Polymerization of lactams

Summary The following limit (ceiling) temperatures of polymerization were extrapolated from kinetic data for the anionic polymerization of 2-pyrrolidone initiated with potassium salt of 2-pyrrolidone and the initiation systems of optimum compositions: 66°C for the nonactivated polymerization, 68°C and 73°C for the polymerization accelerated with 1-(1-pyr-rolin-2-yl)-2-pyrrolidone and carbon dioxide, respectively, 73°C and 76°C for the polymerization activated with N-benzoyl-2-pyrrolidone and N-acetyl-2-pyrrolidone,respectively.     

Selective catalytic reduction of nitric oxide over vanadia grafted on titania. Influence of vanadia loading on structural and catalytic properties of catalysts

The selective catalytic reduction (SCR) of NO by NH₃ has been studied over vanadia/ titania catalysts prepared by selective immobilization of vanadyl alkoxide species on two structurally different titania supports. The loading of vanadia was varied from 1.8 to 7.5 ,mol V⁵⁺ per m² surface area. Comparative kinetic measurements at 150 °C show that the NO turnover frequencies increase by more than an order of magnitude when the vanadia loading is increased from 1.8 to 3 mol V⁵⁺/m². In the region of lower SCR activity, i.e. at lower coverages ( 2 mol V⁵⁺/m²), small clusters and ribbons of vanadia are detected in the Raman spectra, whereas at loadings where maximum NO turnovers are achieved ( 3 mol V⁵⁺/m²) the prevalent vanadia species are well-developed two-dimensional vanadia layers bound to titania.     

Hydrodechlorination of dichlorodifluoromethane on carbon‐supported Group VIII noble metal catalysts

Activated carbonsupported Group VIII noble metals formed CF₂Cl₂ oligomerization products under hydrodechlorination conditions. All the catalysts underwent deactivation during first 15–20 h on stream at 250°C independent of the H₂ partial pressure, with steadystate activity following the order: Pt > Pd Ir > Ru Os Rh. The Pd/C catalyst exhibited high selectivity toward C₂–C₃ hydrocarbons (75% at CF₂Cl₂/H₂ = 1). For the other catalysts except Pt, CF₂=CF₂ and CH₂=CF₂ were the main C₂₊ products.     

Does Density of Cationic Sites Affect Catalytic Activity of Co Zeolites in Selective Catalytic Reduction of NO with Methane?

Selective catalytic reduction of NO with methane (CH₄-SCR) in an excess of oxygen over Co ions located in ZSM-5 of various Si/Al composition and in ferrierite, mordenite, chabazite and beta zeolite was investigated. From the comparison of the dependence of the TOF values per Co ion for NO conversion to N₂ and Co ions distribution among the cationic sites on total Co ion concentration, the catalytic activity of the individual Co ions was estimated. The -type Co²⁺ ions, located in the main channel of mordenite and ferrierite and coordinated above the rectangle of four framework oxygens of the channel wall exhibit the highest activity in these zeolites. On the other hand, the -type Co²⁺ ions coordinated in the plane of four oxygens of the deformed six-member ring located in the channel intersection of ZSM-5 and in channels of beta zeolite control the activity of these Co zeolites. The sequence of activity of Co²⁺ ions in CH₄-SCR of NO was FER Co>ZSM-5 Co>BEA CoZSM-5 CoFER CoMOR CoCHA CoMOR Co. A correlation between the activity of the individual Co ions in CH₄-SCR of NO and a distance between the cationic sites was observed.     

Dependence of the Fluctuation Free Volume of Amorphous Substances on the Cooling Rate

The dependence of the fraction f _g of fluctuation free volume (frozen at the glass transition temperature) on the cooling rate is determined using the Bartenev equation for the dependence of the glass transition temperature on the cooling rate. Both dependences are found to be similar to each other. It is shown that the constancy of the ratio of the empirical coefficients involved in this equation (C ₁/C ₂ const 0.03) stems from the criterion for glass transition (f _g const 0.02–0.03) in the theory of fluctuation free volume.     

Triggering of Detonation upon Flame Interaction with an Expansion Wave

The transition of a deflagration wave into an abruptly expanding part of a plane channel, where a quasisteady supersonic underexpanded jet of an unburned gas is formed, is studied for a propane–oxygen mixture using schlieren pictures. Two explosioninitiation modes (weak and strong) are registered. In the first case, almost instantaneous onset of the detonation wave occurs when the flame front enters the expanding section; the initial velocity of this wave is approximately 1.5 times the Chapman–Jouguet detonation velocity (D_CJ) and then decreases to a value corresponding to selfsustaining detonation. In the second case, the front velocity gradually increases from 0.4D _CJ to 1.0D _CJ. It is established that the starting pulse triggering the transformation of turbulent combustion to explosion and detonation regimes is generated by interaction of the flame front with expansion waves, which are elements of the structure of the initial section of the jet.     

Activity enhancement of copper-containing oxide catalysts by addition of cesium in the reduction of nitric oxide

Catalytic reduction of nitric oxide in the presence of propylene and oxygen over alumina and copper-containing oxide catalysts has been studied. The optimum temperature for this reaction is dependent upon the composition of the catalysts: 640 K on Cu-Cs/Al₂O₃, 680 K on Cu/Al₂O₃, and 780 K on Al₂O₃. IR spectroscopic measurements show that an isocyanate (–NCO) intermediate formed on Cu-Cs/Al₂O₃ is more reactive with NO to give N₂ than the intermediate produced on Al₂O₃ and Cu/Al₂O₃. Electron donation from Cs to Cu may activate the intermediate.     

Possibility of Initiation of Combustion of CH4–O2 (Air) Mixtures with Laser‐Induced Excitation of O2 Molecules

The possibility of initiation of combustion of CH₄–O₂ mixtures with excitation of O₂ molecules to the states a¹_g and b¹⁺ _g by laser radiation with wavelengths of 1.268 m and 762 nm is considered. It is shown that excitation of O₂ molecules significantly decreases the induction period and ignition temperature because of accelerated formation of active atoms and radicals and intensification of the chain mechanism of the process. Even if the specific energy of laser radiation absorbed by the gas is low ( 0.1 eV per molecule), the ignition temperature of the CH₄–O₂ mixture with a ratio of 1:2 can be reduced from 1000 to 300 K.     

Characterization of poly(diethoxyphosphazene) by size exclusion chromatography and viscometry

Two samples of poly(diethoxyphosphazene) (PDEP) having very different molecular weights have been studied by viscometry and size exclusion chromatography in THF solution. The results obtained, together with light scattering data of these samples, allow the calculation of the Mark-Houwink constants a=0.65 and K=2.5 10^-4 in THF at 25°C. The method of calculation employed takes into account the great polydispersity of the samples. The characteristic ratio of the unperturbed dimensions was also calculated giving C_n = r²_o/n² 18, a value slightly higher than those previously reported for poly(dihexoxyphosphazene), C_n13 and poly (dichlorophosphazene), C_n13.5.     

Lean NOx catalysis over alumina‐supported catalysts

aluminasupported catalysts show promise as lean NO_x catalysts. The role of alumina in influencing the structural and chemical properties of the active phase supported on it is discussed using some effective aluminabased lean NO_x catalysts. These include Ag/Al₂O₃, CoO_x/Al₂O₃ and SnO₂/Al₂O₃. Alumina plays an important role in stabilizing Ag in the oxidic phase and cobalt in the 2+ oxidation state. For SnO₂/Al₂O₃, alumina increases the SnO₂ surface area. On both Ag/Al₂O₃ and SnO₂/Al₂O₃, alumina also participates actively in the NO_x reduction reaction. An active organic intermediate is formed on Ag or Sn oxide which reacts with NO_x subsequently on alumina to form N₂.     

Racemic poly(α-alkyl-α-phenyl-βpropiolactone) substituent dependence

Summary The -phenyl--alkyl--propiolactones (alkyl groups =-CH₂CH₃; -CH₂CH₂CH₃; -CH₂CH₂CH₂CH₃) were synthesized and polymerized by anionic ring-opening polymerization by tetra-ethylammonium benzoate (non-chiralic initiator). It was found that the molecular weight of polylactones increased as the size of the alkyl substituent increased. Poly(-propyl--phenyl--propiolactone) showed the highest melting temperature. Lactones polymerized using tetraethylammonium dibenzoiltartrate (chiralic initiator) gave polyesters with higher melting temperature than those obtained with a non-chiralic initiator under the same conditions.     

On the preparation and properties of CuZSM-5 catalysts for NO decomposition

Equilibrium exchange isotherms were determined for the exchange of Cu²⁺ with NaZSM-5 at varying Cu(Ac)₂ concentrations in solutions of constant volume and zeolite weight. At low Cu²⁺ levels the solid scavenged all the copper ions. When copper could be detected in the equilibrated solutions, overexchange was observed. The extent of overexchange was higher at pH 6 than at pH 4. These results were analyzed in relation to catalytic activity.On leave from the Central Institute for Chemistry, Hungarian Academy of Sciences, H1525 Budapest, Hungary.     

Calculation of Temperature Dependences of the Viscosity and Volume Relaxation Time for Oxide Glass-Forming Melts from Chemical Composition and Dilatometric Glass Transition Temperature

The relaxation parameter K _sthat is equal to the ratio of the viscosity to the Kohlrausch volume relaxation time _s is analyzed. It is shown that this parameter can be evaluated from the temperature T ₁₃(corresponding to a viscosity of 10¹³P) and the glass transition temperature T ₈ ⁺determined from the dilatometric heating curve. The maximum error of the estimate with due regard for experimental errors is equal to ±(0.4–0.5)logK _sfor strong glasses and ±(0.6–0.8)logK _sfor fragile glasses, which, in both cases, corresponds to a change in the relaxation times with a change in the temperature by ±(8–10) K. It is revealed that the viscosity, the Kohlrausch volume relaxation time _s , and the shear modulus Gof glass-forming materials in silicate, borate, and germanate systems satisfy the relationship log( _s G/) 1. The procedure for calculating the temperature dependences of the viscosity and the relaxation times in the glass transition range from the chemical composition and the T ₈ ⁺temperature for glass-forming melts in the above systems is proposed. The root-mean-square deviations between the calculated and experimental temperatures T ₁₁and T ₁₃are equal to ±(6–8) K for all the studied (silicate, borate, germanate, and mixed) oxide glass-forming systems. The proposed relationships can be useful for evaluating the boundaries of the annealing range and changes in the properties and their temperature coefficients upon cooling of glass-forming melts.     

Partial oxidation of methane over platinum metal gauze

The partial oxidation of methane to synthesis gas has been studied over a platinum gauze catalyst. The experiments were carried out at atmospheric pressure with a single gauze in a quartz reactor heated in an electric furnace. The furnace temperature was varied in the range 200–900°C and the space time in the range 0.00021–0.00042 s. The feed consisted of a mixture of CH₄O₂Ar2110 and carbon oxides and water were the main products. Oxygen was only partly consumed and relatively small amounts of hydrogen were formed.     

The relaxation and equilibrium behaviour of model polyurethane networks

Summary The mechanical, dielectric and rheo-optical behaviour of model networks prepared from OH-terminated poly(oxypropylene)triols and 4,4-diphenylmethane diisocyanate with various molar ratios of hydroxyl to isocyanate groups, r_H=0.95 to 1.7, was investigated. The observed independence of the stress-optical coefficient of r_H indicates the homogeneity of networks. Networks prepared with r_H1 exhibit a narrow transition zone indicating a narrow chain distribution. With increasing r_h, the transition becomes distinctly broader; dielectric measurements are well correlated with the mechanical ones. The equilibrium modulus markedly decreases with increasing r_H.Presented at the 7th IUPAC Discussion Conference Polymer Networks, Karlovy Vary, CSSR, September 15–19, 1980     

Palladium-Mediated Ring-Opening Reactions of Strained Cyclotetrasilanes

Room-temperature ring-opening polymerization of the strained monomer 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane mediated by palladium complexes was attempted. Examination of the reaction products between the cyclotetrasilane and the metal complex at high concentrations indicated that insertion of one cyclotetrasilane molecule between the ligand–palladium bond was followed by reductive elimination of the tetrasilane. Among the palladium complexes examined were (³-allyl)PdCp [Cp=⁵-cyclopentadienyl], [(³-allyl) PdCl]₂, (³-allyl)PdCl(PPh₃), (³-allyl)PdCl(PPh₃)₂, (³-allyl)Pd(PPh₃)₃ and PdCl₂(PPh₃)₂. Reaction of 1,1,2,3,4-pentamethyl-2,3,4-triphenylcyclotetrasilane with (³-allyl)PdCp provides similar products.     

Electrodeposition, composition and structure of Zn—Cr alloys

The effect of polyethylene glycol (PEG 1500) as additive and of deposition conditions on Zn—Cr alloy electrodeposition from an acidic sulfate electrolyte at room temperature, without agitation was investigated. PEG polarizes the overall cathodic reaction and inhibits Zn deposition. Cr codeposition with Zn starts at a cathodic potential of about –1,95 V vs Hg/Hg₂SO₄, which is reached at current density of about 20 A dm^–2 in galvanostatic conditions. Zn—Cr alloy coatings containing up to 28 at % Cr were obtained depending on the plating conditions. SEM observations showed an island-like structure, formed by the local growth of crystals, which covered the surface during further deposition. In the first stages of electrodeposition the powder diffraction spectra contain lines of b.c.c. -(Zn,Cr) phase (a 3.02 Å). After 30 s deposition time weak lines of Zn-based phase (a 2.67 Å, c 4.90 Å) appear, and become clearly visible in coatings deposited for 90 s. The average Cr content in the alloy coatings decreases with advancing deposition. The as-plated surface contains C in organic compounds and Zn(OH)₂. After 50 min sputtering, Zn and a mixture of Cr, Cr₂O₃ and Cr₇C₃ were found. The presence of organic C and O, probably from inclusions of PEG, were also detected.     

Ultradrawing of “springy” polypropylene films

Summary It is demonstrated that in the process of ultradrawing of semicrystalline polypropylene the morphology of the initial material plays major role. Extremely high draw ratios are obtained (_max50) when drawing hard elastic polypropylene films perpendicular to their initial molecular orientation. This behaviour is explained by the molecular processes of plastic deformation.     

Effect of Kinetic Properties of a Mixture on Wave Macrocharacteristics of Filtration Combustion of Gases

On the basis of the latest experimental data using a detailed kinetic model, the influence of kinetic features of ultrarich methaneair mixtures (in comparison with ultralean ones) on the main characteristics of superadiabatic waves of filtration combustion of gases is considered. It is shown that substantially lower concentrations of O, OH, and H radicals are typical of ultrarich mixtures, which results from effective inhibition of atomic hydrogen participating in the chain branching reaction H + O₂ = OH + O by methane in the reaction H + CH₄ = CH₃ + H₂. Therefore, extension of the preheating zone and noticeable expansion of the heatrelease region are typical of rich compositions. A decrease in generation of the main radicals in ultrarich mixtures (as compared to ultralean compositions) leads to an increase in the maximum skeleton temperature by 300– 350 K and to a significant increase in velocity of wavefront propagation.     

Modeling of the Transformation of Sulfur Compounds in Oxygen Gasification of Coal Dust

It is shown that, owing to the presence of a large amount of Ca and Fe in the mineral part of a fuel, it is possible to substantially reduce the sulfur content in the gaseous phase and, hence, improve ecological indexes of the process under the following conditions: the content of O₂ is close to the stoichiometric value for fuel gasification, the temperature is (1600–1800) K, and the pressure is 10 atm or higher.