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1.
The chemical and physical structure of polycaproamide obtained by low temperature anionic polymerization of caprolactam in solvent in the presence of the sodium salt of caprolactam and carbon dioxide, has been investigated. Solution behaviour of unfractionated and fractionated samples of polymer in 96% sulphuric acid, m-cresol and mixed solvent (2,2,3,3-tetrafluoropropanol-10% H2O-0.1 M LiCl) was studied by viscosity measurements. The constancy of the Huggins viscometric coefficient K′ in 96% H2SO4 and m-cresol enables determination of limiting viscosity number from measurement at one concentration. On the basis of number-average molecular masses and limiting viscosity numbers, the constants of the Mark-Houwink equation were calculated for in the range 3 × 103 to 62 × 103. They are fairly similar to established values for hydrolytic and anionic polycaproamides. The results confirmed our previous suggestion concerning the linear structure of this polyamide. X-ray analysis indicated high degree of crystallinity. The final, chemical treatment causes changes in chemical and physical structure of this polycaproamide. It differs in some respects from hydrolytic and anionic polycaproamides produced in bulk polymerizations of caprolactam. The findings lead to an understanding of several properties of the polycaproamide. 相似文献
2.
The phase relationships of poly(N-vinyl-3,6-dibromo carbazole) (PVK-3, 6-Br2) were examined for four solvents, viz, o-chlorophenol, p-chloro-m-cresol, o-dichlorobenzene and bromobenzene. Upper critical solution temperatures (UCST) have been determined for solutions of PVK-3,6-Br, fractions in o-chlorophenol and p-chloro-m-cresol over the molecular weight range . The Flory temperature, θ, obtained from UCST for the PVK-3,6-Br2/o-chlorophenol and PVK-3,6-Br2/p-chloro-m-cresol systems are 66.0 and 112.9°C, respectively. The θ-temperatures were checked against molecular weight and viscosity data to determine the Mark-Houwink equations for these two theta solvents, with satisfactory agreement. The relations are The characteristic ratio C∞ = 〈R2〉0/nl2 was found to be 16.6 in o-chlorophenol at 60.0°C and 17.6 in p-chloro-m-cresol at 112.9°C. The value of the characteristic ratio C∞ of PVK-3,6-Br2 is of the same order of that for poly(N-vinyl carbazole). This indicates that the bromine atoms at the 3 and 6 (meta) positions have only an inappreciable effect on the hindering potential for rotation about the CC bond. This agreement of C∞ for both polymers may also be taken as indicating that the effect of interaction between polar groups at the m-position on the hindering potential for rotation is small. The phase diagrams of PVK-3,6-Br2 obtained in o-dichlorobenzene and bromobenzene seem to be characteristic of organized phase structures such as those found in systems exhibiting thermoreversible gelation. Light scattering measurement on PVK-3,6-Br2 dissolved in o-dichlorobenzene, a gelation promoting solvent, and tetrahydrofuran, a very good solvent, strongly indicate that the macromolecular species in o-dichlorobenzene contain some extent supermolecular structures (aggregates, association of chain segments, etc.). These characteristic structures of PVK-3,6-Br2 in o-dichlorobenzene and bromobenzene at 25°C are also characterized by high values of the Huggins' constant k′; for tetrahydrofuran solutions, the k′ values were in the range normally found for many good solvent-polymer systems. 相似文献
3.
M.G. Vitovskaya P.N. Lavrenko O.V. Okatova E.P. Astapenko V.B. Novakovsky S.V. Bushin V.N. Tsvetkov 《European Polymer Journal》1982,18(7):583-588
Translational diffusion, velocity sedimentation and viscometry of polyamidobenzimidazole (PABI) solutions in the range of M = (1–61) · 103 have been investigated in N,N-dimethylacetamide (DMA) and 98% H2SO4. The dependences of D0, S0 and [η] on M were obtained. Tsvetkov-Klenin's hydrodynamic invariant was found to be . The equilibrium rigidity of PABI molecules was characterized by the length of the Kuhn segment . The chain diameter was . The values of A in 98% H2SO4 and in an aprotic solvent, DMA, were virtually identical, implying that the rigid-chain conformation of PABI molecules in 98% H2SO4 is due to their geometrical structure rather than to the protonization of amide bonds. The significance of the latter evidently increases in PABI solutions in 100% H2SO4 in which A is 1.5 times as high. The decrease in rigidity of PABI as compared to that of poly-p-phenylene terephthalamide () is in reasonable agreement with the presence of imidazole rings in PABI molecules. The presence of these rings results in kinks in the PABI chain with angles of about 30° and hence, in the depature from parallelism of rotating bonds. 相似文献
4.
Joaquín García Juan Bartolomé Domingo González Rafael Navarro Daniel Fruchart 《The Journal of chemical thermodynamics》1983,15(12):1169-1180
The heat capacity of the solid solution Mn3.2Ga0.8N was measured between 5 to 330 K by adiabatic calorimetry. A sharp anomaly with first-order character was detected at TA = (160.5±0.5) K, corresponding to a magnetic rearrangement and a lattice expansion. No sharp anomaly was observed at Tc ≈ 260 K where the magnetic ordering takes place; instead, a smooth shoulder was detected. The thermodynamic functions at 298.15 K are , , , . At low temperatures the coefficient for the linear electronic contribution to the heat capacity was derived: γ = (0.031±0.003) J·K?2·mol?1. Moreover, the different contributions to the heat capacity were obtained and the electronic origin of the phase transitions was established. 相似文献
5.
The mutual solubilities of {xCH3CH2CH2CH2OH+(1-x)H2O} have been determined over the temperature range 302.95 to 397.75 K at pressures up to 2450 atm. An increase in temperature and pressure results in a contraction of the immiscibility region. The results obtained for the critical solution properties are: To(U.C.S.T.) = 397.85 K and xo = 0.110 at 1 atm; at p < 400 atm and at 800 atm < p < 2500 atm; . 相似文献
6.
The kinetics of the interaction of hexaaquochromium(III) ion with potassium octacyanomolybdate(IV) have been studied using conductance and spectrophotometric data. The mechanism of the reaction is discussed and the effect of H+ ion and the ionic strength on the rate of the reaction determined. The reaction is found to be pseudo-first order with respect to potassium octacyanomolybdate(IV) and inverse first order with [H3O+]. The rate of the reaction increases with increase in ionic strength and temperature. Activation parameters have been calculated using the Arrhenius equation and have the values ΔE* = 1.3 × 102 kJ mol?1, ΔH* = 129 kJ mol?1, ΔS* = ?315 e.u., ΔF* = 2.3 × 102 kJ and A = 1.5 × 10?3. The mechanism proposed is based on ion-pair formation and the rate equation obtained is given by: kobs= 相似文献
7.
8.
The standard enthalpy of formation of γ-UO3 has been critically assessed; the value ?(292.5 ± 0.2) kcalth mol?1 is suggested.The enthalpies of solution of β-UO3 and γ-UO3 in 3 M H2SO4 have been measured and used to derive: 相似文献
9.
It is well known that the apparent specific volume η2 of a polymer may be expressed by the following relationship: where M?n is the number-average molecular weight of the polymer, ηm the specific volume of the infinite polymer, and K a constant. We have shown that this relationship is valid for low molecular weight polystyrenes () with different end-groups, independently of the nature of the solvent. The K values (and variations with the solvent and with the nature of the end-groups) may be predicted through simple calculations proposed here. We conclude that ηm does not represent the specific volume of the infinite polymer, since we observe a rapid decrease of η2 for increasing M (when ). The decrease is much greater than expected from the relationship . 相似文献
10.
《The Journal of chemical thermodynamics》2002,34(12):2083-2092
11.
Joaquín García Juan Bartolomé Domingo González Rafael Navarro Willem Jacobus Crama 《The Journal of chemical thermodynamics》1983,15(12):1109-1126
We present the heat capacities measured by adiabatic calorimetry from 6 to 350 K, and by differential scanning calorimetry from 300 to 500 K, of CsCrCl3 and RbCrCl3. A first-order transition at Tc = (171.1±0.1) K was detected for CsCrCl3. The RbCrCl3 showed at Tc = (193.3±0.1) K a transition with thermal hysteresis at temperatures just below the maximum. At T1 = (440±10) K a continuous transition was also detected. Furthermore, at TN ≈ 16 K, and for both compounds, a small bump due to magnetic long-range ordering was observed. The thermodynamic functions at 298.15 K are
CsCrCl3 | 15.38 | 26.49 | 3503.2 | 14.735 |
RbCrCl3 | 15.76 | 25.99 | 3556.8 | 14.384 |
CrO42?(aq) | (13.8 ± 0.5) | ?(210.93 ± 0.45) | ?(174.8 ± 0.5) |
HCrO4?(aq) | (46.6 ± 1.8) | ?(210.0 ± 0.7) | ?(183.7 ± 0.5) |
Cr2O72?(aq) | (67.4 ± 3.9) | ?(356.5 ± 1.5) | ?(312.8 ± 1.0) |
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