Melting Gel Films for Low Temperature Seals

2013 ◽  
Vol 1547 ◽  
pp. 81-86 ◽  
Author(s):  
Mihaela Jitianu ◽  
Andrei Jitianu ◽  
Michael Stamper ◽  
Doreen Aboagye ◽  
Lisa C. Klein
Keyword(s):  
Room Temperature ◽  
Viscous Fluids ◽  
Methyl Groups ◽  
Scanning Calorimetry ◽  
Hybrid Gels ◽  
Methyl Group ◽  
Oscillatory Rheometry ◽  
Melting Gels ◽  
Viscous Modulus ◽  
Insight Into

ABSTRACTMelting gels are silica-based hybrid gels with the curious behavior that they are rigid at room temperature, but soften around 110°C. A typical melting gel is prepared by mixing methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES). MTES has one methyl group substituted for an ethoxy, and DMDES has two substitutions. The methyl groups do not hydrolyze, which limits the network-forming capability of the precursors. To gain insight into the molecular structure of the melting gels, differential scanning calorimetry and oscillatory rheometry studies were performed on melting gels before consolidation. According to oscillatory rheometry, at room temperature, the gels behave as viscous fluids, with a viscous modulus, G″(t,ω0) that is larger than the elastic modulus, G′(t,ω0). As the temperature is decreased, gels continue to behave as viscous fluids, with both moduli increasing with decreasing temperature. At some point, the moduli cross over, and this temperature is recorded as the glass transition temperature Tg. The Tg values obtained from both methods are in excellent agreement. The Tg decreases from -0.3oC to -56oC with an increase in the amount of di-substituted siloxane (DMDES) from 30 to 50 mole %. A decrease of the Tg follows an increase of the number of hydrolytically stable groups, meaning a decrease in the number of oxygen bridges between siloxane chains.

HINDERED CONFORMATIONAL ISOMERIZATION OF 9,10-DIHYDRO-9,9-DIMETHYL-10-METHYLENEANTHRACENES

1964 ◽  
Vol 42 (3) ◽  
pp. 565-571 ◽  
Author(s):  
D. Y. Curtin ◽  
C. G. Carlson ◽  
C. G. McCarty
Keyword(s):  
Room Temperature ◽  
Methyl Groups ◽  
Conformational Isomerization ◽  
Methylene Carbon ◽  
Methyl Group ◽  
First Order ◽  
Methylene Carbon Atom ◽  
Center Ring ◽  
Bromo Compound ◽  
Dibromo Derivative

While the n.m.r. spectrum of 10,10-dimethyl-9-methylene-9,10-dihydroanthracene (I) shows the geminal methyl group absorption as a sharp singlet the spectrum of the dibromo derivative, 10,10-dimethyl-9-dibromomethylene-9,10-dihydroanthracene (II) shows the methyl absorptions as two sharp well-separated peaks at room temperature which coalesce at 91°. 10,10-Dimethyl-9-phenylbromomethylene-9,10-dihydroanthracene (III), and the methyl ester (V) of IV show a broad geminal methyl spectrum at room temperature which separates to a doublet at lower temperatures and sharpens to a singlet at higher temperatures. Rate constants for the first-order processes responsible for the change in spectrum of II, III, and V have been calculated at the coalescence temperatures to be 57 (364 °K), 35 (305 °K), and 61 (300 °K) sec−1, respectively. The ΔH≠'s were used to extrapolate the rates to 305° to give values of 1, 40, and 100 sec−1, respectively. The process being studied is inferred to be the equilibrium between two boat conformations of the center ring in the dihydroanthracene system, rapid interconversion leading to identical environments for the two methyl groups. A comparison with the geometrically similar o,o′-disubstituted biphenyl racemization gives support for this explanation. A number of compounds with a proton and one substituent on the methylene carbon atom of I (substituents: bromine, chlorine, phenyl, carboxy, carbomethoxy, phenylmercapto) and also 10,10-dimethyl-9-phenylcarbomethoxymethylene-9,10-dihydroanthracene (XII) showed a single methyl absorption at room temperature. The methyl spectrum of the mono bromo compound VI did not broaden at temperatures down to 246 °K.

X+ transfer from the halonium ions of adamantylideneadamantane to acceptor olefins. The possibility of chiral induction in the transfer process

1997 ◽  
Vol 75 (12) ◽  
pp. 1844-1850 ◽  
Author(s):  
Alexei A. Neverov ◽  
Theresa L. Muise ◽  
R.S. Brown
Keyword(s):  
Nmr Spectra ◽  
Room Temperature ◽  
Reaction Rate ◽  
Methyl Groups ◽  
Kinetic Behavior ◽  
Methyl Group ◽  
Chiral Induction ◽  
H Nmr ◽  
Group 12 ◽  
Kinetics Of

The bromonium ion of adamantylideneadamantane (Ad=Ad-Br+) has been used to induce the bromocyclization of a 4-pentenyl glycoside (10) and a 5-hexenyl glycoside (11) in dichloroethane. The kinetics of these processes have been studied at 25 °C in the presence of varying [Ad=Ad] and, in the case of the transfer to 10, in the presence of pentanol. The second-order rate constants for bromocyclization of these two alkenes are (1.04 ± 0.06) × 10−1 M−1 s−1 and (5.34 ± 0.2) × 10−1 M−1 s−1, respectively, and in no case does added Ad=Ad or pentanol alter the reaction rate. The kinetic behavior is interpreted in terms of cyclization occurring directly from a 1:1 complex of Ad=Ad-Br+ and 10 or 11. The chiral induction for the bromocyclization of 10 promoted by AdAd-Br+ was measured at 20% e.e., the (−)-(S)-tetrahydrofurfuryl bromide being the dominant stereoisomer. Ad=Ad molecules substituted at one of the homoallylic carbons by an axial methyl group (12), or by two methyl groups (axial and equatorial), were synthesized and the 1H NMR spectra of their bromonium ions is given. These materials are not stable for prolonged times at room temperature. A limited kinetic study of the reaction of 12-Br+ and 4-pentenol indicated that the Br+ transfer is 500 times faster than the comparable transfer from Ad=Ad-Br+ to 4-pentenol. The possibility of using these materials to induce chiral bromocyclization is discussed. Keywords: bromonium ion, halonium, transfer, chiral, adamantylideneadamantane.

The Influence of Heteroatom-substituted Methyl Groups and of Vinyl Groups (CR2=CR—) Attached to C-2 of 1,3-Dioxolanes on the Ease and Direction of Hydrogenolysis of the 1,3-Dioxolanes by AlH2Cl, AlH3, or LiAlH4

1971 ◽  
Vol 49 (15) ◽  
pp. 2563-2577 ◽  
Author(s):  
H. A. Davis ◽  
R. K. Brown
Keyword(s):  
Diethyl Ether ◽  
Ring Opening ◽  
Room Temperature ◽  
Methyl Groups ◽  
Double Bond Migration ◽  
Methyl Group ◽  
Hydride Ion ◽  
Vinyl Group ◽  
Dialkyl Ethers ◽  
Reflux Temperature

Heteroatom substituents on the methyl group of 2-methyl-1,3-dioxolane retard the rate of hydrogenolysis by AlH2Cl of ether solutions of the 2-substituted 1,3-dioxolanes. The effectiveness of the heteroatoms in decreasing the ease of hydrogenolysis is H < S < O < Br < NR2. This retardation is thought to be due to the destabilization of the transition state leading to the intermediate oxocarbonium ion, caused by the electronegativity of the heteroatom and/or coordination of some of the AlH2Cl with the heteroatom.AlH2Cl or AlH3 in diethyl ether at room temperature reduces 2-vinyl- or 2-[alkyl (or aryl) substituted vinyl]-1,3-dioxolanes to only the β,γ-unsaturated alkyl β-hydroxyethyl ether, the product expected from hydride ion addition to C-2 of the 1,3-dioxolane. The ease of hydrogenolysis increases with increasing alkyl (or aryl) substitution on the 2-vinyl group.LiAlH4 in diethyl ether at room temperature, or in di-n-propyl ether or 1,2-dimethoxyethane (DME) at room temperature or reflux temperature, reduces 2-vinyl-l,3-dioxolane only to α-propenyl β-hydroxyethyl ether. This product is the result of hydride addition to the β-carbon of the vinyl group accompanied by ring opening and double bond migration. Alkyl substituents attached to the vinyl group of 2-vinyl-1,3-dioxolane markedly retard the rate of hydrogenolysis by LiAlH4 in the dialkyl ethers at room temperature, but at the reflux temperature (90°) of di-n-propyl ether the 2-alkylated vinyl-1,3-dioxolanes are hydrogenolyzed, but only to the β,γ-unsaturated alkyl β-hydroxyethyl ether. In refluxing DME (80°) the 2-alkylated vinyl-1,3-dioxolanes give primarily, if not exclusively, the α,β-unsaturated alkyl β-hydroxyethyl ether. A rationale is suggested to account for these results.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

Star-shaped arylacetylene resins derived from silicon

2020 ◽  
Vol 40 (8) ◽  
pp. 676-684
Author(s):  
Niping Dai ◽  
Junkun Tang ◽  
Manping Ma ◽  
Xiaotian Liu ◽  
Chuan Li ◽  
...  
Keyword(s):  
High Performance ◽  
Room Temperature ◽  
Mechanical Test ◽  
Flexural Modulus ◽  
Mechanical Analysis ◽  
Reinforced Composites ◽  
Scanning Calorimetry ◽  
Chemical Structures ◽  
Structures And Properties ◽  
High Performance Resin

AbstractStar-shaped arylacetylene resins, tris(3-ethynyl-phenylethynyl)methylsilane, tris(3-ethynyl-phenylethynyl) phenylsilane, and tris (3-ethynyl-phenylethynyl) silane (TEPHS), were synthesized through Grignard reaction between 1,3-diethynylbenzene and three types of trichlorinated silanes. The chemical structures and properties of the resins were characterized by means of nuclear magnetic resonance, fourier-transform infrared spectroscopy, Haake torque rheomoter, differential scanning calorimetry, dynamic mechanical analysis, mechanical test, and thermogravimetric analysis. The results show that the melt viscosity at 120 °C is lower than 150 mPa⋅s, and the processing windows are as wide as 60 °C for the resins. The resins cure at the temperature as low as 150 °C. The good processabilities make the resins to be suitable for resin transfer molding. The cured resins exhibit high flexural modulus and excellent heat-resistance. The flexural modulus of the cured TEPHS at room temperature arrives at as high as 10.9 GPa. Its temperature of 5% weight loss (Td5) is up to 697 °C in nitrogen. The resins show the potential for application in fiber-reinforced composites as high-performance resin in the field of aviation and aerospace.

scholarly journals The effect of polyhedral oligomeric silsesquioxanes (POSSs) incorporation in ethylene-propylene-diene-terpolymer (EPDM): a thermal study

2021 ◽  
Author(s):  
Ignazio Blanco ◽  
Traian Zaharescu
Keyword(s):  
Room Temperature ◽  
Thermal Characterization ◽  
Polyhedral Oligomeric Silsesquioxanes ◽  
Dsc Analysis ◽  
Γ Irradiation ◽  
Scanning Calorimetry ◽  
Ethylene Propylene ◽  
Oligomeric Silsesquioxane ◽  
Ethylene Propylene Diene Terpolymer ◽  
Dynamic Heating

AbstractA series of ethylene-propylene-diene-terpolymer (EPDM)/polyhedral oligomeric silsesquioxane (POSS) composites at different percentage of POSS were prepared and subjected to γ-irradiation. Both irradiated and non-irradiated EPDM and composites were investigated by the means of thermal analysis to verify if the presence of POSS molecules is able to reduce the oxidation level of free radicals generated during the degradation and to evaluate the effects of the irradiation. EPDM composites at 1, 3 and 5 mass% of POSS were thus degraded in a thermogravimetric (TG) balance in dynamic heating conditions (25–700 °C), in both inert and oxidative atmosphere by flowing nitrogen and air respectively. Thermal characterization was then completed by carrying out Differential Scanning Calorimetry (DSC) analysis from sub-ambient to better highlight the melting of the polymer and polymer composites occurring just above the room temperature. FTIR spectroscopy was also performed for the prepared samples to check the presence of the molecular filler in the composites and for the TG’s residue at 700 °C, in order to evaluate its nature. DSC and TGA parameters were detected and discussed to have information about the effect of the degradation’s environment, the effect of irradiation on polymer stabilization and the effect of POSS content in the polymer matrix.

Synthesis and properties of phthalonitrile-based resins containing spirocycle acetal

2020 ◽  
pp. 095400832097759
Author(s):  
Ke Li ◽  
Hua Yin ◽  
Kun Yang ◽  
Pei Dai ◽  
Ling Han ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Chemical Structure ◽  
Room Temperature ◽  
Laser Desorption Ionization ◽  
Scanning Calorimetry ◽  
Rheological Analysis ◽  
Ionization Time ◽  
Dynamic Mechanical ◽  
Nmr Spectrometry ◽  
Current Context

Designing novel low-melting, high-rigidity phthalonitrile resin is of great significance in the current context of development. In this study, rigid spirocycle acetal structure was introduced into phthalonitrile to reduce the melting point and maintain their thermal stability. The chemical structure of resins was confirmed by nuclear magnetic resonance (NMR) spectrometry, matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry and Fourier-transform infrared (FTIR) spectroscopy. The curing behaviors were studied by differential scanning calorimetry (DSC). Thermal stability and mechanical properties of the cured resins were investigated by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The processability was studied by rheological analysis. The results indicated the three monomers had a low melting temperature, wide processing windows and low viscosities. These polymers did not exhibit Tg from room temperature to 400°C, exhibited superb dynamic mechanical property and thermal stability.

scholarly journals Characteristics of Reconstituted Collagen Fibers from Chicken Keel Cartilage Depends on Salt Type for Removal of Proteoglycans

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3538
Author(s):  
Anna Pudło ◽  
Szymon Juchniewicz ◽  
Wiesław Kopeć
Keyword(s):  
Electron Microscopy ◽  
Rheological Properties ◽  
Thermal Denaturation ◽  
Surface Structures ◽  
Scanning Calorimetry ◽  
Cartilage Extracellular Matrix ◽  
Oscillatory Rheometry ◽  
Freeze Dried ◽  
Basic Features ◽  
Scanning Electron

The aim of the presented research was to obtain reconstituted atelocollagen fibers after extraction from poultry cartilage using the pepsin-acidic method in order to remove telopeptides from the tropocollagen. Firstly, we examined the extraction of collagen from the cartilage extracellular matrix (ECM) after proteoglycans (PG) had been removed by the action of salts, i.e., NaCl or chaotropic MgCl2. Additionally, the effects of the salt type used for PG and hyaluronic acid removal on the properties of self-assembled fibers in solutions at pH 7.4 and freeze-dried matrices were investigated. The basic features of the obtained fibers were characterized, including thermal properties using scanning calorimetry, rheological properties using dynamic oscillatory rheometry, and the structure by scanning electron microscopy. The fibers obtained after PG removal with both analyzed types of salts had similar thermal denaturation characteristics. However, the fibers after PG removal with NaCl, in contrast to those obtained after MgCl2 treatment, showed different rheological properties during gelatinization and smaller diameter size. Moreover, the degree of fibrillogenesis of collagens after NaCl treatment was complete compared to that with MgCl2, which was only partial (70%). The structures of fibers after lyophilization were fundamentally different. The matrices obtained after NaCl pretreatment form regular scaffolds in contrast to the thin, surface structures of the cartilage matrix after proteoglycans removal using MgCl2.

scholarly journals Nonreciprocal charge transport up to room temperature in bulk Rashba semiconductor α-GeTe

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yan Li ◽  
Yang Li ◽  
Peng Li ◽  
Bin Fang ◽  
Xu Yang ◽  
...  
Keyword(s):  
Charge Transport ◽  
Room Temperature ◽  
Theoretical Calculations ◽  
Ferromagnetic Layer ◽  
Spin Splitting ◽  
New Paradigm ◽  
Rashba Spin ◽  
Rashba Spin Splitting ◽  
Fundamental Insight ◽  
Insight Into

AbstractNonmagnetic Rashba systems with broken inversion symmetry are expected to exhibit nonreciprocal charge transport, a new paradigm of unidirectional magnetoresistance in the absence of ferromagnetic layer. So far, most work on nonreciprocal transport has been solely limited to cryogenic temperatures, which is a major obstacle for exploiting the room-temperature two-terminal devices based on such a nonreciprocal response. Here, we report a nonreciprocal charge transport behavior up to room temperature in semiconductor α-GeTe with coexisting the surface and bulk Rashba states. The combination of the band structure measurements and theoretical calculations strongly suggest that the nonreciprocal response is ascribed to the giant bulk Rashba spin splitting rather than the surface Rashba states. Remarkably, we find that the magnitude of the nonreciprocal response shows an unexpected non-monotonical dependence on temperature. The extended theoretical model based on the second-order spin–orbit coupled magnetotransport enables us to establish the correlation between the nonlinear magnetoresistance and the spin textures in the Rashba system. Our findings offer significant fundamental insight into the physics underlying the nonreciprocity and may pave a route for future rectification devices.

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