Showing papers on "Differential scanning calorimetry published in 1970"
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TL;DR: In this article, the curing reactions of epoxy resin with aliphatic diamines and the reaction of phenyl glycidyl ether with butylamine were investigated with a differential scanning calorimeter (DSC) operated isothermally.
Abstract: The curing reactions of epoxy resin with aliphatic diamines and the reaction of phenyl glycidyl ether with butylamine as a model for the curing reactions were investigated with a differential scanning calorimeter (DSC) operated isothermally. The heat of reaction of phenyl glycidyl ether with butylamine is equal to 24.5 ± 0.6 kcal/mole. The rate of reaction was followed over the whole range of conversion for both model and curing reactions. The reactions are accelerated by the hydrogen-bond donor produced in the system. The rate constants based on the third-order kinetics were determined and discussed for the model reaction and for the chemically controlled region of curing reactions. The activation energies for these rate constants are 13-14 kcal/mole. At a later stage of conversion, the curing reactions become controlled by diffusion of functional groups. The final extent of conversion is short of completion for most isothermally cured and even for postcured samples because of crosslinking. It was quantitatively indicated that the final conversion of isothermal cure corresponds to the transition of the system from a viscous liquid to a glass on the basis of the theory of glass transition temperature of crosslinked polymer systems.
436 citations
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TL;DR: Monolayer results indicate that the molecular area occupied by the higher melting component becomes larger because of the increased configurational freedom of its chains, particularly with respect to the effect of temperature on lipids and membranes.
279 citations
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TL;DR: In this paper, the theory of the calorimetric method is applied to DSC data, and a generally applicable procedure is suggested which involves the measurement of the total energy absorbed in the melting region.
168 citations
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TL;DR: This paper showed that tris(hydroxymethyl)acetic acid and diaminopentaerythritol exhibit solid-state transitions to a plastic crystalline state, suggesting that configurational contributions to their entropy increments have been inhibited.
90 citations
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TL;DR: In this paper, the curing reaction of polyester fumarate with styrene was investigated with a differential scanning calorimeter (DSC) operated isothermally, and the change in rate of cure was followed over the whole range of conversion.
Abstract: The curing reaction of polyester fumarate with styrene was investigated with a differential scanning calorimeter (DSC) operated isothermally. The change in rate of cure was followed over the whole range of conversion. The rate of cure is accelerated by the gel effect to about ten to fifty times the rate of model copolymerization of diethyl fumarate with styrene. This autoacceleration is much enhanced for systems with higher crosslinking densities and at lower temperatures. The results confirm that both termination and propagation steps of the curing reaction are controlled by diffusion of polymeric segments and monomer molecules over almost the whole range of conversion. The final extent of conversion is short of completion for isothermal cure and even for postcure of polyester fumarate with styrene because of crosslink formation. The final conversion of isothermal cure decreases with increasing crosslinking density and shows a maximum with increasing reaction temperature. This temperature dependency of the final conversion is caused by the difference in the activation energies for two propagation rate constants kpf and kps, which were evaluated to be 7–10 and 5–8 kcal/mole, respectively, for the intermediate stage of the curing reaction.
80 citations
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TL;DR: For polyvinylchloride fractions having molecular weights between 500 and 105 using differential scanning calorimetry, the Gibbs-DiMarzio relation gave a more satisfactory fit with the data extending to lower molecular weights taking ϵ = 1·51 kcal/mole, V0 = 0·025.
79 citations
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IBM1
TL;DR: Differential scanning calorimetry (DSC) produces thermograms which should be satisfactory for purity analyses using the van't Hoff equation as mentioned in this paper.Using mixtures characterized by accepted alternate methods the precision and accuracy of the DSC method have been explored.
46 citations
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TL;DR: In this paper, the heats and temperatures of transition for fourteen cholesteryl esters of saturated aliphatic acids have been evaluated using a Perkin-Elmer Differential Scanning Calorimeter, DSC-IB.
Abstract: The heats and temperatures of transition for fourteen cholesteryl esters of saturated aliphatic acids have been evaluated using a Perkin-Elmer Differential Scanning Calorimeter, DSC-IB. Most esters tested were first recrystallized from n-pentyl alchol. Among several recrystallization solvents tested, n-pentyl alchol was most effective in removing impurities and eliminating ester transitions caused by these impurities. Ester purity was determined by a recently reported technique which is based on an analysis of the complete DSC recorder scan for transitions. The transition data in this study indicate that the lowest molecular weight saturated aliphatic ester of cholesterol to show mesophase behavior is the propionate. For the formate or acetate less pure samples may be supercooled in the melt so that mesophases may be observed. New transition data for the odd esters of cholesterol from undecanoate to nonadecanoate have also been obtained. Cholesteryl eicosanoate was examined and found to have only...
42 citations
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TL;DR: In this article, differential scanning calorimetry, X-ray diffraction, and electron microscopy were used to characterize the temperatures, energies, and types of thermally induced transformations which occur in the chalcogenide glasses As 30 Te 48 Si 12 Ge 10, As 2 Se 3 ·3 As 2 Te 3, As 2 SE 3 ·2 As 2 TE 3, and 2 As 2 S 3 ·As 2 SE3, while memory effects were observed in only those systems which could be crystallized.
Abstract: Differential scanning calorimetry, X-ray diffraction, and electron microscopy were used to characterize the temperatures, energies, and types of thermally induced transformations which occur in the chalcogenide glasses As 30 Te 48 Si 12 Ge 10 , As 2 Se 3 ·3 As 2 Te 3 , As 2 Se 3 ·2 As 2 Te 3 , and 2 As 2 Se 3 ·As 2 Te 3 . In one composition, 2 As 2 Se 3 ·As 2 Te 3 , neither phase separation nor crystallization was observed. Experimental evidence indicates that crystallization can be induced in the other three compositions. Threshold switching was observed in all four compositions while memory effects were observed in only those systems which could be crystallized. Thus, a thermally induced phase separation or crystallization is not necessary for the occurrence of threshold switching, and crystallization (or in other systems, phase separation) is a mechanism whereby memory effects can be induced.
35 citations
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TL;DR: In this paper, a system for obtaining differential scanning calorimetry (DSC) data under reduced (to 10 microns) or elevated (to 1000 psi) pressure is described.
32 citations
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TL;DR: In this paper, a differential scanning calorimeter has been used to measure the heat capacity of both melt and solution crystallized samples of isotactic polypropylene from 200 to 500°K.
Abstract: A differential scanning calorimeter has been used to measure the heat capacity of both melt and solution crystallized samples of isotactic polypropylene from 200 to 500°K. An estimate has been made of heat capacity values below 200°K. Values of the heat capacity, entropy, enthalpy, and free energy have been estimated for 100% crystalline isotactic polypropylene and are listed at 10°K intervals. The glass transition occurs at about 265°K in both samples. A value of 207 ± 5 Jċg−1 is obtained for the heat of fusion of isotactic polypropylene.
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TL;DR: In this article, the mean lifetime τ2 of ortho-positronium annihilating by pickoff depends upon the free volume of the atom and the number of atoms in the atom.
Abstract: In solid polymers the mean lifetime τ2 of ortho‐positronium annihilating by pickoff depends upon the free volume. τ2 has been measured for five samples of relatively monodisperse atactic polystyrene over a temperature range from room temperature to 120°C. The number average molecular weight of the samples ranged from 50 100 to 640 000. For each sample the variation of τ2 with temperature indicated a glass transition about 13 deg below that measured on a differential scanning colorimeter. An increase in the glass transition temperature with molecular weight was observed. The τ2 lifetime, which depends upon the overlap of the positron component of the ortho‐positronium atom with the lattice wavefunction, seems to be very sensitive to the cooperative motion about the chain axis which is associated with the glass transition.
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TL;DR: In this article, the plastic crystal phenomenon has been observed by others in such tetrahedral substances as neopentane, pentaerythrityl fluoride, tertiary butyl halides, and pentalerythritol, where R's are methyl, methylol, amino and carboxy.
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TL;DR: In this article, the enthalpies and entropies of two series of semicrystalline polyurethanes have been determined for two different methods: X-ray analysis and diluent analysis.
Abstract: Enthalpies and entropies of fusion have been determined for two series of semicrystalline polyurethanes. The H series is based on 1,6-hexamethylene diisocyanate and various α, ω-diols containing from 2 to 10 methylene units. The DP series is based on 4,4′-methylene diphenyl diisocyanate and various α, ω-diols containing from 2 to 10 methylene units. Differential Scanning Calorimetry (DSC) was used in conjunction with X-ray analysis (X-ray method) and low molecular-weight diluents (diluent method) to determine the enthalpies of fusion. Agreement between the X-ray method and the diluent method was good.Differences between the enthalpies and entropies of fusion of the H and DP series could be largely attributed to differences in intermolecular hydrogen bonding in the melts of the two series. On the other hand, differences in the entropies of fusion between the H series and corresponding polyamides arise largely from differences in backbone-chain stiffness between the two series.
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TL;DR: IR spectra and X-ray diffraction patterns of the powder did not show any major differences between samples crystallized from either solvent, and the calculated average heat of transition, for ground samples crystallization from both ammonia solutions and from alcohol, is 1652 ± 56 cal./mole.
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TL;DR: In this article, a differential scanning calorimeter has been used to measure the heat capacities of nylon-6 samples, which had been subjected to different doses (0-1000 Mrads) of cobalt-60 gamma radiation at 298°K, over the temperature range 200-550°K.
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TL;DR: Poly-2-oxazolidones were synthesized by the 1,3-cycloaddition of bisglycidyl ethers to diisocyanates with the use of N, N-dimethylformamide and lithium chloride as solvent and catalyst, respectively as mentioned in this paper.
Abstract: Poly-2-oxazolidones were synthesized by the 1,3-cycloaddition of bisglycidyl ethers to diisocyanates with the use of N,N-dimethylformamide and lithium chloride as solvent and catalyst, respectively. A variety of arylene and alkylene diisocyanates and coreactant bisepoxides were used in the polymer-forming reaction. The polymers, obtained in high yield, were generally soluble in methylene dichloride, chloroform, N,N-dimethylformamide, and dimethyl sulfoxide. They had intrinsie viscosities up to 0.42 dl/g and could be cast into films. In several cases molecular weights were determined by vapor pressure osmometry. The poly-2-oxazolidone based upon 1,6-hexamethylene diisocyanate and the bisglycidyl ether of isopropylidene diphenol gave the highest molecular weight. Confirmation that the base unit of the polymers contains the 2-oxazolidone ring was obtained by elemental analysis, infrared and NMR spectroscopy. The poly-2-oxazolidones synthesized were found to be amorphous by x-ray diffraction. Thermogravimetric analyses indicated that a majority of the poly-2-oxazolidones were stable in dry air up to 300°C. In a number of cases Tg's were also determined by using differential scanning calorimetry.
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TL;DR: In this article, reaction heat for flameless combustion of double base propellant using differential scanning calorimetry and thermogravimetric analysis, noting pressure effects was analyzed.
Abstract: Reaction heat for flameless combustion of double- base propellant using differential scanning calorimetry and thermogravimetric analysis, noting pressure effects
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TL;DR: In this paper, a modified ester interchange procedure was used to synthesize poly(ethylene adipate), poly(methylene suberate), and poly (ethylene sebacate) using dilatometry and differential scanning calorimetry.
Abstract: Poly(ethylene adipate), poly(ethylene suberate), and poly(ethylene sebacate) were synthesized by a modified ester interchange procedure. Polydispersity was reduced and low molecular weight material removed by fractional crystallization. Samples of 50–60% crystallinity were prepared by bulk crystallization and annealing. Melting points and amorphous densities were obtained by dilatometry. Melting points were 7–12°C higher than previously reported. Heats of fusion were measured by differential scanning calorimetry and extrapolated to 100% crystallinity by using measured amorphous densities and recently redetermined crystalline densities. Entropies of fusion were calculated and separated for the first time into volume expansion and conformational contributions.
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TL;DR: In this article, a differential scanning calorimeter was used to study the thermal transformations which occur in the NEt4)2MCl4(M = Mn, Fe, Co, Ni, Cu, and Zn).
Abstract: A differential scanning calorimeter has been used to study the thermal transformations which occur in the complexes (NEt4)2MCl4(M = Mn, Fe, Co, Ni, Cu, and Zn). Values for the temperatures, heats, and entropies of transition are given.
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01 Jan 1970TL;DR: In this article, the thermal behavior of aqueous gelatin solutions prepared from deionized bone gelatin has been studied by differential scanning calorimetry and the peak temperatures of the endotherms associated with the loss of gel structure were found to be a function of the gelation temperature and time.
Abstract: The thermal behavior of aqueous gelatin solutions prepared from deionized bone gelatin has been studied by differential scanning calorimetry. The peak temperatures of the endotherms associated with the loss of gel structure were found to be a function of the gelation temperature and time. For 10% solutions, the transitions for material gelled for 48 hours at 4, 10, and 22.5°C were observed at 32, 33, and 37°C, respectively. In order to achieve the sensitivity required for evaluating the transition enthalpy, a Du Pont Differential Thermal Analyzer was coupled with a Keithley Microvolt Amplifier, The enthalpy changes calculated from the dsc endotherms for 10% solutions varied from 4 to 7 cal/g of gelatin depending on the gelation time and temperature. Preliminary data obtained for 5% solutions indicate that the thermal behavior is similar to that of the 10% solutions.
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TL;DR: Differential scanning calorimetry and thermogravimetric analysis curves were obtained for cotton cellulose in the presence of both flame-retarding and nonflame-rewarding compounds and evaluated quantitatively for ΔH, activation energy, total weight loss, and char remaining after pyrolysis.
Abstract: Differential scanning calorimetry and thermogravimetric analysis curves were obtained for cotton cellulose in the presence of both flame-retarding and nonflame-retarding compounds and evaluated quantitatively for ΔH, activation energy, total weight loss, and char remaining after pyrolysis. Twenty-three compounds were tested and were found to fall roughly into three groups: (I) those which do not undergo decomposition in the temperature interval in which cellulose decomposes (200-400°C); (II) those which decompose appreciably during or preceding this temperature range; and (III) those which do not interact in any way with cellulose. It was found that, with increasing molar add-on, heat liberated from cellulose decreased for group I, increased for group II, and was not a function of molar add-on for III.A study of the kinetics of decomposition for these systems indicates that, while the majority of reactions proceeded as a pseudo first-order process, there are several exceptions to the trend. As would be ex...
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TL;DR: In this paper, the phase transitions of the anion radical salts containing mixed cations represented by [(C6H5)3PCH3]1−x+[(C 6H5]3AsCH3 ]x+(TCNQ)2\ewdot, (0≤x≤1) were investigated by means of a differential scanning calorimeter.
Abstract: The phase transitions of the anion radical salts containing mixed cations represented by [(C6H5)3PCH3]1−x+[(C6H5)3AsCH3]x+(TCNQ)2\ewdot, (0≤x≤1) were investigated. The transition temperature, Tc, and the magnitude of the heat, ΔH, of the transition were determined as a function of the composition parameter, x, by means of a differential scanning calorimeter. It was found that Tc increases, and ΔH decreases, monotonously with an increase in the value of x, and that the phase transition disappears with x=1.00. The mechanism of the phase transitions was discussed on the basis of the theory of triplet exciton-exciton interaction proposed by Chesnut. The theoretical values of the entropy changes of the transitions were found to be much less than those observed. In view of these results, it was concluded that the anomalies in the magnetic susceptibilities of these salts were induced by the change in the crystal structure.
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TL;DR: In this article, a differential scanning calorimeter has been used to measure the heat capacities of polyethylene single crystals and melt crystallized samples of isotactic polypropylene, which had been subjected to different doses (0.1000 Mrads) of cobalt-60 gamma radiation at 298°K and 425°K, respectively.
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TL;DR: In this article, the glass transition temperatures (Tg) of a series of high molecular weight aromatic polyimides were measured by differential scanning calorimetry at heating rates of 8-64°K/min on samples of controlled thermal history, and Tgs at a dilatometric heating rate (0.06°k/min) were estimated.
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IBM1
TL;DR: In this paper, a series of Schiff bases derived from 4′-methoxy-4-biphenylamine and aromatic heterocyclic aldehydes has been prepared.
Abstract: In order to ascertain the effect of heterocyclic rings on liquid crystal stability, a series of Schiff bases derived from 4′-methoxy-4-biphenylamine and aromatic heterocyclic aldehydes has been prepared. The ability of each compound to form a liquid crystal phase, either by melting the crystal or cooling the isotropic liquid, has been determined, and the appropriate heat of transition and corresponding entropy change have been measured by differential scanning calorimetry. The results will be discussed in terms of geometrical considerations, substituent effects, and intermolecular interactions.
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01 Jan 1970TL;DR: In this paper, it was shown that the poly-γ-benzyl glutamate (PBG) molecule adopts an α-helical conformation in helicogenic solvents such as 1,2-dichloroethane (DCE) and a random-coil conformation with strong hydrogen bonding in strong dichloroacetic acid (DCA).
Abstract: It is now well known that the poly-γ-benzyl glutamate (PBG) molecule adopts an α-helical conformation in helicogenic solvents such as 1,2-dichloroethane (DCE) and a random-coil conformation in strong hydrogen bonding solvents such as dichloroacetic acid (DCA) (1). The significant thermodynamic parameters of this prototypical helix-coil transition have been measured by a variety of techniques. Thus the overall van’t Hoff heat of transition (∆HVH) is most conveniently obtained from optical rotatory measurements; the transition enthalpy per peptide residue (∆HO) has been found from measurements of heat capacities (2), heats of solution (3) or dilution (4), or indirectly from studies of transition temperatures as a function of solvent composition (5). Such measurements have provided considerable insight, also, into the effects of variables such as transition temperature and solute concentration on the primary parameters ∆HO and ∆HVH, and their ratio σ1/2. where σ is the Zimm-Bragg cooperativity parameter (6).
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