Copolymerization of allyl butyl ether with acrylates via controlled radical polymerization

The atom transfer radical polymerization (ATRP) and reversible addition–fragmentation chain transfer (RAFT) of acrylates (methyl acrylate and butyl acrylate) with allyl butyl ether (ABE) were investigated. Well‐defined copolymers containing almost 20 mol % ABE were obtained with ethyl‐2‐bromoisobutyrate as an initiator. Narrow molar mass distributions (MMDs; polydispersity index ≤ 1.3) were obtained from the ATRP experiments, and they suggested conventional ATRP behavior, with no peculiarities caused by the incorporation of ABE. The comparable free‐radical (co)polymerizations resulted in broad MMDs. Increasing the fraction of ABE in the monomer feed led to an increase in the level of incorporation of ABE in the copolymer, at the expense of the overall conversion. Similarly, RAFT copolymerizations with S,S′‐bis(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate also resulted in excellent control of the polymerization with a significant incorporation of ABE within the copolymer chains. The formation of the copolymer was confirmed with matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). From the obtained MALDI‐TOF MS spectra for the ATRP and RAFT systems, it was evident that several units of ABE were incorporated into the polymer chain. This was attributed to the rapidity of the cross‐propagation of ABE‐terminated polymeric radicals with acrylates. This further indicated that ABE was behaving as a comonomer and not simply as a chain‐transfer agent under the employed experimental conditions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3271–3284, 2004     

X-ray excited optical luminescence studies on the system BaXY (X,Y=F, Cl, Br, I)

The present paper reports the experimental observations on the x-ray excited optical luminescence (XEOL) along with the afterglow and colour center features found for the barium salts, represented by the formula,BaXY, whereX andY are the halides. The system thus consists of four dihalides (BaF₂,. . . ,BaI₂) and six mixed halides (BaFCl,. . . ,BaBrI). To start with, it was found that on two of the binary halides of barium, BaClI and BaBrI, no literature exists, and so these were prepared for the first time and their crystal structures were determined. An x-ray generator of 3-kW rating was next coupled to a spectrometer via a high throughput fiberoptic sensor for recording the luminescence spectra under x-irradiation. Also presented in this paper are the observations on the BaXY compounds in which about 0.1 mole% of Eu²⁺ was doped, in order to study the efficiency between the prompt luminescence and the photostimulated luminescence in these compounds. The crystal structure varies from fluorite (BaF₂), to matlockite (BaFX) and finally to orthorhombic (BaCl₂,. . .,BaBrI) for these compounds. Hence searching for systematics and empirical relations in the observed XEOL behaviour of these compounds is still a challenging problem.     

Diblock and triblock copolymers of styrene and acetoxymethylstyrene by one‐pot ATRP

We describe the synthesis of diblock and triblock copolymers by sequential atom transfer radical polymerization of styrene and acetoxymethylstyrene. Contrary to the usual block copolymerization involving isolation of the macroinitiator, a convenient one‐pot procedure is developed. This is possible because of the preferential polymerization of acetoxymethylstyrene, even in the presence of residual styrene, as inferred from characterization of the intermediate polystyrenes and the block copolymers by size exclusion chromatography, ¹H NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, and GPEC techniques. The latent acetoxy functionalities in these block copolymers are shown to be easily unmasked to ? OH and ? Br functionalities, with the potential for block ionomers and dense graft architectures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 575–583, 2005     

A novel substrate controlled chemoselective synthesis of aryl bis(thiazole-2-imine)methanes from 2-aminothiazoles and aldehydes

Aryl bis(thiazole-2-imine)methanes have been synthesized chemoselectively for the first time by an unusual reaction between 5-aryl substituted 2-aminothiazoles and aromatic aldehydes with excellent yield using inexpensive and easy available acetic acid as a catalyst under mild conditions. The present protocol was constructed through N-C bond formation by the condensation and nucleophilic addition reactions.     

Bi-objective hypervolume-based Pareto optimization

The search for the best trade-off solutions with respect to several criteria (also called the Pareto set) is the main approach pursued in multi-objective optimization when no additional preferences are associated to the objectives. This problem is known to be compliant with the maximization of the hypervolume (or S-metric), consisting in the Lebesgue measure of the dominated region covered by a set of solutions in the objective space, and bounded by a reference point. While several variants of population-based metaheuristics like evolutionary algorithms address formulations maximizing the hypervolume, the use of gradient-based algorithms for this task has been largely neglected in the literature. Therefore, this paper proposes to solve bi-objective problems by hypervolume maximization through a sequential quadratic programming algorithm. After theoretical developments including the analytical expression of the sensitivities of the hypervolume expressed as functions of the gradient of the objectives, the method is applied to six benchmark test cases, demonstrating the efficiency of the proposed method in comparison with a scalarization of the objectives, and with a state-of-the-art multi-objective genetic algorithm. This method is believed to provide an interesting alternative to metaheuristics when the gradients of the objective functions are available at a limited additional cost, a situation which is encountered in versatile applications, for instance with adjoint methods implemented in computational solid mechanics or fluid dynamics.     

Synthesis of Spirodiones and Their Structure Determination by X-Ray Crystallography

A rational synthesis of Spiro bicyclo (5,4) dec-2-ene-3-methyl-1,6-dione (1) and Spiro bicyclo (5,5) undec-2-ene-3-methyl-1,7-dione (2) from 2-acetyl cycloalkanone is described. Compounds (1) and (2) have very high potentials as important precursors to many naturally occurring bridged tricyclic compounds. A single crystal X-ray crystallographic study of compound (2) was carried out to establish the structure as chemical and spectral methods proved rather inadequate.     

Synthesis of homopolymers bearing novel chromophore 4‐oxy‐4′‐(vinylbarbituratephenyl)azobenzene for nonlinear optical applications

The synthesis of new acrylate, methacrylate, and styrene with 4‐(oxyethoxy)‐4′‐vinylbarbituratephenyl azobenzene chromophore are described. The monomers were well characterized (NMR, UV, and IR) for the structure. These were then homopolymerized and characterized for spectral responses and thermal properties. The stronger acceptor barbiturate would result in more effective second harmonic generation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 962–971, 2000