Polymerization of phenylacetylenes. VI. Chain-transfer reaction in the polymerizations of phenylacetylene and styrene by WCl6

Chain-transfer reactions to alkylbenzenes were investigated in the polymerizations of phenylacetylene and styrene by WCl₆ in benzene at 30°C. In the polymerization of phenylacetylene, alkylbenzenes did not work as chain-transfer agents, and further ethyl iodide was not a terminating agent. These findings suggest that the polymerization of phenylacetylene by WCl₆ differs from the conventional cationic or anionic mechanisms. On the other hand, the ability of alkylbenzenes as chain-transfer agents in the polymerization of styrene by WCl₆ increased in the following order: toluene < p-xylene < m-xylene < o-xylene. This order is similar to that in the polymerization by SnCl₄. These results indicate that the polymerization of styrene by WCl₆ proceeds by a conventional cationic mechanism.     

Real-time mid-IR monitoring of metathesis reactions by fiber optic FTIR spectroscopy

The real-time monitoring of metathesis reactions using a recently developed fiber optic transmission FTIR technique is reported in this paper. The ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene, the ring-closing metathesis (RCM) of 1,7-octadiene and the polymerization of phenylacetylene were investigated. The Schrock carbyne complex, Cl₃(dme)WCCMe₃, was used as the catalyst for these reactions. The phenylacetylene polymerization was also studied with WCl₆ as the catalyst. In the ROMP of 1,5-cyclooctadiene, monomer consumption was followed by monitoring the disappearance of the 1486 cm⁻¹ absorbance, characteristic of the CH₂ deformation vibration (δ_s CH₂) in the monomer. In the RCM of 1,7-octadiene, conversion data was obtained by monitoring the 1832 cm⁻¹ signal, which is an overtone of the wagging absorbance at 910 cm⁻¹ of the CH₂ end group in the monomer. Phenylacetylene polymerization was monitored by the disappearance of the ν -CCH stretch signal at 2110 cm⁻¹. Polymerization was much faster with the Schrock catalyst than with WCl₆, but similar conversions were reached in both reactions. Conversion data obtained by the IR technique agreed well with gravimetric product yields.     

Peroxo salts as initiators of vinyl polymerization—2. Kinetics of polymerization of acrylic acid and sodium-acrylate by peroxodisulphate in aqueous solution—effect of pH and Ag+ catalysis

Results on the rate of polymerization of acrylic acid by S₂O^2?₈ ion in alkaline and acid conditions are presented. R_p depended upon $\text{[S}{}_2\text{O}{}^{\mathrm{2?}}{}_8\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{[monomer]}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ both in acid and alkaline solutions. The influence of ionic strength, the effect of pH on R_p and the catalytic effect of Ag⁺ and Cu²⁺ on the system have been discussed. Suitable mechanisms are proposed.     

Cryogenic degradation of polystyrene in solution

An ultra-high molecular weight and narrow distribution polystyrene ($\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{= 7.3 × 10}{}^6$, M_w/M_n = 1.13) was dissolved in a wide range of solvents. Potential degradation by freezing was studied as a function of solvent type, concentration, cooling rate and number of freezing cycles. Cryogenic experiments were conducted in dioxane, tetrahydrofuran, benzene, dichloroethane, cyclohexanone, p-xylene, methyl methacrylate and styrene. The extent of degradation did not relate to a single solvent parameter, but there seemed to be a tendency towards a limited degradation in solvents with low melting points and/or solubility parameters greatly different from that of polystyrene. A low polymer concentration as well as a high cooling rate promoted chain scission, the latter parameter being the most important. In cyclohexanone and p-xylene, linear relationships were observed between the number of scission per molecule and the number of freezing cycles at high polymer concentrations and at high cooling rates. At lower concentrations and slower cooling, the relationships were non-linear suggesting a different degradation mechanism. The most extensive change in molecular weight distribution was observed on freezing in styrene. After 45 freezing cycles, an $\text{M}$_w of only 2.3 × 10⁶ was observed. The results indicate that chain scission occurred together with polymerization and combination reactions. Freezing of suitable solutions of ultra-high molecular weight polymers can thus be used as a new way of initiating polymerizations by cooling rather than heating.     

Quenching of the Ba + Cl2 chemiluminescence: Estimate of BaCl*2 radiative lifetime

The chemiluminescence produced by the Ba + Cl₂ reaction was recorded as a function of He and N₂ pressure. A modified Stern-Volmer treatment of competitive electronic quenching of BaCl^* and BaCl^*₂ emission yielded upper limits to the half pressures p_{$\text{1}\text{2}$}(He) ? 9.0 ± 3 mtorr and p_{$\text{1}\text{2}$} (N₂) ? 1.1 ± 0.2 mtorr for quenching of BaCl^*₂ by helium and nitrogen, respectively. A lower limit of the BaCl^*₂ radiative lifetime is placed at τ_R ? 100 μ.     

Determination of hydrogen ion activities in various ternary water/methanol/dioxane solvent systems

The practical pH values for solutions in ternary water/methanol/dioxane solvents measured by a pH meter standardized with aqueous buffer solutions do not lie on the conventional scale of hydrogen ion activity referred to the standard state in the corresponding medium (pa^*_H). These values can be converted to pa^*_H by the introduction of a correction term δ = $\text{E}\text{?}$_j ? log(_mγ_H) (where $\text{E}\text{?}$_j is a term incorporating the liquid junction potential, which depends on the solvent composition and _mγ_H is the medium effect on hydrogen ion). Values of δ were determined for various ternary solvents at 25°C and were found to be constant in each medium independent of the solute composition.     

Ferrocene polymers. synthesis and polymerization of p-ferocenecenylphenylacetylene

To investigate the influence of the ferrocenyl residue on the reactivity of phenylacetylene towards polymerization and on the properties of polyphenylacetylene, p-ferrocenylphenylacetylene has been synthesised and then polymerized with initiation by free radicals. Theoretical studies on the reactivity of p-ferrocenylphenylacetylene showed good agreement with the observation that the reactivity of this monomer is lower when compared to that of ferrocenylacetylene. The polymers synthesised showed good thermal stability     

Crystal structures and magnetic properties of BaTiF5 and CaTiF5

Single crystals of BaTiF₅ and CaTiF₅ were obtained by the Czochralski and Bridgman techniques, respectively. The crystal structures were determined by X-ray diffraction; BaTiF₅: $\text{14}\text{m}\text{, a = 15.091(5)}$Å, c = 7.670(3)Å; CaTiF₅: $\text{I2}\text{c}\text{, a = 9.080(4)}$Å, b = 6.614Å, c = 7.696(3)Å, β = 115.16(3)°. Both structures are characterized by the presence of either branched or straight chains of TiF₆ octahedra. BaTiF₅ contains the unusual dimeric unit (Ti₂F₁₀)^4?. Magnetic susceptibility measurements were performed on both compounds in the temperature range 4.2 to 300 K, however, no evidence for magnetic interactions between the Ti³⁺ moments were observed.     

The preperation and coordination properties of 1,4-diaza-3-methylbutadiene-2-ylpalladium(II) complexes with different substituents on the imino nitrogen atoms

The complexes trans-[PdCl{$\text{C(=NR)C}$(ME)=NR'} (PPh₃)₂] (R=C₆H₁₁,p-C₆H₄OMe; R$\text{.}\text{?}$=p-C₆H₄OMe, Me) containing a σ-bonded 1,4-diaza-3-menthyl-butadiene-2-yl group with different substituents on the nitrogen atoms have been prepared by two routes. The first involves initial methylation of the mixed isonitrile complex [PdCl₂(CNR)(CNR')]by HgMe₂, followed by reaction with PPh₃ ($\text{Pd}\text{PPh}{}_3$molar ratio $\text{1}\text{2}$). The second method involves condensation of primary aliphatic amines with the carbonyl group of the 1-azabut-1-en-3-one-2-yl moiety of the complex trans-[PdCl{$\text{C(=NR)C}$(Me) = 0} (PPh₃)₂]. The 1,4-diaza-3-methylbutadiene-2-yl derivatives act through their imino nitrogen atoms as chelating ligands towards anhydrous metal chlorides MCl₂ (M = Co, Ni, Cu, Zn). Magnetic moment measurements and the far-infrared and electronic spectra of these adducts indicate an essentially pseudo-tetrahedral configuration at M in the solid and in solution. With the ZnCl₂ adducts, the ¹H NMR pattern for the phenyl protons of the p-methoxyphenyl N-substituents dependss upon the position of the substituent i the 1,4-diazabutadiene chain.     

Acidic peroxo salts: A new class of initiators for vinyl polymerization—II: Kinetics of polymerization of acrylonitrile initiated by potassium monopersulphate catalysed by Mn(II)

Kinetics of the polymerization of acrylonitrile initiated by an acidic peroxo salt (potassium monopersulphate) catalysed by Mn(II) have been investigated in aqueous systems over the range 30–50°. The rates of polymerization (R_p) have been studied for various concentrations of monomer and initiator. The efficiencies of various metal salts in catalysing the polymerization have been determined from the values of R_p. The effects of catalyst (MnSO₄), initiator, monomer and various aromatic and heterocyclic amines on R_p and conversion have been studied. The end-groups of the recovered polymers have been studied using standard methods. From the observed end-groups and kinetic results, a reaction scheme has been proposed, involving initiation by OH^. or S$\text{O}$₄^. radicals, generated by the interaction of the initiator with manganous sulphate, and termination by mutual combination.     

The rotational spectrum and molecular properties of a hydrogen-bonded dimer of phosphine and hydrogen fluoride

⁵⁷Fe Mössbauer spectra have been obtained for Fe(p-CH₃C₆H₄SO₃)₂ between 2.3 and 300 K in zero field, and at 2.3 and 4.2 K in longitudinal applied magnetic fields ranging from 1.1 to 5.6 T. The complex is a fast-relaxing paramagnet under all conditions studied and there is no evidence of antiferromagnetic exchange coupling. The FeO₆ chromophore is distorted by a trigonal elongation and the orbital ground state is the [($\text{2}\text{3}$)^{$\text{1}\text{2}$}|±2〉 ? ($\text{1}\text{3}$)^{$\text{1}\text{2}$}|?1〉] doublet. The temperature dependence of the quadrupole splitting has been analysed via a crystal-field model to provide estimates of the axial field splitting parameter Ds = -93 cm^-1, spin-orbit coupling constant λ = -70 cm^-1, and fine structure constant Dσ = -28 cm^-1. The magnetic properties of the complex are described by treating the ground state as a non-Kramers doublet with fictitious spin ? = $\text{1}\text{2}$. Five separate Mössbauer-Zeeman spectra can be fitted in this spin-hamiltonian approximation with identical values of the g- and A-tensor components, viz. g_⊥ = 1.0, g_u = 9.0; A_⊥ ≈ 2.0 mm s^-1. A_u = -1.79 mm s^-1. The trigonal z axis, the z axis of the electric field gradient tensor, and the easy axis of magnetisation are collinear, and the saturation value of the internal hyperfine field along this axis is +13.0 T.     

Étude quantitative d'équilibres chimiques en solution dans les sels fondus par spectrophotométrie d'absorption: Application au neptunium

The following reactions: NpO₂⁺+4 HCl ? Np⁴⁺ + 2 H₂O + $\text{1}\text{2}$ Cl₂ + 3Cl^- NpO₂⁺+$\text{1}\text{2}$ Cl₂ ? NpO₂²⁺ +Cl^- 2HCl+O^2- ? H₂O +Cl^- have been examined quantitatively. The reactions were studied in fused LiCl-KCl sparged with gas mixtures of definite compositions. The concentrations of the diffrent neptunium species were measured by absorption spectrophotometry. The values of respective equilibrium constants are: K = (9.3±0.4)· 10^-6 atm(^{-$\text{1}\text{2}$}); K₁ = (2.3±0.1)·10^-2 atm(^{-$\text{1}\text{2}$}); k = 10^3.8 1 mol^-1 atm^-1 The standard potential of the system NpO₂²⁺ / NpO₂⁺ was determinedto be E⁰ = 0.220 V (vs.standard chlorine electrode).     

The thiolate anion as a nucleophile Part XI. Effect of the size of the nucleophile

The nucleophilic substitution reactions of some simple fluorobenzenes, C₆H_6?xF_x with sodium methanethiolates Na⁺SR^?(R=Et, $\text{i}$-Pr, $\text{t}$-Bu) have been studied. Some fully substituted products, C₆H_6?x(SR)_x, could be obtained in DMF as solvent with R = Et and $\text{i}$-Pr, but not when R = $\text{t}$-Bu. All the new products isolated have been characterized by elemental analysis, and NMR (H-1 and F-19), infrared and mass spectroscopy.     

Synthèse et structure cristalline d'un nouvel oxyde mixte FeV2O6H0.5 relation avec la structure type diaspore

Single crystals of a new compound, FeV₂O₆H_0.5, have been obtained by hydrothermal synthesis at 650°C and 2 kbar. An electron microprobe analysis indicated that the chemical formula is FeV₂O₆. This compound has an orthorhombic symmetry, space group P2₁2₁2₁ with Z = 4. The unit cell dimensions are

$\text{a = 4.891}\text{A}\text{?}\text{, b = 9.553}\text{A}\text{?}\text{, c = 8.786}\text{A}\text{?}$

These parameters are related to a′, b′, c′ of the diaspore-type VO₂ by the relations: $\text{a ? a′, b ? b′, c ? 3c′}$. The structure, based on single crystal data, has been determined from Patterson and Fourier syntheses. A structural refinement gave a final R-factor of 2.4%. The new structure can be deduced from that of the diaspore-type VO₂, by displacement of one third of the cations from an octahedral site to an adjacent unoccupied tetrahedral site, which is located in a channel parallel to the c axis. The calculation of the cation and oxygen valences indicated that some O^2? were in fact OH^?. This conjecture was supported by thermogravimetric analysis. The chemical formula was indeed Fe³⁺₂V³⁺V⁴⁺V⁵⁺₂O₁₁(OH). Some intensities of the powder diffraction lines changed strongly when the preparation temperature was reduced from 650°C to 300°C. This was explained by an increase of the hydrogen ratio in the formula FeV₂O₆H_x, which implies a structural change. The different phases FeV₂O₆H_x can be considered as solid solutions between two extreme phases with different structure: one with the present one and the other with a diaspore-type structure.     

Triméthylsilylcycloalcanes: Corrélation structure-réactivité

A comparative study of the physicochemical data (IR, Raman, ¹H, ¹³C and ²⁹Si NMR) of four trimethylsilylcycloalkanes, ($\text{CH}{}_2\text{)}{}_{\mathrm{<mtext>n</mtext>}}\text{C}$HSiMe₃ ( n = 2- 5), allowed a good correlation between their structure and chemical reactivity to be established. The particular chemical behaviour of trimethylsilylcyclopropane, in this series, involves an interaction between the three-membered ring and silicon, in good agreement with a (p → d)π interaction. This study provides a lot of new data for these models and exhibits exemplarily the contribution of physico-chemistry in explaining and predicting the chemical reactivity of organic substrates.     

Single-crystal growth and structure determination of Ag16I12P2O7

Single crystals of the fast-ion conductor Ag₁₆I₁₂P₂O₇ were prepared and their structure ($\text{P6}\text{mcc}\text{, a = 12.054, c = 7.504}$ Å) was determined by X-ray diffraction (r = 0.08). The I atoms form a close-packed array leaving channels occupied by P₂O^4?₇ ions running along the c axis. The Ag atoms are disordered over four different types of site with occupation numbers ranging from 0.12 to 0.52. Each Ag⁺ ion coordination polyhedron shares several faces with adjacent polyhedra providing ready paths for Ag⁺ ion conduction.     

Gradient expansion of the atomic kinetic energy functional

It is demonstrated that the ground-state atomic kinetic energy functional T[?], where ? is the electron density, can be computed to surprising accuracy from the truncated gradient expansion: T[?] = + T₂[?] + T₄[?], with T_o[?] = $\text{3}\text{10}$(3π²)$\text{2}\text{3}$ ∫ ?$\text{5}\text{3}$ d_τ, T₂ [?] = $\text{1}\text{72}$ ∫ (??)²?^?1 d_τ, and T₄ [?] given by the formula of Hodges. Calculations of T₀, T₂ and T₄ are reported for He with ? both the Hartree—Fock and a very accurate density, and for Ne, Ar and Kr with ? the Hartree—Fock density. For Kr, T₀ + T₂ + T₄ is within 0.3% of the exact Hartree—Fock T, with T₂/T₀ = 0.05, T₄/T₂ = 0.17.     

Nephelauxetic effect in some lanthanide(III) complexes with 2-pyridineamidoxime

Diffuse reflectance spectra of tris-(2-pyridineamidoximato) lanthanide(III) chlorides, [Ln(PAO)₃] Cl₃, Ln = Pr, Nd, Sm, Eu, Dy and Ho, in the visible region have been recorded for the first time. Shifts (100–150 cm^?1) of their f ? f transitions have been observed towards lower wave numbers in relation to the lanthanide aquoions. These data have been used for evaluation of the nephelauxetic ratio β′ and the covalency parameters b^{$\text{1}\text{2}$}. Sublevels with J = 0 and J = $\text{1}\text{2}$ as well as hypersensitive bands, obeying the selection rules|ΔJ|?2,|ΔL|?2, have been considered. The results have been discussed in terms of weak covalent bonding between the lanthanide ion and the nitrogen atoms of the ligands.     

Alkali salts of (ω-sulphoxyalkyl)-acrylates and -methacrylates: Radical polymerization and copolymerization

A new preparation of alkali salts of (ω-sulphoxyalkyl)-acrylates and -methacrylates, by reaction of alkali salts of acrylic and methacrylic acids with cyclic sulphates, is described; spectral characterization of the products is described. The kinetics of the radical polymerization of sodium (2-sulphoxyethyl)methacrylate (SSEM) were studied; monomer reactivity ratios for copolymerization with methacrylic acid were: r₁ = 1.1 ± 0.15 and r₂ = 0.73 ± 0.05. Dark electrical surface conductivity of some homopolymers and copolymers with methacrylic acid was found to be 10⁴–10¹¹$\text{Ω}{}^{\mathrm{?1}}$, depending on relative humidity.     

Vinyl polymerization initiated by the (dimethylaniline-n-oxide)/(phenacyl bromide) system

Binary systems consisting of dimethylaniline-N-oxide (DMOA) and some α-halo-carbonyl compounds, such as phenacyl halide and α-halo-acetic acid ester, were found to induce radical polymerization of vinyl monomers. Bromo-derivatives showed higher initiating activities than chloroderivatives. The polymerization of methyl methacrylate (MMA) with DMAO and phenacyl bromide (PBr) was investigated kinetically. The polymerization rate (R_p) was expressed as follows; $\text{R}{}_{\mathrm{<mtext>p</mtext>}}\text{=}\text{k[DMAO]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{PBr}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{MMA}\text{]}$.The overall activation energy of the polymerization was calculated to be 42.7 kJ mol^?1. No noticeable chain-transfer from the polymer radical to DMAO or PBr was observed. The benzoyl radical was trapped by 2-nitroso-2-methylpropane, a spin trapping reagent, in the reaction of DMAO and PBr. The u.v. spectrum of poly (MMA) obtained suggests that the polymer contains end-groups similar to acetophenone and DMA. From the results, an initiation mechanism for the polymerization has been proposed and discussed.