Effect of solvent on chain propagation and termination reaction rates in radical polymerization

The radical polymerizations of acrylamide and methacrylamide and of acrylic, methacrylic and fluoroacrylic acids have been studied in various solvents. The nature of the solvent affects the overall rate due to changes in k_p and E_p. It has been shown that the effect of solvent also depends on the nature of the monomer. A possible explanation of the observed behaviour is discussed.     

Dependencies of the Raman spectra of p-oligophenyls on the chain length and the excitation wavelength

The 1064 nm excited Raman spectra of p-terphenyl, p-quaterphenyl, p-quinquephenyl and p-sexiphenyl have been observed and compared with the 514.5 nm excited spectra. Dependencies of intensities of some major bands on the chain length and the excitation wavelength are discussed in terms of the preresonant Raman effect. A method for estimating the chain length from relative intensities is proposed.     

Dynamic-mechanical properties and melting points of some aliphatic and partially aromatic polyamides

Some aliphatic and partially aromatic polyamides have been prepared from hexamethylene diamine and the following dicarboxylic acids: deca-, octa-, hexa-methylenedicarboxylic, p-carboxymethylphenoxyacetic, p-carboxyethylphenoxyacetic, p-phenylenedipropionic, p-phenylenediacetic, p-carboxymethoxyphenoxyacetic, β(p-carboxymethyl)phenylpropionic.The dynamic-mechanical properties at 110 Hz have been measured between ?140° and about 200. Three relaxation processes α β and γ have been found: only the main transition α appreciably depends on chemical structure.The influences of the length of repeating unit and of in-chain substitution on melting points, crystallinity and the dynamic-mechanical α transition have been investigated. The results have been discussed in terms of chain flexibility, chain packing and intermolecular forces.     

On the intersystem crossing of pentacene in p-terphenyl

Applying methods developed for single molecule spectroscopy to small ensembles, we have recorded high-resolution fluorescence-excitation spectra for pentacene in all substitutional sites of a p-terphenyl single crystal. The difference in intersystem crossing efficiency for pentacene molecules in the various substitutional sites is discussed on the basis of these spectra and data from optically detected magnetic resonance experiments.     

The preferred conformations of 2,4-dichlorophenol, 2,4-dichloroanisole and their sulphur analogues

Analysis of the benzene dipole moments of 2-chloroanisole and 2,4-dichloroanisole, 2-chlorothioanisole and 2,4-dichlorothioanisole shows these compounds to exist as trans. 2-Chlorophenol and 2,4-dichlorophenol, and their sulphur analogues, are mixtures of Cis and trans conformers. The populations of the cis conformers are, at 25°C, 86 and 78% for the phenols, and ca. 70 and 50% for the corresponding thiophenols. The influence of various factors, such as the non-additivity of the (2-ClC₆H₄X)-group moment and torsional oscillation of the H-X bond (especially the H-S bond), on the calculated populations has been discussed. Incidentally it has been shown that p-dimethoxybenzene and p-di-(methylthio)benzene, as well as p-phenylenediamine and p-diformylbenzene, are equimolecular mixtures of cis and trans conformers.     

Preparation and photoluminescence of p-terphenyl derivatives containing cyano groups

Fifteen p-terphenyls containing alkoxylated backbones with and without cyano groups on the phenyl moieties have been designed and synthesized. The influences of the position and the number of cyano groups on the phenyl moieties as well as the skeleton to the absorption and emission spectra both, in solution and in solid state of these new p-terphenyls are discussed.     

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.     

Studies on some oxovanadium(IV) complexes of acyl pyrazolone analogues

A series of novel bidentate pyrazolone based Schiff base ligands were synthesized by interaction of 4-benzoyl-3-methyl-1-(4′-methylphenyl)-2-pyrazolin-5-one with various aromatic amines like aniline, o-,m-,p-chloroaniline and o-,m-,p-toluidine in a ethanolic medium. All of these ligands have been characterized on the basis of elemental analysis, IR and ¹H NMR data. The molecular geometries of five of these ligands have been determined by single crystal X-ray study. Crystallographic study reveals that these ligands exist in the amine-one tautomeric form in the solid state. NMR study also suggests the existence of the amine-one form in solution at room temperature. Ab initio calculations for representative ligand HL¹ has been carried out to know the coordination site of the ligand. Novel vanadium Schiff base complexes of these ligands with general formula [OV(L^1–7)₂(H₂O)] have been prepared by interaction of aqueous solution of vanadyl sulfate pentahydrate with DMF solution of the appropriate ligands. The resulting complexes have been characterized on the basis of elemental analysis, vanadium determination, molar conductance and magnetic measurements, thermo gravimetric analysis, infrared and electronic spectral studies. Suitable distorted octahedral structures have been proposed for these complexes.     

A study on the reaction between N-substituted p-phenylenediamines and ozone: experimental results and theoretical aspects in relation to their antiozonant activity

The following p-phenylenediamines (PPD): N,N,N^′,N^′-tetramethyl-p-phenylenediamine (TMPPD), N,N^′-dimethylbutyl-p-phenylenediamine (6PPD), N,N^′-diaryl-p-phenylenediamine (DPPD), tris-(N-dimethylpentyl-p-phenylenediamine)-N^′,N^′,N^′-1,3,5-triazine (6PPDTZ), have been oxidized under the action of O₃ in diluted solutions. In all cases the radical cation or semiquinone radical was the first derivative formed by monoelectronic oxidation of the substrate. The radical cation has been studied by electronic spectroscopy and the electronic spectral changes of all mentioned PPD has been followed as function of the ozonation time. The results have been discussed in the frame of the antiozonant properties of these PPD which are used as antiozonant agents in diene rubber protection. It is shown that the antiozonant activity of each PPD considered correlates with the free enthalpy of formation of the respective radical cation. The lowest is the free energy of formation of a PPD radical cation and the highest is the antiozonant activity in a diene rubber compound.     

The hydroxylation of aromatic compounds with hypofluorous acid

The reaction of hypofluorous acid with aromatic substrates (benzene, p-xylene, naphthalene, and various monosubstituted benzenes) leads to phenolic products. Isomer distribution studies suggest that the reagent has the characteristics of an electrophilic species which is not the OH radical, and which may be regarded as HO^δ+?F^δ-. The p-methoxyphenol isolated from the p-deuterioanisole/hypofluorous acid reaction shows a marked NIH effect (77% incorporation of deuterium). The bearing of these results on microsomal hydroxylation is discussed briefly.     

Identification and investigation of impurities in undoped Hg1−xCdxTe

The effect of impurities on electrical properties has been the most sought information for the well-known infrared sensing material mercury-cadmium telluride. The relationship between the excess holes (p-type) or excess electrons (n-type) of undoped mercury-cadmium tellurideHg_1?xCd_xTe(0.23 ? x ? 0.4)and the residual impurities in the crystals were investigated. The impurities in the undoped material were determined using emission spectrometry, atomic absorption, and spark sources mass spectrometry.Trace analysis indicates that impurities such as Cu and Ag consistently appear inp-type samples. Although these elements are not frequently observed inn-type substance, occasionally they are found in the material in a minute amount. Impurities such as Si, Cr, Pb, Li, Rb, Co, and Sn have been detected in bothp-type andn-type materials. The possible correlation of these impurities with thep-type orn-type behavior of the undoped material is discussed.     

Complexation of p-Sulphonato-calix[6]arene by Glycine, Glycyl-glycine, and Glycyl-glycyl-glycine in Aqueous Solution

The complexing ability of p-sulphonato-calix[6]arene towards glycine, glycyl-glycine, and glycyl-glycyl-glycine has been evaluated at pH?=?1.8 and 7.9 using UV?CVis spectrophotometry. At these pHs the guest molecules are in their cationic and zwitterionic forms, respectively. The results showed that the host is capable of complexing with the guests in 1:1 guest-to-host ratios. Formation constants of the systems have been determined at different temperatures (20?±?0.1 to 40?±?0.1?°C). Considering the formation constant values, the binding selectivity of the host towards the guests is in the order glycyl-glycyl-glycine?>?glycyl-glycine?>?glycine. The thermodynamic parameters have been evaluated and are interpreted in terms of the importance of the various interactions responsible for the complexation. A roughly linear relationship between ??H ^o and T??S ^o has been observed for the studied systems and is discussed.     

Approximation of the temperature integral in the evaluation of thermoanalytical measurements

Values of the temperature integral (i) of the Arrhenius equation have been calculated. An approximately linear relationship has been established between log i and the activation energy and between log i and the reciprocal temperature. The approximate expressions are given and the accuracy of the results obtained using these expressions is compared with the accuracies achievable using other approximations in a selected activation energy and temperature range. The applicability of various approximations is briefly discussed.     

One-dimensional order in atactic polyacrylates containing aromatic side groups

To help in the understanding of the relations between chemical structure and morphological order in polymers of the type of poly(p-biphenyl acrylate) (PPBA), some polymers of similar structure have been synthesized and some of their physical properties studied. These polymers are: poly(p-biphenyl methacrylate), poly(vinyl p-phenyl benzoate), poly(p-phenyl benzyl acrylate), poly(p-benzyl phenyl acrylate) and poly(p-cyclohexyl phenyl acrylate) (PPCPA). Only PPCPA has been shown to possess a one-dimensional order in the solid state for reasons which are briefly discussed.The effect of copolymerization on the structural order of PPBA has also been given preliminary study. Copolymers of p-biphenyl acrylate (PBA) with p-biphenyl methacrylate (PBMA), N-vinyl carbazole (NVC) and p-cyclohexyl phenyl acrylate (PCPA) have been prepared and their properties have been studied by DSC and X-ray techniques. Small concentrations of PBMA or NVC units are sufficient to cancel the order of PPBA. On the contrary, copolymers of PBA and PCPA of any composition display morphological order in the solid state.     

Acid—base equilibria of some benzhydryl piperazine derivatives

The ultraviolet spectral and polarographic behaviour of several benzhydryl piperazine derivatives is described. Attempts have been made to associate the pK data obtained with protonations at various nitrogen atoms in the molecules. Analysis of the plots of E_{$\text{1}\text{2}$} vs. pH have yielded direct polarographic methods for determining some of these compounds in the presence of possible metabolic products.     

Wide-line 1H NMR and DSC study of mesomorphic transformations of p-(alkoxybenzylidene)-p′-toluidines

p-(Alkoxybenzylidene)-p′-toluidines (ABTs) with 7, 8, and 10 carbon atoms in the alkyl moiety have been studied by wide-line ¹H NMR and DSC. The thermotropic properties of these compounds have been studied in the temperature range 20–80°C, including main mesomorphic transformations of ABTs. The 1H NMR line shapes, widths, and second moments, as well as specific features of their temperature-induced changes, are discussed. The DSC data are compared with the character of mesomorphic transformations and ¹H NMR data. The formation limits and ranges and stabilities of liquid-crystalline states of the ABT structure emerging on heating are determined.     

Notes sur les méthodes de dosage du tryptophane

1. A large part of the literature concerning the chemical determination of tryptophan and the explanation of the coloration given by tryptophan with aldehydes is reviewed. 2. The causes of the erroneous results obtained by using the p-dimethylamino-benzaldehyde method, in the presence of hydrochloric acid, have been ascertained. Contrarily to what some authors think, these erroneous results are not due to a lack of specificity of the method. 3. The results and the sensitivity of various methods are discussed. The most advantageous method for the determination of tryptophan in proteins seems to be at the present time,the method described by Spies and Chambers ⁶².     

Cleavage of α-halo-substituted alkyl groups from silicon. The mechanism of catalysis by ammonia buffer

Kinetic studies have been made of the base-catalysed cleavage of α-dihalo-substituted alkyl groups from silicon in n-propanol—water in the presence of ammonia buffer. The separate rate constants for the concurrent base-catalysed and base-plus-nucleophile-catalysed processes have been determined for the compounds XC₆H₄(Me₂)SiCHCl₂ with X = H, p-MeO, p-Me, p-Cl, m-Cl, m-CF₃ and a good correlation with σ-constants found for both types of catalysis. Solvent isotope effects and steric effects of substituents have also been studied. Possible mechanisms are discussed.     

Beam-foil lifetime data for 3s 3p 3 and 3s 2 3p 3d levels of Si-like Ni14+

In the EUV spectrum of foil-excited 24 MeV Ni ions the decays of the 3s 3p ³ and 3s ² 3p 3d levels to the 3s ² 3p ² levels of the ground configuration have been observed. For most of the levels decay curves have been obtained. The lifetime results compare well with predictions from semi-empirically scaled HXR calculations. Some problems with cascade repopulations will be discussed.     

The infrared spectra of the hydrogen halide-olefin complexes in argon matrices

On the basis of Mulliken's charge-transfer theory the frequency shifts of vibration of the hydrogen halides in its complexes with olefins have been discussed. The relations between the a/b coefficient and the ionization potential of olefin, i_d, or pK_a of acid component has been found.