Poly(methyl methacrylate)-block-polysulfide-block-poly(methyl methacrylate) copolymers obtained by free-radical polymerization combined with oxidative coupling

Summary Poly(methyl methacrylate)-block-polysulfide-block-poly(methyl methacrylate) copolymers were synthesized for the first time through a new method involving the free radical polymerization of MMA in the presence of a thiocol oligomer as a chain transfer agent, followed by chemical oxidation of the remaining SH end-groups. The chain transfer constant of the SH end-groups of the thiocol was estimated from the rate of consumption of the thiol groups versus the rate of consumption of the monomer (C_T=0.67). The triblock copolymers synthesized were characterized by SEC and ¹H NMR measurements.     

Multilevel Gradient Uzawa Algorithms for Symmetric Saddle Point Problems

In this paper, we introduce a general multilevel gradient Uzawa algorithm for symmetric saddle point systems. We compare its performance with the performance of the standard Uzawa multilevel algorithm. The main idea of the approach is to combine a double inexact Uzawa algorithm at the continuous level with a gradient type algorithm at the discrete level. The algorithm is based on the existence of a priori multilevel sequences of nested approximation pairs of spaces, but the family does not have to be stable. To ensure convergence, the process has to maintain an accurate representation of the residuals at each step of the inexact Uzawa algorithm at the continuous level. The residual representations at each step are approximated by projections or representation operators. Sufficient conditions for ending the iteration on a current pair of discrete spaces are determined by computing simple indicators that involve consecutive iterations. When compared with the standard Uzawa multilevel algorithm, our proposed algorithm has the advantages of automatically selecting the relaxation parameter, lowering the number of iterations on each level, and improving on running time. By carefully choosing the discrete spaces and the projection operators, the error for the second component of the solution can be significantly improved even when comparison is made with the discretization on standard families of stable pairs.     

Comparison of computational performance of GA and PSO optimization techniques when designing similar systems – Typical PWR core case

This paper compares the performance of two optimization techniques, particle swarm optimization (PSO) and genetic algorithm (GA) applied to the design a typical reduced scale two loop Pressurized Water Reactor (PWR) core, at full power in single phase forced circulation flow. This comparison aims at analyzing the performance in reaching the global optimum, considering that both heuristics are based on population search methods, that is, methods whose population (candidate solution set) evolve from one generation to the next using a combination of deterministic and probabilistic rules. The simulated PWR, similar to ANGRA 1 power plant, was used as a case example to compare the performance of PSO and GA. Results from simulations indicated that PSO is more adequate to solve this kind of problem.     

Influence of urethane group on properties of crosslinked polyurethane elastomers

Three series of weakly crosslinked polyurethanes based on a hydroxyterminated polybutadiene, hydroxyterminated butadiene–acrylonitrile copolymer, and hydroxyterminated ethylene–adipate–maleate–fumarate copolymer were prepared while varying the hard segment content between 1.72 and 2.36 mol ? NH? COO? /1000 g polymer. Information on the microphase structure and the properties of the synthesized polyurethanes was obtained by differential scanning calorimetry, wide‐angle X‐ray scattering, and mechanical studies. Up to a urethane concentration of around 2 mol ? NH? COO? /1000 g polymer, there is a mixture of hard–hard and hard–soft segments. Above this concentration a large part of the hard–soft segments passes into hard–hard crystallites, liberating the soft segments. The best mechanical properties of the studied polyurethanes were found for a urethane concentration of around 2 mol ? NH? COO? /1000 g polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1858–1867, 2003     

The Influence of UV Light on Photodegradation of Acetylsalicylic Acid

Photodegradation of the aqueous solutions of acetylsalicylic acid, in the absence (ASA) and the presence of excipients (ASE), is demonstrated by the photoluminescence (PL). A shift of the PL bands from 342 and 338 nm to 358 and 361–397 nm for ASA and ASE in solid state and as aqueous solutions was reported. By exposure of the solution of ASA 0.3 M to UV light, a decrease in the PL band intensity was highlighted. This behavior was revealed for ASA in the presence of phosphate buffer (PB) having the pH equal to 6.4, 7, and 8 or by the interaction with NaOH 0.3 M. A different behavior was reported in the case of ASE. In the presence of PB, an increase in the intensity of the PL band of ASE simultaneously with a change of the ratio between the intensities of the bands at 361–364 and 394–397 nm was highlighted. The differences between PL spectra of ASA and ASE have their origin in the presence of salicylic acid (SAL). The interaction of ASE with NaOH induces a shift of the PL band at 405–407 nm. Arguments for the reaction of ASA with NaOH are shown by Raman scattering and FTIR spectroscopy.     

BioCatNet: A Database System for the Integration of Enzyme Sequences and Biocatalytic Experiments

The development of novel enzymes for biocatalytic processes requires knowledge on substrate profile and selectivity; this can be derived from databases and from publications. Often, these sources lack time‐course data for the substrate or product, and an unambiguous link between experiment and enzyme sequence. The lack of integrated, original data hampers the comprehensive analysis of enzyme kinetics and the evaluation of sequence–function relationships. In order to accelerate enzyme engineering, BioCatNet integrates protein sequence, protein structure, and experimental data for a given enzyme family. BioCatNet explicitly assigns the enzyme sequence to the experimental data, which consists of information on reaction conditions and time‐course data. BioCatNet facilitates the consistent documentation of reaction conditions, the archiving of time‐course data, and the efficient exchange of experimental data among collaborators. Data integration is demonstrated for three case studies by using the TEED (Thiamine diphosphate‐dependent Enzymes Engineering Database).     

Poly(Vinyl Alcohol)-Inorganic Hybrid Materials with Thermocleavable Groups

A series of novel hybrid materials have been prepared by the Diels-Alder reaction of poly(vinyl furfural) to maleimide compound followed by the sol-gel condensation of triethoxysilyl groups with water and acetic acid. The poly(vinyl furfural) having acetalization degree of 15% and 25% were obtained by the acid-catalyzed homogenous acetalization of poly(vinyl alcohol) with 2-furfural in a nonaqueous media. The resulting hybrid materials were characterized by the Fourier transform infrared spectroscopy, X-ray diffractions, scanning electron microscopy and atomic force microscopy. The thermal properties were investigated by differential scanning calorimetry, thermogravimetric and dynamic mechanical analysis. The thermal stability of the hybrid materials increased with increasing the inorganic content.