Structural investigation of microbial poly(ε-L-lysine) derivatives with azo dyes by solid-state 13C and 15 N NMR

Summary Solid-state high-resolution ¹³C and ¹⁵N NMR spectra of microbial poly(-lysine) (-PL) derivatives with azo dyes have been measured. Chemically modified derivatives of -PL, -PL/MO and -PL/DC were prepared through reactions with methyl orange (MO) and dabsyl chloride (DC), respectively. Side chain -amino groups of -PL in -PL/MO are involved in ionic bonds with methyl orange to form poly-ion complexes, (-PL)-NH₃⁺SO₃^--(MO). On the other hand, -PL is allowed to react with dabsyl chloride in -PL/DC to form covalent sulfonamide bonds, (-PL)-NH-SO₂-(DC). These chemically modified -PLs exhibit ¹⁵N NMR signals characteristic of the binding mode at the -amino groups. The spectral analysis reveals that the -PL/DC sample contains a small amount of ion complexes with MO. It has been shown that ¹⁵N solid-state NMR is a useful tool for structural determination of -PL and its derivatives.     

Voidage of bulk solution in a tall vertical gasevolving cell

Vertical electrolysers with parallel-plate electrodes and with a narrow interelectrode gap or with narrow gaps between the membrane and each of the electrodes are used industrially to produce gases. Conductivity measurements were carried out with a small conductivity cell built within one compartment of the cell and just above the top of the working electrode. KOH solutions were used as electrolytes and gas bubbles were evolved at a 20-segment electrode. The effect of various parameters, including current passed through the 20-segments electrode, flow rate of liquid, temperature and nature of gas evolved, was studied. From the normalized conductivity measured, the gas voidage was obtained. It was found that for a bubbly flow the gas voidage just above the gas-evolving electrode is given by the relation:/(max – ) = 1.4 Qg/Qlwhere max is the maximum voidage for gas bubbles in a solution; max=0.69 for oxygen as well as hydrogen in a concentrated and a dilute KOH solution at different liquid flow rates. Qg is the volumetric flow rate of gas saturated with water vapour and Ql is the volumetric flow rate of liquid. This relation can be used to calculate the voidage distribution in the bulk solution of the cell compartment with a gas-evolving electrode.     

The effect of hydrogenation in the presence of raney nickel on the content of microimpurities of unsaturated compounds in ε-caprolactam

Conclusions 1. It has been confirmed that the qualitative indices of -caprolactam are improved after hydrogenation in the presence of Raney nickel.2. It has been shown that hydrogenation reduces the content of microimpurities of unsaturated compounds in -caprolactam.State Institute for the Nitrogen Industry (GIAP). Translated from Khimicheskie Volokna, No. 5, pp. 5–6, September–October, 1969.     

Characteristics,Linetics and Mechanism of ε-Caprolactone Polymerization by Lanthanide Tris(2.6-dimethylphenolate)s

Summary PolycaproIactone(PCL) was synthesized via the ring-opening polymerization of -caprolactone(-CL) with lanthanide tris(2.6 -dimethylphenolate)s[Ln(ODMP)₃] as initiator under mild conditions for the first time. The effects of reaction conditions on the -CL polymerization are discussed. Kinetic studies indicate that the polymerization rate is first order with respect to both monomer concentration and catalyst concentration, respectively, and the overall reaction activation energy amounts to 62.3kJ/mol. ¹H NMR end group analysis on the polymer demonstrates the ring-opening polymerization of -CL proceeds according to coordination-insertion mechanism with acyl-oxygen bond cleavage of the monomer.     

Enzymatic grafting modification of polyethylene film in nonaqueous solvents

Summary Diblock and triblock copolymer of -caprolactone(-CL) and styrene(St) were obtained by the combination of two different polymerization process, namely enzymatic ring-opening polymerization(ROP) and atom transfer radical polymerization(ATRP) methods. Mono-/di- hydroxyl terminated macromolecules were prepared by enzymatic ROP of -CL in the presence of Novozyme-435 and methanol/ethylene glycol as biocatalyst and initiator, respectively, and subsequently converted to bromine ended polycaprolactone(PCL) by the esterification of the resulting macromolecules with -bromopropionyl bromide. The mono- and difunctional macroinitiators were employed in ATRP of styrene using CuCl/2, 2-bipyridine(bpy) as the catalyst system. The GPC and ¹H-NMR analysis indicated a controlled/living radical polymerization which resulted in the formation of block copolymers with narrow polydispersities.     

Synthesis and characterization of nylon-polyisobutylenenylon triblock copolymers

Nylon-6-polyisobutylene-nylon-6 triblock copolymers have been synthesized by converting telechelic polyisobutylene diols to , -diisocyanate polyisobutylenes and using these macroactivators, in conjunction with strong base, to induce the subsequent anionic polymerization of -caprolactam. Pure block copolymer was obtained by suitable sequential extraction. Products were characterized by composition, molecular weight and DSC.     

Vapour phase beckmann rearrangement of cyclohexanone oxime over MEL type zeolites

The vapour phase Beckmann rearrangement of cyclohexanone oxime to -caprolactam is reported over different MEL zeolites viz., silicalite-2, titanium silicate-2 (TS-2), ZSM-11 and alumino-titanium-silicate (Al-TS-2) and fumed silica. TS-2 exhibits 100% conversions with lactam selectivities close to 90%. The titanium containing analogs are also more resistant to deactivation than the parent zeolites. The conversion of cyclohexanone oxime and selectivity for -caprolactam increase with temperature. The selectivity for -caprolactam increases with the duration of run at all the temperatures.     

Synthesis of new polydimethylsiloxane-ε-caprolactam block copolymers

Summary Poly(dimethylsiloxane--caprolactam) block copolymers were prepared from -caprolactam and anhydride-terminated polydimethylsiloxane oligomers under anionic conditions in the melt.     

Supertough poly(lactide)s

Summary Semi-crystalline and amorphous copolymers of lactide and glycolide were rubber modified with degradable rubbers based on -caprolactone. The influence of crystallinity of the matrix, type of rubber and chain architecture on the impact resistance of the resulting materials was investigated. With a poly(l-lactide-co--caprolactone) rubber semi-crystalline poly(lactide)s could be impact modified to a greater extent than amorphous non-crystallizable lactide matrices. Poly(trimethylene carbonate-co--caprolactone) was used in blends and linear and star-shaped block copolymers which yield supertough materials that do not break in Izod notched impact testing. Rubber content appears critical around 20 weight percent, where a sharp transition is observed.     

Viscous Flow and Plastic Deformation of Glasses in the Model of Excited Atoms

The critical displacement of an atom (a group of atoms) r _max, which corresponds to the interatomic interaction force at the maximum, is treated as the atomic excitation in liquids and glasses. The formation and migration of excited atoms are governed by local fluctuations of the configurational entropy. In amorphous linear polymers, the role of an excited kinetic unit is played by a small-sized macromolecular segment (an atomic group in a monomer). The atomic excitation in silicate glasses corresponds to the critical displacement of a bridging oxygen atom in the Si–O–Si bridge upon switching of adjacent bridging bonds. The activation energy _h = P _{max h} and the activation volume _h = d ²r _max of the atomic excitation are introduced. The activation energy _h is determined by the work done against the forces of the internal pressure P _max. The formation of an excited kinetic unit in polymers and glasses is a small-scale low-energy process ( _h = 10–20 kJ/mol, _h = 5–70 ų). The total activation volume of the system V _f = _h N _h is termed the fluctuation volume, and the model under consideration is referred to as the fluctuation volume model (or the model of excited atoms). The viscosity equation and other relationships of the hole theory are interpreted in the framework of the proposed model. This model is also applied to analyze the plasticity of amorphous polymers and glasses. A relationship between the glass transition condition and the Lindemann melting criterion is established.     

Mass transfer to planar and expanded metal electrodes in bubble columns

Mass transfer rates at planar electrodes and electrodes of expanded metal placed in the centre of a bubble column were measured. The gas velocity and the physical properties of the electrolytic solutions were varied and different types of expanded metal were investigated. In some cases increases in the mass transfer coefficient over the planar electrode value of more than 100% were obtained. Dimensionless correlations are presented for the different systems.Nomenclature A mean mesh aperture - D diffusivity - D _c column diameter - g acceleration due to gravity - Ga Galileo number =gL ³/v ² - Gr Grashof number =gL ³/v ² - k mass transfer coefficient - L electrode height - r radial position - R column radius - Re Reynolds number =R _h V _s/ - R _h hydraulic radius = / - Sc Schmidt number = /D - Sh Sherwood number =kL/D - V_s superficial velocity - gas void fraction - _M porosity of expanded metal - kinematic viscosity - density - electrode area per unit volume - electrode area per unit net area     

Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen

According to previous Mössbauer data [1] -sites formation at the activation of Fe-containing zeolites is accompanied by irreversible self-reduction of the iron, proceeding without participation of an external reducing agent. Reduced Fe²⁺ ions are inert to O₂ but are reversibly oxidized to Fe³⁺ by N₂O, generating the -oxygen species, O, which provide selective oxidation of hydrocarbons.In this work, the mechanism of -sites formation was studied via quantitative measurement of the dioxygen amount desorbed into the gas phase at the step of self-reduction. A prominent role of the zeolite matrix chemical composition has been revealed. For example, with zeolites of Al–Si composition (FeZSM-5 and Fe-), heating to 900 °C in a closed vacuum space leads to irreversible evolution of O₂, which is accompanied by the immediate formation of -sites. Similar heating of B–Si and Ti–Si zeolites also leads to dioxygen evolution; however, this evolution is reversible and is not accompanied by formation of -sites. Activation of these zeolites occurs only in the presence of water vapor. Stoichiometric measurements showed that in terms of charge one regular O^2- ion, removed at the activation, is equivalent to two -oxygen atoms. So, -oxygen is identified as an ion-radical species O ^-., whose unique oxidation properties still distinguish it from the generally observed O^-. radicals.The mechanism of -sites formation is proposed, in which the process of strong chemical stabilization of reduced Fe²⁺ atoms in the zeolite structure is a key step, making impossible the reoxidation of the iron with O₂.     

Synthesis of monocarboxylic polyoxyethylenes

Summary The various methods of synthesis which can be used to prepare -carboxy polyoxyethylenes are reviewed. The synthesis and the purification of -methoxy -carboxy polyoxyethylenes ( ) are reported. The process consists of the reaction of halogenoacetic acids with an -methoxy -sodium hydroxylate polyoxyethylene followed by a purification by extraction. ,-dimethoxy and -methoxy -ethyl carboxylate polyoxyethylenes were synthesized.     

Reason for the luminescence of polycaproamide and caprolactam

Conclusions It is suggested that the luminescing structures in polycaproamide and in the corresponding monomer have a single nature.One of the products from decomposition of caprolactam -hydroperoxide has well-defined luminescence properties; some conditions for its formation have been investigated.The most probable reason for the luminescence is the appearance of -ketoimide groups in caprolactam and polycaproamide due to thermal oxidation.Translated from Khimicheskie Volokna, No. 5, pp. 30–31, September–October, 1985.     

On the Polar Structural Fragments in Glasses from Dielectric Spectroscopic Data

The dielectric spectra of vitreous, glass-ceramic, and single-crystal Pb₅Ge₃O₁₁ are measured in the frequency ranges 3–33 and 30–1000 cm^–1. The inference is made that the Pb₅Ge₃O₁₁ glass can represent a polar medium in which the origin of dipoles is associated with the spatial inhomogeneity and the possible existence of crystal-like structural nanofragments that had time to form during cooling of the melt and are responsible for the medium-range order in the glass. This assumption is confirmed by the fact that low-frequency (at 30 cm^–1) values of " for the glass and the crystal along the polar axis are equal to each other and that the permittivity "_s of the glass (20.7) at submillimeter frequencies is intermediate between the permittivities " of the crystal along the polar (34.3) and nonpolar (19.5) axes. Such a ratio between the permittivities "_s of a crystal and a glass of the same composition is revealed for the first time owing to the high accuracy in measurements of the spectrum in the submillimeter region and strong anisotropy of the Pb₅Ge₃O₁₁ crystal. At the same time, the close values of the permittivities "_s for the glass and the crystal along the nonpolar axis indicate that polar atomic groupings in the glass are disordered and their structure on the nanoscale only resembles the structural motif of the crystal. The presence of microcrystals in the Pb₅Ge₃O₁₁ glass-ceramics leads to a noticeable increase in the permittivity " (25). The similarity between the IR spectra of all the Pb₅Ge₃O₁₁ crystalline modifications studied and the spectrum of a glass of the same composition (with due regard for the diffuseness of the spectrum of the glass) suggests that the glass and its crystalline analog have similar short- and medium-range order structures.     

Phase-structure analysis of brass by anodic linear-sweep voltammetry

Anodic linear-sweep voltammetry (ALSV) was applied to electrodeposited alloy layers and to metallurgically obtained Cu–Zn alloys of different composition and structure. Metallurgically obtained samples covered the range of composition in which , (+), and (+) intermediate phases were detected by X-ray. The ALSV of samples containing less than 30 wt % Zn exhibited a single peak at –0.08 to –0.1 V/SCE before massive dissolution, starting at about –0.05 V/SCE. The presence of the -phase gave another peak at a significantly more negative potential (–0.25 to –0.35 V/SCE). The ALSV of electrodeposited alloys were significantly more complex than the former, depending on the deposition potentials, with peaks attributable to pure Zn, to the -phase, to the -phase as well as to the -phase, present in most cases and dissolving at potentials similar to that of pure Cu. ALSV was shown to be a reliable and practical method for a fast determination of both the composition and the phase structure of electrodeposited brass.     

Behaviour of a tall vertical gas-evolving cell Part II: Distribution of current

Vertical electrolysers with a narrow electrode gap are used to produce gases, for example, chlorine, hydrogen and oxygen. The gas voidage in the solution increases with increasing height in the electrolyser and consequently the current density is expected to decrease with increasing height. Current distribution experiments were carried out in an undivided cell with two electrodes each consisting of 20 equal segments or with a segmented electrode and a one-plate electrode. It was found that for a bubbly flow the current density decreases linearly with increasing height in the cell. The current distribution factor increases with increasing average current density, decreasing volumetric flow rate of liquid and decreasing distance between the anode and the cathode. Moreover, it is concluded that the change in the electrode surface area remaining free of bubbles with increasing height has practically no effect on the current distribution factor.Notation A _e electrode surface area (m²) - A _e,s surface area of an electrode segment (m²) - A _{e, 1–19} total electrode surface area for the segments from 1 to 19 inclusive (m²) - A _e,a anode surface area (m²) - A _e,a,h A _e,a remaining free of bubbles (m²) - A _e,e cathode surface area (m²) - A _e,c,h A _e,c remaining free of bubbles (m²) - a ₁ parameter in Equation 7 (A^–1) - B current distribution factor - B _r B in reverse position of the cell - B _s B in standard position of cell - b _a Tafel slope for the anodic reaction (V) - b _c Tafel slope for the cathodic reaction (V) - d distance (m) - d _ac distance between the anode and the cathode (m) - d _wm distance between the working electrode and an imaginary membrane (m) (d _wm=0.5d _wt=0.5d _ac) - d _wt distance between the working and the counter electrode (m) - F Faraday constant (C mol^–1) - h height from the leading edge of the working electrode corresponding to height in the cell (m) - h _e distance from the bottom to the top of the working electrode (m) - I current (A) - I _s current for a segment (A) - I ₂₀ current for segment pair 20 (A) - I _1–19 total current for the segment pairs from 1 to 19 inclusive (A) - i current density (A m^–2) - i _av average current density of working electrode (A m^–2) - i _b current density at the bottom edge of the working electrode (A m^–2) - i ₀ exchange current density (A m^–2) - i _0,a i ₀ for anode reaction (A m^–2) - i _l current density at the top edge of the working electrode (A m^–2) - n ₁ parameter in Equation 15 - n _s number of a pair of segments of the segmented electrodes from their leading edges - Q _g volumetric rate of gas saturated with water vapour (m³ s^–1) - Q ₁ volumetric rate of liquid (m³ s^–1) - R resistance of solution () - R ₂₀ resistance of solution between the top segments of the working and the counter electrode () - R _p resistance of bubble-free solution () - R _p,20 R _p for segment pair 20 () - r _s reduced specific surface resistivity - r _s,0 r _s ath=0 - r _s,20 r _s for segment pair 20 - r _s, r _s for uniform distribution of bubbles between both the segments of a pair - r _s,,20 r _s, for segment pair 20 - T temperature (K) - U cell voltage (V) - U _r reversible cell voltage (V) - v ₁ linear velocity of liquid (m s^–1) - v _1,0 v ₁ through interelectrode gap at the leading edges of both electrodes (m s^–1) - x distance from the electrode surface (m) - gas volumetric flow ratio - ₂₀ at segment pair 20 - specific surface resistivity ( m²) - _t at top of electrode ( m²) - _p for bubble-free solution ( m²) - _b at bottom of electrode ( m²) - thickness of Nernst bubble layer (m) - ₀ ath=0 (m) - _{0,i 0} ati - voidage - _x,0 atx andh=0 - _0,0 voidage at the leading edge of electrode wherex=0 andh=0 - _0,0 ati _b - _0,0 ati=i _t - _,h voidage in bulk of solution at heighth - _,20 voidage in bubble of solution at the leading edge of segment pair 20 - _lim maximum value of _0,0 - overpotential (V) - _a anodic overpotential (V) - _c cathodic overpotential (V) - _h hyper overpotential (V) - _h,a anodic hyper overpotential (V) - _h,c cathodic hyper overpotential (V) - fraction of electrode surface area covered by of bubbles - _a for anode - _c for cathode - resistivity of solution ( m) - _p resistivity of bubble-free solution ( m)     

High molecular weight copolymers of l-lactide and ε-caprolactone as biodegradable elastomeric implant materials

Summary High molecular weight copolymers of L-lactide and -caprolactone have been synthesized by ring opening copolymerization with stannous octoate as catalyst. The good mechanical properties of the 50/50 copolymers make it a suitable material for biomedical applications such as nerve guides etc., where degradation of the elastomeric implant is required. In contrast to the frequently used MDI containing polyurethanes, degradation products of the P(LLA--CL) are non toxic. The use of such a material is therefore preferable.     

Statistical Copolymers of l,l-lactide and ε-caprolactone

Summary Copolymers of l,l-lactide with -caprolactone have been investigated in order to develop valuable biodegradable materials for medical applications. The syntheses of homopolymers and copolymers of l,l-lactide and -caprolactone by ring-opening bulk polymerization were performed using stannous octoate as initiator at 120 °C. The compositions of the copolymers were systematically varied by polymerization of monomer mixtures containing from 10 to 90 95 of -caprolactone, at 10% step of variation. High polymerization conversions were observed for homopolymers and copolymers syntheses. Synthesized products were characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance spectrometry (NMR). The analyses of the segment lengths by ¹³C-NMR spectroscopy indicated the predominance of random copolymers formation and the transesterification reaction was not detected.     

Analysis of the inductance influence on the measured electrochemical impedance

The high-frequency region of the impedance diagram of an electrochemical cell can be deformed by the inductance of the wiring and/or by the intrinsic inductance of the measuring cell. This effect can be noticeable even in the middle frequency range in the case of low impedance systems such as electrochemical power sources. A theoretical analysis of the errors due to inductance effects is presented here, on the basis of which the admissible limiting measuring frequency can be evaluated. Topology deformations due to the effect of inductance in the case of a single-step electrochemical reaction are studied by the simulation approach. It is shown that an inductance can not only change the actual values of the parameters (electrolytic resistance, double layer capacitance, reaction resistance), but can also substantially alter the shape of the impedance diagram, this leading to erroneous structure interpretations. The effect of the size and surface area of the electrode on its intrinsic inductance is also evaluated.Nomenclature A linear dimension of the surface area confined by the circuit (cm) - C _D double layer capacitance (F) - C _M measured capacitance - d diameter of the mean effective current line (mm) - f _max limiting (maximum) frequency of measurement (Hz) - K ₁,K ₂ shape coefficients with values of 2×10^–9 and 0.7 for a circle, and 8×10^–9 and 2 for a square (dimensionless) - L intrinsic inductance of the electrochemical cell assumed as an additive element (H) - R _E electrolyte resistance () - R _M measured resistance () - R _P reaction resistance () - r ₀ specific resistance ( cm) - S electrode surface area (cm²) - T _c time constant (s) - Z impedance () - Z _lm imaginary component of the impedance without accounting for the influence of inductance () - Z _lm imaginary component of the impedance accounting for the influence of the additive inductance () - shape coefficient; =1 for a square and =^1/2/2 for circle (dimensionless) - _L relative complex error due to the influence of inductance (dimensionless) - _L ^A relative amplitude error due to inductance (%) - ^L relative phase error due to inductance (%) - ratio between the effective inductance time constant and the capacitive time constant (dimensionless) - angular frequency (s^–1) - _R characteristic frequency at which the inductive and capactive parts of the imaginary component of impedance are equal (s^–1)