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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Evolved Gas Analysis–Mass Spectrometry Exposes Polymer Network Structures

Polymer network structures in epoxy thermosets play an important role in the final thermoset material properties. However, analytical characterization of these network structures is difficult due to their amorphous nature. In this work, the application of evolved gas analysis–mass spectrometry (EGA-MS) to characterize the polymer network structures of bisphenol A (BPA)-based thermosets is demonstrated. Analytical characterization of the polymer network structures is accomplished by monitoring the Product-Specific Kinetics (PSK) of BPA monomer formation during thermal degradation investigations. We relate observed differences in the activation energy (E a ) of BPA monomer formation to the local packing environment around the BPA monomer units within the polymer network. Variations in the local environment related to the polymer networks manifest qualitatively as broadening in the thermal profile of the BPA monomer evolution and quantitatively as changes in the activation energy (E a ). Three BPA thermoset formulations were investigated; two amine-cured thermoset with 4,4′-diaminodiphenylmethane (DDM) or poly(propylene glycol) bis(2-amino-propyl ether) (PPG400) and a homopolymerized thermoset via curing with Epikure 3253 catalyst (3253). Results revealed that the 3253 thermoset contained two distinct packing densities in the polymer network, while DDM and PPG400 thermosets had uniform distributions of packing densities. Results from the DDM thermoset revealed a gradually decreasing E a , while the apparent E a of PPG400 was consistent over the entire degradation. Furthermore, these differences in E a were concluded to stem from the flexibility of the corresponding polymer networks and the ability of the network components to rearrange and occupy formed voids. Due to the minimal sample required for analysis (100–200 μg), this EGA-MS technique has great potential for postproduction evaluation of composite parts to identify changes in the polymer networks from use and aging, which could signal compromised performance.

Degradation↗
DOE OSTI2026

Recyclability of reversible polymer networks over a Dozen reprocessing cycles

Reversible polymer networks capable of reversible reactions along their backbone provide a promising strategy for addressing waste management challenges associated with conventional thermoset products. However, reversible polymer networks cannot be recycled infinitely. Unavoidable side reactions eventually cause significant degradation of mechanical properties or loss of recyclability. This study aims to answer a simple yet critical question on reversible polymer network systems: how many reprocessing cycles can be achieved before profound mechanical degradation or a loss of recyclability? The recyclability of Diels–Alder (DA) network samples was evaluated by repeating consistent reprocessing cycles until they were no longer reprocessable. To enhance their recyclability, the chemical structure of the maleimide precursor was tailored to mitigating side reactions by maleimide homopolymerization. Remarkably, by employing a maleimide precursor with alkyl substitutions on its phenyl group, the DA network system attained 12 reprocessing cycles using injection molding at 160 °C without significant degradation of mechanical properties. However, the 13th reprocessing cycle did not succeed. Rheological analysis revealed the accumulation of non-reversible bonds within the network structure during repeated reprocessing, despite fairly consistent mechanical properties under operating conditions. This study demonstrates that the rational design of the maleimide precursor is an effective means to enhance the reprocessability of DA networks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

High-Performance, Semi-Interpenetrating Polymer Network

High-performance polymer made by new synthesis in which one or more easy-to-process, but brittle, thermosetting polyimides combined with one or more tough, but difficult-to-process, linear thermoplastics to yield semi-interpenetrating polymer network (semi-IPN) having combination of easy processability and high tolerance to damage. Two commercially available resins combined to form tough, semi-IPN called "LaRC-RP49." Displays improvements in toughness and resistance to microcracking. LaRC-RP49 has potential as high-temperature matrix resin, adhesive, and molding resin. Useful in aerospace, automotive, and electronic industries.

Pater, Ruth H.↗
NASA NTRS1992

Semi-interpenetrating polymer network for tougher and more microcracking resistant high temperature polymers

This invention is a semi-interpenetrating polymer network which includes a high performance thermosetting polyimide having a nadic end group acting as a crosslinking site and a high performance linear thermoplastic polyimide. An improved high temperature matrix resin is provided which is capable of performing at 316 C in air for several hundreds of hours. This resin has significantly improved toughness and microcracking resistance, excellent processability and mechanical performance, and cost effectiveness.

Pater, Ruth H.↗
NASA NTRS1988

Interpenetrating polymer network approach to tougher and more microcracking resistant high temperature polymers. I - LaRC-RP40

Interpenetrating polymer networks in the form of the LaRC-RP40 resin, prepared by the in situ polymerization of a thermosetting imide prepolymer and thermoplastic monomer reactants, are presently used to obtain toughness and microcracking resistance in a high-temperature polymer. Attention is presently given to the processing, physical, and mechanical properties, as well as the thermooxidative stability, of both the neat resin and the resin as a graphite fiber-reinforced matrix. Microcracking after thermal cycling was also tested. LaRC-RP40 exhibits significant resin fracture toughness improvements over the PMR-15 high-temperature matrix resin.

Pater, Ruth H.↗
NASA NTRS1989

Morphological control of inter-penetrating polymer networks

Synthetic organic polymer chemistry has been successful in producing composition of matter with thermal oxidation stability and progressively higher glass transition temperatures. In part, this was done by increasing the steric-hindrance of moieties in the chain of a macromolecule. The resulting polymers are usually quite insoluble and produce molten polymers of very high viscosities. These types of polymers are not easily processed into graphite fiber prepregs by melt or solution impregnation methods. Hence, a technological need exists to produce new knowledge of how to produce polymer-fiber composites from this class of polymers. The concept of freeze drying amic-acid prepolymers with reactive thermoplastic was proposed as a research topic for the ASEE/NASA Summer Faculty Program of 1989 as a means of producing polymer-fiber composites. This process scheme has the thermodynamic attribute that the magnitude of phase separation due to differences in solubility of two organic constituents in solution will be greatly reduced by removing a solvent not by evaporation but by sublimation. Progress to date on evaluating this polymer processing concept is briefly outlined.

Hansen, Marion↗
DOE OSTI2025

Isomerization kinetics of azobenzene crosslinked to a liquid crystal polymer network

Azobenzene is an important chromophore having numerous applications that are a direct implication of its ability to change shape upon irradiation with a suitable wavelength. Here, in this study, photoisomerization kinetics of a diacrylate azobenzene molecule (A3MA) cross-linked to a liquid crystal polymer network (LCN) is investigated. Isomerization experiments were conducted on planar LCN thin films with varying cross-linking densities for a fixed azobenzene concentration. The experiments were conducted at approximately 26 °C, which is significantly below each film’s glass transition temperature. The forward trans-cis and reverse cis-trans isomerization slows down in crosslinked azobenzene liquid crystal polymer networks (ALCNs) as compared to a solution and an uncrosslinked polymer mixture. The observed slowdown is due to the reduction in the free volume and increased steric hindrances with an increase in crosslinking. A single-term first-order kinetics rate equation is known to describe the isomerization kinetics in solutions or uncrosslinked mixtures while the same form fails to represent the reaction kinetics in moderate to highly cross-linked ALCNs. Our results for the first time indicate that a two-term first-order reaction rate is an accurate way to describe the forward trans-cis and reverse thermal cis-trans isomerization in crosslinked azobenzene liquid crystal polymer networks. In addition, the effect of film thickness and incident intensities on the reaction kinetics is investigated. Finally, the two-term isomerization kinetics is incorporated into a finite element photo-chemo-mechanical model to reveal the consequent slowdown in the actuation response of ALCN films. The current findings will be of particular interest to theoreticians and experimentalists alike, for it will help predict and understand accurately the responses of azobenzene-based coatings, and actuators and may have potential applications in underwater soft robotics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1978

Membrane consisting of polyquaternary amine ion exchange polymer network interpenetrating the chains of thermoplastic matrix polymer

An ion exchange membrane was formed from a solution containing dissolved matrix polymer and a set of monomers which are capable of reacting to form a polyquaternary ion exchange material; for example vinyl pyride and a dihalo hydrocarbon. After casting solution and evaporation of the volatile component's, a relatively strong ion exchange membrane was obtained which is capable of removing anions, such as nitrate or chromate from water. The ion exchange polymer forms an interpenetrating network with the chains of the matrix polymer.

Rembaum, A.↗
NASA NTRS1990

Improving processing and toughness of a high performance composite matrix through an interpenetrating polymer network. VI

The use of a semiinterpenetrating polymer network (SIPN) of the high-performance polyimide NR-150B2 to reduce brittleness and improve processability in the highly crosslinked acetylene-terminated polyimides Thermid LR-600, AL-600, MC-600, and FA-700 is described. The theoretical basis of the SIPN process is reviewed; the preparation and characterization of the neat SIPN resins and unidirectional graphite-fiber composites are explained; and the results are presented in extensive tables, graphs, and micrographs and discussed in detail. Significant increases in fracture energy were observed with SIPN, from 93 J/sq m for unmodified LR-600 to 283-603 J/sq m for the SIPN materials; the room-temperature flexural strength of the unidirectional composites also increased, from 1344 MPa for an unmodified MC-600 composite to 2020-1751 MPa for the SIPN composites. The potential applicability of SIPN-based composites to aerospace structures and electronic components is indicated.

Pater, Ruth H.↗
NASA NTRS1990

Improving processing and toughness of a high performance composite matrix through an interpenetrating polymer network. VI

A simultaneous semi-interpenetrating polymer network (semi-IPN) concept is presented which combines easy-to-process, but brittle, thermosetting polyimides with tough, but difficult to process, linear thermoplastic polyimides. The combination results in a semi-IPN with the easy processability of a thermoset and good toughness of a thermoplastic. Four simultaneous semi-IPN systems were developed from commercially available NR-150B2 combined with each of the four Thermid materials (LR-600, AL-600, MC-600, and FA-700). It is concluded that there is a significant improvement in resin fracture toughness of Thermid-polyimide-based semi-IPN systems and some improvement in composite microcracking resistance compared to Thermid LR-600. Excellent composite mechanical properties have been achieved. These new semi-IPN materials have the potential to be used as composite matrices, adhesives, and molding materials.

Pater, Ruth H.↗
DOE OSTI2025

Sulfur Conversion to Donor‐Acceptor Ladder Polymer Networks through Mechanochemical Nucleophilic Aromatic Substitution for Efficient CO 2 Photoreduction

The development of synthetic methods capable of converting elemental sulfur into conjugated porous sulfur‐rich polymers remains a great challenge, although direct utilization of this readily available feedstock can significantly enrich its uses and circumvent environmental problems during sulfur storage. Here, we report herein mechanochemical (MC) nucleophilic aromatic substitution (S N Ar) that enables sulfur conversion into thianthrene‐bridged porous ladder polymer networks with dense donor‐acceptor (D−A) molecular junctions. We demonstrate that the key lies in the generation of bent thianthrene units through a solid‐state ball‐milling condensation reaction between 1,2‐dihaloarenes and elemental sulfur. We also show that the assembling of D−A structural motifs into porous networks affords efficient visible‐light‐driven photocatalytic reduction of carbon dioxide (CO 2 ) with water (H 2 O) vapor, in the absence of any additional photosensitizer, sacrificial agents or cocatalysts. Exceptional photoinduced charge separation along with boosted exciton dissociation results in a high‐performance of carbon monoxide (CO) production rate of 306.1 μmol g −1 h −1 with near 100 % CO selectivity, which is accompanied by H 2 O oxidation to O 2 , as confirmed by both experimental and theoretical results. We anticipate this novel MC S N Ar approach will advance processing techniques for direct sulfur utilization and facilitate new possibilities for the synthesis of D−A ladder polymer networks with promising potential in photocatalysis.

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

Infinitely Recyclable Network Polymers, Enabling Sustainable Manufacturing (CRADA Final Report)

This FLO Materials project was aimed at commercializing a new, infinitely recyclable material that can enable closed-loop lifecycles for hard-to-recycle plastics and plastic products. Four hundred million metric tons of virgin plastic is produced each year, yet less than 10% of this material is recycled. In the US alone, 2% of energy consumption is dedicated to the manufacture of virgin plastics, polymer resin, and synthetic rubbers. By keeping plastic materials in circulation longer, we can reduce waste, lower manufacturing costs, cut energy and oil consumption, and drastically reduce greenhouse gas (GHG) emissions. Specifically, FLO’s innovation overcomes the complications associated with salvaging difficult-to-recycle plastics (i.e., contaminated thermoplastic linear polymers, thermoset cross-linked network polymers), which represent at least 20% of total polymer global production, with a recycling rate of near 0%. Chemical recycling of these new polymers through depolymerization allows all additives to be easily removed at room temperature and the recovered monomers to be remanufactured into next generation materials with 100% recovery of mechanical performance and aesthetic quality.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Phase stability of weakly crosslinked interpenerating polymer networks

A phenomenological theory is formulated for chemically quenched binary interpenetrating polymer networks (IPNs), considering both simultaneously crosslinked networks and sequentially crosslinked networks, as well as pseudointerpenetrating networks (where only one component is crosslinked and the other is a linear polymer). The construction of free energy functionals for homogeneous weakly crosslinked IPNs and pseudo-IPNs and their spinodal curves and critical points of unmixing is described. These free energy functionals are augmented with gradient energy terms in order to consider effects due to spatially varying small inhomogeneities in the network chain concentration. The dynamic response and the initial spinodal decomposition of IPNs are discussed.

Binder, K.↗
NASA NTRS1994

Tough, processable semi-interpenetrating polymer networks from monomer reactants

A high temperature semi-interpenetrating polymer network (semi-IPN) was developed which had significantly improved processability, damage tolerance, and mechanical performance, when compared to the commercial Thermid materials. This simultaneous semi-IPN was prepared by mixing the monomer precursors of Thermid AL-600 (a thermoset) and NR-150B2 (a thermoplastic) and allowing the monomers to react randomly upon heating. This reaction occurs at a rate which decreases the flow and broadens the processing window. Upon heating at a higher temperature, there is an increase in flow. Because of the improved flow properties, broadened processing window and enhanced toughness, high strength polymer matrix composites, adhesives and molded articles can now be prepared from the acetylene end-capped polyimides which were previously inherently brittle and difficult to process.

Pater, Ruth H.↗
DOE OSTI2026

Cross-Linker Selection Controls Glass Transition Elevation or Reduction in Dynamic Covalently Bonded Polymer Networks

Introducing cross-links is a powerful approach to improve polymeric material performance relevant to controlling viscoelasticity, thermal and creep resistance, degradability, and efficient membrane separations. The chemically specific glass transition temperature T g is of fundamental importance in determining the time scales of key dynamical processes and physical state of the material in such applications. Here, we study experimentally how the introduction of relatively large cross-linking molecules in slowly exchanging dynamic bond-forming polymers (vitrimers) impacts vitrification for diverse polymer chemistries and a wide range of cross-link fractions. We find T g can increase, decrease, or even remain essentially unchanged, in qualitative contrast to the generic elevation of T g in traditional permanent polymer networks. We formulate an effective terpolymer network model to understand this rich behavior, which emerges as a consequence of a competition between pure cross-linking and generalized plasticization effects. The latter is associated with the tunable cross-linker size and intrinsic dynamic mobility that can offset slowing down due to traditional permanent cross-linking constraints. Here, a new strategy for functional polymer network design is suggested based on adjusting the relative importance of the two competing physical effects, which potentially can significantly enhance energy savings in applications while retaining other intrinsic properties germane to advanced materials performance.

Copolymers↗
NASA NTRS1985

Semi-2-interpenetrating polymer networks of high temperature systems

A semi-interpenetrating (semi-IPN) polymer system of the semi-2-IPN type is described in which a polymer of acetylene-terminated imidesulfone (ATPISO2) is cross linked in the presence of polyimidesulfone (PISO2). Six different formulations obtained by mixing of either ATPISO2-1n or ATPISO2-3n with PISO2 in three different proportions were characterized in terms of glass transition temperature, thermooxidative stability, inherent viscosity, and dynamic mechanical properties. Adhesive (lap shear) strength was tested at elevated temperatures on aged samples of adhesive scrim cloth prepared from each resin. Woven graphite (Celion 1000)/polyimide composites were tested for flexural strength, flexural modulus, and shear strength. The network polymers have properties intermediate between those of the component polymers alone, have greatly improved processability over either polyimide, and are able to form good adhesive bonds and composites, making the semi-2-IPN systems superior materials for aerospace structures.

Hanky, A. O.↗
DOE OSTI2026

Functional silicon crosslinks in conjugated polymer networks

The first conjugated polymers with functional Si–Si crosslinks are reported. In addition to complete structural characterization using solid-state NMR techniques, the electronic structure of the polymers are supported by electrochemical studies.

Wentz, Kelsie E. [Department of Chemistry, Johns H↗
DOE OSTI2025

Flow-Driven Stretch Fluctuations Govern the Nonlinear Viscoelasticity of Elongating Associative Polymer Networks

We use nonequilibrium molecular dynamics simulations to verify recent tube-model predictions that associative polymer networks exhibit broad stretch fluctuations during elongational flow. Simulations further show that these fluctuating dynamics give rise to the rate-dependent extensional viscosity 𝜂 𝐸 measured in filament stretching experiments on H-bonding networks. Simulations model bivalent associative networks with a reactive bead-spring model for varying association strength and extensional strain rate. We observe that stretch fluctuations are driven by a new form of chain tumbling, where chains continually collapse and elongate as their associations break and reform within the advecting network. This produces a broad, nearly uniform distribution of chain stretch over a wide range of strain rates, manifesting as a rate-independent plateau in the extensional stress. Our results show that the nonlinear viscoelasticity of associative networks is dominated by large fluctuations in molecular response, which cannot be captured by current mean-field models.

biomimetic & bio-inspired materials↗