New main chain nonlinear optical polymers with high glass transition temperatures

Summary Various 4-methoxy-4-carbomethoxy--amino--cyanostilbenes were prepared as mixtures of E and Z isomers, and polymerized via condensation polymerization using dibutyltin diacetate as catalyst. The resulting low molecular weight homopolymers showed higher glass transition temperatures (168–183°C) than previously reported main chain nonlinear optical (NLO) homopolymers. A high molecular weight (M_n30, 200) copolymer possessed an even higher glass transition temperature of 187°C. The hyperpolarizability of the polymers and a model compound were found by EFISH measurements to be in the range of 61 to 79x10^-48 esu.     

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.     

Synthesis and properties of aromatic polyesters and brominated polyesters derived from α,α′-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene

The interfacial polycondensation technique was used for the preparation of polyarylates and brominated polyarylates. Polyarylates and brominated polyarylates were prepared by mixing a solution of diacid chloride such as terephthaloyl chloride, isophthaloyl chloride, or their mixture in dichloromethane with an aqueous alkaline solution of ,-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene or ,-bis(4-hydroxy-3,5-dibromophenyl)-1,4(or 1,3)-diisopropylbenzene using triethylbenzylammonium chloride as the phase transfer agent. Moderate to high molecular weight polyarylates with _inh up to 1.27 dL/g were obtained, and most of them could be cast into tough and flexible films depending on the polymer composition. In general, polymers containing more 1,3-isomer or isophthaloyl chloride moieties gave transparent and flexible films and had lower glass transition temperatures and higher solubility. Although these polymers have two isopropylidene linkages in their repeating units, they still exhibit moderately high thermal stability and show no obvious weight loss before 400 °C. The introduction of bromine on the polymer backbone caused a decrease of inherent viscosity, crystallinity, and thermal stability of the polyarylates, while causing an increase in glass transition temperature and a great enhancement of fire retardancy.     

Crystallization of barium diborate glass

The conditions for crystallization of a new modification of barium diborate in the glass of stoichiometric composition are investigated. This modification is characterized using X-ray diffraction analysis. In order for the -BaO 2B₂O₃ modification to crystallize, the glass should be purified from dissolved gases and have an undisturbed fire-polished surface. Otherwise, the modification crystallizes under the same conditions. The melting temperature of the -BaO 2B₂O₃ modification is determined to be T _melt = 805°C. Upon heating, the modification in the form of a powder transforms into the modification, whereas the modification in the form of a polycrystalline monolithic sample remains stable up to the melting temperature.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Polyakova, Pevzner.     

Viscosity and relaxation times temperature behaviour above the glass transition in some glassy polymers

We have performed mechanical and dielectric dynamic measurements above the glass-transition temperature range of two glassy-polymers: Poly(Hydroxyether of Bisphenol-A) and Poly(Carbonate of Bisphenol-A). From these measurements the temperature dependence of mechanical and dielectric mean relaxation times has been calculated. Results obtained have been compared with the viscosity temperature behaviour of the same polymers, which has been reported elsewhere. Both, relaxation times and viscosity temperature behaviour can well be described by Doolittle functional forms, exp{1/[_f(T-To)]}, with the same values of To but different values of the apparent free-volume expansion coefficient, _f. This difference in the experimental behaviour has been addresed in the framework of the free-volume model ideas. In this context, the different values of _f obtained from viscosity and relaxation times temperature behaviour can be understood assuming different values of critical volume controlling the molecular motions associated to viscosity and relaxation processes. Similar conclusions have also been obtained by means of a fine revision of the viscosity and relaxation times data of another two glassy-polymers: Poly(Arylate) and Poly(Sulfone of Bisphenol-A), reported previously.     

Chemical modification of copoly(methylsilylene/1,4-phenylene) by Pt-catalyzed hydrosilation reactions with functionally substituted alkenes

Copoly(methyl-3-biphenoxypropylsilylene 1,4-phenylene), copoly(methyl-3-cyanopropylsilylene 1,4-phenylene), copoly(methyl-3-ethoxypropylsilylene 1,4-phenylene), copoly(methyl-3-phenoxypropylsilylene 1,4-phenylene), and copoly(methyl-4,7,10,13-tetraoxatetradecanylsilylene 1,4-phenylene) have been prepared by platinum-catalyzed hydrosilation graft reactions between poly (methylsilylene 1,4-phenylene) and appropriate functionally substituted alkenes. These polymers have been characterized by¹H,¹³C, and²⁹Si NMR as well as by FT-IR and UV-vis spectroscopy. The molecular weight distribution of these polymers has been determined by gel permeation chromatography (GPC), and their glass transition temperatures (T _e) by DSC.     

Determination of complexation equilibria of macromolecules with small molecules by means of size exclusion chromatography

Summary The insertion of oligo(tetraflouroethene) segments into the main chain of poly(aramide)s and poly(amide imimide)s is accompanied by a decrease of the glass temperature. The decrease is strictly related to the number of CF₂-units and is the same for both poly(aramide)s and poly(amide imide)s. The absolute glass temperature depends, however, on the initial structures of the monomeric units. As a consequence mastercurves can be constructed by shifting the individual Tg vs. number of CF₂-units curves along the temperature axis. A detailed analysis of the data indicates that besides the Tg-mass/flexible bond of monomeric unit criterion additional volume and interaction dependant packing effects have to be considered for an accurate prediction of the glass temperatures of polymers.Dedicated to the 65th anniversary of Prof. Dr. Dr.-lng. E. h. Hansjörg Sinn     

Formation and reactions of isocyanic acid during the catalytic reduction of nitrogen oxides

Reactions which can produce and consume isocyanic acid (HNCO) over two types of catalysts active for the reduction of nitrogen oxides have been investigated. More than 1000 ppm HNCO can be produced by the reduction of 3000 ppm NO with H₂/CO mixtures over a Pt/SiO₂ catalyst. Complete hydrolysis of HNCO to ammonia and carbon dioxide occurs if even weakly catalytic materials, such as CeO₂/SiO₂ and BaO/SiO₂, are placed downstream. Isocyanic acid is also involved as an intermediate in the reaction of nitromethane over CoZSM5 and CuZSM5 under the conditions of hydrocarbon SCR. In the initial stages of reaction there is complete conversion through to N₂ with CuZSM5 but the process stops at ammonia with CoZSM5 at temperatures below 350°C. In both cases, but especially with CoZSM5, isocyanic acid becomes observable as the catalyst deactivates during continuous exposure at temperatures below about 290°C. In situ FTIR measurements indicate that deactivation is due to a reaction between isocyanic acid and ammonia which generates cyclic striazine compounds.     

Parameters of the Fluctuation Free Volume Theory for Glasses in the Ge-As-Se System

The fraction of fluctuation free volume (f _g = V _f/V) frozen at the glass transition temperature T _g is determined from the temperature dependence of the viscosity in the glass transition range in terms of the Vogel-Fulcher-Tammann equation and the formula _f T _g T _g = f _gln(1/f _g). The fluctuation free volume fractions f _g obtained according to these two procedures for glasses in the Ge-As-Se system are in quite reasonable agreement. The energies E _h of formation of fluctuation microvoids and their volumes V _h are calculated. It is demonstrated that the quantities f _g, E _h, and V _h and the ratio of the microhardness H to T _g depend substantially on the glass structure and can serve as characteristics of the rigidity of the glass networks. It is noted that the fluctuation free volume fraction f _g is a nonmonotonic function of the mean coordination number Z _m and that it exhibits a specific dependence on the lattice Grüneisen parameter . The Poisson ratios are estimated from the fluctuation free volume fraction f _g with the use of the relationship f _gln(1/f _g) = . It is shown that the Poisson ratios thus obtained are close to those calculated from the data on the transverse (V _s) and longitudinal (V _l) velocities of ultrasound.     

Synthesis and properties of aromatic polyamides and polyesters containing spiroacetal and silphenylene units

Summary New polyamides and polyesters containing spiroacetal and silphenylene units were prepared by the low-temperature interfacial polycondensation reaction of 4,4-diaminodibenzalpentaerythritol (4-ABP) or 4,4-dihydroxydibenzalpentaerythritol (4-HBP) with bis(4-chlorocarbonylphenyl)dimethylsilane (DMS) or bis(4-chlorocarbonylphenyl)diphenylsilane(DPS). The resulting polymers have inherent viscosities in the range of 0.130.90 dL/g at 30°C in N,N-dimethylacetamide. These polymers were readily soluble in various polar solvents and were able to be cast into transparent and tough films. The glass transition temperatures of the polymers were detected in the range of 161253°C in their differential scanning calorimetry traces. No evidence of melting point was observed in all polymers. The solution-casted film of polyamide (PA-I) derived from 4-ABP and DMS showed ultimate strength of 73.4 MPa and initial modulus of 13.4 GPa.     

Relaxation fluctuations in poly(2-hydroxyethyl methacrylate) gels swollen in butanol

Summary Quasielastic light scattering measurements on transparent poly (2-hydroxyethyl methacrylate) (PHEMA) gels were performed under temperature equilibrium conditions at several temperatures from 40 to 80°C. All observed correlation functions departed from the single exponential decay with a long-time limit. The asymptotic value relaxation frequency _a decreased steeply with decreasing temperature. The observed temperature dependence of _a is interpreted as resulting from polymer fluctuations near the glass transition of weakly swollen PHEMA gels.     

ΔCp, Δα and related quantities for epoxy-aromatic amine networks

Summary The parameters of glass transition in several epoxyamine polymer networks were obtained. The changes C_p (T_g) and (T_g) were proved to be correlated with the concentration of crosslinks in these systems. The difference in glass transition parameters for linear and densely crosslinked polymers was analysed in terms of Simha-Boyer (T_g) and Boyer (C_p·T_g) rules and Eyring's hole theory.     

Calculation of the Viscosity of Glass-Forming Melts: VI. The R2O–B2O3–SiO2and RO–B2O3–SiO2Ternary Borosilicate Systems

A method for calculating the viscosity from composition and temperature for melts in the R _m O _n –B₂O₃–SiO₂systems is proposed. The change in the concentrations of structural groups depending on the melt composition is taken into account in calculations. The results of calculations are compared with the experimental data available in the literature on the viscosity of 1200 melts with the use of the SciGlass information system. The root-mean-square deviation between the experimental and calculated characteristic temperatures varies from 30 K (for the glass transition temperature and the Littleton point) to 50 K (for a viscosity of 10⁴P).     

Glass transition of polystyrene model molecules

Sumnary The glass transition temperatures of 2,4-diphenylpentane, 2,4,6triphenylheptane and 2,4,6,8-tetraphenylnonane are shown to follow the relation Tg = 325 – 2.64 × 10⁴/M_n where M_n is the molecular weight. 2,4-diphenylpentane-2,4,6-triphenylheptane mixtures exhibit only one glass transition temperature which follow the relation Tg = (1 – ₂) Tg₁ + ₂ Tg₂ where ₂ is the weight % of 2,4-diphenylpentane. The configurational structure of these polystyrene model molecules is shown to slightly influence the Tg's values.     

New Poly(Methacrylate)s Containing Benzylpiperazine and Methylpiperidine Moieties

The synthess of two new methacrylate esters containing 2-(4-benzyl piperazin-1-yl)-2-oksoethyl and 2-(4-methylpiperidin-1-yl)-2-oksoethyl group are described. The monomers produced from the reaction of corresponding 4-methylpiperidinechloroacetamide and 1-benzylpiperazinechloroacetamide with sodium methacrylate were polymerized in DMSO solution at 65°C using AIBN as an initiator. The monomers and their polymers were characterized by IR, ¹H- and ¹³C-NMR spectroscopy. The glass transition temperature of the polymers were investigated by DSC and the apparent thermal decomposition activation energies (E _d ) were calculated by Ozawa method using the SETARAM Labsys TGA thermobalance. By using gel permeation chromatography, weight average ( ) and number average ( ) molecular weights and polidispersity, indices of the polymers were determined.     

Turbulent mass transfer in small radius ratio annuli

Mass transfer in annuli for both fully developed laminar and turbulent flow conditions has been studied with respect to available experimental data. It is shown that prediction of the Sherwood number for the inner annular wall based on the hypothesis of coincidence of the zero shear stress position for laminar and turbulent flows leads to serious error in the case of small radius ratio. Also it is shown that in contrast with plain tubes the curvature in small radius ratio annuli should be taken into account for the case of small Reynolds numbers. In consequence, the well-known Leveque equation can be used for the calculation of the mass transfer coefficient in annuli only under certain conditions. Possibilities of electrodiffusion diagnostics for the precise determination of the zero shear stress position in annuli are discussed.List of symbols A cross-section flow area (m²) - a =r ₁/r ₂ annular radius ratio (–) - mean fluctuation and bulk concentration (mol m^–3) - D molecular diffusivity (m²s^–1) - d _b hydraulic diameter (m) - f,f ₁,f ₂ overall, inner and outer wall friction factors (–) - f = ₁/ near wall velocity gradient (s^–1) - pressure drop per unit of length (Pam^–1) - K _L average mass transfer coefficient (ms^–1 ) - k =r ₀/r _0,L ratio of zero shear stress position in turbulent and laminar flows (–) - L mass transfer surface length (m) - L _D diffusion leading edge length (m) - L _ent diffusion entrance length (m) - P _W wetted perimeter (m) - Re =U _av d _h/ Reynolds number (–) - r radial distance from conduit axis (m) - r ₀,r _o,L radial distance of zero shear stress position in turbulent and laminar flows (m) - r ₁,r ₂ radius of inner and outer annular cylinders (m) - Sc = /D molecular Schmidt number (–) - Sh =K _L d _h/D Sherwood number (–) - U _av average liquid velocity (ms^–1) - u,u mean and fluctuation axial velocity (ms^–1) - , mean and fluctuation radial velocity (ms^–1) - y = r – r ₁ distance from the inner wall (m) - y = (/₁)^1/2 dynamic length (m) - Z distance in direction of the flow (m) Greek symbols _D diffusion layer thickness (m) - µ dynamic viscosity (Pa s) - kinematic viscosity (m²s^–1) - density (kgm^–3) - shear stress (Pa) - _W wall shear stress for tube and plate channel (Pa) - ₁, ₂ wall shear stress for inner and outer annular cylinders (Pa) - Geometrical factor with respect to k-function (–) - _R, _K geometrical factor with respect to Rothfus or Kays-Leung equations (–) - ratio of radial distance of zero shear stress position to outer radius in laminar flow (–)     

Determination of the Fluctuation Free Volume Fraction for Glasses in the As–S(Se) Systems

The fraction f _g of fluctuation free volume frozen at the glass transition temperature is determined from the temperature dependence of the viscosity in terms of the Vogel–Fulcher–Tammann equation and the formula T _g = f _gln(1/f _g). The fluctuation free volume fractions obtained using these two procedures for glasses in the As–S(Se) systems are in quite reasonable agreement. It is demonstrated that the difference in the ratios between the fraction of fluctuation free volume and the lattice Grüneisen parameter for chalcogenide and oxygen-containing glasses is associated with the specific structure of the network of chalcogenide glasses. It is found that the dependence of the fluctuation free volume fraction on the mean coordination number Z _m, which characterizes the degree of connectivity of the network in noncrystalline materials, exhibits nonmonotonic behavior.     

On the rate-determining step and the role of potassium in the catalytic synthesis of ammonia

The simple concept of a single rate-determining step, the dissociation of N₂(a), in ammonia synthesis is inconsistent with experimental results. It is proposed that three reaction steps, N₂(a) 2N(a) (1) N(a) + H(a)NH(a) (2) NH₃(a)NH₃(g) (3) are dominant in determining the rate of synthesis. Under industrial conditions reactions (2) and (3) are more important than (1). The role of K⁺ as promoter in these reactions is discussed, especially as an anchor for adsorbed oxygen.     

The effect of support structure on CO2 hydrogenation over a rhodium catalyst supported on niobium oxide

The hydrogenation of CO₂ was investigated over a rhodium catalyst supported on niobium oxide at atmospheric pressure. Niobium oxide was prepared by the hydrolysis of niobium chloride and its crystallitic structure was controlled by calcination temperature. It was found that the activity was lower but the selectivity of C₂₊ hydrocarbons was higher for the and forms than for the and forms of the niobium oxide.     

Properties ofSrMO 3-δ(M=Fe,Co) as oxygen electrodes in alkaline solution

Strontium ferrates and cobaltates with compositions SrFeO_3- (0.060.40) and SrCoO_3- (0.040.30) were synthesized. The dependence of the oxygen electrode properties on the value was examined in 1 mol dm^–3 KOH solution. In the SrFeO_3- series, the samples with 0.24<<0.29, showed the highest activity in both oxygen evolution and reduction reactions. In contrast, no strong dependence on the value was observed in SrCoO_3-, which also showed a high catalytic activity for oxygen evolution.