Nouvelles données sur les composés graphite VOF3

A new method of synthesizing graphite-VOF₃ is presented. The action of VOF₃-saturated anhydrous hydrogen fluoride on HOPG gives, after several weeks, a compound C₄₀ VOF₃. A radiocrystallographic analysis was carried out. The 001 reflexions shown on Fig. 1 allow determining the identity period $\text{I}{}_{\mathrm{c}}\text{= 18.07}\text{A}\text{?}$. This value is confirmed by the macroscopic dilation of the samples.If the positions of atoms in the intercalated molecules is the same as that shown in Fig. 2, the structure factor can be calculated and the values obtained are in good agreement with the experimental values. The hk0 reflexions indicated on Fig. 3 show the 100 and 110 graphite reflexions as well as others: the narrowness of these latter ones proves the existence of a certain organization of the intercalant between the carbon layers.A study using the double rotation technique of some hk0 reflexions is represented on Fig. 4; it allows indexing in a hexagonal cell of parameter $\text{a = 15.53}\text{A}\text{?}$ and for which the a axis makes an angle of 30° with that of the graphite. Furthermore a study of intensities of graphitic hk 1 reflexions confirmed that the c axis parameter is equal to the identity period given above. The rotating crystal photograph of Fig. 5 shows that VOF₃ molecules are organized without correlation between layers.     

Insertion de lanthanoides dans le graphite

The intercalation of lanthanides is possible by two different ways: direct action of the metal vapor in metallic tubes sealed under vacuum or by heating compressed mixture of powders of the metal and of graphite.The first method was used only for the most volatile metals: samarium, europium, thulium and ytterbium (see Table 1). The 00 l reflexions of the corresponding first stage graphitides MC₆ (M = Sm, Eu, Tm or Yb) were obtained for samples prepared from pyrolytic graphite HOPG (Tables 2 and 3, Fig. 1).Using the second method, we determined the identity period along the c axis (I_c) for the most fusible lanthanides graphitides (Table 4).We did a study of the evolution vs temperature of a compressed mixture of initial composition Yb + 6C (Fig. 2).A structural study was carried out on single crystals of europium and ytterbium graphitides, using a special method developed in the laboratory.Figure 3 shows the three possible types of sites available to the metal atoms and the different stacking modes of the metallic layers.The hkO and hkl reflexions of the graphitide YbC₆ (see Table 5) shown in Fig. 5 allow to choose between the three possible unit cells of Fig. 4. The hexagonal unit cells of EuC₆ and YbC₆ belong to the space group P6₃/mmc with two of three sites occupied regularly by the metal atoms. The two metal atoms are in position b and the twelve carbon atoms in i. The parameters are respectively $\text{a = 4.314 ± 0.003}\text{A}\text{?}$, $\text{c = 9.745 ± 0.008}\text{A}\text{?}\text{(EuC}{}_6\text{)}$ and $\text{a = 4.320 ± 0.004}\text{A}\text{?}$, $\text{c = 9.147 ± 0.004}\text{A}\text{?}\text{(YbC}{}_6\text{)}$.     

The structure of vitreous carbon from wide angle and low angle x-ray diffraction

Both wide angle and low angle X-ray diffraction patterns have been measured for a sample of vitreous carbon which has been subjected to a maximum heat-treatment of 1800°C. The wide angle scattering was used to calculate a radial distribution function, which showed that the basic atomic arrangement was that of hexagonal graphite like sheets with no graphitic registration between the sheets. The low angle scattering pattern was interpreted in terms of a theory due to Debye, and an exponential correlation function was found to be a reasonable approximation for representing the electron density fluctuations giving rise to this scattering. The electron density fluctuations originate from pores in the matrix with a mean chord intercept length of ? 8 Å. The mean chord intercept for the matrix is ? 16 Å in reasonable agreement with “crystallite sizes” $\text{L}{}_{\mathrm{c}}\text{? 15}\text{A}\text{?}$ and $\text{L}{}_{\mathrm{a}}\text{? 22}\text{A}\text{?}$, calculated from the Scherrer equation. L_c should be interpreted as a distance between pores, and L_a as a defect distance in the matrix rather than indicating sharp crystallite boundaries.     

Experiments on the small-strain behaviour of crosslinked natural rubber: 1. Torsion

The torsional behaviour of 1, 3 and 5 phr peroxide crosslinked natural rubber has been characterized over a range of strains from near the undistorted state (γ ≈ 0.017) to γ ≈ 1.0. Isochronal measurements of both torque and normal force were used to calculate values of the derivatives of the strain energy function W with respect to the first and second stretch invariants I₁ and I₂. In the course of our work we found that, contrary to many reports in the literature, $\text{?W}\text{?I}{}_1$ was affected significantly by the amount of crosslinking. Finally for the 1 phr peroxide crosslinked rubber it was found that, while ageing for 14 months at ambient conditions did not significantly affect the small-strain torsional modulus, $\text{G = 2(}\text{?W}\text{?I}{}_1\text{+}\text{?W}\text{?I}{}_2\text{)}$, it did significantly affect the individual derivatives $\text{?W}\text{?I}{}_1$ and $\text{?W}\text{?I}{}_2$.     

X-ray studies of structural ordering changes on annealing a non-crystalline polycarbonate

Structural ordering changes of a non-crystalline polycarbonate (trade name ‘Bistan AW’) were investigated. Three interference halo signals were recorded on the X-ray diffraction patterns at reflection angles equal to $\text{θ}{}_1\text{= 3.1° (d = 14.3}\text{A}\text{?}\text{)}$, $\text{θ}{}_2\text{= 8.5° (d = 5.2}\text{A}\text{?}\text{)}$, and $\text{θ}{}_3\text{= 12.7° (d = 3.5}\text{A}\text{?}\text{)}$. The areas of peaks at θ₁ were found to decrease and those at θ₂ to increase with increasing the time of annealing the previously melted polycarbonate samples at a temperature of 190°C. It was concluded that morphological changes were taking place in the polycarbonate prior to its thermal crystallization. These changes may be explained by assuming the existence of two morphological forms of structural ordering in non-crystalline polycarbonate macromolecules. On annealing, macromolecules belonging to the cis-form having a lower degree of structural ordering most probably tend to straighten out and assume a zigzag structure, i.e. all-trans conformation. After straightening out of the chains, these macromolecules link up with areas exhibiting a much higher degree of structural ordering and most probably exist in the trans-form.     

Raman scattering from mixtures of poly(ethylene oxide) 2000 with poly(ethylene oxide) 200

The longitudinal acoustic mode fundamental (v₁) and third harmonic (v₃) in 2000 MW PEO with both hydroxy- and methody-end-groups have been observed in the Raman spectrum as a function of 200 MW PEO oligomer content. Measurements of small-angle X-ray spacing I_x permit interpretation using a composite rod model. A good fit to the measured quantities v₁I_x and $\text{v}{}_3\text{v}{}_1$ is obtained with crystal length I_c≈9 nm, crystal modulus $\text{E}{}_{\mathrm{<mtext>c</mtext>}}\text{= 9 ×}\text{10}{}^{10}\text{N}\text{m}{}^2$ and amorphous modulus $\text{E}{}_{\mathrm{a}}\text{= 1 ×}\text{10}{}^{10}\text{N}\text{m}{}^2$. The value of Ic implies a crystalline content of ～70% for the pure polymer; the value of Ec is larger than static determinations and similar discrepancies in other materials are discussed.     

Temperature dependence of birefringence and stress for natural rubber vulcanizates at strained state

The temperature dependence of stress and birefringence for natural rubber vulcanizates under medium and large deformation was measured for the processes of cooling, heating and re-cooling. In order to investigate the relation between the stress and crystal phase, the observed birefringence, Δt, was converted into the crystallinity, X_v, by the following equation:

$\text{X}{}_{\mathrm{<mtext>v</mtext>}}\text{=}\text{Δt?Δn}{}_{\mathrm{<mtext>a</mtext>}}\text{°f}{}_{\mathrm{<mtext>a</mtext>}}\text{Δn}{}_{\mathrm{<mtext>c</mtext>}}\text{°f}{}_{\mathrm{<mtext>c</mtext>}}\text{?Δn}{}_{\mathrm{<mtext>a</mtext>}}\text{°f}{}_{\mathrm{<mtext>a</mtext>}}$

where Δn⁰_c, Δn⁰_a, f_a and f_c are the intrinsic birefringence of the crystal, that of the amorphous phase, the orientation factor of crystallites, and that of amorphous phase, respectively. The fusion of crystallites induced by the thermal crystallization resulted in the increasing contractile force, while the fusion of strain-induced crystallites induced the reduction of contractile force.     

Comparison of the unperturbed dimension of polystyrene for endothermal and exothermal heats of dilution within the same system

Light scattering measurements for two samples of polystyrene (I, M_w = 2.15 × 10⁵; II, M_w = 2.5 × 10⁶) were performed in the iso-refractive mixed solvent dimethoxymethane-diethyl ether. For sample I the temperature dependence of the second osmotic virial coefficient A₂ was determined for three constant compositions of the mixed solvent. In the range ?30° to +25°C the three curves run practically parallel and exhibit a maximum at approximately ?10°C. For the volume fraction of 0.7 diethyl ether in the mixed solvent, an endothermal theta-temperature θ₊ was found at ?27.0° ± 1.5°C and θ_?, the exothermal theta-temperature, at ?5.0 ± 1°C. The investigation of sample II in the abovementioned solvent confirmed the observed θ_?-temperature and displayed a higher exothermicity compared with I. Similarly to the temperature variation of A₂, the chain dimensions of II, determined from the angular dependence of the scattered light, run through a maximum. The unperturbed dimensions in the mixed solvent are found to be: $\text{r}{}_{\mathrm{w}}\text{= 448 ± 5}\text{A}\text{?}$ at θ₊ = ?27°C and $\text{r}{}_{\mathrm{w}}\text{= 443 ± 5}\text{A}\text{?}$ at θ_? = ?5°C, as compared with $\text{r}{}_{\mathrm{w}}\text{= 420 ± 10}\text{A}\text{?}$ at θ₊ = +33°C in cyclohexene. The inter-relation of the chain expansion coefficient and A₂ is quantitatively described by the Zimm-Stockmayer-Fixman equation over the entire range of heats of dilution.     

The structure of α-keratin

High-resolution low-angle meridional and near-meridional X-ray diffraction data have been collected from specimens of α-keratin and various heavy-atom derivatives of α-keratin. The observed reciprocal spacings of the layer lines satisfy the selection rule

$\text{Z=m/h+n/P+s/P}{}_{\mathrm{d}}$

where $\text{h = 67.1}\text{A}\text{?}$, $\text{P = 220}\text{A}\text{?}$, $\text{P}{}_{\mathrm{d}}\text{= 235}\text{A}\text{?}$ and m, n and s are integers. Taken in conjunction with observations on the lateral distribution of intensity this evidence suggests that the microfibrils in α-keratin have a helical structure with $\text{pitch}\text{= 220}\text{A}\text{?}$ and unit $\text{height}\text{= 67.1}\text{A}\text{?}$ which is subject to a regular axial distortion of period 235Å. Possible relationships between this helix and the coiled-coil α-helix rope segments of the constituent molecules are discussed.     

Isothermal crystallization of poly(ethylene-terephthalate) of low molecular weight by differential scanning calorimetry: 1. Crystallization kinetics

The isothermal crystallization of poly(ethylene-terephthalate) (PETP) fractions, from the melt, was investigated using differential scanning calorimetry (d.s.c.). The molecular weight range of the fractions was from 5300–11750. Crystallization temperatures were from 498–513 K. The dependence of molecular weight and undercooling on several crystallization parameters has been observed. Either maxima or minima appear at a molecular weight of about 9000, depending on the crystallization temperature. The activation energy values point to the possibility of different mechanisms of crystallization according to the chain length. A folded chain process for the higher $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ chains and an extended chain mechanism for the lower $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ chains. The values of the Avrami equation exponent n vary from 2–4 depending on the crystallization temperature; non-integer values are indicative of heterogeneous nucleation. The rate constant K depends on T_c and $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$, showing maxima related to the T_c used. The plot of log K either vs. (ΔT)^?1 and (ΔT)^?2 or $\text{T}{}_{\mathrm{<mtext>m</mtext>}}\text{T(ΔT)}$ and $\text{T}{}^2{}_{\mathrm{<mtext>m</mtext>}}\text{T(ΔT)}{}^2$ is linear in every case.     

Interaction parameters in the n-undecane/butanone/poly(dimethyl siloxane) system

Intrinsic viscosities, [η], second virial coefficients, A₂, preferential solvation coefficients, λ, and binary interaction potential as measured by light scattering, g₁₂, for the system n-undecane(1)/butanone(2)/poly(dimethylsiloxane) (3) have been determined at 20.0°C. The system shows cosolvent character, as the inversion in λ and the maxima in A₂ and in [η], at $\text{ø}{}_{10}\text{?0.65}$, seem to indicate. (g₁₃ – sg₂₃) and the ternary interaction potential, g_T, and its derivatives on system composition, and , have been evaluated. Global interaction parameters, χ_m3, have also been evaluated and a critical analysis on the approximations usually followed for χ_m3 calculations is undertaken.     

Relationship between crystal structure and properties and irradiation behavior of reactor graphites

Nineteen graphites manufactured with a wide variety of raw materials and processes were characterized and correlations sought between structure and properties. The raw materials of the graphites ranged from highly isotropic cokes to anisotropic needle cokes and processing from conventional molding and extrusion to proprietary processes that produce high-strength isotropic materials. Strength, thermal expansivity, and the degree of anisotropy were found to correlate with crystallite size. The materials with relatively large mean apparent crystallite sizes $\text{L}\text{?}{}_{\mathrm{c}}$ were anisotropic and weak and had low thermal expansivity values, whereas those with smaller $\text{L}\text{?}{}_{\mathrm{c}}$ values were isotropic and strong and had large thermal expansivities. The graphites were irradiated at 625°–1625°C to fluences of up to 2 × 10²²n/cm². The only strong correlation found was between preirradiation strength and dimensional and volumetric changes. High-strength isotropic graphites with intermediate $\text{L}\text{?}{}_{\mathrm{c}}$ values were most stable with lowest initial contraction rates and lowest expansion rates after turnaround. Low-strength isotropic graphites were in the same range of stability with low-strength anisotropic graphites, except distortion was minimized due to their isotropic dimensional changes     

Properties of extremely high molecular weight polystyrene in solution

Extremely high molecular weight polystyrenes with a $\text{M}\text{?}{}_{\mathrm{w}}$ in the range 10.8 × 10⁶ to 2.2 × 10⁷ were prepared by emulsion polymerization initiated with a heterogeneous initiator at 30°C, which has a ‘living character’. Samples of polystyrene were characterized by light scattering and viscometry in toluene and benzene at 25°C, and in θ-solvent cyclohexane at 34.8°C. Also determined were the relationships of mean-square radius of gyration 〈s²〉 (m²) and the second virial coefficient A₂ (m³ mol kg^?2) on the molecular weight, which for toluene and benzene are described in equations: Toluene (25°C) $\text{〈s}{}^2\text{〉=1.59 × 10}{}^{\mathrm{?23}}\text{M}\text{?}{}_{\mathrm{w}}{}^{1.23}$; $\text{A}{}_2\text{=4.79 × 10}{}^{\mathrm{?3}}\text{M}\text{?}{}_{\mathrm{w}}{}^{\mathrm{?0.63}}$; Benzene (25°C) $\text{〈s}{}^2\text{〉=1.23 × 10}{}^{\mathrm{?22}}\text{M}\text{?}{}_{\mathrm{w}}{}^{1.20}$; $\text{A}{}_2\text{=2.59 × 10}{}^{\mathrm{?3}}\text{M}\text{?}{}_{\mathrm{w}}{}^{\mathrm{?0.59}}$. The parameters in the Mark-Houwink-Sakurada equation were established, for extremely high molecular weight polystyrene in toluene and in benzene, at 25°C into the form giving for $\text{[η] (}\text{m}{}^3\text{kg}{}^{\mathrm{?1}}\text{): [η] = 8.52 × 10}{}^{\mathrm{?5}}\text{M}\text{?}{}_{\mathrm{w}}{}^{0.61}$; $\text{[η] = 1.47 × 10}{}^{\mathrm{?4}}\text{M}\text{?}{}_{\mathrm{w}}{}^{0.56}$. The mentioned relations, as well as the obtained values of Flory parameter ?₀ and of ratio $\text{[η]}\text{M}\text{?}{}_{\mathrm{w}}{}^{0.5}$ were compared with solution properties of high molecular weight polystyrene with narrow molecular weight distribution prepared by anionic polymerization by Fukuda et al.     

Kinetics of the graphite-oxygen reaction near 1000°K

The kinetics of oxidation of spectroscopic grade polycrystalline graphite have been studied by a flow method which allowed the partial pressure of oxygen (P_o2) to be changed abruptly during the course of the reaction. The changes were made in two alternative ways: by changing the total pressure of an oxygen/nitrogen mixture of constant composition or by changing the composition at constant total pressure. After the effect of diffusion resistance on the rate had been shown to be negligible and the effects of self-heating, burn-off and traces of gaseous impurities allowed for, the order of reaction (ń in the empirical expression: rate α ) was found to vary from 0.34 (at 993°K and mean ) to 0.19 (at 963°K and mean P_o2 = 245 torr). In certain circumstances, the response of the rate to changes in P_o2 is subject to a “memory” effect. This is attributed to fast, diffusion-controlled chemisorption of a minute amount of hydrogenous impurity on part of the active surface of the graphite.     

Synthesis and solution properties of comb polystyrenes

A new method for the synthesis of comb shaped polystyrenes of predetermined structure is described. Silicon-chlorine bonds are introduced into the backbone polystyrene by reaction of SiMe₂Cl₂ with hydrolysed styrene/vinyl acetate copolymers and coupled with polystyryl-lithium in benzene. From a common backbone polymer a series of comb polymers are prepared that have a constant number of branches but vary in branch length. The $\text{M}{}_{\mathrm{w}}\text{M}{}_{\mathrm{n}}$ of the whole comb polymers is about 1.3. The comb polymers with high branch density show θ (A₂) temperatures lower than that for linear polystyrene. The radius of gyration at θ (A₂) [〈S²〉_{θ (A2)}] is always larger than calculated from random flight statistics. For comb polymers with 20–30 branches increases with λ^?0.46 where λ is the fraction of polymer in the backbone. The intrinsic viscosities of the comb polystyrenes at θ (A₂) are equal to that of the parent backbone polymer when λ > 0.25 and increase only little when λ becomes equal to 0.1. Similar behaviour is found in toluene. Intrinsic viscosities in cyclohexane at 35°C show a complex pattern because of the θ-temperature variation.     

Pressure dependence of upper critical solution temperatures in the polystyrene - cyclohexane system

The pressure dependence of the upper critical solution temperature $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ in the polystyrene-cyclohexane system has been measured over the pressure range of 1 to 50 atm. The value of $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ determined over the molecular weight (M_w) range of 3.7 × 10⁴ to ～145 × 10⁴ greatly depends on the molecular weight of polystyrene. The value of $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ for a polystyrene solution of low molecular weight (M_w = 3.7 × 10⁴) is positive (3.14 × 10^?3 degree atm^?1), while the values are negative (?0.52 × 10^?3～?5.64 × 10^?3 degree atm^?) for solutions of polystyrene over the high molecular weight range of 11 × 10⁴ to ～145 × 10⁴. The Patterson-Delmas theory of the corresponding state and the newer Flory theory have been used to explain this behaviour.     

Raman spectra,effective Debye parameter and magnetoresistance of graphitized cokes

The Raman intensity ratio R ($\text{I}{}_{1360}\text{I}{}_{1580}$), the effective Debye parameter B_eff and the maximum transverse magnetoresistance ($\text{Δρ}\text{ρ}\text{)}{}_{\mathrm{mx}}$ at liquid nitrogen temperature and 10 kG were measured on various cokes heat-treated at high temperatures. The observed values of R, B_eff and ($\text{Δρ}\text{ρ}\text{)}{}_{\mathrm{mx}}$ are closely related with each other and are discussed in relation to the lattice defects in the graphite layer planes. The plot of R against B_eff shows a linear relation, suggesting that both parameters are related to projections along a- and c-axes respectively of the same carbon atom displacement due to lattice defects. With decreasing B_eff, ($\text{Δρ}\text{ρ}\text{)}{}_{\mathrm{mx}}$ increases gradually but almost linearly with B_eff and then rapidly. This behavior has been interpreted by an analysis based on a simple two band model.     

Synthesis of electroreactive polymers from poly (m,p-chloromethylstyrene) and copoly (m,p-chloromethylstyrene-styrene)

Polymerization, and copolymerization with styrene, of m,p-chloromethylstyrene have been carried out at 75°C, in chlorobenzene and in the presence of AIBN ($\text{[}\text{AIBN}\text{] ? 6 × 10}{}^{\mathrm{?2}}$, and $\text{12 × 10}{}^{\mathrm{?2}}\text{m}$, respectively). The polymer molecular weights, determined by g.p.c., are: $\text{M}\text{?}{}_{\mathrm{w}}\text{= 8670}$, $\text{M}\text{?}{}_{\mathrm{n}}\text{= 5860}$, and $\text{M}\text{?}{}_{\mathrm{w}}\text{/-M}{}_{\mathrm{n}}\text{= 1.48}$ for the homopolymer, poly(m,p-chloromethylstyrene), (1a); and $\text{M}\text{?}{}_{\mathrm{w}}\text{= 8805}$, $\text{M}\text{?}{}_{\mathrm{n}}\text{= 5144}$, and $\text{M}\text{?}{}_{\mathrm{w}}\text{/-M}{}_{\mathrm{n}}\text{= 1.71}$ for the copolymer, copoly(m,p-chloromethylstyrene-styrene), (2a). A series of phosphine derivatives of both 1a and 2a are prepared by the reaction of the polymers with either chlorodiphenylphosphine/lithium, or diphenylphosphine/potassium tert. butoxide. A number of other potentially electroreactive derivatives of 2a are obtained by reacting the polymer with 2-aminoanthraquinone, 3-N-methylamino-propionitrile, or 2-(2-aminoethyl) pyridine. The phosphinated polymers are reacted with bis-benzonitrilepalladium-(II) chloride to obtain a series of polymer-palladium(II) complexes containing 8.5–12.9% palladium. Similarly, reaction of the last-named bidentate polymeric ligand with cupric acetylacetonate, or cupric sulphate pentahydrate, produces polymer-copper(II) complexes having 5.8, or 3.3% copper, respectively. The inter/intra-chain nature of some of the side reactions during the derivatization of the chloromethylated polymers, and that of the complex formation between transition metal centres and macromolecular ligands, are briefly discussed in view of the experimental results.