Cyclische ester in poly(alkylenterephthalaten)

From poly(alkylene terephthalates) (n = 2, 3, 4) with intrinsic viscosities of 0.75–0.80 dl/g the cyclic oligomers with x = 2, 3, 4 were extracted and analysed by gel permeation chromatography. For comparison with the experimental equilibrium contents of cyclic oligomers the molar cyclization constants K_x were calculated according to Jacobson and Stockmayer. To describe the statistical conformations of the corresponding open chain molecules (end-to-end distances) the rotational isomeric state model of Flory and Williams was used.     

Synthesis and characterization of phenolic and amino resins based on α, β-unsaturated aldehydes

Phenolic and amino resins on the basis of α,β-unsaturated aldehydes were synthesized in bulk or solution. Catalysts were HCl, H₃PO₄, or formic acid, and in some cases NaOH. The course of the reactions was followed by GPC and NMR while the structure of the reaction products was determined by one- and two-dimensional NMR. The course of the reactions is influenced by experimental conditions: the type of monomers, their molar ratio, the type and quantity of the catalyst, the reaction time and temperature, and the reaction medium. At the beginning of the reaction the addition of a nucleophile to an aldehyde takes place through parallel 1,2-addition to and 1,4-addition to group. Oligomers with ? OH, , and ? CHO functional groups are able to add new monomer units or to react mutually to form higher molecular weight addition and condensation products. The overall rate constants for the beginning of the reactions were between 10^?3 L/mol s for the high reactive mixtures and 10^?7 L/mol s for the less reactive mixtures. The resins were cured by heating at temperatures above 135°C with the addition of hexamethylenetetramine.     

Reversed substituent effect on CO Stretching Vibrations in Maleinimide Derivatives

The arithmetic means of wave numbers of symmetric and antisymmetric CO stretching vibrations measured in tetrachloro- and trichloromethane of 31 substituted maleinimides were correlated with Taft inductive σ^* substituent constants. The series of N-phenyl and N-(4-methylphenyl) derivatives exhibit normal i.e. positive values of slope of vs σ^* correlations. In series of substituted N-methylmaleinimides (and probably also in maleinimides) the negative values of slope of vs σ^* correlations indicate a reversed substituent effect on the CO stretching vibration. The mechanism of transmission of substituent effects in maleinimidee system is discussed considering the results of above mentioned observations.     

Modification of poly(vinyl alcohol) through reaction with tin reactants

The modification of poly(vinyl alcohol) was effected via condensation with tin compounds, utilizing the interfacial technique. Products obtained with R₂SnCl₂ are crosslinked. Thermal properties are reported.     

Elektrosynthese von N-substituierten DL-Arylglycinestern und 1,2-Diarylamino-1,2-diarylethanen durch Kathodische Reduktion von Azomethinen in Gegenwart von CO2

Electosynthesis of N-Substituted DL-Arylglycineesters and 1,2-Diarylamino-1,2-diarylethanes by Cathodic Reduction of Azomethines in the Presence of Carbon Dioxide The electroreduction of the N-arylidene-arylamines 1–12 in CO₂-saturated solvents of low proton availability as DMF at markedly more positive potentials than carbon dioxide end up in carboxylating the C-atom and hydrogenating the nitrogen of the double bond. The resulting N-arylsubstituted DL-arylglycines and traces of carbamates may be isolated as esters, adding ethylchloride during the electrolysis. A competing pathway of the electrocarboxylation is the C C-hydrodimerisation and the hydrogenation of the double bond, whose importance increases with the water content of the solvent. Based on cyclic-voltametric evidence and product analysis the mechanism of the reductive electrocarboxylation reaction is discussed in terms of nucleophilic attack of the azomethine anion radical on a proton or CO₂.     

13C-NMR studies of commercial and partially self-condensed hexakis(methoxymethyl)melamine (HMMM) resins

¹³C-nuclear magnetic resonance (NMR) spectroscopy was employed to study the linkages in three commercial fully methylocated melamine-formaldehyde (HMMM) resins and their partially self-condensed resins by acid catalysis, in order to probe the structures linking melamine units. Distortionless enhancement by polarization transfer (DEPT) experiments show that the partially self-condensed resins contain both methylene ether and methylene linkages between melamine units. The extent of these linkages were estimated by quantitative ¹³C-NMR spectroscopy using inverse gated decoupling techniques. The results show that the ratios of methylene ether and methylene linkages to the triazine moiety vary from resin to resin. © 1996 John Wiley & Sons, Inc.     

Thiolation of starch and other polysaccharides

Thiolated starches with a degree of substitution of 0.01–0.6 were obtained by pyrolysis of starch dithiobis(thioformates) followed by saponification. The pyrolytic decomposition of dithiobis(thioformates) followed two pathways: (1) to thionocarbonate , carbon disulfide, and sulfur, and (2) to dithiocarbonate , carbonyl sulfide, and sulfur. Only the second pathway affords thiolation. Thiol groups were determined by Ellman's reagent, by sulfur analyses, and, following acetylation, by the ratio of O-acetyl versus S-acetyl absorption in nuclear magnetic resonance spectra. The poly-saccharides cellulose, dextran, and xylan were thiolated by the same procedure.     

d-NMR-Untersuchungen der behinderten Rotation am Bindungsinkrement. IX. Behinderte Rotation um partielle Doppelbindungen in kernsubstituierten Phenyl-β-dimethylaminovinyl-thioketonen

d-N.M.R.-Investigations of the Restricted Rotation at the Bonding Increment. IX. Restricted Rotation about Partial Double Bonds in Nucleo-substituted Phenyl-β-dimethylaminovinyl-thioketones Due to resonance stabilization restricted rotations about partial and double bonds have been observed in some substituted phenyl-β-dimethylaminovinyl-thioketones 2. The free enthalpies of activation have been determined by means of d-n.m.r.-spectroscopy in dependence on the properties of the p-phenyl substituents and the solvent. The measured ΔG^≠-values depend on the σ-substituent constants and on the E_T-values of solvent polarity linearly. Substituents with electron-withdrawing properties and solvents with increasing polarity enhance the free enthalpies of activation of the restricted rotation.     

Synthesis and thermal analysis of hafnium polyesters

The synthesis of hafnium polyesters by the solution and interfacial techniques is presented: Thermal properties of the polyesters were studied by differential scanning calorimetry and thermal gravimetric analysis.     

In‐Line Monitoring and Control of Conversion and Weight‐Average Molecular Weight of Polyurethanes in Solution Step‐Growth Polymerization Based on Near Infrared Spectroscopy and Torquemetry

Summary: It is well known that the weight‐average molecular weight ( ) is strictly dependent on conversion in step‐growth polymerizations performed in batch and that the is very sensitive to impurities and molar imbalance. This makes the work of controlling a non trivial job. In this paper a new methodology is introduced for in‐line monitoring and control of conversion and of polyurethanes produced in solution step‐growth polymerizations, based on near‐infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight‐average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of . The proposed monitoring and control procedures can also be applied to other step growth polymerizations.

Proposed control scheme.     

Polymer swelling 2: A restudy of poly(styrene-co-divinylbenzene) swelling in terms of the cross-link density1

A very convenient and reliable gravimetric method was developed for measuring swelling of poly(styrene-co-divinylbenzene) in particulate form. The method is based on the gravimetric procedure reported earlier² for monitoring liquid uptake by thin (<0.3 mm) microporous composite films, consisting of swellable particulate (80% by weight) enmeshed in poly(tetrafluoroethylene) microfibers (20%). The swellability S (in milliliter of liquid absorbed per gram of polymer in equilibrium with excess liquid) for six sty-co-DVB polymers with crosslink densities ranging from 0.01 to 0.12 was measured in 19 organic liquids. In each study of S as a function of the relationship was given by where is the average number of carbon atoms in the “backbone” of the polystyrene segments between cross-link junction, C is the relative swelling power of the liquid, and is the critical cross-link density above which S is equal to zero.     

Permeability of dense (homogeneous) cellulose acetate membranes to methane,carbon dioxide,and their mixtures at elevated pressures

Mean permeability coefficients for CH₄ and CO₂ (P̄ and P̄) in cellulose acetate (CA, DS = 2.45) were determined at 35°C (95°F) and at pressures up to about 54 atm (800 psia). The measurements were made with pure CH₄ and CO₂ as well as with CH₄/CO₂ mixtures containing 9.7, 24.0, and 46.1 mol % CO₂. In the measurements with the pure gases, P̄ was found to decrease with increasing pressure, as expected from the “dual-mode” sorption model. By contrast, P̄ passes through a minimum and then increases with increasing pressure, probably due to the plasticization (swelling) of CA by CO₂. The values of P̄ and P̄ determined with the mixtures containing 9.7 and 24.0 mol % CO₂ decrease with increasing total pressure; this behavior is adequately described by the extended “dual-mode” sorption model for mixtures. By contrast, the values of P̄ and P̄ obtained with the mixture containing 46.1 mol % CO₂ pass through a minimum and then increase as the total pressure is raised, probably also due to the plasticization of CA by CO₂. The CO₂/CH₄ selectivity (≡P̄/P̄) of the CA membrances decreases with increasing total pressure and, at constant pressure, decreases with increasing CO₂ concentration in the feed mixture. The effects of exposing the CA membranes to high-pressure CO₂ prior to the permeability measurements (“conditioning” effects) on P̄ and P̄ have also been studied. © 1996 John Wiley & Sons, Inc.     

Polymer melt elongation—methods,results, and recent developments

For film blowing of polyethylene it has been shown previously that melt elongation is very powerful for polymer characterization. With two types of rheometers, simple (also called “uniaxial”) elongational tests as well as creep tests can be performed homogeneously. In simple elongation, the melts of branched polyethylene show a remarkable strain hardening. With respect to their advantages and disadvantages, these rheometers complement each other. For multiaxial elongations the various modes of deformation can be performed by means of the rotary clamp technique. With the strain rate components ordered such that \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₁₁ ? \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₂₂ ≥ \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₃₃, the ratio m = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₂₂/\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}₁₁ characterizes the test mode. The Stephenson definition of the elongational viscosities makes use of the linear viscoelastic material equation and proves to be very efficient because the linear shear viscosity (t) (“stressing” viscosity) can act as the reference for the nonlinear behavior in elongation. Results are given for polyisobutylene measured not only in simple, equibiaxial, and planar elongations, but also in new test modes with a change of m during the deformation. This allows one to investigate the consequences of a deformation-induced anisotropy of the rheological behavior.     

Kinetics of Reduction of Some CoIII(NH3)5 L Complexes by Substituted Pyridinyl Radicals. A Pulse Radiolytic Study

The rates of reduction of some Co^III pentaamine complexes by HINA·, and , HNA·, radicals were measured. It was found that HNA· is more reactive than HINA·. The redox potential for the couple HINA·/HINA⁺ was calculated, E° = 0.80 ± 0.02 V. In the presence of large excess of NA, a catalytic enhancement in the reduction of Co^III(NH₃)₅ NA and Co^III(NH₃)₅ Pyridine by Eu²⁺ was observed. The difference in the mechanism of reduction of Co^III(NH₃)₅ X by Eu²⁺ where X = NA or INA is discussed. The redox potential of the HNA·/HNA⁺ couple was estimated, 0.80 < E° < 1.1 V.     

Stress relaxation behaviour of liquid crystalline solutions of ethyl celluloses with different molecular weight in m-cresol

The stress relaxation behaviour of liquid crystal-forming ethyl celllulose (EC) solutions in m-cresol was determined by means of a cone-plate type viscometer at 30°C. The effect of molecular weight (MW) on the behaviour was also determined. The relaxation behaviour could be fitted with the following equation: where σ_i and σ_f are steady-state shear stresses at shear rate $\dot \gamma _{\rm i}$ and $\dot \gamma _{\rm f}$, σ(t) is time- dependent stress, A₁ and A₂ are constants, τ₁ and τ₂ are relaxation times, t is time, and t_c is a characteristic time. When log σ* was plotted against time, one straight line was obtained for isotropic solutions, whereas anisotropic solutions yielded two straight lines. This suggests that the liquid crystalline solutions have two separate relaxation processes: Process 1 has a relatively short relaxation time, and process 2 has a long one. The parameters τ₁, τ₂, and A₂ were greatly dependent on polymer concentration, combination of $\dot \gamma _{\rm i}$ and $\dot \gamma _{\rm f}$, and MW, whereas A₁ was independent thereof and was close to unity. The process 1 was supposed to be valid for individual molecules, and process 2 for liquid crystalline domains or randomly aggregated or entangled molecules.     

Ammoxidation of propylene by pulse reaction technique

The ammoxidation of propylene on Fe-Bi-P mixed oxide catalyst was studied at 500 °C by the pulse reaction technique, to examine the effects of P(P = 0–4) and P (P/P = 0–3) on the catalyst activity. Since the ammoxidation of propylene proceeds through consumption of oxygen from the catalyst even in the absence of oxygen, the reduction of catalyst progresses with the number of O₂-free pulse, losing its activity. In the presence of oxygen, however, the conversion of propylene and the selectivities of acrylonitrile, acetonitrile, CO₂, and CO vary with the pulse number, but settle to some steady values corresponding to P/P. It is also found that the conversion and the selectivities depend on the oxidation state of the catalyst, the latter also depending on P/P in the reactants, and that the catalyst working in the flow system may be being reduced to some extent.     

Kinetics of ion exchange in monodisperse resin

Ion-exchange kinetics within a conventional strong base resin, Dowexl-8X®, and a resin with uniform particle size, Dowex® Monosphere® Tough Gel® TG550A®, were investigated using neutron activation analysis and radio-tracer techniques. The kinetics of ion exchange were measured in a batch and in a “shallow-bed” flow system. The experimental data were compared with the results of model computations. The diffusivities of several anions within TG550A and Dowexl-8X were deduced. It was found that at 25°C Br^-, Cl^-, OH^-, and Na⁺ diffuse within TG550A with the diffusion coefficients = 6.0 × 10^-7 cm²/s, = 1.2 × 10^-6 cm²/s, = 7.0 × 10^-8 cm²/s, and = 5 × 10^-7 cm²/s. Diffusion of anions within a conventional resin, Dowexl®, was slower: = 3.5 × 10^-7 cm²/s, = 6 × 10^-7 cm²/s, = 2.7 × 10^-8 cm²/s, and = 5 × 10^-7 cm²/s. A higher rate of ion diffusion and the bead-size uniformity may make monodisperse Dowex Monosphere Tough Gel TG550A resin attractive for analytical applications. The difference in properties between conventional and monodisperse resins is not sufficient to affect the large volume applications of resins. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:1271–1283, 1997     

Nonlinear programming methods to determine surface free energy components of polymers using harmonic mean approximation

The dispersion and polar surface free energy components, γ and γ, and the critical surface free energy, γ_c, of polymers were determined from contact angle data by the application of a nonlinear programming method using harmonic mean approximation. The surface free energy components of the probe liquids, γ and γ, which reflect the conditions of the maximized interaction parameter, Φ, were also simultaneously determined by this method.     

Elektrochemisches Verhalten von N-Aryl-Δ2-pyrazolinen. VIII. Zusammenhänge zwischen dem anodischen und kathodischen Verhalten und den Absorptions- und Fluoreszenz-eigenschaften von N-Aryl-Δ2-pyrazolinen

Electrochemical Behavior of N-Aryl-Δ²-pyrazolines. VIII. Relationships between the Anodic and Cathodic Behaviour and the Absorption and Fluorescence Properties of N-Aryl-Δ²-pyrazolines The anodic and cathodic half-wave potentials in acetonitrile and dimethylformamide (DMF) and the absorption and fluorescence spectra in DMF and cyclohexane of 61 N-aryl-Δ²-pyrazolines have been measured. The following correlation has been found between the difference of the half-wave potentials E–E of the first oxidation and reduction steps and the fluorescence maximum in DMF, h · ν: This confirms the charge-transfer character of the corresponding spectroscopical transition. The deviations of some compounds from this correlation are due to differences in the electrochemical behaviour as, e.g., the cathodic elimination of halogen from halogen substituted pyrazolines or the intramolecular hydrogen bond in 1, 5-diaryl-3-o-hydroxyphenyl-Δ²-pyrazolines.     

Synthesis and electrochemistry of grafted copolymers of cellulose with 4-vinylpyridine, 1-vinylimidazole, 1-vinyl-2-pyrrolidinone,and 9-vinylcarbazole

Some new cellulosic materials, suitable for the adsorption of noble metal ions, were syn-thesized by chemical and electrochemical modification of cellulose. The polymerizable groups were introduced in cellulose with ∼ 80% yield of substitution by esterification with acryloyl chloride. The vinyl monomers (4-vinylpyridine, 1-vinylimidazole, 1-vinyl-2-pyrrolidinone, and 9-vinylcarbazole) were readily grafted into cellulose acrylate via radical polymerization in acetonitrile. The grafted copolymers of cellulose with 4-vinylpyridine and 4-vinylimidazole were reacted with methyl iodide and the corresponding 1-methylpyridinium iodide ( 6 ) and 3-methylimidazolium iodide ( 7 ) copolymers of cellulose were obtained. Copolymers 6 and 7 were transformed into new polymeric regents, differing in anions (ClO, CF₃COO⁻, NO, p-TsO⁻, BF, PF) by using a supporting electrolyte carrying the desired anions through the ion-exchange-electrochemical oxidation of the released iodide at a controlled anodic potential. © 1996 John Wiley & Sons, Inc.