Estimation of monomer reactivity ratios in free‐radical solution copolymerization of lauryl methacrylate–isobutyl methacrylate

Copolymers of isobutyl methacrylate (i‐BMA) and lauryl methacrylate (LMA) were prepared by free‐radical solution copolymerizations at 70 °C with azobisisobutyronitrile (AIBN) as an initiator. The synthesis of these copolymers was investigated over a wide composition range both at low and high conversion levels. Copolymer compositions were determined from the %C, %H, and %O contents of copolymer by elemental analysis. Monomer reactivity ratios were estimated by analyzing composition data with nonlinear least‐squares (NLLS) models based on Marquardt optimization and van Herk methods. The point estimates, 95% individual confidence intervals and 95% joint confidence intervals are obtained from differential and integral approaches. Even though no explicit integral form for penultimate unit model (PUM) is available, a numerical approach is developed for integral estimation of reactivity ratios from PUM. A simulator program was developed which upon coupling of experimental data, NLLS analysis, and D‐optimal criteria calculates the best optimized values of monomer reactivity ratios and monomer feed compositions in a sequential and iterative order for terminal and penultimate unit models. Moreover, the simulator has the capibilities to calculate all features of van Herk method, maximum compositional drift in each monomer feed composition, and data reconciliation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 112–129, 2004     

Ab Initio Study of the Various Pathways of the Decomposition ([2+2]elimination) of 2-Chloroethyltrichlorosilane

Abstract

The decomposition of 2-chloroethyltrichlorosilane (1) to ethylene-tetrachlorosilane (2), hydrogen chloride-ethylenetrichlorosilane (3), and ethylenechloride-trichlorosilane (4) was investigated using ab initio Molecular Orbital (MO) and Density Functional Theory (DFT). Study on the HF/6-31G level of theory revealed that the required energy for the decomposition of compound 1 to 2, 3, and 4 is 59.86, 101.13, and 63.29 kcal mol^?, respectively. MP2/6-31G*//HF/6-31G* calculated barrier height for the decomposition of compound 1 to 2, 3, and 4 is 60.59, 94.04, and 66.91 kcal mol^?1, respectively. Also, B3LYP/6-31G*//HF/6-31G* results indicate that the barrier height for the decomposition of compound 1 to 2, 3, and 4 is 51.71, 85.38, and 53.74 kcal mol^?1, respectively. Among the three methods, which have been used to calculate the barrier height of the decomposition of compound 1 to 2–4, B3LYP/6-31G**//HF/6-31G** is in good agreement with the reported experimental data. Contrary to the previously evaluated experimental values for the decomposition of compoun 1 to 3 and 4, all three methods predict a higher energy barrier for these reactions.     

Determination of atenolol in human plasma using ionic‐liquid‐based ultrasound‐assisted in situ solvent formation microextraction followed by high‐performance liquid chromatography

An efficient analytical method called ionic‐liquid‐based ultrasound‐assisted in situ solvent formation microextraction followed by high‐performance liquid chromatography was developed for the determination of atenolol in human plasma. A hydrophobic ionic liquid (1‐butyl‐3‐methylimidazolium hexafluorophosphate) was formed by the addition of a hydrophilic ionic liquid (1‐butyl‐3‐methylimidazolium tetrafluoroborate) to a sample solution containing an ion‐pairing agent during microextraction. The analyte was extracted into the ionic liquid phase while the microextraction solvent was dispersed throughout the sample by utilizing ultrasound. The sample was then centrifuged, and the extracting phase retracted into the microsyringe and injected to liquid chromatography. After optimization, the calibration curve showed linearity in the range of 2–750 ng/mL with the regression coefficient corresponding to 0.998. The limits of detection (S/N = 3) and quantification (S/N = 10) were 0.5 and 2 ng/mL, respectively. A reasonable relative recovery range of 90–96.7% and satisfactory intra‐assay (4.8–5.1%, n = 6) and interassay (5.0–5.6%, n = 9) precision along with a substantial sample clean‐up demonstrated good performance of the procedure. It was applied for the determination of atenolol in human plasma after oral administration and some pharmacokinetic data were obtained.     

Rheological and swelling behavior of semi‐interpenetrating networks of polyacrylamide and scleroglucan

Preparation and characterization of novel semi‐interpenetrating polymer network (semi‐IPN) hydrogels based on partially hydrolyzed polyacrylamide (HPAM) and scleroglucan solution crosslinked with chromium triacetate are described. Effects of scleroglucan concentration on the gelation process and swelling behavior of synthesized hydrogels in different media were investigated using dynamic rheometery and swelling tests, respectively. Oscillatory shear rheology showed that the limiting storage modulus of the semi‐IPN gels increased with increase in scleroglucan concentration. It was also found that the viscous energy dissipating properties of the semi‐IPN gels decreased with increase in the crosslinker concentration of the gelation system. In addition, the loss factor slightly decreased by increasing the scleroglucan content, indicating that the viscous properties of this gelling system decreased more than its elastic properties. The swelling tests showed that the equilibrium swelling ratio (ESR) of the semi‐IPN networks decreased with increase in scleroglucan content, due to the decrease of ionic groups of polyelectrolyte hydrogel. However, the semi‐IPN gels showed lower salt sensitivity in synthetic oil reservoir water as compared with HPAM gels. Therefore, these semi‐IPN hydrogels may be considered potentially good candidates for enhanced oil recovery (EOR) applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation of highly exfoliated polyester-clay nanocomposites: process-property correlations

A large number of polyester nanocomposite batches featuring different kinds of nanoclay surface modifiers and up to 6 wt % nanoclay were manufactured using a solvent-based technique. Montmorillonite platelets modified with ammonium ions of different chemical architectures were examined to study the effect of ammonium ions on the extent of surface reactions with long-chain fatty acids. The ammonium montmorillonite was first dispersed and suspended in acetone. This suspension was further esterificated with dotriacontanoic (lacceroic) acid to form high density brushes on the clay surface. This led to achieving higher basal plane spacing of the montmorillonite platelets due to the reduction of electrostatic interactions holding them. The outcome of the surface esterification was analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The esterificated ammonium-modified clays were then mixed by five different mixing strategies based on the use of a three-roll mill mixer (TRM) and/or ultrasonication (US) to obtain the desired polyester-nanoclay dispersion, intercalation, and exfoliation. The dispersion states of the modified nanoclay in polymer were characterized from XRD, scanning electron microscopy (SEM), and low and high magnification transmission electron microscopy (TEM). Mechanical, thermal, and barrier properties of the resulting composites were experimentally characterized. The Mori-Tanaka method along with an orientation distribution function was used to verify the experimental effective stiffness of the polyester nanocomposite systems. The aspect ratio of nanoclays and their level of intercalation and/or exfoliation after mixing were also confirmed by the comparison of the experimental diffusivity results with those of Fick's diffusion model. Systems having 4 and 6 wt % esterificated ammonium nanoclay and prepared according to a combined TRM/US mixing procedure showed optimal performance with balanced properties and processing ease, thereby showing potential for use in the automotive, transportation, and packaging industries.     

Fischer-Tropsch Reaction Kinetics of Cobalt Catalyst in Supercritical Phase

Fischer-Tropsch synthesis under supercritical phase condition was examined in a continuous and a high-pressure fixed bed reactor by employing a cobalt catalyst (Co-R.Ru/γ-Al2O3). An integral reactor model involving Fischer-Tropsch reaction kinetics in the supercritical fluid n-hexane was used to describe the overall performance. On the basis of Langmuir-Hinshelwood-Hougen-Watson (LHHW) model, the reaction rate constants were obtained for the rate equations of CO conversion to CH4 formation under supercritical conditions.     

Adaptive iterative regularization schemes for two‐dimensional integral‐algebraic systems

The main idea of this paper is to utilize the adaptive iterative schemes based on regularization techniques for moderately ill‐posed problems that are obtained by a system of linear two‐dimensional Volterra integral equations with a singular matrix in the leading part. These problems may arise in the modeling of certain heat conduction processes as well as in the dynamic simulation packages such as compressible flow through a plant piping network. Owing to the ill‐posed nature of the first kind Volterra equation that appears in the system, we will focus on the two families of regularization algorithms, ie, the Landweber and Lavrentiev type methods, where we treat both the exact and perturbed data. Our aim is to work directly with the original Volterra equations without any kind of reduction. Two fast iterative algorithms with reasonable computational complexity are developed. Numerical experiments on a few test problems are used to illustrate the validity and efficiency of the proposed iterative methods in comparison with the classical regularization methods.     

Robust supply chain network design with service level against disruptions and demand uncertainties: A real-life case

We have developed a stochastic mathematical formulation for designing a network of multi-product supply chains comprising several capacitated production facilities, distribution centres and retailers in markets under uncertainty. This model considers demand-side and supply-side uncertainties simultaneously, which makes it more realistic in comparison to models in the existing literature. In this model, we consider a discrete set as potential locations of distribution centres and retailing outlets and investigate the impact of strategic facility location decisions on the operational inventory and shipment decisions of the supply chain. We use a path-based formulation that helps us to consider supply-side uncertainties that are possible disruptions in manufacturers, distribution centres and their connecting links. The resultant model, which incorporates the cut-set concept in reliability theory and also the robust optimisation concept, is a mixed integer nonlinear problem. To solve the model to attain global optimality, we have created a transformation based on the piecewise linearisation method. Finally, we illustrate the model outputs and discuss the results through several numerical examples, including a real-life case study from the agri-food industry.     

The hyper-Zagreb index and some graph operations

Let G be a simple connected graph. The Hyper-Zagreb index is defined as \(\textit{HM}(G)=\sum _{uv\in E_{G}}(d_{G}(u)+d_{G}(v))^2\). In this paper some exact expressions for the hyper-Zagreb index of graph operations containing cartesian product and join of n graphs, splice, link and chain of graphs will be presented. We also apply these results to some graphs to chemical and general interest, such as \(C_4\) nanotube, rectangular grid, prism, complete n-partite graph.