135 °C), excellent tensile strength (∼94 MPa), and fast repairing rate (10 min at 190 °C). Recycling of the TEOA-mediated epoxy vitrimer and reuse of the recyclate are also studied. In an…

The Kremer–Grest (KG) polymer model is a standard model for studying generic polymer properties in molecular dynamics simulations. It owes its popularity to its simplicity and computational efficiency, rather than its ability to represent specific polymers species and conditions. Here we show that by tuning the chain stiffness it is possible to adapt the KG model to model melts of real polymers. In particular, we provide mapping relations from KG to SI units for a wide range of commodity polymers. The connection between the experimental and the KG melts is made at the Kuhn scale, i.e., at the crossover from the chemistry-specific small scale to the universal large scale behavior. We expect Kuhn scale-mapped KG models to faithfully represent universal properties dominated by the large scale conformational statistics and dynamics of flexible polymers. In particular, we observe very good agreement between entanglement moduli of our KG models and the experimental moduli of the target polymers.

Vitrimers undergoing dynamic bond exchange enable reprocessing and recycle of thermosets. However, vitrimers are susceptible to creep, leading to their poor dimensional stability, which limits their applications. Here, a facile method via integration of metal complexes was utilized to address this issue, and cross-linked polyimine was selected as an example of vitrimer. Three different metal complexes were introduced into a polyimine vitrimer via a one-pot preparation involving the formation of metal complexes and cross-linking of polyimine. The addition of 0.5 mol % Cu 2+ relative to imine bond reduced creep degree from 30% to 20% at 60 °C, and the creep resistance was enhanced with increasing Cu 2+ content. Loading 5 mol % Cu 2+ increased the initial creep temperature from 60 to about 100 °C and raised the Arrhenius activation energy ( E a ) for stress relaxation from 52.3 to 67.7 kJ mol –1 . The ability of different metal complexes to suppress creep followed the order of Fe 3+ > Cu 2+ > Mg 2+, and the initial creep temperature reached around 120 °C for vitrimer with 5 mol % of Fe…

For vitrimer systems obtained by dynamic cross-linking of polymer chains, incompatibility effects between the cross-links and polymer backbone can lead to microphase separation, resulting in a network made of cross-linked aggregates. Additionally, when there is a wide distribution of the number of cross-links per chain, macrophase separation can occur. Here, we investigate the linear viscoelasticity and flow of a polyethylene (PE) vitrimer that has cross-linkable dioxaborolane maleimide grafts, which aggregate into a hierarchical nanostructure. To elucidate the role of self-assembly, noncross-linked graft functionalized PE was first studied. It had a terminal relaxation time that was orders of magnitude larger than both neat PE and partially peroxide cross-linked PE. When dioxaborolane cross-linker was added to form the vitrimer, the resulting material could not achieve terminal relaxation within 8 hr. The graft-poor soluble and graft-rich insoluble portions of the PE vitrimer were then isolated and characterized. The soluble portion expressed similar flow behavior as neat PE, while…

Thermally conductive, robust, but self-healable polymer/carbon nanocomposites are the research focus in functional materials. However, the trade-off between molecular interaction and cross-linking makes it difficult to simultaneously achieve excellent self-healing, high strength, and thermal conduction. Herein, we fabricated boroxine poly(dimethylsiloxane) 2-ureido-4[1 H ]-pyrimidinone selectively cross-linked by molecular boron ester bonds and hydrogen bonds. By optimizing the reversible interaction, a maximum strength of 7.33 MPa and a high self-healing efficiency of 97.69 ± 0.33% were achieved at a boroxine-to-2-ureido-4[1 H ]-pyrimidinone molar ratio of 1:3 (BE-PDMS 1:3 -UPy). Highly robust composites of BE-PDMS 1:3 -UPy were obtained using a UPy-modified graphene aerogel. A transected sample recovered its mechanical properties (78.83 ± 2.40%) and thermal conductivity (98.27 ± 0.13%) after self-healing at 40 °C for 6 h. The outstanding reversible association/disassociation of hydrogen bonds at the polymer–graphene interface makes the composites to be used as structure–function…

REACTER is a heuristic protocol that allows complex, predefined reactions to be modeled in atomistic, fixed-valence molecular dynamics (MD) simulations. The method is applicable to a broad range of chemical reactions and permits much larger and longer reactive simulations than existing approaches. One or more competing multistep reactions or series of reactions can be invoked simultaneously. Special treatment can be applied to neighboring atoms to relax high-energy configurations while the simulation progresses. The original implementation of REACTER, which was included in the open-source LAMMPS simulation package as fix bond/react, was only available for serial simulations. This work describes the expansion of the REACTER protocol for use in parallel simulations, as well as the addition of various new options, including deletion of reaction byproducts, reversible reactions, and custom reaction constraints. The capability of the parallel implementation is demonstrated through large-scale simulations (200000+ atoms) of the polymerization of polystyrene and nylon-6,6. The morphologies…

This work presents a straightforward strategy to introduce highly dynamic and adaptable cross-links into common epoxy resin formulations. For this, an oligomeric amine-based curing agent containing vinylogous urethane (VU) bonds was developed. This novel polyfunctional amine curing agent can be used as a drop-in solution for existing epoxy resin technologies, resulting in transparent, rigid, and, at the same time, highly reprocessable catalyst-free epoxy vitrimers. The oligomeric VU-curing agents are prepolymerized via a straightforward condensation reaction between acetoacetates extended with different classical amine monomers and epoxy hardeners. It is found that vitrimer properties can be readily introduced into these epoxy formulations by converting <50 mol % of the hardener’s amine functionalities into dynamic vinylogous urethane bonds. In this way, epoxy vitrimers can be obtained with material properties comparable to ones of the VU-free epoxy formulations. In addition, remarkably short processing times are observed in the absence of any catalyst, and the material displayed…

Currently, a variety of elastomers with a self-healing capacity and reprocessability have been developed by dynamic chemistry to extend the service life, increase the reliability of polymeric materials, and reduce the waste. However, it is still a large challenge to seek an appropriate dynamic interaction that may perfectly match the general performance of the target polymeric materials such as polyurethane. Herein, we report a poly(thiourethane-urethane) (PTUU–N x ) elastomer containing dynamic thiourethane bonds prepared via a thiol–isocyanate click reaction, which is stable at room temperature, healable at moderate temperature, and reprocessable at high temperature. Importantly, it exhibits a mechanical strength similar to the polyurethane because of a very similar structure. The dynamic feature of PTUU–N x is demonstrated theoretically and experimentally to originate from the exchange of thiourethane bonds via the reversible generation of isocyanates and thiols. Most importantly, the thiourethane bond possesses a much lower bond dissociation energy than the urethane bond, which…

The realization of covalent adaptable networks with excellent mechanical and dynamic properties remains a major challenge. Herein, the acylsemicarbazide (ASC) moieties with dynamic reversibility and multiple hydrogen bonding were disclosed and used to prepare transparent, high modulus, and malleable polymer networks. It was found that the ASC moiety can reversibly generate isocyanate and hydrazide at elevated temperatures, that is, exhibiting dynamic reversibility. ASC can also produce the disordered multiple hydrogen bonds that contribute to superior mechanical strength for dynamic polymers. The hydrogen bonding in ASC moieties can diminish the energy barrier for the cleavage of dynamic covalent bonds, and the dissociation of ASC moieties further promotes the disruption of hydrogen bonds, showing the synergistic dynamic effects. ASC moieties provide a valuable molecular engineering opportunity toward high-performance dynamic polymer materials. The polymer containing ASC moieties possesses excellent optical transparency, superb mechanical performance (Young’s modulus up to 1.7 GPa),…

Abstract Treating a viral disease is no simple feat. Drug resistance, latent reservoirs in the body, emerging novel viruses, and a frequent lack of specific treatments all complicate antiviral therapy. For decades, antiviral polymers have been studied for a range of infectious diseases. The field has emerged, expanded, and adapted over the past 70 years, producing unique classes of materials that hold promise for overcoming these obstacles. Antiviral polymers can directly inhibit viral replication and infection, usually by binding to the virus and preventing it from invading a host cell. They can also serve as microbicides or antiviral drug-delivery vehicles. This Perspective outlines the significant advances and challenges in the field. We discuss polymers with activity against viruses with limited treatment options (hepatitis C), ubiquitous presence (influenza, norovirus), or long-term complications (HIV). We also explore insights into different mechanisms of action, and we offer ideas on how the field of antiviral polymers might advance in the future.

Understanding the key factors influencing the mechanical and electrical properties of semiconducting polymers is crucial to the development of stretchable electronics. In this work, a high-mobility diketopyrrolopyrrole-based conjugated polymer with varied number-average molecular weights ( M n ) was used as the model system to explore the impact of molecular weight on the electrical and mechanical properties. Higher- M n films are more ductile and stretchable. Both hole mobilities of thin-film transistors and elastic modulus become maximum at a moderate M n of 88 kg/mol. It was found that film continuity, entanglements, and relative degree of crystallinity are critical factors for approaching the best device performance and highest elastic modulus. The transition molecular weight of a given polymer semiconductor is the key to achieving stretchable high-mobility transistors that are practically useful. This work would help to offer guidance to manipulate the mechanical and electrical properties for other polymer semiconductors.

Recycling thermosets have become extremely important due to their ecological and economic benefits. The development of thermosets that undergo reversible polymerization provides a solution to the end-life disposal issue of thermosetting materials. However, the synthesis and recycling of the current chemically recyclable thermosets are harsh, complex, and energy-intensive, and their stability is often low. Here, we designed asymmetric acetal-containing thermosets (PRCs) from general phenolic resin and 1,4-cyclohexanedimethanol divinyl ether through one-step “click” cross-linking without using catalysts and solvents and without releasing small-molecule byproducts. PRCs exhibited conspicuous stress relaxation via a dissociative mechanism, corresponding to the superior malleability and reprocess recyclability. Importantly, PRCs presented excellent creep resistance even at 100 °C. In addition, PRCs could be readily and highly efficiently recovered to original phenolic resin via hydrolysis under specific mild acidic conditions but possessed high chemical stability under neutral conditions…

Ten years have passed since the conception of what was termed Lewis pair polymerization (LPP) that employs Lewis acid and base in pairs to not only activate monomers but also effect chain initiation, propagation, and transfer events. Compared to other polymerization methodologies, LPP’s cooperative and synergistic two-component catalytic mechanism empowers several unique or advantageous features, including extraordinary tunability of catalyst/initiator systems, compounded thermodynamic and kinetic control over comonomer sequences in one-pot LPP of monomer mixtures for highly resolved block copolymers, complete chemoselectivity in LPP of multifunctional vinyl monomers, independent tuning of polymerization activity and target polymer molecular weight, controlled heat dissipation in bulk polymerization with unactivated monomers functioning as solvent molecules, and coupled selectivity and livingness with immortality of the active species to produce ultrahigh molecular weight polymers and block copolymers with record-number (53) blocks. Focusing on four fundamental attributes of any…

Thermoplastic elastomers (TPE) can be easily molded, extruded, and reused like plastics and exhibit typical elastic properties like rubbers. They are widely used in the automotive sector and household appliances sector. The synthesis of thermoplastic polyolefin elastomers using only ethylene as feedstock in a single step is a fascinating concept. The synthesis of polyethylene thermoplastic elastomers through α-diimine nickel catalyzed ethylene polymerization has been successfully achieved in recent years. However, the utilization of α-diimine palladium catalysts for this purpose is much more challenging due to their greater chain-walking tendency versus the nickel counterpart, thereby leading to the formation of highly branched polyolefins with poor mechanical properties. In this contribution, we report the direct synthesis of polyethylene thermoplastic elastomers through α-diimine palladium catalyzed ethylene polymerization. With exquisite catalyst design and polymerization regulation, polyethylene thermoplastic elastomers with great mechanical and elastic properties can be…

Near-infrared (NIR) photoinduced chemical processes are highly attractive for specific applications owing to the deep penetration of NIR into the nontransparent materials including biological and synthetic materials. Robust NIR photoinduced atom transfer radical polymerization (photoATRP) was achieved using upconversion nanoparticles (UCNPs) as an internal light converter to turn a 980 nm NIR light to the wavelength of UV/vislight. This NIR photoATRP was capable of polymerizing both hydrophobic and hydrophilic monomers at a low loading of ppm concentrations of the CuBr 2 /tris(2-pyridylmethyl)amine catalyst under the irradiation of a 980 nm NIR light (4 W/cm 2 ) and UCNPs with reusable performance, providing well-defined polymers with predetermined molecular weight, low dispersity, and excellent chain-end fidelity. The switching of light “on/off” showed an excellent temporal control of the polymerization. The NIR photoATRP exhibited excellent penetrations through several visible light-proof barriers using NIR light, and it may provide future directions of photopolymerization in…

Quantitative characterization of the energy dissipative zone around the crack tip is the central issue in fracture mechanics of soft materials. In this research, we present a mechanochemical technique to visualize the bond scission of the first network in the damage zone of tough double-network hydrogels. The mechanoradicals generated by polymer chain scission are employed to initiate polymerization of a thermoresponsive polymer, which is visualized by a fluorophore. This technique records the spatial distribution of internal fracturing from the fractured surface to the bulk, which provides the spatial profiles of stress, strain, and energy dissipation around the crack-tip. The characterized results suggest that, in addition to the dissipation in relatively narrow yielded zone which is mostly focused in the previous works, the dissipation in wide pre-yielding zone and the intrinsic fracture energy have also significant contribution to the fracture energy of a DN gel.

In this study, we synthesized a new crown ether-functionalized benzoxazine monomer (crown-ether BZ) in high yield and purity through reduction of the Schiff base prepared from a dibenzo[18]crown-6 diamine derivative and salicylaldehyde and subsequent reaction of the resulting o -hydroxybenzylamine species with CH 2 O. We used differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis to examine the thermal ring opening polymerization and thermal stability of the crown-ether BZ monomer during various types of thermal treatment. DSC revealed that this crown-ether BZ monomer featured a relatively low curing temperature (210 °C; that of the typical Pa-type 3-phenyl-3,4-dihydro-2 H -benzooxazine monomer: 263 °C) because the flexibility of the crown ether moiety on the main chain backbone structure catalyzed the ring opening polymerization. We also used DSC, FTIR spectroscopy, and ionic conductivity measurements to investigate the specific metal–crown ether interactions of crown-ether BZ/LiClO 4 complexes. The presence of Li +…

The influence of ball-mill grinding process parameters and polymer properties on the mechanochemical degradation of amorphous polymers was explored. For process parameters, the grinding frequency was found to have the greatest impact on the degradation rates of polystyrene (PS), with ca. 17 times difference in rate constants between the lowest and the highest frequencies studied. For polymer properties, molecular weight and molecular weight dispersity were shown to both influence degradation rates but in an indirect manner. Linear relationships were found between degradation rate constants and the initial glass transition temperature ( T g ) for PS and poly(methyl methacrylate) samples, suggesting that the T g was a better predictor of the degradation rate than molecular weight (above a limiting molecular weight value). Ultrasonication experiments also further highlighted that polymer properties can have a disparate impact on mechanochemical reactivity depending on the method used to apply mechanical forces to polymers.

Thermoelectricity has gained considerable interest in the past decade due to the advent of organic thermoelectric materials. Crystallinity and doping level crucially determine the thermoelectric figure of merit of semiconducting polymers. Hence, detailed insight into these factors is prerequisite for developing efficient devices. Here we show that the semicrystalline structure of aligned P3HT films shows superior thermoelectric efficiencies as compared to the smectic-like phase because of both a higher in-plane orientation and a higher doping level. Conductivities up to 160 S/cm and power factors of 56 μW m –1 K –2 along the rubbing direction are obtained versus a few μW m –1 K –2 for nonoriented films. Different intercalation mechanisms of F 4 TCNQ in the layers of alkyl side chains are evidenced by electron diffraction in doped oriented films of the smectic-like and the semicrystalline phases. We provide compelling evidence that doping of the smectic-like phase promotes ordering of P3HT backbones along the chain direction within individual π-stacks, whereas for the semicrystalline…

An optimized acid hydrolysis method was developed to yield carboxylic acid-functionalized PIM-1 (PIM-COOH) with >89% conversion in 48 h using a postpolymerization reaction of PIM-1. Physical characterization of PIM-1 and PIM-COOH revealed that the average size of free volume elements in PIM-COOH decreased relative to that in PIM-1. Compared to PIM-1, PIM-COOH showed a significant increase in CO 2 - and H 2 -based selectivities with a corresponding decrease in permeabilities and sorption capacities for all gases considered. The dual-mode sorption model, time-lag method, and sorption–diffusion model were applied to glean molecular-level insights into diffusion and sorption in these polymers. Results indicate that improvements in selectivities for CO 2 -based gas pairs for PIM-COOH are primarily driven by diffusion selectivity and that PIM-COOH displays transport behavior consistent with the sorption–diffusion model. To better understand performance under more realistic conditions, pure- and mixed-gas permeation values for CO 2 /CH 4 are reported for a 330 day aged PIM-COOH sample.

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTCritical Strains Determine the Tensile Deformation Mechanism in Semicrystalline PolymersYongfeng MenYongfeng MenMore by Yongfeng Menhttp://orcid.org/0000-0003-3277-2227Cite this: Macromolecules 2020, 53, 21, 9155–9157Publication Date (Web):November 10, 2020Publication History Published online10 November 2020Published inissue 10 November 2020https://pubs.acs.org/doi/10.1021/acs.macromol.0c02076https://doi.org/10.1021/acs.macromol.0c02076editorialACS PublicationsCopyright © 2020 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views4403Altmetric-Citations48LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated…

The inherent low thermal conductivity of polymeric materials along with their capability for nonconventional processability, light weight, and flexibility makes them potential candidates for low-power thermoelectrical applications. However, it requires the improvement of both Seebeck coefficient and electrical conductivity simultaneously. This Perspective addresses some of the concepts in the literature to achieve this by considering the intricacies and interconnectivities of different thermoelectric parameters. Especially, the applicability of the Wiedemann–Franz rule as well as DOS engineering by blending two semiconductors, valid in inorganics, is reviewed for polymeric systems. One of the biggest advantages of polymeric semiconductors is that their thermal conductivity is mostly phononic (lattice thermal conductivity) and remains low with increasing charge carrier concentrations, as needed for TE applications. The momentum in polymer synthetic strategies has to be coupled with the studies on doping efficiency and doping mechanisms to overcome the bottlenecks in polymeric…

Vitrimer network polymers are very special in that, above a characteristic temperature T v, their dynamic covalent network connectivity allows macroscopic flow while remaining cross-linked. The vitrimer is able to change from being a typical elastomer to a network polymer with thermoreversible bond-exchange reactions. This has aroused enthusiastic interest, especially for designing novel materials to meet the increasing requirements of environmental protection, self-healing, and sustainable development. In this work, the viscoelasticity of the curing and cured epoxy vitrimer was investigated. Time-resolved multifrequency rheometry during the early stages of curing disclosed network ripening due to transesterification. After being fully cured, one of the most defining properties of vitrimers is a reversible, temperature-induced transition at T v, where the vitrimer assumes a pronounced critical state. Surprisingly, this transition state was found to behave like a critical gel having a relaxation modulus, G ( t ) = St – n, over a fairly broad temperature interval of 20 K. Viscoelastic…

Polyampholyte hydrogels (PA gels) are drawing great attention for their excellent mechanical properties including self-healing, high toughness, and fatigue resistance. These mechanical performances are found to be attributed to the hierarchical structure of the PA gels, consisting of reversible ionic bonds at the 1 nm scale, permanent polymer network at the 10 nm scale, and bicontinuous phase network at the 100 nm scale. In this work, we systematically studied the phase network formation of these gels aiming to answer the following three questions: (1) how the phase separation occurs? (2) what determines the phase structure? and (3) is this structure in thermodynamic equilibrium or not? Our results show that the phase separation occurs during dialysis of counterions from the gels and it is driven by the Coulombic and hydrophobic interactions. The phase size d 0 and the number of aggregated chains in a unit cell of the phase structure n scale with the molecular weight of the partial chain between permanent effective cross-linking M eff as d 0 ∼ M eff and n ∼ M eff 2, respectively. A…

The substitution of petroleum-based self-healing elastomers with biobased counterparts is crucial to the global sustainable development of the rubber industry, which highly depends on the ease of the synthesis procedure. Herein, we show that highly stretchable, recyclable, and self-healable biobased elastomers were synthesized via condensation polymerization of succinic acid, adipic acid, sebacic acid, and 1,4-butanediol in the presence of a small amount of glycerol as a curing agent and 3,3′-dithiodipropionic acid as a dynamic covalent monomer. The macroscopic properties of our elastomers, including thermal, mechanical, stress relaxation, and self-healing performance, were finely regulated via microscopic chemical and topological structure. As such, a highly stretchable (up to ∼1700%), recyclable (almost without degradation of the mechanical performance over several repeats), rapid room temperature self-healable (in 20 min) biobased vitrimeric elastomer was achieved, which is the first aliphatic disulfide metathesis assisted self-healing polymer achieved at such low temperatures.…

The conjugated polymer poly(3,4-ethylenedioxythiophene) polymerized and stabilized in the presence of polystyrenesulfonate (best known as PEDOT:PSS) is a working horse of organic electronics and bioelectronics and one of the most important conductive polymers. While its morphology is complex and depends on the details in synthesis and post-treatment, its distinctive and common feature is a two-phase granular structure attributed to PEDOT- and PSS-rich regions. Yet, there is still no well-established consensus concerning the precise nature of PEDOT- and PSS-rich regions as well as their chemical composition and structure. In this study we perform coarse-grained MARTINI molecular dynamics simulations of PEDOT:PSS focusing on understanding its two-phase morphology as well as water intake and ion exchange. We demonstrate that PEDOT:PSS is an essentially three-component system consisting of positively charged PEDOT chains, PSS chains with mostly deprotonated sulfonate groups, and protonated PSS chains. PEDOT-rich regions are predominantly composed of PEDOT and deprotonated PSS chains,…

Conductive, self-healing, and adhesive hydrogels are of great significance in wearable electronic devices. The most important properties of conductive self-healing hydrogels are the efficient recovery of both electrical and mechanical properties at room temperature and prolonged durability. In this work, we developed a novel double-network hydrogel consisting of poly(4-styrene sulfonate- co -methyl-uracil-imidazolium) chloride (PSS-MUI), gelatin, and ferric ions (Fe 3+ ). Here, the MUI serves as a supramolecular crosslinker, while ferric ions act as ionic crosslinkers between gelatin and PSS functional groups. The hydrogel demonstrated excellent stretchability and outstanding ionic conductivity. The reversible nature of dynamic hydrogen bonding and ionic and metal coordination interactions rendered the hydrogel self-healing ability, strong adhesion, and rapid electrical performance recovery. Variation in the Fe 3+ concentration proved to influence the time window of hydrogel processability and allowed tuning the hydrogel mechanical and ion-conducting properties. The optimal Fe 3+…

Abstract Different anion-exchange membranes (AEMs) based on polystyrene (PS)-carrying benzyltrimethyl ammonium cations are currently being developed for use in alkaline fuel cells and water electrolyzers. However, the stability in relation to these state-of-the-art cations needs to be further improved. Here, we introduce highly alkali-stable mono- and spirocyclic piperidine-based cations onto PS by first performing a superacid-mediated Friedel–Crafts alkylation using 2-(piperidine-4-yl)propane-2-ol. This is followed by quaternization of the piperidine rings either using iodomethane to produce N,N-dimethyl piperidinium cations or by cyclo-quaternizations using 1,5-dibromopentane and 1,4-dibromobutane, respectively, to obtain N-spirocyclic quaternary ammonium cations. Thus, it is possible to functionalize up to 27% of the styrene units with piperidine rings and subsequently achieve complete quaternization. The synthetic approach ensures that all of the sensitive β-hydrogens of the cations are present in ring structures to provide high stability. AEMs based on these polymers show high…

The role of polyelectrolyte-solvent interactions, among other non-Coulomb interactions, in dictating the thermodynamics and kinetics of polyelectrolyte complexation is prominent, yet sparingly studied. In this article, we present systematic comparisons of the binodal phase behavior of polyelectrolyte complexes (PECs) comprising polyelectrolytes with varying quality of backbone-solvent interactions. Experimental phase diagrams of polyelectrolyte complexes with either a peptide or an aliphatic backbone highlight the influence of backbone chemistry on the composition of complexes and their salt resistance. Corresponding theoretical phase diagrams, obtained from a framework combining the random phase approximation and Flory- Huggins approach, reveal a transition from closed phase boundaries with confined two-phase regions for PECs in good solvents to open phase boundaries, wherein two-phase systems are predicted to exist even at very high salt concentrations, for PECs in poor solvents. These predictions compare fittingly with experimental observations of low salt resistance (~1 M NaCl)…

Polyelectrolyte complexes (PECs) offer enormous material tunability and desirable functionalities, and consequently have found broad utility in biomedical and material industries. While poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) are a commonly used pairing, various aspects of the phase behavior of PAA–PAH complexes have not been sufficiently quantified. We present a comprehensive experimental study depicting the binodal phase boundaries for the PAA–PAH complexes prepared under acidic, neutral, and basic conditions using thermogravimetric analysis, turbidimetry, and optical microscopy. Under neutral and basic conditions, phase behaviors of the complexes were largely similar to one another and followed general expectations of PEC phase behavior, except for unusually high resistance to disruption of the complex with added salt. Stable complexes are observed up to 4 M NaCl concentrations. Under acidic conditions, strikingly different phase behaviors of the PAA–PAH complexes were observed. The polymer content in the complex phase increased initially, followed by an…

Dynamic covalent materials have properties such as self-healing, recyclability, and stress relaxation because of the dynamic exchange in polymer networks. Here, kinetic exchange in anilinium salts and viscoelastic properties of dynamic covalent networks with anilinium linkages are extensively studied. Mechanistic studies show that dynamic exchange in anilinium salts follows a dissociative pathway. Small-molecule kinetics study suggests that despite the dissociative mechanism, there is an essentially constant molar composition or bond density across a wide temperature profile. Rheological studies indicate that covalent adaptable networks (CANs) with anilinium linkages provide viscoelastic properties similar to CANs with associative exchange process networks. Additionally, thermal- and microwave-responsive self-healing and malleability properties can be achieved in this network, along with the materials showing excellent creep resistance and creep recovery.

Abstract The current goal in functional polymeric material research is the preparation of polymers with high-fidelity nanoscale self-assembled structures and advanced functionality. Thus, recent research efforts have focused on linking chemistry for the development of tailor-made polymers with desired properties. The design of α- or ω-functionalized telechelic polymers with strongly associative interactions is connected to their unique supramolecular self-assembly behavior in homopolymers and blends. In addition, the end-group modification of block copolymers has shown to alter the polymer morphology radically, resulting in unprecedented property changes arising from confinement effects. This is fascinating because the content of terminal moieties is small compared to that of macromolecular polymer backbones. As an emerging theme in polymer designs and end-group chemistry, the controlled synthesis of polymers with complex architectures and functional linkages has been performed extensively in the past few decades. However, the effects of this linkage on the resultant polymer…

Surface-initiated, photoinduced atom transfer radical polymerization (SI-photoATRP) enables the controlled and rapid synthesis of compositionally diverse polymer brushes over large areas by employing very small reaction volumes under ambient conditions and without the need for prior deoxygenation of monomer mixtures. The concentration of copper species and the type and content of amine-based ligands determine the mechanism of SI-photoATRP, regulate the kinetics of polymer-brush growth, and govern the tolerance of this polymer-grafting method toward oxygen. Despite mechanistic analogies with the corresponding solution processes, the intrinsic, highly confined nature of SI-photoATRP leads to significant differences from polymerizations within homogeneous systems. This is especially important to attain controlled/living polymerization and temporal control over polymer-brush growth by using UV light as a trigger.

The combination of high-throughput (HTP) processes and flow-mediated synthesis allows large data sets to be generated quickly while also permitting large quantities of materials to be prepared in a continuous fashion. In this work, the benefits of well-plate-based HTP polymerization and flow-mediated chemistry are used to streamline the screening and upscaling of value-added biomedical materials through a robust photopolymerization strategy, namely, photoinduced electron/energy transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization. A library of potential antimicrobial polymers was generated from an initial pool of monomers and tested for their activity against Pseudomonas aeruginosa (PA). The antimicrobial activity of the most promising candidates was then elucidated through structure–property analyses performed via both plate and flow polymerization processes; interestingly, terpolymerization of mixtures of acrylate and acrylamide monomers produced terpolymers with gradient architectures due to their reactivity ratios, which ultimately dictated the…

Abstract The synthesis of PIM-1 is reported from step-growth polymerizations of 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane with the commercially cheaper monomer, tetrachloroterephthalonitrile. Nitrogen-purged polymerizations (100–160 °C) were quenched after a monitored increase in viscosity. A combination of multiple detector size exclusion chromatography, nuclear magnetic resonance, matrix-assisted laser desorption/ionization-time of flight (MALDI TOF) mass spectrometry, dynamic light scattering, and elemental analysis was used to elucidate significant structural differences (cyclic, branched, tadpole, extended, and network topologies) in the polymers produced under different conditions. A significant proportion of the apparent surface area (up to 200 m2 g–1) associated with PIM-1 can be attributable to whether its contorted polymer chains in fact link to form cyclic or other nonlinear structures. Membranes cast from solutions of polymer samples containing higher branching and network contents exhibited higher gas pair selectivities (CO2/CH4 and CO2/N2), above…

Electrolytes featuring negatively charged polymers, such as nonaqueous polyelectrolyte solutions and polymerized ionic liquids, are currently under investigation as potential high cation transference number ( t + ) electrolytes for lithium-ion batteries. Herein, we use coarse-grained molecular dynamics simulations to characterize the Onsager transport coefficients of polyelectrolyte solutions as a function of chain length and concentration. For all the systems studied, we find that the rigorously computed transference number is substantially lower than that approximated by the ideal solution (Nernst–Einstein) equations typically used to characterize these systems due to the presence of strong anion–anion and cation–anion correlations. None of the polyelectrolyte solutions achieve t + greater than that of the conventional binary salt electrolyte, with some solutions having negative t + . This work demonstrates that the Nernst–Einstein assumption does not provide a physically meaningful estimate of the transference number in these solutions and calls into question the expectation of…

There remains a lack of fundamental understanding in the role of backbone rigidity on the thermomechanical properties of conjugated polymers. Here, we provide the first holistic approach to understand the fundamental influence of backbone rigidity on an n-type naphthalene diimide-based conjugated polymer, denoted by PNDI-Cx, through insertion of a flexible conjugation break spacer (CBS). CBS lengths are varied from fully conjugated with zero alkyl spacer (PNDI-C0) to a seven-carbon alkyl spacer (PNDI-C7), with the CBS engineered into each repeat unit for systematic evaluation. Solution small-angle neutron scattering and oscillatory shear rheometry were employed to provide the first quantitative evidence of CBS influence over conjugated polymer chain rigidity and entanglement molecular weight ( M e ), demonstrating a reduction in the Kuhn length from 521 to 36 Å for fully conjugated PNDI-C0 and PNDI-C6, respectively, as well as a nearly consistent M e of ∼15 kDa upon the addition of CBS. Thermomechanical properties, such as elastic modulus and glass-transition temperature, were shown…

Contrary to thermosets, vitrimers adjust their topology upon heating without loss of network integrity. Here, the proposed simulation methodology utilizes coarse-grained molecular dynamics in conjunction with a Monte Carlo method to capture the network integrity and flowability of vitrimers at high temperatures. The model vitrimer shows two transition temperatures. In addition to the conventional glass transition temperature, the topology freezing temperature is detected from the volumetric and rheological data. In the glassy state, the mobility of the vitrimer and thermoset is identical, whereas increasing the temperature results in a diffusive behavior in the vitrimer. The rheological data capture the main feature of vitrimers, which is the terminal regime of the elastic modulus at low frequencies. The zero-shear viscosity of the model vitrimer follows an Arrhenius-like temperature dependence at temperatures above the topology freezing temperature. The horizontal shift factors obtained from collapsing the rheological data onto master curves also display the same temperature…

Processability of vitrimers strongly relies on the temperature dependence of viscosity. In this study, we analyzed temperature-dependent viscoelasticity of vitrimers based on the dioxaborolane metathesis reaction. A sol-to-gel transition process and a reverse gel-to-sol process are observed in the linear viscoelasticity with increasing content of the cross-linker. The latter gel-to-sol process is owing to a reverse reaction between a two-site interchain cross-linking point with an excess cross-linker, forming two noncross-linking sites. For samples above the gel point, the increasing temperature leads to a weaker acceleration of the decross-linking process than the Rouse-type relaxation, and accordingly, broadening of the plateau region. This trend is easily visualized in samples slightly above the gel point for which the stress relaxation arising from the Rouse-type relaxation and the decross-linking process are not well separated over time. This temperature-dependent behavior reflects a case that the lifetime of the dynamic covalent bond is significantly larger than the Rouse time…

Circularly polarized luminescence (CPL) materials with aggregation-induced emission (AIE) performance have attracted extensive attention. In this study, we successfully achieve CPL emissions in chiral helical substituted polyacetylenes with tetraphenylethene (TPE) pendants. The polymers are constructed by copolymerization of an achiral TPE-containing acetylenic monomer with a chiral monomer. The obtained polymer exhibits unique state-dependent CPL behavior. More specifically, the polymer is CPL-silent in a dispersion state but CPL-active in solid thin films with a high luminescence dissymmetry factor (| g lum | = 3.6 × 10 –2 ). Moreover, significantly different from the common chirality transfer mechanism for preparing CPL-active materials, the CPL generation herein is due to the “matching rule” between fluorescent moieties and chiral helical polyacetylene. The present study provides new perspectives for preparing CPL materials with large g lum values in the solid state.

Twenty-two superbase-derived ionic liquids (SILs) (16 novel) including 16 1,8-diazabicyclo[5.4.0]undec-7-enium carboxylate (DBU-SILs) and 6 1,5-diazabicyclo[4.3.0]non-5-enium carboxylate (DBN-SILs) were facilely synthesized by coupling superbase cations with different carboxylic anions for cellulose dissolution. Systematic investigations revealed that the combination of the electron-donating groups, small steric hindrance groups, and short-chain groups in carboxylate anions with a larger ring in superbase cations facilitated cellulose dissolution. The regenerated cellulose films produced from seven SILs ([DBUH][CH 3 CH 2 OCH 2 COO], [DBUH][CH 3 OCH 2 COO], [DBUH][CH 2 ═CHCOO], [DBUH][CH 3 COO], [DBUH][CH 3 CH 2 COO], [DBNH][CH 3 CH 2 OCH 2 COO], and [DBNH][CH 3 OCH 2 COO]) with excellent cellulose solubility exhibited similar chemical structures, a high degree of polymerization, sufficient thermostability, smooth morphology, and high mechanical strength. Moreover, room-temperature SILs with low viscosity displayed a promising opportunity for large-scale production of renewable…

Abstract In a sustainable development context, epoxidized vegetable oils (EVO) have unlimited and promising future prospects as renewable and environmentally friendly feedstock. The only drawback to their use is their low and non-selective reactivity compared to the aromatic epoxides. Properly, a small optimized amount of “true” initiators can overcome this issue and also beneficially serve in properties such as glass transition, modulus, strength, elongation at break, and chemical resistance. This paper presents efforts to understand and identify the initiator’s effect to more accurately predict how to select a good initiator on EVO/dicarboxylic acid systems. A new bio-based reprocessable epoxy resin was prepared from epoxidized linseed oil (ELO) and 2,2′-dithiodibenzoic acid (DTBA). The evolution of the chemical structures and the reactions’ mechanisms have been systematically studied by in situ Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopies and differential scanning calorimetry (DSC). A screening of 10 initiators was performed for the…

The radical ring-opening polymerization (RROP) of thionolactones provides access to thioester backbone-functional copolymers but has, to date, only been demonstrated on acrylic copolymers. Herein, the thionolactone dibenzo[ c, e ]oxepane-5-thione (DOT) was subjected to azobisisobutyronitrile (AIBN)-initiated free-radical homopolymerization, which produced a thioester-functional homopolymer with a glass-transition temperature of 95 °C and the ability to degrade exclusively into predetermined small molecules. However, the homopolymerization was impractically slow and precluded the introduction of functionality. Conversely, the reversible addition–fragmentation chain-transfer (RAFT)-mediated copolymerization of DOT with N -methylmaleimide (MeMI), N -phenylmaleimide (PhMI), and N -2,3,4,5,6-pentafluorophenylmaleimide (PFPMI) rapidly produced well-defined copolymers with the tendency to form alternating sequences increasing in the order MeMI ≪ PhMI < PFPMI, with estimated reactivity ratios of r DOT = 0.198 and r PFPMI = 0.0078 for the latter system. Interestingly, defects in the…