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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Fundamental Limitations of Ionic Conductivity in Polymerized Ionic Liquids

In this paper, we present detailed studies of ionic conductivity in several polymerized ionic liquids (PolyILs) with different size of mobile ions. Presented analysis revealed that charge diffusion in PolyILs is about 10 times slower than ion diffusion, suggesting strong ion–ion correlations that reduce ionic conductivity. The activation energy for the ion diffusion shows a nonmonotonous dependence on the mobile ion size, indicating a competition between Coulombic and elastic forces controlling ion transport in PolyILs. The former dominates mobility of small ions (e.g., Li), while the latter controls mobility of large ions (e.g., TFSI). We propose a simple qualitative model describing the activation energy for the ion diffusion. In conclusion, it suggests that an increase in dielectric constant of PolyILs should lead to a significant enhancement of conductivity of small ions (e.g., Li and Na).

36 MATERIALS SCIENCE↗
DOE OSTI2019

Strong Near-Infrared Solid Emission and Enhanced N-Type Mobility for Poly(naphthalene Diimide) Vinylene by a Random Polymerization Strategy

Organic semiconductors possessing both strong solid emission and charge transport ability are crucial for certain applications such as organic light-emitting transistors and injection lasers, but they are rather rare. Among those which are successful, n-type materials with long emission wavelength are even more scarce. Here, a series of random polymers with the dithiophene unit into a poly(naphthalene diimide) vinylene are synthesized. A strong near-infrared solid emission under wavelength of 730 nm and photoluminescence efficiency of 11.2% is achieved, with an enhanced n-type OFET performance of electron mobility up to 0.011 cm 2 V -1 s -1 . GIXRD and AFM analysis reveal that the introduction with confined dithiophene can improve the localized pi-pi intermolecular interaction, while retaining the overall low crystalline state for thin films of these polymers, which should be the vital factor for balancing the solid emission and charge transport ability. This simple random polymerization strategy might be beneficial in future molecular design for such dual functional materials.materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Formation of Alternating trans - A - alt - B Copolymers through Ring-Opening Metathesis Polymerization Initiated by Molybdenum Imido Alkylidene Complexes

Ring-opening metathesis polymerization (ROMP) is enabled to prepare trans-poly(A-alt-B) polymers from a 1:1 mixture of A and B where A is a cyclic olefin such as cyclooctene (A 1 ) or cycloheptene (A 2 ) and B is a large norbornadiene or norbornene derivative such as 2,3-dicarbomethoxy-7-isopropylidenenorbornadiene (B 1 ) or dimethylspirobicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1'-cyclopropane (B 2 ). The most successful initiators that were examined are of the type Mo(NR)(CHCMe 2 Ph)[OCMe(CF 3 ) 2 ] 2 (R = 2,6-Me 2 C 6 H 3 (1) or 2,6-i-Pr 2 C 6 H 3 (2)). The trans configuration of the AB linkages is proposed to result from the steric demand of B. Both anti-MB and syn-MB alkylidenes are observed during the copolymerization, where B was last inserted into a Mo=C bond, although anti-MB dominates as the reaction proceeds. anti-MB is lower in energy than syn-MB, does not react readily with eitherA or B, and interconverts slowly with syn-MB through rotation about the Mo=C bond. Syn-MB does not readily react with B, but it does react slowly with A (rate constant ~1 M –1 s –1 ) to give anti-MA and one trans-AB linkage. anti-MA then reacts with B (rate constant ~300 M –1 s –1 or larger) to give syn-MB and the second trans-AB linkage. The reaction has been modeled using experimental data in order to obtain the estimated rate constants above. The reaction between anti-MA and A is presented to give rise to AA linkages, but AA dyads can amount to <5%. Several other A and B monomers, initiators, and conditions were researched.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Highly Conductive Anion-Exchange Membranes Based on Cross-Linked Poly(norbornene): Vinyl Addition Polymerization

Cross-linked (XL) anion-exchange membranes (AEMs) synthesized by vinyl addition polymerization of norbornene were prepared for use in anion-exchange membrane electrochemical devices, including fuel cells and electrolyzers. Tetrablock copolymers composed of an all-hydrocarbon backbone with a very high ion-exchange capacity (IEC), 3.46 mequiv/g, were synthesized. Light cross-linking was found to be adequate for providing critical control over unwanted water uptake. This enabled use of very high IEC membranes. Without light cross-linking, the unwanted water uptake would cause swelling and softening of the membrane. The best performing membrane had no significant drop in ionic conductivity over 1000 h of aging in 1 M NaOH at 80 °C and a record high ionic conductivity of 198 mS/cm at 80 °C (for a chemically stable AEM). The number of bound and free water molecules per ion pair is described along with ion mobility comparisons to previous materials. Here, the membranes are suitable for electrochemical devices and were used in AEM fuel cells

08 HYDROGEN↗
DOE OSTI2017

Continuous Flow Processing of ZIF-8 Membranes on Polymeric Porous Hollow Fiber Supports for CO 2 Capture

We have utilized an environmentally friendly synthesis approach for the accelerated growth of a selective inorganic membrane on a polymeric hollow fiber support for postcombustion carbon capture. Specifically, continuous defect-free ZIF-8 thin films were grown and anchored using continuous flow synthesis on the outer surface of porous supports using water as solvent. These membranes demonstrated CO 2 permeance of 22 GPU and the highest reported CO 2 /N 2 selectivity of 52 for a continuous flow synthesized ZIF-8 membrane.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Controlled Synthesis of Sulfur-Rich Polymeric Selenium Sulfides as Promising Electrode Materials for Long-Life, High-Rate Lithium Metal Batteries

High-energy lithium/sulfur (Li/S) batteries still suffer from unsatisfactory cycle life and poor rate capability caused by the polysulfides shuttle and insulating nature of S cathodes. Here, we report our findings in the controlled synthesis of selenium (Se)-containing S-rich co-polymers of various compositions as novel cathode materials through a facile inverse vulcanization of S with selenium disulfide (SeS2) and 1,3- diisopropenylbenzene (DIB) as co-monomers. Nuclear magnetic resonance and X-ray photoelectron spectroscopy results show that divinyl functional groups of DIB were chemically cross-linked with S/SeS2 chain radicals through a ring-opening polymerization. The newly formed bonds of C-S, C-Se, and S-Se in novel S-SeS2-DIB copolymers effectively alleviate the shuttle effects of polysulfides/polyselenides. Furthermore, various electrochemical techniques confirm the positive roles of Secontaining co-polymers in enhancing the electrode reaction kinetics and the formation of stable solid electrolyte interphase layer with low charge-transfer resistance, leading to improved high-rate performances. The as-synthesized co-polymer was then infiltrated into well-interconnected, porous nanocarbon networks (Ketjenblack EC600JD, KB600) to provide effective paths for the fast electron transport. Due to the synergistic combination of chemical and physical confinement of the reaction intermediates during cycling, good reversibility for 500 cycles with a low decay rate of 0.0549% per cycle was achieved at 1000 mA g-1. These encouraging results suggest that the combination of chemical incorporation of SeS2 into S-rich co-polymer and the physical confinement of carbon networks is a promising strategy for advancing Li/S batteries and their viability for practical applications.

Dong, Panpan↗
DOE OSTI2023

Polymer Architecture-Induced Trade-off between Conductivities and Transference Numbers in Salt-Doped Polymeric Ionic Liquids

Recent experiments have demonstrated that polymeric ionic liquids that share the same cation and anion but possess different architectures can exhibit markedly different conductivity and transference number characteristics when doped with lithium salt. In this study, we used atomistic molecular simulations on polymer chemistries inspired by the experiments to probe the mechanistic origins underlying the competition between conductivity and transference numbers. Our results indicate that the architecture of the polycationic ionic liquid plays a subtle but crucial role in modulating the anion–cation interactions, especially their dynamical coordination characteristics. Chemistries leading to longer-lived anion–cation coordinations relative to lithium–anion coordinations lead to lower conductivities and higher transference numbers. Furthermore, our results suggest that higher conductivities are accompanied by lower transference numbers and vice versa, revealing that alternative approaches may need to be considered to break this trade-off in salt-doped polyILs.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2025

Thiol- and Disulfide-Functionalized Polycyclooctene: Metathesis Polymerization, Degradation, and Reformation

The enormous global production and use of polymers and plastics, combined with slower and less efficient disposal and recycling methods, have led to a worldwide growth in plastic waste. Here, we describe an approach that builds degradability into macromolecular polyolefins through the design of telechelic oligomers with reactive functional groups that enables control over polymer deconstruction and reconstruction. Our work exploits disulfide-containing polymers that have emerged as promising cyclable materials due to their dynamic reversibility (bond formation and cleavage) driven by redox chemistry under mild conditions. Specifically, we describe the synthesis of a telechelic α,ω-dithiopolycyclooctene (PCOE) by ring-opening metathesis polymerization using a dithioacetate chain transfer agent, followed by deprotection to convert the chain-end thioacetates to thiols. This process was studied towards control over the degree of oxidation to yield disulfide-containing PCOE, followed by an evaluation of reductive degradation and oxidative repolymerization. Overall, this approach facilitates the production of disulfide-containing unsaturated polyolefins and the integration of degradable and reformable moieties into soluble, processable, metathesis-derived polymers.

Lee, Kyoungwon↗
DOE OSTI2026

Hierarchical Epoxy Structures via Tunable Polymerization-Induced Phase Separation Combined with Additive Manufacturing

Polymerization-induced phase separation (PIPS) allows for the control of thermoset morphologies and properties, enabling the tuning of domain sizes and thermomechanical response. However, its use in generating substructural features in additively manufactured materials has been limited. In this work, we combine epoxy PIPS with UV curable acrylate and rheological modifiers to print nano- to macro-phase separating materials via a two-step, dual-cure approach. This method enables direct ink write printing of hierarchical structures with both controlled morphologies through phase separation and macroscale architecture through print design. We find that formulations for phase-separating materials require judicious incorporation of additives to enable printability and to provide sufficient green strength. Atomic force microscopy-nano infrared mapping reveals tunable, reticulated nano- to micron-scale domains of the resultant multiphase materials and their morphology changes due to additives, resulting in alterations to thermomechanical and tensile properties. Shape memory behavior is also demonstrated through multimaterial additive manufacturing of epoxies with functionally graded internal morphology using active mixing techniques, highlighting this method’s ability to fabricate complex architectures with controlled morphologies and thermomechanical response.

Van Meter, Kylie E [Organic Materials Science, San↗
DOE OSTI2024

Observation of a Picosecond Light-Induced Spin Transition in Polymeric Nanorods

Spin transition (ST) materials are attractive for developing photoswitchable devices, but their slow material transformations limit device applications. Size reduction could enable faster switching, but the photoinduced dynamics at the nanoscale remains poorly understood. Here, we report a femtosecond optical pump multimodal X-ray probe study of polymeric nanorods. Simultaneously tracking the ST order parameter with X-ray emission spectroscopy and structure with X-ray diffraction, we observe photodoping of the low-spin–lattice within ~150 fs. Above a ~16% photodoping threshold, the transition to the high-spin phase occurs following an incubation period assigned to vibrational energy redistribution within the nanorods activating the molecular spin switching. Above ~60% photodoping, the incubation period disappears, and the transition completes within ~50 ps, preceded by the elastic nanorod expansion in response to the photodoping. These results support the feasibility of ST material-based GHz optical switching applications.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Self-Supporting, Hydrophobic, Ionic Liquid-Based Reference Electrodes Prepared by Polymerization-Induced Microphase Separation

Interfaces of ionic liquids and aqueous solutions exhibit stable electrical potentials over a wide range of aqueous electrolyte concentrations. This makes ionic liquids suitable as bridge materials that separate in electroanalytical measurements the reference electrode from samples with low and/or unknown ionic strengths. However, methods for the preparation of ionic liquid-based reference electrodes have not been explored widely. We have designed a convenient and reliable synthesis of ionic liquid-based reference electrodes by polymerization-induced microphase separation. This technique allows for a facile, single-pot synthesis of ready-to-use reference electrodes that incorporate ion conducting nanochannels filled with either 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-dodecyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide as ionic liquid, supported by a mechanically robust cross-linked polystyrene phase. This synthesis procedure allows for the straightforward design of various reference electrode geometries. These reference electrodes exhibit a low resistance as well as good reference potential stability and reproducibility when immersed into aqueous solutions varying from deionized, purified water to 100 mM KCl, while requiring no correction for liquid junction potentials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Backbone-Photodegradable Polymers by Incorporating Acylsilane Monomers via Ring-Opening Metathesis Polymerization

Materials capable of degradation upon exposure to light hold promise in a diverse range of applications including biomedical devices and smart coatings. Despite the rapid access to macromolecules with diverse compositions and architectures enabled by ring-opening metathesis polymerization (ROMP), a general strategy to introduce facile photodegradability into these polymers is lacking. Here, we report copolymers synthesized via ROMP that can be degraded by cleaving the backbone in both solution and solid states under irradiation with a 52 W, 390 nm Kessil LED to generate heterotelechelic low-molecular-weight fragments. To the best of our knowledge, this work represents the first instance of the incorporation of acylsilanes into a polymer backbone. Mechanistic investigation of the degradation process supports the intermediacy of an α-siloxy carbene, formed via a 1,2-photo Brook rearrangement, which undergoes insertion into water followed by cleavage of the resulting hemiacetal.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Using Data Science Tools to Reveal and Understand Subtle Relationships of Inhibitor Structure in Frontal Ring-Opening Metathesis Polymerization

The rate of frontal ring-opening metathesis polymerization (FROMP) using the Grubbs generation II catalyst is impacted by both the concentration and choice of monomers and inhibitors, usually organophosphorus derivatives. Herein we report a data-science-driven workflow to evaluate how these factors impact both the rate of FROMP and how long the formulation of the mixture is stable (pot life). Using this workflow, we built a classification model using a single-node decision tree to determine how a simple phosphine structural descriptor (V bur-near ) can bin long versus short pot life. Additionally, we applied a nonlinear kernel ridge regression model to predict how the inhibitor and selection/concentration of comonomers impact the FROMP rate. Furthermore, the analysis provides selection criteria for material network structures that span from highly cross-linked thermosets to non-cross-linked thermoplastics as well as degradable and nondegradable materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Vinylsilanes as Chain-Transfer Agents in Ethylene Polymerization: Direct Synthesis of Heterotelechelic Polyolefins

A single-step route to heterotelechelic polyethylene is enabled by palladium-diimine-catalyzed polymerization of ethylene using vinylsilanes as chain-transfer agents. The reaction affords α-alkenyl-ω-silyl end-capped heterotelechelic polymers whose molecular weights are controllable over a wide range by adjusting the [ethylene]/[vinylsilane] molar ratios. Notably, highly efficient end-capping with silanes carrying a variety of functionalities can be achieved under the optimized conditions. Furthermore, the alkenyl- and silyl-terminated telechelics serve as polymer precursors for further reactions and can be converted into additional telechelic functionalized polyolefins in good yields.

Chen, Zhi-Hao [University of Houston, TX (United S↗
DOE OSTI2016

Intermolecular Structural Change for Thermoswitchable Polymeric Photosensitizer

A switchable photosensitizer (PS), which can be activated at a spe-cific condition beside light, has tremendous advantages for photo-dynamic therapy (PDT). Herein, we developed a thermo-switchable polymeric photosensitizer (T-PPS) by conjugating PS (Pheophor-bide-a, PPb-a) to a temperature-responsive polymer backbone of biocompatible hydroxypropyl cellulose (HPC). Self-quenched PS molecules linked in close proximity by pi-pi stacking in T-PPS were easily transited to an active monomeric state by the tempera-ture induced phase transition of polymer backbones. The tempera-ture responsive inter-molecular interaction changes of PS molecules in T-PPS were demonstrated in synchrotron small-angle X-ray scattering (SAXS) and UV-Vis spectrophotometer analysis. The T-PPS allowed switchable activation and synergistically enhanced cancer cell killing effect at the hyperthermia temperature (45 °C). Our developed T-PPS has the considerable potential not only as a new class of photomedicine in clinics but also as a biosensor based on temperature responsiveness.

Park, Wooram↗
DOE OSTI2017

Conjugated ladder polymers by a cyclopentannulation polymerization

Here, we report a nontraditional synthesis of cyclopentafused-polycyclic aromatic hydrocarbon embedded ladder polymers using a palladium catalyzed cyclopentannulation polymerization followed by a cyclodehydrogenation reaction. Donor–acceptor type polymers containing a cyclopenta[hi]aceanthrylene acceptor groups can be synthesized by a palladium catalyzed copolymerization between 9,10-dibromoanthracene and a variety of bis(arylethynyl)arenes to give polymers with molecular weights (Mn) of 9–22 kDa. The bis(arylethynyl)arenes were composed of benzene, thiophene, or thieno[3,2- b ]thiophene moieties, which provided access to a series of four donor–acceptor copolymers. The polymers were subjected to cyclodehydrogenation with FeCl 3 to access rigid ladder type polymers with the conversion investigated by 13 C NMR of isotopically labeled polymers. As a result, the ladder polymers possess broad UV–Vis absorptions and narrow optical band gaps of 1.17–1.29 eV and are p-type semiconductors in organic field effect transistors.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Quasi one-dimensional band dispersion and surface metallization in long-range ordered polymeric wires

We study the electronic structure of an ordered array of poly(para-phenylene) chains produced by surface-catalyzed dehalogenative polymerization of 1,4-dibromobenzene on copper (110). The quantization of unoccupied molecular states is measured as a function of oligomer length by scanning tunnelling spectroscopy, with Fermi level crossings observed for chains longer than ten phenyl rings. Angle-resolved photoelectron spectroscopy reveals a quasi-one-dimensional valence band as well as a direct gap of 1.15 eV, as the conduction band is partially filled through adsorption on the surface. Tight-binding modelling and ab initio density functional theory calculations lead to a full description of the organic band-structure, including the k-dispersion, the gap size and electron charge transfer mechanisms, highlighting a strong substrate-molecule interaction that drives the system into a metallic behaviour. In summary, we have fully characterized the band structure of a carbon-based conducting wire. This model system may be considered as a fingerprint of -conjugation of surface organic frameworks.

36 MATERIALS SCIENCE↗