The effect of ultrasound on the solvolysis of 2-chloro-2-methylpropane in aqueous ethanol

Ultrasonic irradiation has been found to accelerate the solvolysis of 2-chloro-2-methylpropane in aqueous ethanol mixtures from 20 to 60% w/w in ethanol at temperatures between 10° and 25°. The effects are more marked at lower temperatures and higher alcohol compositions with a 20 fold rate acceleration occurring at 10° and 60% w/w. The results also lend independent support to two previous observations that (a) the position of maximum in solvent structuredness is 50% w/w and (b) a logarithmic relationship exists between solvent vapour pressure and ultrasonically enhanced rate constant. At solvent compositions of 50 and 60% w/w ethanol the absolute rate of reaction under irradiation increases with decreasing reaction temperature below 20°.     

Gel permeation chromatographic studies of the degradation of polyethylene with fuming nitric acid. I. Single crystals

This paper describes the application of gel permeation chromatography to the morphology of polymer single crystals. Various types of single crystals of polyethylene were etched with fuming nitric acid, and the molecular weight distributions of the degraded fragments determined. The crystal preparations studied were monolayer crystals grown from xylene solution at 85°C and multilayer crystals grown at 84°C and 70°C. In all cases peaks in the molecular weight distribution were observed corresponding to single and double transverses of the molecular chains through the lamellae. By using the chromatograph calibration described in a previous paper, the position of these peaks were compared and correlated with previous estimates of lamellar thickness from low-angle x-ray measurements. The relative positions of the peaks provide information regarding the nature of the fold surface. The results are found to be consistent with a model in which the majority of the molecules are tightly folded.     

Polymerization of vinyl chloride in the presence of precipitants. I

The kinetics of bulk and precipitation polymerization of vinyl chloride has been studied over wide range of reaction temperature by using γ-ray induced initiation. The autoacceleration effect, which has been observed by many investigators in the case of chemically initiated bulk polymerization of vinyl chloride above 40°C and has been the most controversial aspect of the bulk polymerization of vinyl chloride, was found to disappear in the bulk polymerization below 0°C. In the bulk polymerization at 40°C, the autoacceleration effect was observed up to 20%, in agreement with the results of previous investigators, and a pronounced effect of the size of polymer particles on the time–conversion curve was observed. The kinetics of precipitation polymerization of vinyl chloride in the presence of some nonsolvents was successfully described by a oneparameter equation. A kinetic scheme, which clearly explains the zero-order reaction behavior of bulk polymerization at low temperature and the kinetic behavior of precipitation polymerization described by the empirical equation, is proposed. The autoacceleration effect in the bulk polymerization at 40°C was considered to be essentially the same phenomenon as the small retardation period observed in the bulk polymerization at low temperature.     

Radiation-induced copolymerization of isobutyl vinyl ether with trichloroethylene

The radiation-induced copolymerization of isobutyl vinyl ether with trichloroethylene was investigated in the temperature range from ?50°C to 100°C over a wide range of comonomer compositions. A copolymer was obtained in which the monomers alternate with regularity along the polymer chain over essentially the entire range of comonomer compositions. Both the rate of copolymerization and the number-average molecular weight of the resulting copolymer were found to depend strongly on the initial comonomer composition. The monomer reactivity ratios were determined and correspond well with calculated values. An apparent activation energy of 3.2 kcal/mole was obtained for the copolymerization process which exhibits a dose rate dependence of 0.72. The number-average molecular weight was found to be strongly dependent on the irradiation temperature, reaching a maximum value at 5°C.     

Sorption and transport properties of MY720/DDS epoxy reacted with blocking reagents

Thin films of the epoxy formed by the reaction of tetraglycidyl 4,4'-diamino-diphenylmethane and 4,4'-diaminodiphenyl sulfone (73:27 w/w) were reacted with acrylonitrile (ACN) and isocyanates as blocking reagents for hydroxyl, amine, and epoxy groups. The water uptake at 30, 45, 55, and 70°C of the epoxy resin was monitored gravimetrically. At each temperature the epoxy exhibited case I or Fickian behavior. The diffusion coefficient D increased from 30 to 55°C, but decreased at 70°C because of the reaction of water with residual oxirane groups. Diffusion of ACN is accompanied by both reaction and polymerization, so equilibrium could not be reached. Sorption of the isocyanates essentially follows case I or Fickian behavior. Equilibrium moisture absorptions showed a correspondence between the reduction of moisture absorption and the number of blocked functional groups, irrespective of the nature of the blocking groups. Moisture absorption reductions as high as 68% were obtained. Moisture diffusion of the films after blocking with the various reactants exhibits case I or Fickian behavior. At 30°C, D values are significantly higher for reacted films. At 70°C, the value of D is unchanged as compared with the 30°C value for films reacted with ACN, but D values are significantly lower for films reacted with isocyanate blocking reagents as compared with the epoxy resin.     

Interactions of 2,2,2‐trifluoroethanol with melittin

Melittin dissolved in 42% trifluoroethanol‐water at pH 2 has been shown to be α‐helical between residues 6 and 12 and between residues 13 and 25, with the two helical regions separated by a bend at the Leu13 residue. The inter‐helix angle was found to be 154 ± 3° at 0 °C and 135 ± 3° at 25 °C. The dominant conformation of the peptide is thus similar to those observed by previous workers for the peptide in a variety of media. At 25 °C, intermolecular nuclear Overhauser effects arising from nuclear spin dipole‐dipole interactions between melittin hydrogens and fluorines of the solvent are essentially those expected for a system that is homogeneous as regards concentration and translational diffusion of the peptide and fluoroalcohol components. However, at 0 °C, peptide‐trifluoroethanol cross‐relaxation terms are negative, a result consistent with the conclusion that fluoroalcohol molecules associate with the peptide for times (～1 ns) that are long compared to the time of a typical peptide‐fluoroalcohol diffusive encounter (～0.2 ns). Such interactions may be responsible for the reduction of the translational diffusion coefficient of trifluoroethanol produced by dissolved peptides. Copyright © 2009 John Wiley & Sons, Ltd.     

Mechanochemical reaction of polymers by ultrasonic irradiation. I. Mechanochemical reaction in mixtures of polystyrene,styrene, and cyclohexanone

Mechanical degradation and mechanochemical polymerization in polystyrene–styrene–cyclohexanone mixtures have been studied by ultrasonic irradiation at 60°C. The number of fresh polymer chains after the degradation is 2 × 10^?5 mole l^?1 hr^?1. The rate equations for mechanical scission and mechanochemical polymerization have been deduced. The rate equation for mechanical scission was found to be in agreement with the expression of a previous paper. In addition, the rate equation for mechanochemical polymerization is not essentially different from that for the general radical polymerization in the presence of solvents. The kinetic chain length for polymeric free radicals in the polymerization process has been calculated. The mechanochemical polymerization of styrene was initiated by only one of the two kinds of end radicals after mechanical scission of polystyrene. The molecular weight distributions of the samples after the degradation and the polymerization have been compared and discussed.     

The evolution of toxic gases from heated polymers—III. Isocyanate products

Attempts have been made to measure the amount of toluene di-isocyanate evolved from flexible polyurethane foam heated at temperatures in the range from 200° to 470°. This study involved heating a sample of about 2 g in a stream of air in a furnace followed by titration of the isocyanate fumes trapped in an absorber. Further investigation concerning the identity of the isocyanate species was also made using chromatographic and spectroscopic techniques. Most of the products which are isocyanate-active appear to be oligomeric ureas having isocyanate end groups. The amount of titratable isocyanate varied from 0·7 to 1·6% w/w calculated as toluene di-isocyanate, and the free toluene di-isocyanate is considered not to exceed 0·02–0·04% (w/w).     

On the Thermal Stability of β‐Peptides: A Two‐Dimensional Vibrational Spectroscopy Study

A temperature‐dependent 2D‐IR study of the amide‐I band of a β‐peptide forming a 12/10/12/10 helix is presented. Cross‐relaxation of a spectrally separated marker amide‐I mode, which could be assigned with the help of the NMR structure of the molecule, can be used as measure of conformational flexibility of the molecule. We find that the conformational flexibility of the N‐terminal part of the helix increases slightly upon increasing the temperature from 0° to 80°. The cross‐peaks in the 2D‐IR spectrum, and hence the connectivity of the corresponding peptide units, do not change, suggesting that the N‐terminal part of the helix remains essentially intact at 80°. This conclusion is in agreement with previous NMR and CD measurements.     

NMR observations of drawn polymers. VII. Nylon 66 fibers

Wide-line NMR spectra have been obtained on an oriented sample of drawn nylon 66 fibers at temperatures between ?196°C and 200°C and at alignment angles between the fiber axis and the magnetic field of 0°, 45°, and 90°. At ?196°C, 20°C, and 180°C, the complete angle dependence of the NMR spectrum has been measured. The second moments of these spectra have been compared to theoretical second moments calculated for various models of chain segmental motion in an attempt to elucidate the mechanisms involved in the low-temperature segmental motion (γ process) and the high-temperature segmental motion (α_c process). In agreement with earlier suggestions, the present results indicate that the γ process consists of segmental motion in noncrystalline regions. The overall decrease in second moment caused by the γ process is consistent with a model in which all noncrystalline segments rotate around axes nearly fixed in space. Furthermore, this decrease shows a pronounced dependence on the alignment angle. It is believed that this is due to tie molecules which become highly oriented along the fiber axis during drawing; their axes of rotation will therefore be nearly parallel to the fiber axis. The segments in noncrystalline entities such as chain folds and chain ends are less well oriented along the fiber axis and make an essentially isotropic contribution to the second moment decrease. The second moment at 180°C indicates the presence of considerable motion in the crystalline regions, and this motion is denoted the α_c process. The second moment S_c of the crystalline regions is strongly dependent on the alignment angle, the predominant feature being a relatively high value of the second moment when the fiber axis is directed parallel to the magnetic field. This is in qualitative, but not quantitative, agreement with the motional model recently advanced by McMahon, which assumes full rotation of the chains around their axes. Excellent quantitative agreement with experiment has been obtained by superimposition of rotational oscillation around the chain axis of amplitude roughtly 50°, and torsion of the chains with neighboring CH₂ groups oscillating around the C? C bond with a relative amplitude of about 40°. A model in which the chains perform rotational jumps of 60° between two equilibrium sites has also been considered (60° flip-flop motion). A distinction between this model and rotational oscillation has not been possible.     

Structures of polyfluoroaromatic compounds. Part IX [1]. Crystal structure of decafluorofluoranthene

Crystals of decafluorofluoranthene, C₁₆F₁₀, are monoclinic, space group C2/c with unit cell dimensions a = 18.92(1), b = 4.84(1), c = 29.01(2) Å, β = 105.34(5)°. The structure was refined to a conventional discrepancy factor R of 4.7% and weighted discrepancy factor R_w of 4.9% for 1841 observed counter amplitudes. Estimated standard deviations average 0.004 Å; for bond lengths and 0.3° for bond angles. The molecule is essentially planar. Detailed comparison with the parent hydrocarbon indicates that substitution of fluorine for hydrogen has brought about only quite small changes in molecular geometry.     

Investigation of thermal behavior of Heliotropium indicum L. lyophilized extract by TG and DSC

Thermogravimetric (TG) techniques and differential scanning calorimetry (DSC) used for the study of pre-formulation or drug–adjuvant compatibility have been gaining importance in Brazil. These techniques are being used for the verification of possible interactions between drugs and adjuvants. Aiming at studying the behavior of a plant extract and its mixture with adjuvants, using these thermoanalytical techniques the plant species Heliotropium indicum L. was used. This plant which is originally from India and has been well acclimatized in Brazil has healing and anti-inflammatory properties. The methodology for obtaining the extract followed the Brazilian Pharmacopoeia methodology. And the incorporation of the extract with adjuvants was through binary mixtures (1:1 w/w). The TG and DSC curves were obtained under nitrogen atmosphere (25 mL min^?1) at a heating rate of 5 °C min^?1; TG tests were analyzed within a temperature range from 25 to 600 °C and DSC from 25 to 300 °C. The TG curves show good thermal stability of the extract and its mixtures with adjuvants up to 150 °C, except the propylene glycol (PLG). The DSC curves revealed an incompatibility of the extract with methylparaben and PLG mixture.     

The influence of temperature and photoinitiator concentration on photoinitiated polymerization of diacrylate monomer

The behavior of p-methoxybenzoyldiphenylphosphine oxide, previously synthesized, as a photoinitiator for the polymerization of diacrylate monomer, in the presence of 3% (w/w) tertiary amine (triethyl amine) as synergist additive, was studied. The influence of temperature in the range 30–90°C at 3% (w/w) photoinitiator concentration and the influence of the photoinitiator concentration in the range 0.5–3.5% (w/w) at 30°C was investigated by differential scanning photocalorimetry (photo-DSC). In all experiments the photopolymerization was performed at constant light intensity (3 mW cm⁻²). The maximum conversion was obtained at temperature of 90°C at 3% (w/w) photoinitiator concentration and 3% (w/w) triethyl amine. The optimal concentration of photoinitiator to obtain maximum conversion was 3% (w/w), at 30°C. No thermal polymerization occurred at higher temperature.     

Synthesis and properties of aromatic polyamides with oligobenzamide pendent groups. I. Poly-5-(4-benzoylamino-1-benzoylamino)isophthalamides

A series of polyisophthalamides having pendent oligomeric benzamide groups were prepared by the Yamazaki reaction from common aromatic diamines and 5-(4-benzoylamino-1-benzoylamino)isophthalic acid. The latter was synthesized from 5-aminoisophthalic acid in a three-step synthesis by successive incorporation of benzamido groups. The new polymers were characterized by NMR, DSC, TGA, and WAXD and the properties were compared to those of corresponding unsubstituted polyisophthalamides. All of the polymers were essentially amorphous and their T_gs were about 20°C higher than the reference polymers. Initial thermal decomposition temperatures ranged from 375 to 420°C. All of the polymers were soluble in aprotic polar solvents without added salts. Properties of particular note were: the water uptake, which was particularly high, ranging from 7.5 to 18.2%, and the temporary insolubilization in concentrated sulfuric acid of films of the polymers heated for a short time to ≥ 200°C. © 1995 John Wiley & Sons, Inc.     

Gas phase thermolysis of sulfur compounds. II. Ditertiary butyl sulfide

The pyrolysis of di-tert-butyl sulfide has been investigated in static and stirred-flow systems at subambient pressures. The rate of consumption of the sulfide was measured in some experiments, and the rate of pressure increase was followed in others. The results suggest that the reaction is essentially homogeneous in a seasoned reactor and proceeds through a free radical mechanism. In the initial stages, the decomposition rate follows first-order kinetics, and the rate coefficient in the absence of an inhibitor is given by between 360 and 413°C. The stoichiometry of the uninhibited reaction at 380°C and 50% decomposition is approximately between 360 and 413°C. The stoichiometry of the uninhibited reaction at 380°C and 50% decomposition is approximately.     

Reactions of Azolium cations. II [1]. Regioselective N2 alkylation of 5-aryltetrazoles with isopropyl alcohol in sulfuric acid media: Effect of electronic properties of aryl substituents on the reaction rate

Kinetics of regioselective N2 alkylation of a series of 5-(R-phenyl)tetrazoles with isopropyl alcohol has been studied in 88.2, 94.3, and 98.3% (w/w) sulfuric acid at 25°. The true rate constants were evaluated, logarithms of which were found to correlate with σ° constants of phenyl substituents as log k = ?0.488 σ° ? 0.417. Small value of Hammett constant ρ is evidence of a considerable isolation of the reaction center from the influence of the substituent at position C5 of the heteroring. This conclusion is confirmed by results of MNDO quantum chemical calculations of a series of 5-substituted tetrazolium cations. A correlation between logarithms of the true rate constants and the calculated net effective charges on atoms N2(N3) for 5-(R-phenyl)tetrazolium cations has been revealed. © 1995 John Wiley & Sons, Inc.     

Grafting Vinyl Monomers onto Cellulose. IX. Graft Copolymerization of Methyl Methacrylate onto Cellulose Using Peroxydiphosphate-Fe(ll) and Mn(ll) Redox Systems

The vacuum or inert-atmosphere condensation of diphenyl isophthalate and 2,2′,3,3′-tetraaminobiphenyl to poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole has been investigated. Evidence from polymer and model compound (diphenylbibenzimidazole) spectral studies, elemental analysis, and analysis of volatile effluent indicates that the prepolymer formed at 260 to 300°C contains both benzimidazole and hydroxybenzimidazoline but is essentially free from phenoxybenzimidazole structures. A mechanism involving loss of phenol initially, followed by evolution of water to give benzimidazole structures, is established from experimental evidence. Polymerization in vacuum to 400°C gives the polybenzimidazole.     

Isolation and characterization of thermophilic benzothiophene-degrading Mycobacterium sp.

A bacterial strain, SWU-4, capable of using benzothiophene (BT) as a sole carbon and energy source was isolated from a petroleum-contaminated site in Thailand and identified by 16S rRNA gene sequence analysis to be in the genus of Mycobacterium. The strain was Gram-positive, nonspore former, and grew at 50° C. Colonies of the strain on nutrient agar were rod-shaped, smooth with a convex surface, slightly mucoid, and yellow pigmented. The thermophilic Mycobacterium sp. strain SWU-4 rapidly degraded 2% (w/v) BT at 50°C. Interestingly, this strain was able to degrade a wide variety of organosulfur compounds including thiophene, bromo(α)thiophene, and 3-methylthiophene in liquid minimum medium at 50°C, which will be beneficial for industrial applications.     

Xanthan gum production by Xanthomonas campestris w.t. fermentation from chestnut extract

Xanthomonas campestris w.t. was used for production of xanthan gum in fermentations with chestnut flour for the first time. Fermentations were carried out with either chestnut flour or its soluble sugars (33.5%) and starch (53.6%), respectively, at 28°C and 200 rpm at initial pH 7.0 in flasks. The effect of agitation rate (at 200, 400, and 600 rpm) on xanthan gum production was also studied in a 2-L batch reactor. It was found that xanthan production reaches a maximum value of 3.3 g/100 mL at 600 rpm and 28°C at 45 h.     

Difunctional initiator based on 1,3-diisopropenylbenzene. IV. Synthesis and modification of poly(alkyl methacrylate- b-styrene-b-butadiene- b-styrene-b-alkyl methacrylate (MSBSM)) thermoplastic elastomers

MSBSM five-block copolymers where B stands for butadiene, S for styrene, and M for either methyl methacrylate (MMA) or tert-butyl methacrylate (tBMA) have been synthesized by sequential anionic polymerization in an apolar solvent by using a difunctional anionic initiator derived from 1,3-diisopropenylbenzene. These block copolymers show improved mechanical properties and an extended service temperature compared to traditional SBS thermoplastic elastomers. Upon hydrolysis and further neutralization of the PolytBMA end-blocks, the upper glass transition temperature (T_g) of the five-block copolymers has been raised up to about 150°C. A further increase in this service temperature (up to ca. 160°C) has resulted from the blending of sPMMA-SBS-sPMMA five-block copolymers with isotactic poly(methacrylate) (iPMMA), due to the formation of a stereocomplex. The tensile properties of these modified five-block copolymers have remained essentially unchanged. © 1996 John Wiley & Sons, Inc.