Rates of copolymerization of acrylonitrile and ethylenesulfonic acid

Use was made of differential absorption in the near-infrared region to follow the rates of copolymerization of acrylonitrile (AN, M₁) with ethylenesulfonic acid (ESA, M₂) in aqueous zinc chloride solution. The concentrations of the monomers were followed separately and simultaneously. It was found experimentally that the ratios d log [M₁]/dt and d log [M₂]/dt were each constant. This was interpreted to mean that the product of the reactivity ratios of the two monomers (r₁,r₂) is unity and that the ratio of termination rate constants is equal to the propagation reactivity ratio. It was found that d log [M₁]/d log [M₂] = r₁ = 4.5₂. This value is in fair agreement with polymer composition data obtained independently. In the Q—e system the equality r₁r₂ = 1 is equivalent to the monomers having equal e values. Thus, in the AN—ESA system, P₁/P₂ = k₁₁/k₂₁ = k₁₂/k₂₂ = k_1T/k_2T, where P₁ is the resonance constant of polymer radicals ending in units of M₁; and k₁₁, k₁₂, and k_1T are the rate constants involving the reaction of this radical with M₁, M₂, and T (terminating agent), respectively. A gel effect was not observed even at M₁ conversions as high as 88%.     

Estimation of the lattice heat capacity of rare-earth compounds

On the basis of the experimental data reported in literature, the contributions of cation mass (m) and molar volume (V) to lattice heat capacity (C) were analyzed. The volumetric-mass formula, C_x=(l —f)·C₁+f·C₂+C_m·(m_x — m_x′), was presented for estimating the heat capacities of rare-earth compounds. In the formula C₁ and C₂ represent the lattice heat capacities of two reference substances respectively, f = V_x—V₁/V₂—V₁ and C_m represents the lattice heat capacity variation with the variation 1 g of cation mass. The equation relating the C_m with temperatures was derived as follows: C_m = 0.084 e ?0.0074T ?0.27 e ?0.045T, and m_x and m_x′ (= (1 - f) m₁₊f m₂) represent the practical and “assumed” cation masses of the substance in question respectively.     

Relationships on the effect of water on glass transition temperature and young's modulus of nylon 6

The glass transition temperature T_g of nylon 6 decreases monotonically toward a finite value T_gl upon increase of the moisture content. The mechanism of this decrease entails the reversible replacement of intercaternary hydrogen bonds in the accessible regions of the polyamide. The limiting glass transition temperature T_gl is approached when the moisture content approaches W_l, which corresponds to the amount of water required for complete interaction with all accessible amide groups. Denoting with T_g0 the glass transition temperature of the dry polymer, the effect of water on T_g is represented by the equation, T_g = (ΔT_g)₀ exp{?[ln(ΔT_g)₀]W/_τW_l} + T_gl, where (ΔT_g)₀ = T_g0 ?T_gl, and τ = W(T_gl+1)/W_l. This equation appears to be generally applicable to hydrophilic polymers, since correspondingly calculated data are also in very good agreement with experimental data for polymers such as nylon 66, poly(vinyl alcohol), and polyN-vinylpyrrolidone. The effect of water of Young's modulus E of nylon 6 is represented by an analogous relationship, and the quantity In[(E?E_l)/(T_g?T_gl)] is a linear function of the moisture content.     

Temperature dependence of the relative rate constants of the reactions of alkanes with oh radicals in aqueous solution

A study was carried out on the rate constant ratio (k _RH/k _EtH) in reactions of alkanes C₃H₈, n-C₄H₁₀, n-C₅H₁₂, n-C₆H₁₄, i-C₄H₁₀, c-C₅H₁₀, and c-C₆H₁₂ with OH radicals in water at 5-55°C and the relative activation parameters A _RH/A _EtH and E _EtH – E _RH. The values of E _EtH – E _RH in water and the gas phase have opposite signs. The values of k _RH/k _EtH decrease with increasing temperature in the gas phase but increase in water. The behavior of these reactions in water may be attributed to a solvent cage effect.     

Excitonic Bands in the Spectra of Some Organic-Inorganic Hybrid Compounds Based on Metal Halide Units

 The optical absorption, photoluminescence, and photoconductivity spectra of some compounds of the formulas [R(CH₂) _n NH₃] _x M _y X _z , [R(CH₂) _n NH(CH₃)₂] _x M _y X _z , [R(CH₂) _n S(CH₃)₂] _x M _y X _z , [R(CH₂) _n SC(NH₂)₂] _x M _y X _z , and [R(CH₂) _n SeC(NH₂)₂] _x M _y X _z (R = organic residue; M = Bi(III), Pb(II), Sn(II), Cu(I), Ag(I) etc; X = I, Br, Cl; n, x, y, z = 0, 1, 2, 3, …) are briefly reviewed, and some new results are reported. The position, intensity, and shape of the excitonic bands depend on the dimensionality and size of the inorganic network as well as on the nature of the M, X, R, and onium moieties.     

A variation principle for energy differences between states of two different Hamiltonians

A modification of a variation principle due to Delves, is derived which permits the direct calculation of energy differences between states of two different Hamiltonians: [Δ ??] = 〈X₀| ??_x – W_x|X₁〉 – 〈Y₀|??_y – W_y|y₁〉 + 〈X₀| Δ ??|Y₀〉 · 〈X₀| Y₀〉^?1. Δ ?? = ??_y – ??_x, |X₀〉 and |Y₀〉 are the wave functions for the X and Y states and |X₁〉 and |Y₁〉 are functions defined in the text. The principle is applied to a few simple examples.     

Synthesis of cationic indenyl- and fluorenyl-arene complexes of ruthenium

Interaction of [Ru(-C ₆ H ₆ )Cl ₂ ] ₂ with indenyl- or fluorenyllithium in THF gives, together with cationic benzene complexes [Ru( ⁵ -C ₉ H ₇ )(-C ₆ H ₆ )]⁺ and [Ru( ⁵ -C ₁₃ H ₉ )(-C ₆ H ₆ )]⁺, the neutral cyclohexadienyl derivatives Ru( ⁵ -C ₉ H ₆ -C ₉ H ₇ ) and Ru( ⁵ -C ₁₃ H ₉ )( ⁵ -C ₆ H ₆ -C ₁₃ H ₉ ), respectively. Interaction of the cyclohexadienyl complexes with Al ₂ O ₃ , Ph ₃ C⁺, and CF ₃ CO ₂ H has been studied. Reaction of Ru( ⁵ -C ₁₃ H ₉ )( ⁵ -C ₆ H ₇ ) with CF ₃ CO ₂ H in the presence of an arene yields cationic cyclohexadienylarene complexes: [Ru( ⁵ -C ₁₃ H ₉ )( ⁶ -arene)]⁺ (arene=C ₆ H ₆ or 1,3,5-Me ₃ C ₆ H ₃ ).A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 699–706, March, 1992.     

Copolymerization characteristics of S-vinyl-O-tert-butylthiocarbonate

Poly-S-vinyl-O-tert-butylthiocarbonate is an excellent precursor to poly(vinyl mercaptan) because the tert-butyloxycarbonyl blocking group can be removed by either acid hydrolysis or thermolysis under conditions which minimize the oxidation of the liberated mercaptan to disulfide. Dilatometric studies of the homopolymerization of S-vinyl-O-tert-butylthiocarbonate demonstrated that the polymerization rate was directly proportional to the concentration of free-radical initiator; no thermal initiation was observed. The molecular weight of the homopolymers and copolymers ranged from 30,000 to 50,000 (GPC). Copolymerization of S-vinyl-O-tert-butylthiocarbonate (M₂) with styrene, (r₁ = 3.0, r₂ = 0.2), methyl methacrylate (r₁ = 1.40, r₂ = 0.17) and vinyl acetate (r₁ = 0.04, r₂ = 11.0) indicated that a sulfur atom adjacent to the vinyl group increases the resonance stability (Q₂ = 0.5) and the electron density (e₂ = ?1.4) of the double bond and the corresponding radical. Water-soluble copolymers could be prépared by incorporating either N-vinylpyrrolidone (r₁ = 0.12, r₂ = 3.94) or N-isopropylacrylamide (r₁ = 1.17, r₂ = 0.3) with M₂. The water solubility of the copolymers decreased markedly when the tert-butyloxycarbonyl group was removed. Copolymers of M₂ with N-vinyl-O-tert-butylcarbamate (r₁ = 0.13, r₂ = 5.10) were utilized to prepare crosslinked poly(vinyl amine–vinyl mercaptan); the crosslinking resulted from urea linkages formed during thermolysis of the copolymer.     

Theoretical calculation of the steric effects of ortho substituents by the AM1 method

The AM1 calculation was done for ortho-substituted toluenes (o-X-C₆H₄-CH₃) and ortho-substituted tert-butylbenzenes (o-X-C₆H₄-t-Bu). The difference in the calculated heat of formation between o-X-C₆H₄-CH₃ and o-X-C₆H₄-t-Bu was used as a theoretical steric index for ortho-X. The correlation of this theoretical steric index with the empirical steric parameter sets such as our recently defined E_s(AMD) and the Taft–Kutter–Hansch (TKH) E_s was examined. In spite of the simplicity of the model system, the theoretical index was linear with the E_s(AMD) constant with a correlation coefficient of r = 0.972 for 17 substituents of various structures. Including the phenyl group, the correlation with the TKH E_s constant was r = 0.948. The theoretically calculated index was shown to serve as a measure of the ortho steric effect.     

Kinetic interpretation of the glass transition: Glass temperatures of n-alkane liquids and polyethylene

On the basis of an isoviscosity criterion for the glass transition (η_g ? 10¹³ poise) in liquids of low molecular weight, theoretical T_g values were calculated for the n-alkane series by the equation log η = log A + B/(T ? T₀), with the use of values reported by Lewis for the parameters. The T_g/T₀ ratio reaches a limiting value of 1.25 and ?_g = (T_g ? T₀)/2.3B = 0.027, a constant. Extrapolation to (CH₂)_∞ gives T_g = 200°K., T₀ = 160°K., and B = 640°K. This T_g is consistent with other estimates for poly-ethylene, and T₀ coincides with the temperature at which the “excess” liquid entropy for (CH₂)_∞ becomes zero from thermodynamic data. For polymer liquids it is proposed that E₀ = 2.3RB is determined by the internal barriers to rotation for the “isolated” polymer chains. Thus, E₀ = 2.9 kcal./mole for polyethylene, 3.0 kcal./mole for polystyrene, 5.7 kcal./mole for polyisobutylene, and 1.9 kcal./mole for polydimethylsiloxane.     

Adsorption of gas mixtures on heterogeneous solid surfaces: I. Extension of Tóth isotherm on adsorption from gas mixtures

Summary It was proved that the partial adsorbed quantities can be calculated from the individual adsorption isotherms. This calculation can be carried out by equations which take into' account the energetical heterogeneity of the surface of adsorbent as well. Thus, the partial isotherms equations which can be applied are as followsV _A (p _A ,p _B ) =p _A /[b _a + (p _A +b _AB p _B ) ^m ] ^1/m andV _B (p _A ,p _B ) =p _B /[b _B + (p _B +b _BA p _A ) ^m ] ^1/m wherep _A andp _B are the partial equilibrium pressures, whileb _A ,b _B andm are constants which can be determined on the basis of the individual isotherms.

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Zusammenfassung Es wurde nachgewiesen, daß die partialen Adsorbatmengen aus den individuellen Isothermen berechnet werden können. Die Berechnung kann mit Hilfe von Gleichungen durchgeführt werden, die auch die energetische Inhomogenität der adsorbierenden Oberfläche berücksichtigen. Benutzt werden die Gleichungen: V_A(p_A,p_B) = p_A/ [b_A + (PA + b_ABp_B)^m]^1/m und V_B(p_A,p_B) p_B/[b_B + (p_B + b_BAp_A)^m]^1/m , wop _A undp _B die Gleichgewichtspartialdrucke undb _A ,b _B undm die aus den individuellen Isothermen zu bestimmenden Konstanten darstellen.

     

Entanglement networks of 1,2-polybutadiene crosslinked in states of strain. VII. Stress-birefringence relations

Crosslinks are introduced by γ irradiation into 1,2-polybutadiene while strained in uniaxial extension near T_g with stretch ratio λ₀, thereby trapping a proportion of the entanglements originally present. The stress at any subsequent strain λ is accurately given by the sum σ_N + σ_x, where σ_N is the stress contributed by a trapped entanglement network with λ = 1 as reference and a Mooney–Rivlin stress-strain relation, and σ_x is that contributed by a crosslink network with λ = λ₀ as reference and neo-Hookean stress-strain relation. The birefringence is accurately given as δn = ?_Nσ_N + ?_xσ_x, where the ?'s are the respective stress-optical coefficients. From measurements at λ = λ₀ where σ_x = 0, ?_N can be determined separately. For polymer with 88% 1,2 microstructure, ?_N and ?_x are nearly equal and independent of irradiation dose, though strongly dependent on temperature. For polymer with (95–96)% 1,2, ?_N and ?_x are different (even opposite in sign) and dependent on dose. This behavior is associated with a side reaction of cyclization by the γ irradiation, which is inhibited by the 1,4 moiety in the polymer with lesser 1,2 content. It is responsible for residual birefringence in the state of ease (λ = λ_s) where σ_N = –σ_x and the stress is zero.     

Self-diffusion in melts of statistical copolymers: The effect of changes in microstructural composition

We have used nuclear reaction analysis to measure diffusion coefficients D in couples consisting of hydrogenated polybutadienes of structure (C₂H₃(C₂H₅))_x(C₄H₈)_1?x and their partly deuterated counterparts. The 1,2- and 1,4-olefinic isomers are randomly distributed along the chains and the mean vinyl fraction x varies between 0.38 and 0.94. We find that the effective monomeric mobility D₀ [defined by D = D₀(N_e/N²) for each copolymer, where N is the backbone length and N_e the entanglement spacing] decreases monotonically with increasing vinyl content x. Over the range of microstructures and temperatures T (?14?40°C) investigated we find log(D₀/T) varies smoothly with (T ? T_g), where T_g is the glass transition temperature of the respective melts. An analysis of our data in terms of a simple activated rate process model suggests that D₀ is controlled by thermally activated hopping of segments whose effective volume is close to that of the respective statistical segment lengths of the copolymeric chains. ©1995 John Wiley & Sons, Inc.     

Synthesis and Structures of Ruthena-octahydrotetraborane Complexes

The reactivity of κ²-N,S-chelated ruthenium borate complexes, [Ru(PPh₃)(κ²-N,S-(NC₇H₄S₂)Ru{κ³-H,S,S′-H₂B (NC₇H₄S₂)₂}] ( 1 a ) and [Ru(PPh₃)(κ²-N,S-(NC₅H₄S){κ³-H,S,S′-H₂B(NC₅H₄S)₂}] ( 1 b ) with monoboranes have been explored. The prolonged room temperature reaction of [Ru(PPh₃){κ²-N,S-(NC₇H₄S₂)}{κ³-H,S,S′-H₂B(NC₇H₄S₂)₂}], 1 a with an excess of [BH₃ ⋅ THF] led to the formation of hydrogen-rich complex, arachno-[PPh₃(κ²-B₃H₈)Ru{κ³-H,S,S′-H₂B(NC₇H₄S₂)₂] ( 2 ). In a similar fashion, the isomeric ruthenatetraborane complexes of [Ru(PPh₃)(κ²-N,S-(B₃H₈){κ³-H,S,S′-H₂B(NC₅H₄S)₂}], 4 and 5 were isolated from the room temperature reaction of 1 b with [BH₃ ⋅ THF]. In complex 2 , the borate ligand, [H₂B(NC₅H₄S)₂] and the PPh₃ occupy the endo and exo sites of the butterfly-shaped RuB₃ core, respectively. In contrast, the borate unit [H₂B(NC₅H₄S)₂] in 4 sits on the exo position of the butterfly core, while the phosphine ligand occupies the endo site. Multinuclear spectroscopic analyses were done to characterize all new complexes and the structures were further confirmed by single-crystal X-ray diffraction analysis. Density functional theory (DFT) calculations were performed to probe into the bonding modes of these complexes.     

Coordination compounds of hydrazine derivatives with transition metals,XXIII cobalt(II) chelates of bis(N-salicylidene)dicarboxylic acid dihydrazides

The reaction of bis(N-salicylidene)dicarboxylic acid dihydrazides (H₄ Lig) with cobalt(II) salts was investigated. Chelates of the types Co(H₃ Lig)X ·nH₂O, Co₂(H₂ Lig)X ₂, Co₃(H₃ Lig)₂ X ₄, Co(H₂ Lig) ·nH₂O and Co(H₃ Lig)₂ ·nH₂O (X=Cl, Br, I or SCN) were isolated and characterized by their infrared and electronic spectra as well as their magnetic properties.

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Koordinationsverbindungen von Hydrazinderivaten mit Übergangsmetallen, 23. Mitt.: Kobalt(II)-Chelate von Bis(N-salicyliden)dicarbonsäuredihydraziden

Zusammenfassung Die Reaktion von Bis(N-salicyliden)dicarbonsäuredihydraziden (H₄ Lig) mit Kobalt(II)-Salzen ergab Chelate vom Typ Co(H₃ Lig)X ·nH₂O, Co₂(H₂ Lig)X ₂, Co₃(H₃ Lig)₂ X ₄, Co(H₂ Lig) ·nH₂O and Co(H₃ Lig)₂ ·nH₂O (X=Cl, Br, I oder SCN). Die Charakterisierung erfolgte mittels IR, Elektronenspektren und magnetischer Eigenschaften.

     

Silicophosphates of Rhodium and Indium

Single crystals of Rh(Si₂O)(PO₄)₃ and In₄(Si₂O) · (PO₄)₆ were prepared by chemical transport reactions in silica tubes and their structures were determined. Crystal data of Rh(Si₂O)(PO₄)₃: trigonal, space group P 3 c1, a = 8.088(3) Å, c = 8.740(2) Å, Z = 2, R(F²) = 0.0379, R_w(F²) = 0.0518 for 601 unique reflections. In₄(Si₂O)(PO₄)₆: hexagonal, space group P6₃/m, a = 8.5149(10) Å, c = 7.7481(12) Å, Z = 1, R(F²) = 0.0436, R_w(F²) = 0.0522 for 509 unique reflections. Both of the compounds have hexagonal close packed array of phosphate groups with metal atoms and SiOSi units in the octahedral interstices, where the SiOSi units show occupational disorder. The structure of the indium compound is considered to be a disordered structure of the reported Mo₄Si₂P₆O₁₃ structure, and contains confacial bioctahedral units.     

Reactions of β-keto sulfones with t-butyl aluminum compounds: Reinvestigation of tri-t-butyl aluminum synthesis

t-Butyl derivatives play a significant role in the organometallic chemistry of group 13 metals. It was shown on the basis of reactions of t-Bu₃Al·OEt₂ with [p-RC₆H₄S(O)₂C(H)₂C(Ph) = O] (where R = CH₃, Cl) β-keto sulfones that the structure of the reaction products depends on the purity of the aluminum compound used. In the reactions, in addition to the expected complexes [p-RC₆H₄S(O₂)C(H) = C (Ph)-OAl(t-Bu)₂] [where R = CH₃ ( 2 ); R = Cl ( 4 )] possessing β-keto sulfone ligands, complexes with β-hydroxy sulfone ligands [p-RC₆H₄S(O₂)C(H)₂-C (Ph)-OAl(t-Bu)₂] [where R = CH₃ ( 1 ); R = Cl ( 3 )] were formed. Compounds 1 and 3 were the result of the hydroalumination reaction of the β-keto sulfone ligands with t-Bu₂AlH, which is an impurity of t-Bu₃Al. These compounds are obtained, for the first time, as intermediate products in the hydrogenation reaction of β-keto sulfones. In this work, during t-Bu₃Al·OEt₂ production t-Bu₂AlH·OEt₂ formed as a by-product. Re-examination of reaction conditions of AlCl₃ with t-BuMgCl resulted in a control of the t-Bu₂AlH·OEt₂ by-product content in t-Bu₃Al·OEt₂.     

N-representability of diagonal elements of second-order reduced density matrices

The problem of pure-state N-representability of the two-particle spin-dependent density function ρ(x₁, x₂) is considered for an N-electron system, and a procedure for finding an N-representable ρ(x₁, x₂) is advanced. The problem is formulated in the framework of a family of N × N matrices formed from integrals of auxiliary two-particle functions θ_n(x₁, x₂) converging at n → ∞ to ρ(x₁, x₂)/[N(N−1)]. The simple requirement of positive definiteness of these matrices is shown to play a decisive role in finding an N-representable ρ(x₁, x₂). The results obtained may open new possibilities for using ρ(x₁, x₂) in the density-functional theory. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 127–142, 1997     

Structural Investigation of New Lithium Amidinates and Guanidinates

A series of potentially useful lithium amidinates and guanidinates were prepared and fully characterized. Treatment of N,N′‐diisopropylcarbodiimide with phenyllithium in diethyl ether afforded the lithium amidinate [PhC(NiPr)₂Li(OEt₂)]₂ ( 1 ). Similar treatment of N,N′‐diorganocarbodiimides R′–N=C=N–R′ [R′ = iPr, cyclohexyl (Cy)] with secondary lithium amides LiNR₂ [R₂ = Et₂, iPr₂, (CH₂)₄] followed by crystallization from THF or 1,4‐dioxane gave the lithium guanidinates [R₂NC(NR′)₂Li(S)]₂ [ 2 : R = Et, R′ = iPr, S = THF; 3 : R₂ = (CH₂)₄, R′ = iPr, S = THF; 4 : R = R′ = iPr, S = ½ 1,4‐dioxane; 5 : R₂ = (CH₂)₄, R′ = Cy, S = 1,4‐dioxane] as crystalline solids. Reaction of N‐lithioaziridine with the corresponding carbodiimides afforded solvent‐deficient [{C₂H₄NC(NiPr₂)₂}₂Li₂(THF)]₂ ( 6 ), and [C₂H₄NC(NEt)(NtBu)Li(THF)]₂ ( 7 ). Crystal structure determination revealed the presence of common ladder‐type dimeric structures for 1 – 5 . Compound 6 exists as a dimer of two ladder‐type dimers in the crystal, and 7 exhibits an unusual dimeric structure comprising an eight‐membered C₂N₄Li₂ ring.