Synthesis of copolymers of methoxy polyethylene glycol acrylate and 2-acrylamido-2-methyl-1-propanesulfonic acid: Its characterization and application as superplasticizer in concrete

Water-soluble copolymers of methoxy polyethylene glycol acrylate (mPEGA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) were synthesized by free radicalic polymerization and evaluated as slump-retaining dispersant for cement particles. The slump-retaining effect of the synthesized copolymers was studied in terms of reaction pH, composition, and molecular weight of mPEG side chains. mPEG grafted copolymers (mPEGA-co-AMPS) were characterized by FTIR, ¹H NMR. In this study, dilute solution viscometry measurements were performed to compare the molecular weight effect on fluidity of the copolymers and mechanical properties of the mortar samples prepared by the copolymers were investigated to determine the flexural strength and compressive strengths. It was observed that the reaction pH had a noticeable effect on the molecular weight of the PEG-grafted samples thus causing a significant effect on fluidity. mPEGA-co-AMPS synthesized at a pH of 6 has given the highest fluidity result. Copolymers with mPEG side chains with a molecular weight of 1100 gave higher fluidity and viscosity average molecular weight values than the copolymers with mPEG 2000 side chains. Furthermore, for all the samples tested in this research, increase in molecular weight caused an increase in fluidity, however, a decrease in mechanical properties due to the different air contents of these copolymers.     

ESR studies of solvent penetration into polymer-blend-like material: Particles formed from poly(methyl methacrylate) and polyisobutylene

Solvent penetration into nonaqueous dispersions (NAD) of poly(methyl methacrylate) (PMMA) sterically stabilized by PIB were studied by ESR spectroscopy. These colloidal particles were exposed to dilute solution of spin probe 3-carbomoyl 2,2,5,5-tetramethyl 3-pyrolin-1-yloxy and the bimodal distribution of ESR spectra of this probe molecules were carefully monitored as a function of time. Fickian type diffusion of spin probes into the particles was observed and a spherical model was employed to obtain the diffusion coefficients (D) in various solvents. D values were found around 10^?15 cm²/s, and interpreted as the parameter, inversely proportional to the apparent viscosity of the environment inside the colloid particle. Maximum amount of diffused solvent molecules (M_∞) into the PMMA particle was found inversely proportional to polymer-solvent interaction through the solubility parameters. The interconnected network of PIB was found to be responsible for the penetration of spin-probe (i.e., solvent) molecules into the glassy PMMA phase and/or PIB-PMMA interface.     

Geometrically enhanced morphology-dependent resonances of a dielectric sphere

The effect that geometrical resonances of orbiting internally reflecting rays have on the morphology-dependent resonances of microspheres is investigated heuristically and numerically using generalized Lorenz-Mie theory. Angularly resolved off-axis Gaussian beam elastic scattering spectra are presented. The results obtained show that the elastic scattering intensity of morphology-dependent resonances is noticeably enhanced in the vicinity of the geometrical resonance scattering angles.     

Effect of alkali metal hydroxides on the morphological development and optical properties of ceria nanocubes under hydrothermal conditions

Nanocrystalline cerium(LV) oxide (CeO2, ceria) particles were produced via the hydrothermal treatment of cerium nitrate hexahydrate with various alkali metal hydroxides (MOH: M = Li, Na, K). Experimental conditions such as [MOH], reaction temperature, and reaction time were studied. Particle morphology as well as size of crystallites was precisely controlled by choice of experimental conditions. While rod-shaped particles were obtained at 120 degrees C, well-defined nanocubes were formed at higher temperatures regardless of the choice of MOH. Examination of particle growth kinetics, in the final stages of crystallization, showed that particle growth rate is controlled by two different mechanisms. Grain boundary diffusion controls the particle growth in the presence of NaOH with an activation energy of 113.8 kj/mol and surface diffusion for LiOH ad KOH with the activation energy of 43.0-150.9 kj/mol, respectively. In addition, the particles exhibit strong violet and blue emissions at 400 nm and 370 nm. The former emission originates from excitation of a wide band gap of CeO2. The latter one is attributed to the trivalency of the cerium ion and appears to be sensitive to all the experimental conditions studied. Both extending reaction time and increasing temperature reduce the intensity of the 370 nm emission and increase the intensity of the 400 nm emission.     

Investigation of a historic masonry structure by numerical and operational modal analyses

This paper presents the results of model calibration conducted on a historical mosque called Hafsa Sultan in Manisa, Turkey. The finite element model of the mosque was calibrated by the use of the results obtained from ambient vibration tests of the structure. In order to develop a solid model of the structure, the dimensions of the structure, defects such as cracks and material degradations in the structure, and the materials used in different parts were identified. For the evaluation of the material properties of the structure, nondestructive and destructive testing methods were used. The numerical and experimental modal parameters of the structure were obtained by finite element method (FEM) and Operational Modal Analysis (OMA), respectively. The natural frequencies and corresponding mode shapes were obtained from both FEM and OMA and compared with each other. While a good compatibility was achieved between mode shapes, some differences between natural frequencies occurred. It was thought that the differences resulted from variations in the Young's modulus of masonry, cracks in elements or boundary conditions. Therefore, the finite element model was calibrated by changing material parameters. Finally, a more realistic numerical model of the mosque was put forward and the results were discussed in detail. Copyright © 2015 John Wiley & Sons, Ltd.     

Regioselective Alkylations of Cyclic 1,3-Diketones via Metalated Dimethylhydrazones

Cyclic 1,3- diketones 1 are transformed into their 2,2-dimethylhydrazones 2 , which can be alkylated regio-selectively at different positions after mono-, di-, tri-, and tetrametalation. Monometalated C-2 unsubstituted hydrazones afford C-2 and N-alkylation, monometalated C-2 substituted hydrazones afford only C-2 alkylation. The regioselectivity of the alkylation of the polymetalated hydrazones follows Hauser's rule according to the sequence: NH- > C-4 Ha > C-5 > C-4 Hb. Hydrolysis of the product hydrazones 3–5 afforded mono- and polyalkylated 1,3- diketones 7 in good yields.     

Enantioselective Synthesis of α‐Hydroxy Ketones via Benzaldehyde Lyase‐Catalyzed C−C Bond Formation Reaction

(R)‐Benzoins and (R)‐2‐hydroxypropiophenone derivatives are formed on a preparative scale by benzaldehyde lyase (BAL)‐catalyzed C−C bond formation from aromatic aldehydes and acetaldehyde in aqueous buffer/DMSO solution with remarkable ease in high chemical yield and high optical purity. The substrate range of this thiamin diphosphate‐dependent enzyme was examined with respect to a broad applicability of this benzoin condensation‐type reaction in stereoselective synthesis.