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1.
Dissociation equilibria of lithiumthiocyanate (LiSCN) in N,N-dimethylformamide (DMF) solutions of poly (propylene oxide) (PPO) were investigated by using infrared spectroscopy. The stretching bands due to the thiocyanate ions SCN?1 and the LiSCN ion pair were found at 2058 and 2072 cm?1, respectively. At high LiSCN concentration C of ca. 20 wt %, another weak band due to the dimer (LiSCN)2 was observed. From the ratio of the areas of the absorption bands, the dissociation constant K1 for the equilibrium LiSCN ? Li+ + SCN?1 and that K2 for (LiSCN)2 ? 2LiSCN have been determined. With increasing DMF content, K1 increases from 1 × 10?4 for bulk PPO to 4.8 × 10?1 for pure DMF at 299 K. Log K1 is not linear against inverse of the dielectric constant ? of the medium and decreases with increasing temperature. The enthalpy (ΔH) and entropy (ΔS) changes for the dissociation of LiSCN are both negative. ©1995 John Wiley & Sons, Inc.  相似文献   

2.
Volume flow of poly(methyl methacrylate) (PMMA) (M?n = 43,000 and Tg = 384) has been measured in an Instron Capillary Rheometer. Elastic modulus of the longitudinal wave, longitudinal volume viscosity, initial longitudinal volume viscosity, and retardation times are described at temperatures above Tg (418–483K) and compression rates of about 1.00–200.00 × 105 s?1. An initial increase followed by a decrease in longitudinal volume viscosity has been observed as the compression rate increases and the volume deformation decreases, this last behavior being at the lowest values of the compression rate (6.0 and 30.0 × 10?5 s?1) a typical nonequilibrium one. ηL also increases with increasing temperature (Tg decreases 0.18°C/MPa), and volume flow activation energy decreases as the volume deformation increases.  相似文献   

3.
Three reactive epoxy–amine systems based on diglycidyl ether of bisphenol A (DGEBA) with 4,4′-diaminodiphenylsulfone (DDS), 4,4′-methylenebis [3-chloro 2,6-diethylaniline] (MCDEA), and 4,4′-methylenebis [2,6-diethylaniline] (MDEA), were studied during isothermal curings at 140 and 160°C. The simultaneous kinetic and dielectric studies allow to express conductivity, σ, in terms of conversion, x, and of glass transition temperature, Tg. The conductivity, σ0, of the initial monomer mixture and, σ of the fully cured network are measured. It is found that:
  • The glass transition temperature, Tg, versus conversion, x, curves follows the equation of Di Benedetto modified by Pascault and Williams
  • There exists a linear relation between log σ/log σ0 and Tg.
So, it is possible to predict both kinetic and dielectric behaviors of these epoxy-amine systems by the knowledge of Tg0, ΔCp0, and σ0, respectively, glass transition temperature, heat capacity, and conductivity of initial monomer mixture, Tg and ΔCp, and σ, respectively, glass transition temperature and heat capacity and conductivity of fully cured network. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2911–2921, 1998  相似文献   

4.
Change in the glass transition temperature, Tg, of poly(2,6-dimethyl phenylene oxide), PPO, due to the dissolved CO2 has been measured as a function of the gas pressure, p, using a high-pressure DSC cell. At 61.2 atm, the highest pressure studied, Tg is depressed by 31.6°C. The depression in Tg is found to be linear with pressure, with dTg/dp of ?0.5°C atm?1. The experimental results are in fair agreement with those calculated from a quasilattice solid-solution model for polymer-diluent systems. The present results, however, differ markedly from a recent investigation on PPO-CO2 system which reported a depression in Tg of 226°C at 60 atm and a dTg/dp of ?3.8°C atm?. © 1994 John Wiley & Sons, Inc.  相似文献   

5.
A formal definition of TLL as a function of M?n for polystyrene was prepared with literature TLL values from torsional braid analysis (TBA), differential scanning calorimetry (DSC), and zero-shear melt viscosity η0. Data from six authors using anionically prepared PS and blends thereof were involved. The resultant linear least-squares regression line, TLL(°C) = 148.5 ? 11.487 × 104M? [standard error in TLL (calculated) 4.056 K, correlation coefficient R2 = 0.9534] is considered valid from M?n = 2000 to the entanglement molecular weight Mc = 35,000. The “best” TLL values reported by Orbon and Plazek from double Arrhenius plots are well below this line for M?v = 47,000, 16,400, 3400, and above it for M?v = 1100. These best TLL values are artifacts arising from no or insufficient data points above or below TLL and/or too many data points near Tg. The associated high enthalpies of activation which they report confirm this diagnosis. The fact that these artificial TLL values tend to disappear when checked by the three-parameter Vogel equation, logη = logA + B exp[(T ? T)?1], has no relevance to the controversy concerning the existence and meaning of TLL. The claim by Orbon and Plazek that TLL values obtained by TBA, DSC, and melt viscosity are all artifacts of the individual methods by which they were obtained is inconsistent with the excellent master plot which they generate. Alternative plotting devices which reveal TLL > Tg from η0 vs. T?1 data, as developed by van Krevelen and Hoftyzer and by Utracki and Simha (not previously considered by either party), are reviewed. A statistical examination of the nature of the Vogel–Fulcher–Tammann–Hesse equation, based on synthetic data, is presented. Evidence for TLL in atactic polypropylene is offered based on published data by Plazek and Plazek. TLL is considered to possess both relaxational and quasiequilibrium attributes, just as Tg does.  相似文献   

6.
Abstract— The present study attempts to correlate the phosphorescence life time τp at 77°K of a definite solute: tetramethylparaphenylenediamine (TMPD) with various solvents viscosity and polarity. A few experiments with benzene in the same solvents are also reported. The following results have been obtained:
  • 1 The measured τp vary regularly with the sample immersion time in liquid N2, reaching a constant value after a few hours. This effect is related to the glass matrix relaxation. The rate constant Kisc (S, 1T1) is also found to vary during relaxation of the solvent.
  • 2 In the expression giving the nonradiative rate constant Knr (T1S0), the bimolecular quenching term appears negligible for high viscosity matrices i.e. for η= 109 poises for benzene and for TMPD. Knr is found to vary linearly with log η, as well as the intersystem crossing S1T1 rate constant Kisc.
  • 3 Both Knr (T1S0) and Kisc (S1T1), increase with decreasing polarity of the solvent.
  • 4 From our own observations and literature data[6] for C6H6 it appears that solvent viscosity does not contribute appreciably to the observed temperature effect on the solute τp when only a monomolecular triplet deactivation is operative.
  相似文献   

7.
A new method of preparation of segmented copolymer amide-ester type is described here starting from two oligomers, one hard crystallizable (A) having a glass transition temperature (Tg) above room temperature and the other soft, amorphous (B) having Tg well below room temperature. A, an oligo amide-ester terminated with hydroxyl groups has been synthesized from bis(hydroxy acylo amide) alkane, a reaction product of a lactone and diamine and dicarboxylic acid. B, an oligoester hydroxyl terminated was synthesized by the conventional method. The two oligomers A and B were transesterified removing diol as by-product to obtain segmented (amide-ester)-ester copolymer. The polymer showed mostly two Tgs one at ?40 to ?50°C and other at +40 to +50°C; and one melting temperature 200°C. Maxm inherent viscosity was recorded at 1.75 dL/gm. © 1993 John Wiley & Sons, Inc.  相似文献   

8.
Polarization modulation infrared linear dichroism has been used to study the molecular orientation and relaxation of polystyrene/poly(2,6‐dimethyl 1,4‐phenylene oxide) (PS/PPO) miscible blends, containing up to 20% PPO, during and after a rapid uniaxial deformation above Tg. In general, it is found that both the PS and PPO chain orientation functions increase with stretching rate and PPO content, and decrease with temperature. For all blends investigated, between Tg + 5 and Tg + 13 °C, the relaxation occurs at the same rate for PS and PPO and, therefore, the relaxation times calculated are similar indicating, under those conditions, a strong relaxation coupling between the two polymers at both short and long times. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1405–1415, 2000  相似文献   

9.
The X(X) values1 of the halogens (which resemble the Pauling electronegativities) and of some oxa substituents can be interpreted in terms of the inductive and resonance parameters σI and σoR according to the regression equation
and η*R=η(X)?η(R) it is found that for some substituted methyl, phenyl and benzoyl groups [σ*]XR=αηXR where α equals ?10.6 and ?10.9 for R = Me and R = Ph, CHO and PhCO respectively. Thus [σ*]XRand ηxr represent Taft σ* and [σI(X)?σoR(X)] values relative to that of the parent R group. The hydroxyl frequencies of phenol, and benzoic, acrylic, acetic and formic acids measured in dilute carbon tetrachloride solutions correlate with σI(X) and σoR(X) according to the equations v(OH) = ?423.0 σI(X) + 3654.7 v(OH) = ?270.0 σ0R(X) + 3586.7 where X = Ph, PhCO, CH2=CHCO, MeCO and HCO. From these results, it is inferred that the σ* values of substituents having an α sp2 hybridized carbon atom are proportional to σ0R according to the equation σ*(X) = 3.97 σ0R(X) + 1 New σI σoR and σ* values of some acyi, benzoyl and substituted phenyl groups are presented.  相似文献   

10.
The effect of various diallyl (diallyl ortho phthalate, diallyl terephthalate and diethylene glycol diallyl carbonate) and triallyl monomers (triallyl cyanurate and triallyl isocyanurate) on the processability of polyphenylene oxide (PPO) was studied. The solubility parameters of the monomers indicated that diallyl orthophalate, dially terephthalate and triallyl cyanurate should be miscible with PPO suggesting their applicability as reactive plasticizers to improve the processability of PPO. Rheological studies of 60:40 wt:wt PPO:allylic blends indicate that the addition of 40 wt% of allylic monomers significantly improved processability – blends of 60PPO:40DEGDAC indicates the highest viscosity and the highest Tg. Rheological studies and dynamic mechanical analysis on various PPO/DAOP blends show that the increasing amounts of DAOP progressively decreases the viscosity and Tg of the blends. Phase separation at room temperature was observed by visual opacity, cloud point studies and DMTA in PPO:DAOP blends with less than 60 wt% PPO but at elevated temperatures the blends were miscible.  相似文献   

11.
The melt viscosity, the glass transition, and the effect of pressure on these are analyzed for polystyrene on the basis of the Tammann-Hesse viscosity equation: log η = log A + B/(T ? T0). Evidence that the glass transition is an isoviscosity state (log ηg ? 13) for lower molecular weight fractions (M < Mc) is reviewed. For a polystyrene fraction of intermediate molecular weight (M ? 19,000; tg = 89°C.), it is shown that B is independent of the pvT state of the polymer liquid and that dT0/dP = dTg/dP. This is consistent with the postulate that B is determined by the internal barriers to rotation in the isolated polymer chain. Relationships are derived for flow “activation energies” at constant pressure and at constant volume, and for the “activation volume.” Values for polystyrene along the zero-pressure isobar and along the constant viscosity, glasstransition line are reported. For the latter, ΔVg* is constant and corresponds to about 10 styrene units. The “free volume” viscosity equation: log η = log A + b/2.3?, is reexamined. For polystyrene and polyisobutylene, ?g/b = 0.03, but ?g and b themselves differ appreciably in these polymers. The parameter b is the product of an equilibrium term Δα and the kinetic term B, and none of these is a “universal” constant for different polymers. The physical significance of the free volume parameter ?, particularly with regard to the “excess” liquid volume, remains undefined. Two new relationships for dTg/dP, one an exact derivation and the other an empirical correlation, are presented.  相似文献   

12.
Friction was measured and analyzed for rubber belts sliding against paper and polymer film surfaces of different roughness. As expected, increased paper smoothness created an increase in the friction coefficient. However, it was found that continuous rubber usage during testing also created an increase in friction coefficient for constant surface roughness of both paper and film. This was analyzed as due to an increase in N and C values for the load-dependent friction coefficient, μ = CW?N where W is normal load and Nmax ≈ 0.33 (papers) or Nmax ≈ 0.6 (polymer films). Using adhesion friction theory, it was shown that friction data can be fitted with a unified equation: C = μ0c?N, where μ0 = μ N = 0 and c is a constant for the rubber and belt configuration tested.  相似文献   

13.
The chemical shifts of aromatic nitriles of the general structure para-Y? C6H4? X? CN with X = O, S, Se and N(CH3) have been investigated by the 13C NMR technique. For cyanates (X = O) the 14N shifts and for Y = F the 19F shifts were likewise measured. The chemical shifts and the corresponding 13C shift increments Δn have been found to correlate with the appropriate substituent constants σR0, σp0 and σI, as well as with the π-electron densities calculated in the PPP approximation.  相似文献   

14.
The optimization of three-dimensional (3D) MXene-based electrodes with desired electrochemical performances is highly demanded. Here, a precursor-guided strategy is reported for fabricating the 3D SnS/MXene architecture with tiny SnS nanocrystals (≈5 nm in size) covalently decorated on the wrinkled Ti3C2Tx nanosheets through Ti−S bonds (denoted as SnS/Ti3C2Tx-O). The formation of Ti−S bonds between SnS and Ti3C2Tx was confirmed by extended X-ray absorption fine structure (EXAFS). Rather than bulky SnS plates decorated on Ti3C2Tx (SnS/Ti3C2Tx-H) by one-step hydrothermal sulfidation followed by post annealing, this SnS/Ti3C2Tx-O presents size-dependent structural and dynamic properties. The as-formed 3D hierarchical structure can provide short ion-diffusion pathways and electron transport distances because of the more accessible surface sites. In addition, benefiting from the tiny SnS nanocrystals that can effectively improve Na+ diffusion and suppress structural variation upon charge/discharge processes, the as-obtained SnS/Ti3C2Tx-O can generate pseudocapacitance-dominated storage behavior enabled by engineered surface reactions. As predicted, this electrode exhibits an enhanced Na storage capacity of 565 mAh g−1 at 0.1 A g−1 after 75 cycles, outperforming SnS/Ti3C2Tx-H (336 mAh g−1), SnS (212 mAh g−1), and Ti3C2Tx (104 mAh g−1) electrodes.  相似文献   

15.
The viscoelastic (VE) response of freeze-dried blends of polystyrene (PS) and poly-(2,6-dimethyl phenylene oxide) (PPO) has been studied as a function of composition, frequency, and temperature to examine the degree of rheological compatibility. When blended together, the relaxation processes of both molecular species exhibit the same temperature dependence. However, the temperature dependence of the VE response is a function of composition. It is shown that this behavior can be predicted from the measured glass transition temperatures by assuming the additivity of the free volumes of the components. The properties of the blends are compared at equal free volumes. The effective segmental friction factor is found to be independent of composition while the modulus of the rubbery plateau increases with PPO concentration. This result is interpreted as a change in the entanglement molecular weight Me of the blends. When the changes in Me are considered, the relationship between the zero-shear viscosity η0 and the 3.4 power of the weight-average molecular weight, commonly found for high molecular weight homopolymers, predicts the compositional dependence of η0 for the PPO–PS blends. It is concluded that the PPO–PS system forms a rheologically compatible blend.  相似文献   

16.
The effect of radiation on the breaking of secondary bonding in protein was studied by measuring the viscosity change at different radiation doses and urea concentrations. An experimental equation for the viscosity change was obtained, and the observed behavior was explained on the basis of the molecular mechanism. The general equation for the viscosity change is given by ηred = A(X ? Be?kx) + C log R, where ηred is the reduced viscosity of the solution, R is the dose of γ-radiation, X is the concentration of urea, and A, B, C, and k are adjustable constants.  相似文献   

17.
The surface glass transition temperature (T g surface) of the bulk samples of miscible blends formed of amorphous polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been characterised in terms of an adhesion approach we proposed recently. T g surface has been measured as the temperature transition “occurrence of autoadhesion–nonoccurrence of autoadhesion” by employing a lap-shear joint mechanical testing method. The effect of the reduction in T g surface with respect to the glass transition temperature of the bulk (T g bulk), which had been observed earlier in pure homopolymers, has been found to exist in the blends of PS with PPO as well. The values of this effect for the blends have been compared with those for pure homopolymers, and the differences found have been discussed.  相似文献   

18.
为探索一种高性能的锂离子电池负极材料,采用酸刻蚀法制备了高导电性、高稳定性的二维层状Ti3C2Tx,通过溶剂热法制备了具有高理论比容量的花瓣状VS2纳米片,再经过简单的液相混合得到了二维层状Ti3C2Tx-MXene@VS2复合物。通过扫描电子显微镜、透射电子显微镜、X射线光电子能谱、X射线衍射和能谱分析对复合材料的形貌和结构进行了表征,采用循环伏安、恒流充放电、长循环和交流阻抗谱对复合材料的电化学性能进行了研究。结果表明:VS2纳米片均匀地分布在Ti3C2Tx的层间及表面,该复合物具有高的可逆容量(电流密度为0.1A·g-1时,比容量为610.5mAh·g-1)、良好的倍率性能(电流密度为2A·g-1时,比容量为197.1mAh·g-1)和良好的循环稳定性(电流密度为0.2 A·g-1时,循环600圈后比容量为874.9 mAh·g-1;电流密度为2 A·g-1时,循环1 500圈后比容量为115.9mAh·g-1)。  相似文献   

19.
The 13C NMR spectra of MM′(CO)6(DAB) complexes (M = M′ = Fe, Ru; M = Mn, Re and M′ = Co; DAB = 1,4-diazabutadiene) show very characteristic features which are directly related with the bonding mode of the DAB ligand to the binuclear metal carbonyl fragment. In these complexes the DAB ligand is σ2-N, μ2-N′, η2-C=N or σ2-N, σ2-N′, η2-C=N coordinated. Chemical shifts of about 175 ppm are observed for the σ-coordinated imine fragments and about 60 or 80 ppm for the η2-C=N coordinated imine fragments.In MnCo(CO)6[diacetylbis(cyclopropylimine)] the DAB ligand is fluxional, and the changes in the spectra when recorded at various temperatures can be interpreted in terms of an exchange between the σ- and π-coordinated part of the DAB ligand.The homodinuclear M2(CO)6(DAB) complexes (M = Fe or Ru) contain M(CO)3 fragments on which the carbonyl groups are involved in a local scrambling process with very different activation parameters (Tc = ?50°C and +85°C).MCo(CO)6(DAB) complexes (M = Mn, Re), which contain a semi-bridging carbonyl group according to the crystal structure, show rapid interchange of this carbonyl group with the terminal carbonyl groups on cobalt. The electronic balance is kept in equilibrium by an internal compensation within the DAB ligand.  相似文献   

20.
Alkylation of K[η5-C9H7Cr(CO)3] (Xa) with CH3I and C6H5CH2Br leads to σ-alkyl derivatives of η5-C9H7Cr(CO)3Alk type. These complexes undergo innersphere “ricochet” rearrangement, with the alkyl group being shifted to the endo position at C(1) and the chromium tricarbonyl group shifted to the benzene nucleus. The structure of the product of such a rearrangement in the case of η5-C9H7(CO)3CrCH2C6H5, i.e. (1-benzyl-3a,4-7,7a-η6-indene)chromium tricarbonyl (XVIII), is established by a low temperature X-ray study, indicating an endo position for the benzyl radical.On alkylation of equilibrium tautomeric mixtures of η5- and η6-fluorenylchromium tricarbonyl anions XIa ? XIb under similar conditions, the η5-anion (Xa) yields a σ-alkyl derivative, which is rearranged to (9-endo-alkyl-1-4,4a,9a-η6-fluorene)chromium tricarbonyl. Electrophilic attack of the η6-anion (XIb) takes place on the outer side at C(9) and leads to a corresponding 9-exo-alkyl derivative.  相似文献   

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