Cold crystallization and thermal shrinkage of uniaxially drawn poly(ethylene 2,6-naphthalate) by solid-state coextrusion

Solid-state coextrusion has been used to prepare uniaxially drawn films from isotropic poly(ethylene 2,6-naphthalate) (PEN) of a minimum degree of crystallinity (ca. 5%) both below and above its glass transition temperature T_g. The onset of cold crystallization (T_c) of the drawn films has been studied as a function of the extrusion temperature (ET) and the draw ratio (EDR). It has been shown that T_c decreases markedly on draw, as much as 95°C, and, at constant draw ratio T_c goes through a minimum in the T_g region. For undrawn PEN, annealing below 153°C has no significant effect on T_c. To evaluate the crystallization rate constant (k) and the activation energy (E_a) of the drawn specimens, a nonisothermal DSC procedure has been used. With increasing EDR, k increases markedly and E_a goes down over threefold compared with the undrawn polymer. At high ET, strain-induced crystallization has also been shown to play an important role in lowering E_a for cold crystallization. Thermal shrinkage above T_m indicates a high elastic recovery, underlining the efficiency of deformation, ca. 93%, achieved by solid-state coextrusion.     

C11-Chirasil-Dex as chiral stationary phase in GC: enantioselective separation of cyclopropane derivatives

Chirasil-β-Dex containing an undecamethylene spacer (C11-Chirasil-Dex) was used as chiral stationary phase (CSP) in enantioselective gas chromatography (GC). The versatility of the new stationary phase in the simultaneous enantiomeric separation of a set of cyclopropane derivatives is demonstrated. The GC method provides information about the chemical yields of the cyclopropane products, enantioselectivity, substrate specifity, and catalytic activity of the chiral catalysts used in the intermolecular cyclopropanation of olefins and avoids time-consuming work-up procedures.     

Enantioselective Gas Chromatographic Analysis of Cyclopropane Derivatives

Chirasil--Dex was used as chiral stationary phase for the enantioselective gas chromatographic analysis of several new chiral cyclopropane derivatives. The GC method provides information about the chemical yields of the cyclopropane products, enantioselectivity, substrate specifity, and catalytic activity of the chiral catalysts used in the inter- and intra-molecular cyclopropanation reactions and avoids time-consuming work-up procedures.     

Direct Enantioselective HPLC Monitoring of Lipase-Catalyzed Kinetic Resolution of 2-Phenoxy Propionic Acid in Non-Standard Organic Solvents

In this work, a direct enantioselective HPLC monitoring system is developed. The system consists of an HPLC equipped with an immobilized cellulose-based chiral stationary phase Chiralpak IB, UV and a polarimetric detector in series. The developed system is used in the direct monitoring of the enantioselectivity of lipase-catalyzed enantioselective esterification of 2-phenoxy propionic acid of which the (R)-enantiomer is a precursor of the (R)-2-(p-hydroxyphenoxy)propionic acid known as an important intermediate in synthesizing aryloxyphenoxypropionic acid based agrochemicals. The versatility of the biocatalyzed reaction in chiral separation to access to both enantiomers of racemic 2-phenoxy propionic acid is demonstrated. The solvent versatility of the immobilized chiral stationary phase used in the direct monitoring of such reaction in non-standard HPLC solvent is shown.     

The interaction between polymerization initiators and inhibitors in solutions—II. The reaction between benzoyl peroxide and p-benzoquinone in concentrated solutions; Some observations on the induced decomposition of the peroxide

The reaction between benzoyl peroxide and p-benzoquinone in concentrated solutions in a wide variety of solvents has been investigated by isolation and identification of the reaction products. Despite the high efficiency of p-benzoquinone as a trap for benzoyloxy radicals, partial decarboxylation to phenyl radicals usually occurs. Complete suppression of decarboxylation is achieved only when p-benzoquinone is present at such a high concentration that it is effectively the solvent for the reaction.The benzoyloxy- and phenyl semiquinones show marked differences in reactivity, the former tend to combine to form dibenzoyloxy dibenzoquinone while disproportionation is favoured by the latter to form quinhydrone of monophenylbenzoquinone.At lower quinone ratio, the peroxide undergoes induced decomposition by phenyl radicals both in “reactive” and “unreactive” solvents. The induced decomposition involves the formation of radical intermediates which undergo disproportionation, but not intramolecular rearrangement, to form p-phenylbenzoyloxy radicals. The latter can be captured, before undergoing decarboxylation, by the benzoyloxysemiquinones formed in the reaction.A correlation between the electron donating property of a radical and its capability to induce the decomposition of the peroxide was developed.     

Effect of different concentrations of sulfuric acid on leaching of radionuclide isotopes in sedimentary rock samples,Sinai, Egypt

Journal of Radioanalytical and Nuclear Chemistry - This research focused on studying the effect of sulfuric acid concentrations on the leaching of different radionuclides (238U and 235U series) in...     

A Priori Error Estimates for Obstacle Optimal Control Problem,Where the Obstacle Is the Control Itself

In this paper we deal with the convergence analysis of the finite element method for an elliptic penalized unilateral obstacle optimal control problem where the control and the obstacle coincide. Error estimates are established for both state and control variables. We apply a fixed point type iteration method to solve the discretized problem.To corroborate our error estimations and the efficiency of our algorithms, the convergence results and numerical experiments are illustrated by concrete examples.     

Lipase-mediated enantioselective kinetic resolution of racemic acidic drugs in non-standard organic solvents: Direct chiral liquid chromatography monitoring and accurate determination of the enantiomeric excesses

The enantioselective resolution of a set of racemic acidic compounds such as non-steroidal anti-inflammatory drugs (NSAIDs) of the group arylpropionic acid derivatives is demonstrated. Thus, a set of lipases were screened and manipulated in either the esterification or hydrolysis mode for the enantioselective kinetic resolution of these racemates in non-standard organic solvents. The accurate determination of the enantiomeric excesses of both substrate and product during such reaction is demonstrated. This was based on the development of a direct and reliable enantioselective high performance liquid chromatography (HPLC) procedure for the simultaneous baseline separation of both substrate and product in one run without derivatization. This was achieved using the immobilized chiral stationary phase namely Chiralpak IB, a 3,5-dimethylphenylcarbamate derivative of cellulose (the immobilized version of Chiralcel OD) which proved to be versatile for the monitoring of the lipase-catalyzed kinetic resolution of racemates in non-standard organic solvents.