首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
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 Mn 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 Mw × 10?4 = 125.0 to 4.8. 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
[ν] = 27.54 × 10?10 × M0.50w (o-chlorophenol, 60.0°C
[ν] = 30.24 × 10?10 × M0.50w (p-chloro-mcresol, 112.9°C
The characteristic ratio C = 〈R20/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 CC 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.
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 A0 = 3.55 · 10?10erg deg?1mol?13. The equilibrium rigidity of PABI molecules was characterized by the length of the Kuhn segment A = 250 ± 100 A?. The chain diameter was 7 ± 4 A?. 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 (A = 400 ± 100 A?) 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.
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 Cp,mR = 15.16, SmoR = 18.57, {Hmo(T)?Hmo(0)}R = 2896 K, ?{Gmo(T)?Hmo(0)}RT = 8.85. 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; (dTodp) = ?(12.0±0.5)×10?3K atm?1 at p < 400 atm and (dTodp) = ?(7.0±0.7)×10?3K atm?1 at 800 atm < p < 2500 atm; (dxodT) = ?(4.0±0.5)×10?4K?1.  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=[kKE[H3O+]+k′K′kEkh][Mo(CN)84?][H3O+]+kh+[KE[H3O+]+K′Ekh][Mo(CN)84?]  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:
ΔHf°(β?UO3, 298.15 K) = ?(291.6 ± 0.2) kcalth mol?
  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: η2= ηm + K/Mn 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 (Mn < 4·104) 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 Mn < 4·104). The decrease is much greater than expected from the relationship η2 = ? (1/M).  相似文献   

10.
11.
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
  相似文献   

12.
The incongruent vaporization reactions of Ta2S and Ta6S have been investigated by mass-loss effusion in the temperature range 1576 to 1902 K. By extrapolation of PS(obs) to equilibrium the enthalpies of the reactions 32Ta2S(s) = 12Ta6S(s) + S(g) and Ta6S = 6 Ta(s) + S(g) were found to be ΔH0298R = 53.0(0.3) · 103K and ΔH0298R = 58.1(0.4) · 103K, respectively. Comparison between the above values, determined by a 2nd law treatment, and 3rd law values was used to derive fef (“free energy function”) values for Ta and S in the compounds. These postulated fef's, which apply only to the elements as present in the compounds measured, are compared to tabulated quantities for the pure solid elements to provide a criterion for 2nd and 3rd law evaluation.  相似文献   

13.
Paramagnetic resonance and magnetic measurements were performed on powdered samples of GdGa2. The magnetic data indicated ferrimagnetic behavior with Tc ? 181° K. Above 250° K the susceptibility obeys the Curie-Weiss law χg = 2.662 × 10?2(T ? 27.6)emu/g-Oe which corresponds to an effective moment of 7.95 Bohr magnetons. Over the range from 190 to 300°K the data obey a Néel type law, χg?1 = 35.95 (T ? 12.5) ? 2.20 × 104(T ? 177), which is indicative of ferrimagnetic order. The resonance measurements were performed at 9.013 gHz at 247, 296, and 349°K. The spectra were analyzed with a computerized curve-fitting technique that involves a linear combination of Lorentzian absorption and dispersion susceptibility components. Following demagnetization corrections, the g-factor was found to be 1.9832 while the half-power, half-linewidth was 592.7 Oersteds.  相似文献   

14.
Reactions between MX(PPh3)2(η-C5H5) (M = Ru, X = Cl; M = Os, X = Br) and 2-CH2CHC6H4PPh2 afford MX(η2-CH2CHC6H4PPh2)(η-C5H5); the Os complex is obtained in two isomeric forms. The X-ray structure of the major isomer shows the CC double bond (OsC, 2.214, 2.195 Å; CC, 1.57 Å) is almost coplanar with the OsBr vector, with the terminal C cis to Br; the minor isomer is assumed to have the alternative, more sterically congested conformation, with the β-C cis to Br. The chlororuthenium complex reacts with NaOMe/MeOH to give the corresponding hydrido complex, which also exists as two isomers in solution; reaction of this complex with CS2 gives the expected dithio acid derivative Ru(S2CCHMeC6H4PPh2)(η-C5H5), together with small amounts of a complex assumed to be Ru[S2C(CH2)2C6H4PPh2](η-C5H5). The X-ray structure of the major product reveals an unusual η3-S2C mode of coordination of the dithio acid fragment (RuS, 2.418, 2.426(1) Å; RuC 2.175(4) Å). Crystals of OsBr(η2-CH2CHC6H4P)Ph2)( η-C5H5) are monoclinic, space group P21/n, with a 12.696(2), b 21.719(6), c 15.929(3) Å, β 79.77(2)°, Z = 8; 2867 data (I > 2.5σ(I)) were refined to R = 0.040, Rw = 0.044. Crystals of Ru(η3-S2CCHMeC6H4PPh2)(η-C5H5) are orthorhombic, space group Pbca, with a 8.921(2), b 15.982(9), c 32.216(5) Å, Z = 8; 1685 data (I > 2.5σ(I)) were refined to R = 0.027, Rw = 0.030.  相似文献   

15.
The theta temperature for the system poly(o-chlorostyrene)-methyl ethyl ketone has been determined as 24·5°. The samples used in the determination were prepared by radical polymerization. The dependence of intrinsic viscosity on molecular weight has been measured in methyl ethyl ketone at 24·5° and found to be ηθ = 4·68 × 10?4MwM12. The ratio 〈s=2〉/M was found, by light scattering, to be 5·60 × 10?18 cm2. Analysis of the solution properties indicates that the Kurata-Yamakawa theory is valid in the vicinity of the Flory temperature (UCST).  相似文献   

16.
Photon-correlation spectroscopy has been used to measure the diffusion coefficient D and first-mode intramolecular relaxation time τ1 of polystyrene in a theta solvent, cyclohexane at 34.5°C. Measurements were made on five narrow fractions (Mw = 2.88 × 106 to 9.35 × 106) as a function of concentration c, in the dilute regime. D varied linearly with c, D = Do (I + kDc), with Do = (1.4 ± 0.2) × 10?4Mw?(0.508±0.007) cm2 s?1. Although the values obtained for τ1 were reproducible to within 5%, no systematic variation with c was detected. The results are fitted by the relation τ1 = (7.7 ? 0.3) × 10?8Mw(1.42±0.05) μs, which agrees well with the theoretical expression of Zimm for the non-draining bead-and-spring model, modified for the light-scattering case.  相似文献   

17.
18.
In order to elucidate the defect structure of the perovskite-type oxide solid solution La1?xSrxFeO3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, PO2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of PO2 ≥ 0.13 atm, δ in La1?xSrxFeO3?δ was found to be close to 0. With decreasing log PO2, δ increased and asymptotically reached x2. The log(PO2atm) value corresponding to δ = x2 was about ?10 at 1000°C. With further decrease in log PO2, δ slightly increased. For LaFeO3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log PO2 is interpreted on the basis of the defect equilibrium among Sr′La (or V?La for the case of LaFeO3?δ), V··O, Fe′Fe, and Fe·Fe. Calculations were made for the equilibrium constants Kox of the reaction
12O2(g) + V··o + 2FexFe = Oxo + 2Fe·Fe
and Ki for the reaction
2FexFe = FeFe + Fe·Fe·
Using these constants, the defect concentrations were calculated as functions of PO2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements.  相似文献   

19.
Treatment of [{Ir(COD)(μ-Cl)}2] with excess of the electron-rich olefin [CN(Ar)(CH2)2NAr]2 (abbreviated as (LAr)2, Ar = C6H4Me-p or C6H4OMe-p) affords the ortho-metallated tricycle [Ir(LAr)3], which for Ar = C6H4Me-p (Ia) with HCL yields [Ir(LAr)2(LAr)]Cl (IV); X-ray data show that in IV there is an unexpectedly close Ir?C(o-aryl) contact (2;52(1) Å) involving the “free” LAr which compares with an IrC(o-aryl) distance of 2.09(3) Å in Ia or 2.07(3) Å in the ortho-metallated LAr ligand of complex IV.  相似文献   

20.
Calorimetric measurements of the enthalpy of solution of cesium chromate gave ΔHsoln = (7622 ± 24) calth mol?1 for a dilution of Cs2CrO4·21128H2O. This result, along with the enthalpy of dilution gave the standard enthalpy of solution, ΔHsolno = (7512 ± 31) calth mol?1, whence the standard enthalpy of formation, ΔHf0(Cs2CrO4, c, 298.15 K), was calculated to be ?(341.78 ± 0.46) kcalth mol?1. Recomputed thermodynamic data for the formation of the other alkali metal chromates have been tabulated. From their solubilities and enthalpies of solution, the standard entropies, S0(298 K), of BaCrO4 and PbCrO4 were estimated to be (38.9 ± 0.9) and (43.7 ± 1.2) calth K?1 mol?1, respectively. There is evidence that ΔHf0(SrCrO4, c, 298.15 K) may be in error. Thermochemical, solubility, and equilibrium data, have been combined to update the thermodynamic properties of the aqueous chromate (CrO42?), bichromate (HCrO4?), and dichromate (Cr2O72?) ions. The new values at 298.15 K are as follows:
Cp,mRSmoR{Hmo(T)?Hmo(0)}RK?{Gmo(T)?Hmo(0}RT
CsCrCl315.3826.493503.214.735
RbCrCl315.7625.993556.814.384
  相似文献   

S0/calth K?1 mol?1ΔHf0/kcalth mol?1ΔGf0/kcalth mol?1
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)
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号