Kinetic Study of Radical Polymerization v. Determination of Reactivity Ratio in Copolymerization of Acrylonitrile and Itaconic Acid by 1H‐NMR

Many reports exist in the literature about the application of ¹H and ¹³C‐NMR techniques to analyze the copolymer structure and composition and also determination of reactivity ratios. In this work, on‐line ¹H‐NMR spectroscopy has been applied to identify reactivity ratios of itaconic acid and acrylonitrile in the solution phase (DMSO as the solvent) and in the presence of AIBN as the radical initiator. All the peaks corresponding to the existing protons were assigned quietly. Therefore, the kinetics of the copolymerization reaction was investigated by studying the variation of integral of two characteristic peaks regarding each monomer. The obtained data were used to find the reactivity ratios of acrylonitrile and itaconic acid by linear least‐squares methods such as Finemann‐Ross, inverted Finemann‐Ross, Mayo‐Lewis, Kelen‐Tudos, extended Kelen‐Tudos and Mao‐Huglin. In addition, a non‐linear least‐square method (Tidwell‐ Mortimer) was used at low conversions. Extended Kelen‐ Tudos and Mao‐Huglin were applied to determine reactivity ratio values at high conversions as well.     

Synthesis,crystal structure,and electrochemical properties of Ni(II) and Cu(II) complexes with two unsymmetrical N2O2 Schiff base ligands

Nickel(II) and copper(II) complexes of two unsymmetrical tetradentate Schiff base ligands [Ni(Me-salabza)] (1), [Cu(Me-salabza)] (2) and [Ni(salabza)] (3), {H₂salabza = N,N′-bis[(salicylidene)-2-aminobenzylamine] and H₂Me-salabza = N,N′-bis[(methylsalicylidene)-2-aminobenzylamine]}, have been synthesized and characterized by elemental analysis and spectroscopic methods. The crystal structures of 2 and 3 complexes have been determined by single crystal X-ray diffraction. Both copper(II) and nickel(II) ions adopt a distorted square planar geometry in [Cu(Me-salabza)] and [Ni(salabza)] complexes. The cyclic voltammetric studies of these complexes in dichloromethane indicate the electronic effects of the methyl groups on redox potential.     

Poly(<Emphasis Type="Italic">n</Emphasis>-octyl methacrylate) viscosity index improver: Kinetic study via on-line <Superscript>1</Superscript>H-NMR technique

The free radical solution polymerization of n-octyl methacrylate has been studied in benzene-d ₆ in the presence of 2,2′-azobisisobutyronitrile as thermal initiator. An on-line nuclear magnetic resonance spectroscopy was applied to record the reaction data and to determine the monomer conversion at different times during the polymerization reaction. Effect of monomer and initiator concentration as well as reaction temperature on polymerization rate was studied. The order of the reaction with respect to initiator (0.45) was consistent with the classical kinetic rate equation, while the order of reaction with respect to monomer (1.87) was much greater than unity. An overall activation energy (E _a = 53.8 kJ/mol) was obtained over the temperature range 328?338 K. Also, the efficiency of the synthesized poly(n-octyl methacrylate) for improving the viscosity index of the lube oil was investigated.     

Evaluation of essential oils for maintaining postharvest quality of Thompson seedless table grape

The effects of postharvest spraying of essential oils from sweet basil (Ocimum basilicum), fennel (Foeniculum vulgare), summer savory (Satureja hortensis) and thyme (Thymus vulgaris) on fungal decay and quality parameters of the 'Thompson seedless' table grape stored at 0?±?1°C for 60 days were evaluated. Results showed that the essential oils, especially of thyme and fennel, have a good inhibitory effect on the development of fungal decay in Thompson table grapes. In addition, essential oils reduced weight loss, berry and rachis browning and had no considerable adverse effect on the flavour of the fruits. GC-MS analysis showed that the main compounds identified in sweet basil, fennel, summer savory and thyme oils are linalool (65.25%), trans-anethole (64.72%), carvacrol (54.14%) and β-ocimene (12.62%), respectively. Therefore, these essential oils have good potential for use as an alternative to synthetic fungicides for the preservation and storage of table grapes.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Qualitative characterization of the diffusion of cationic-modified PVA into the cellulose fiber pores

In this work, the diffusion of cationic poly (vinyl alcohol) (CPVA) with well-defined structures into the pores of bleached kraft fibers was investigated at equilibrium level of adsorption by means of adsorption, solute exclusion technique (SET), and nuclear magnetic resonance (NMR) relaxation method. The results showed that the interaction between CPVA and dextran polymers was weak, which allowed us to use the SET method to investigate the variation in the pore size of fibers upon diffusing CPVAs. Both adsorption and SET methods confirmed the diffusion of CPVA polymers into the fiber pores. However, the NMR technique was unable to reflect the pore size changes. The main reason for such results was probably the error that occurred in removing water between fibers via applying the water retention value (WRV) test prior to the NMR analysis. In fact, not all of the water on the fiber surface, especially on the surface of CPVA-modified fibers, could be removed by the WRV, introducing some error in the NMR analysis.     

Quantum Zeno and anti-Zeno paradoxes

Continuous observation of a time independent projection operator is known to prevent change of state (the quantum Zeno paradox). We discuss the recent result that generic continuous measurement of time dependent projection operators will in fact ensure change of state: an anti-Zeno paradox.