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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Phase transformations in metastable liquids combined with polymerization

Here, we report on the theory of nucleation and growth of crystals in a metastable polymer melt with allowance for the polymerization of a monomer. A mathematical model consisting of the heat balance equation, equations governing the particle-radius distribution function and the polymerization degree is formulated. The exact steady-state analytical solutions are found. In the case of unsteady-state crystallization with polymerization, the particle-size distribution function is determined analytically for different space–time regions by means of the Laplace transform. Two functional integro-differential equations governing the dimensionless temperature and polymerization degree are deduced. These equations are solved by means of the saddle-point technique for the evaluation of a Laplace-type integral. The time-dependent distribution function, temperature and polymerization degree at different polymerization rates and nucleation kinetics are derived with allowance for the main contribution to the Laplace-type integral. In addition, the general analytical solution by means of the saddle-point technique and an example showing how to construct the analytical solutions in particular cases are given in the appendices. The analytical method developed in this paper can be used to describe the similar phase transition phenomena in the presence of chemical reactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

A General Autofluorescence Method to Characterize Polymerization Progress

Abstract An autofluorescence technique to characterize polymerization progress in real time/in line was developed, which functioned in the absence of typical fluorogenic groups on the monomer or polymer. The monomer dicyclopentadiene and polymer polydicyclopentadiene are hydrocarbons that lack traditional functional groups for fluorescence spectroscopy. Here, the autofluorescence of formulations containing this monomer and polymer during ruthenium‐catalyzed ring‐opening metathesis polymerization (ROMP) was harnessed for reaction monitoring. The methods fluorescence recovery after photobleaching (FRAP) and here‐developed fluorescence lifetime recovery after photobleaching (FLRAP) characterized polymerization progress in these native systems—without requiring exogenous fluorophore. (Auto)fluorescence lifetime recovery changes during polymerization correlated linearly to degree of cure, providing a quantitative link with reaction progress. These changing signals also provided relative rates of background polymerization, enabling comparison of 10 different catalyst‐inhibitor‐stabilized formulations. Multiple‐well analysis demonstrated suitability for future high‐throughput evaluation of formulations for thermosets. The central concept of the combined autofluorescence and FLRAP/FRAP method may be extendable to monitoring other polymerization reactions previously overlooked for lack of an obvious fluorescence handle.

López, Pía A.↗
DOE OSTI2017

Highly efficient reversible addition-fragmentation chain-transfer polymerization in ethanol/water via flow chemistry

Here, utilization of a flow reactor under high pressure allows highly efficient polymer synthesis via reversible addition–fragmentation chain-transfer (RAFT) polymerization in an aqueous system. Compared with the batch reaction, the flow reactor allows the RAFT polymerization to be performed in a high-efficiency manner at the same temperature. The adjustable pressure of the system allows further elevation of the reaction temperature and hence faster polymerization. Other reaction parameters, such as flow rate and initiator concentration, were also well studied to tune the monomer conversion and the molar mass dispersity (Ð) of the obtained polymers. Gel permeation chromatography, nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopies (FTIR) were utilized to monitor the polymerization process. With the initiator concentration of 0.15 mmol L –1 , polymerization of poly(ethylene glycol) methyl ethermethacrylate with monomer conversion of 52% at 100 °C under 73 bar can be achieved within 40 min with narrow molar mass dispersity (D) Ð (<1.25). The strategy developed here provides a method to produce well-defined polymers via RAFT polymerization with high efficiency in a continuous manner.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Anionic polymerization of oxadiazole-containing 2-vinylpyridine by precisely tuning nucleophilicity and the polyelectrolyte characteristics of the resulting polymers

Anionic polymerization is one of the most powerful techniques for preparation of well-defined polymers. However, this well-known and widely employed polymerization technique encounters major limitations for the polymerization of functional monomers containing heteroatoms. This work presents the anionic polymerization of 2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole (VPyOzP), a heteroatom monomer that contains both oxadiazole and pyridine substituents within the same pendant group, using various initiating systems based on diphenylmethyl potassium (DPM-K) and triphenylmethyl potassium (TPM-K). Remarkably, well-defined poly(2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole) (PVPyOzP) polymers having predicted molecular weights (MW) ranging from 2200 to 21 100 g/mol and polydispersity indices (PDI) ranging from 1.11 to 1.15 were prepared with TPM-K, without any additional additives, at –78 °C. The effect of temperature on the polymerization of PVPyOzP was also studied at –78, –45, 0, and 25 °C, and it was observed that increasing the polymerization temperature produced materials with unpredictable MW’s and broader molecular weight distributions. Furthermore, the nucleophilicity of PVPyOzP was investigated through copolymerization with methyl methacrylate and acrylonitrile, where only living poly(methyl methacrylate) (PMMA) prepared by DPM-K/VPPy and in the absence of additives such as lithium chloride (LiCl) and diethyl zinc (ZnEt 2 ) could be used to produce the well-defined block copolymer of PMMA-b-PVPyOzP. It was also demonstrated by sequential monomer addition that the nucleophilicity of living PVPyOzP is located between that of living PMMA and polyacrylonitrile (PAN). Here, the pyridine moiety of the pendant group also allowed for quaternization and produced PQVPyOzP homopolymer using methyl iodide (CH 3 I) and bis(trifluoromethylsulfonyl)amide [Tf 2 N – ]. The resulting charged polymer and counterion complexes were manipulated and investigated for potential use as membranes for carbon dioxide (CO 2 ) capture.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Tailored Mesoporous Microspheres by Polymerization-Induced Microphase Separation in Suspension

We describe the preparation of block polymer beads by aqueous suspension polymerization to create poly(caprolactone) (PCL)-block-poly(styrene-co-divinylbenzene) beads that can be selectively etched under basic conditions to yield mesoporous polymer microspheres with uniform pore size. Polyvinylalcohol was used to stabilize the suspension polymerization in which styrene and divinylbenzene monomers were polymerized from a PCL macrochain transfer agent (macroCTA). The resulting polymerization-induced microphase separation process led to a nanostructured bicontinuous morphology. The particle size and pore size were independently tunable: the particle size was controlled by the stir rate of the suspension polymerization-yielding average diameters ranging from 60 to 300 μm-while the pore size was determined by the molar mass of the PCL block, with the mode pore diameters being 6 nm and 11 nm after etching beads made using 13 and 45 kg/mol PCL blocks, respectively. Based on nitrogen sorption measurements, the surface areas of the beads were ~300 m 2 /g when using a PCL macroCTA of 13 kg/mol. The beads were homogenous throughout on the micron length scale as determined by confocal Raman microscopy and lacked an impermeable skin layer as confirmed by scanning electron microscopy. Furthermore, the scalability of suspension polymerization allows for the simple synthesis of large quantities of thermoset microspheres with uniform pore size. We also demonstrate the ability to incorporate functional pore walls into the beads using multiblock precursor polymers. These functionalized mesoporous polymer beads show high affinity for ionic dyes in aqueous solutions (as a proof of principle) and remove dye from the solution at rates exceeding those of commercial ion-exchange resins. The developed procedure could be used to generate other functional surface chemistries with important applications in heterogeneous catalysis, chromatography, and water remediation.

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

An in situ generated polymer electrolyte via anionic ring-opening polymerization for lithium–sulfur batteries

The use of solid polymer electrolytes has previously proven to be an effective approach to address the lithium polysulfide dissolution and high electrode interfacial impedance of Li–S batteries via an in situ polymerization process. However, the conventional in situ synthesis employs a cationic ring-opening polymerization (CROP) of 1,3-dioxolane (DOL) catalyzed by a strong Lewis acid. New polymerization chemistry that is more compatible with Li–S chemistry needs to be developed to mitigate the disadvantages associated with the CROP process. Herein we report a new approach to in situ polymerize a set of new episulfide monomers in solution with LiTFSI salt via an anionic ring-opening polymerization (AROP). This new polymer system takes advantage of the inherent cell chemistry present in the Li–S cell through the nucleophilic lithium sulfides which are generated during the initial discharge cycle and act as the initiator for the polymerization. Additionally, their presence was shown to initiate the monomer solvents through AROP with no need for additional catalysts, rather than the more commonly utilized cationic systems which require an external Lewis acid catalyst. This work offers an important pathway toward in situ polymer electrolytes for Li–S batteries and offers a new avenue of exploration for polymer electrolyte synthesis.

25 ENERGY STORAGE↗
NASA NTRS1990

Nonintrusive method and apparatus for monitoring the cure of polymeric materials

The invention is a nonintrusive method of monitoring the cure of a polymeric material using an electromagnetic field to sense a change of resistance of the polymeric material in the electromagnetic field that occurs during curing. This change of resistance is used to vary the impedance of an alternating voltage power supply that produces the electromagnetic field and which change of impedance is measured periodically or continuously to monitor the cure of said polymeric material. The apparatus for practicing the method of this invention may include a nonintrusive sensing head providing an inner, electromagnetic core within an open ended outer pot formed of magnet material. The open end of the pot core is positioned from a selected area of the surface of a sheet of the polymeric material. An alternating voltage supply circuit includes an inductance coil around the electromagnetic core and capacitor connected in parallel with the inductance coil forms a resonant tank circuit when energized. The resulting change in resistance of the polymeric material opposite the open end, a function of the curing, is measured as a corresponding change in the impedance of the power supply circuit to thereby monitor the cure of the polymeric material in the selected area.

Johnston, David F.↗
NASA NTRS1989

Equilibrium polymerization on the equivalent-neighbor lattice

The equilibrium polymerization problem is solved exactly on the equivalent-neighbor lattice. The Flory-Huggins (Flory, 1986) entropy of mixing is exact for this lattice. The discrete version of the n-vector model is verified when n approaches 0 is equivalent to the equal reactivity polymerization process in the whole parameter space, including the polymerized phase. The polymerization processes for polymers satisfying the Schulz (1939) distribution exhibit nonuniversal critical behavior. A close analogy is found between the polymerization problem of index the Schulz r and the Bose-Einstein ideal gas in d = -2r dimensions, with the critical polymerization corresponding to the Bose-Einstein condensation.

Kaufman, Miron↗
NASA NTRS1998

Investigation of Solution Polymerizations in Microgravity and 1 G

The in-situ dielectric spectra for the solution polymerization of polydiacetylene has been successfully measured. The results show a distinct difference between the response for the bulk solution and surface polymerization. It also shows a low frequency peak in the dissipation factor which is present in both the bulk and surface polymerizations. These features may prove to be significant indicators for important polymerization processes. Future studies will investigate the mechanisms responsible for these dielectric responses. This technique will eventually be used to monitor microgravity polymerizations and provide in-situ data on how microgravity affects solution polymerization.

Kennedy, Alvin P.↗
DOE OSTI2012

Ternary europium mesoporous polymeric hybrid materials Eu({beta}-diketonate){sub 3}pvpd-SBA-15(16): host-guest construction, characterization and photoluminescence

Novel organic-inorganic mesoporous luminescent polymeric hybrid materials containing europium(III) complexes incorporated to mesoporous silica SBA-15/SBA-16 have been prepared by simple physical doping (impregnation) methods, followed by the addition polymerization reaction of the monomer 4-vinylpyridine (vpd) extending along the mesoporous channels. The precursor europium(III) complexes are synthesized by {beta}-diketonate ({beta}-diketonate=2-thenoyltrifluoroacetonate (tta), hexafluoroacetylacetonate (hfac), trifluoroacetylacetonate (taa)) and monomer 4-vinylpyridine (vpd) coordinated to Eu{sup 3+}, and SBA-15/SBA-16 are obtained via a sol-gel process. After the physical doping and the polymerization reaction, the final ternary materials Eu({beta}-diketonate){sub 3}pvpd-SBA-15/Eu({beta}-diketonate){sub 3}pvpd-SBA-16 ({beta}-diketonate=tta, hfac, taa) are received. The physical properties and espeically the photoluminescence of these hybrids are characterized, and the XRD and BET results reveal that all of these hybrid materials have uniformity in the mesostructure. The detailed luminescence investigation on all the materials show that Eu(tta){sub 3}pvpd-SBA-16 have the highest luminescence intensity and the materials with taa ligands have longer lifetimes. - Grapical abstract: Luminescent mesoporous polymeric hybrid materials containing europium complexes hydrogen bonding to silica SBA-15/SBA-16 followed by the addition polymerization reaction of 4-vinylpyridine (vpd) extending along the mesoporous channels. Highlights: Black-Right-Pointing-Pointer Functional mesoporous with simple impregnation method. Black-Right-Pointing-Pointer New lanthanide mesoporous hybrids with polymer ligands. Black-Right-Pointing-Pointer Luminescence in visible region.

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

How Close Is Too Close? Polymerization Behavior and Monomer-Dependent Reorganization of a Bimetallic Salphen Organotitanium Catalyst

The binuclear salphen Ti polymerization catalyst N,N'-1,2-phenylene[(salicylideneaminato)Ti(Cp*)Me 2 )] 2 (2) is synthesized by reaction of salphen-H 2 with Cp*TiMe 3 . Mononuclear [N-(2,6-diisopropyl)phenyl(salicylideneaminato)]Ti(Cp*)Me 2 (1) serves as a control. Activation studies of 2 with cocatalyst Ph 3 C + B(C 6 F 5 ) 4 – yield the cationic polymerization-inactive complex [N,N'-1,2-phenylene(salicylideneaminato)Ti(Cp*)] + B(C 6 F 5 ) 4 – (4) and polymerization-active Cp*TiMe 2 + B(C 6 F 5 ) 4 – . Polymerization studies comparing 2 with Cp*TiMe 3 suggest that, within the catalytic time frame, while 2 retains bimetallic character under an ethylene atmosphere, it rapidly decomposes to 4 and Cp*TiMe 2 + in the presence of 1-hexene. These monomer-dependent reorganization results highlight the importance of olefin polymerization activation mechanistic studies while providing insight for improved bimetallic catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Highly efficient and selective pressure-assisted photon-induced polymerization of styrene

The polymerization process of condensed styrene to produce polystyrene as an industrially important polymeric material was investigated using a novel approach by combining external compression with ultraviolet radiation. The reaction evolution was monitored as a function of time and the reaction products were characterized by in situ Fourier transform infrared spectroscopy. By optimizing the loading pressures, we observed highly efficient and selective production of polystyrene of different tacticities. Specifically, at relatively low loading pressures, infrared spectra suggest that styrene monomers transform to amorphous atactic polystyrene (APS) with minor crystalline isotactic polystyrene. In contrast, APS was found to be the sole product when polymerization occurs at relatively higher loading pressures. The time-dependent reaction profiles allow the examination of the polymerization kinetics by analyzing the rate constant and activation volume as a function of pressure. As a result, an optimized pressure condition, which allows a barrierless reaction to proceed, was identified and attributed to the very desirable reaction yield and kinetics. Finally, the photoinitiated reaction mechanism and the growth geometry of the polymer chains were investigated from the energy diagram of styrene and by the topology analysis of the crystal styrene. This study shows strong promise to produce functional polymeric materials in a highly efficient and controlled manner.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

SI-PET-RAFT Polymerization via Electrodeposited Macroinitiator Thin Films: Toward Biomedical and Sensing Applications

Surface-initiated photoinduced electron transfer-reversible addition–fragmentation chain transfer (SI-PET-RAFT) polymerization has been preferentially used for preparing thin polymeric film coatings due to its simple execution under ambient conditions (e.g., in air) and visible light requirement. In this study, we demonstrate the preparation of polymer brushes by SI-PET-RAFT polymerization on a thin macroinitiator film electrodeposited on electrically conductive indium tin oxide and gold surfaces. An electrochemically active carbazole-containing chain transfer agent as macroinitiator was shown to be not only effective in mediating SI-PET-RAFT polymerization for various monomers but also capable of forming block copolymers. Additionally, the fabricated polymer brush films were able to encapsulate colloidal gold nanoparticles, thereby demonstrating potential use for biomedical and sensing applications.

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

Exploration of the Effect of Chitosan and Crosslinking Agent Concentration on the Properties of Dual Responsive Chitosan-g-Poly (N-Isopropylacrylamide) Co-polymeric Particles

The objective of the present study was to synthesize and evaluate the effect of change in concentration of chitosan (CS) and N,N-methylenebisacrylamide (MBA)- a cross linking agent, on various properties such as lower critical solution temperature (LCST), zeta potential, particle size and poly dispersity index (PDI) of the synthesized co-polymer. Nine different formulations of chitosan-g-poly (N-isopropylacrylamide) (CS-g-PNIPAAm) co-polymer with varying CS and MBA concentrations were synthesized by a surfactant free dispersion copolymerization method. The synthesized co-polymer was further characterized and confirmed for its structure, morphology, particle size, zeta-potential, thermo and pH responsive properties, in-vitro cyto-compatability and stability studies using various analytical tools. The data confirms the successful synthesis of co-polymer. The increase in the concentrations of CS and MBA during the polymerization of co-polymer, resulted in proportional increase of LCST and zeta potential with decrease in particle size of co-polymeric nanoparticles. pH responsive studies showed that as the pH of the medium increases particle size and zeta potential decreases with increase in LCST of co-polymeric nanoparticles. From the results, it can be inferred that the synthesized co-polymeric nanoparticles exerted thermo and pH responsive properties with biocompatibility. By varying the CS and MBA concentrations in the co-polymer, desired LCST, particle size and zeta potential for co-polymeric nanoparticles can be obtained and thus the synthesized co-polymer may have great potential to be used as a drug carrier (nanoform) with both thermo and pH responsiveness.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Supramolecular intermediates in the synthesis of polymeric carbon nitride from melamine cyanurate

The adduct of melamine and cyanuric acid (MCA) was used in past research to produce polymeric carbon nitride and precursors. The reaction yield was considerably incremented by the addition of sulfuric acid. The polymeric carbon nitride formation occurs around 450 °C at temperatures above the sublimation of the adduct components, which occurs around 400 °C. In this report the effect of sulfuric acid on MCA was investigated. It was found that the MCA rosette supramolecular channel structures behave as a solid solvent able to host small molecules, such as sulfuric acid, inside these channels and interact with them. Therefore, the sulfuric acid effect was found to be close to that of a solute that causes a temperature increment of the “solvent sublimation” enough to allowing the formation of polymeric carbon nitride to occur. Sulfate ions are presumably hosted in the rosette channels of MCA as shown by simulations. - Graphical abstract: The blend of melamine cyanurate and sulfuric acid behaves like a solution so that melamine cyanurate decomposition is shifted to temperatures high enough to react and form polymeric carbon nitride. - Highlights: • The adduct of melamine and cyanuric acid behaves as a solid solvent. • The blend of sulfuric acid and melamine cyanurate behaves like a solution. • Melamine cyanurate decomposition is shifted to higher temperatures by sulfuric acid. • The formation of polymeric carbon nitride occurs for these higher temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Development of a Reactive Force Field for Simulating Photoinitiated Acrylate Polymerization

Light-driven and photo-curable polymer based additive manufacturing (AM) has enormous potential due to its excellent resolution and precision. Acrylated radical chain-growth polymerized resins are widely used in photopolymer AM due to their fast kinetics, and often serve as a departure point for developing other resin materials for photopolymer-based AM technologies. For successful control of the photopolymer resins, the molecular basis of the acrylate free-radical polymerization has to be understood in detail. We present an optimized reactive force field (ReaxFF) for molecular dynamics (MD) simulations of acrylate polymer resins that captures radical polymerization thermodynamics and kinetics. The force field is trained against an extensive training set including density functional theory (DFT) calculations of reaction pathways along the radical polymerization from methyl acrylate to methyl butyrate, bond dissociation energies, and structures and partial charges of several molecules and radicals. We also found that it was critical to train the force field against an incorrect, nonphysical reaction pathway observed in simulations that used parameters not optimized for acrylate polymerization. As a result, the parameterization process utilizes a parallelized search algorithm, and the resulting model can describe polymer resin formation, crosslinking density, conversion rate, and residual monomers of the complex acrylate mixtures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Route to high-energy density polymeric nitrogen t-N via He-N compounds

Polymeric nitrogen, stabilized by compressing pure molecular nitrogen, has yet to be recovered to ambient conditions, precluding its application as a high-energy density material. Here we suggest a route for synthesis of a tetragonal polymeric nitrogen, denoted t-N, via He-N compounds at high pressures. Using first-principles calculations with structure searching, we predict a class of nitrides with stoichiometry HeN 4 that are energetically stable (relative to a mixture of solid He and N 2 ) above 8.5 GPa. At high pressure, HeN 4 comprises a polymeric channel-like nitrogen framework filled with linearly arranged helium atoms. The nitrogen framework persists to ambient pressure on decompression after removal of helium, forming pure polymeric nitrogen, t-N. t-N is dynamically and mechanically stable at ambient pressure with an estimated energy density of ~11.31 kJ/g, marking it out as a remarkable high-energy density material. As a result, this expands the known polymeric forms of nitrogen and indicates a route to its synthesis.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Active light-controlled frontal ring-opening metathesis polymerization

Frontal ring-opening metathesis polymerization (FROMP) is a promising energy-efficient approach to fabricate polymeric materials. Recent advances have demonstrated FROMP for diverse applications, including additive manufacturing, composites, and foams. However, the characteristic properties of the front are currently controlled primarily by varying the resin composition or the environmental conditions. In this work we present an approach to control FROMP of dicyclopentadiene (DCPD) using photochemical methods. A photobase generator is used to inhibit FROMP of DCPD with UV light while a photosensitizer and co-initiator are used to accelerate FROMP with blue light, enabling orthogonal active photocontrol of front velocity. In addition, photoinhibition-enabled lithographic patterning of frontal polymerizations is demonstrated. Frontal polymerizations are spatially controlled, redirected, and even split into diverging fronts. This work establishes a foundation for advanced control of frontal polymerizations, enabling innovation in traditional and additive manufacturing, as well as emerging processes like morphogenic manufacturing.

Polymer synthesis↗