Dramatic effect of heteroatom backbone substituents on the ethylene polymerization behavior of bis(imino)pyridine iron catalysts

Bis(imino)pyridine iron complexes bearing ether and thioether backbone substituents have been synthesized and evaluated for the polymerization of ethylene. The methoxy derivative is inactive whereas bulky phenoxides or thioether derivatives afford activities as high as the most active systems reported to date.     

Synthetic deuterated erythrite--a vibrational spectroscopic study

A comparison of deuterated and non-deuterated erythrite has been made using a combination of infrared and Raman spectroscopy. Infrared spectrum shows bands at 3442, 3358, 3194 and 3039 cm(-1). The band at 3442 cm(-1) is attributed to weakly hydrogen bonded water and the band at 3039 cm(-1) to strongly hydrogen bonded water. Deuteration results in the observation of OD bands at 2563, 2407 and 2279 cm(-1). The ratio of these bands change with deuteration. Deuteration shows that the strongly hydrogen bonded water is replaced in preference to the weakly hydrogen bonded water. Three HOH bending modes are observed at 1686, 1633, 1572 and DOD bending modes at 1236, 1203 and 1176 cm(-1). Deuteration causes the loss of intensity of the bands at 841, 710 and 561 cm(-1) and new bands are observed at 692, 648 and 617 cm(-1). These three bands are attributed to the water librational modes. Deuteration results in an additional Raman band at 809 cm(-1) with increasing intensity with extent of deuteration. Deuteration results in the shift of Raman bands to lower wavenumbers.     

Tuning selectivity in macrotricyclic carbohydrate receptors; CH-->N mutations in aromatic spacers

Dipicolinoyl spacer groups are used to control the conformational and H-bonding properties of tricyclic carbohydrate receptors 3 and 4. Binding selectivities are changed in relation to all-isophthaloyl system 1b.     

Scaling behavior of delayed demixing, rheology, and microstructure of emulsions flocculated by depletion and bridging

This paper describes an experimental comparison of microstructure, rheology, and demixing of bridging- and depletion-flocculated oil-in-water emulsions. Confocal scanning laser microscopy imaging showed that bridging-flocculated emulsions were heterogeneous over larger length scales than depletion-flocculated emulsions. As a consequence, G' as determined from diffusing wave spectroscopy (DWS) corresponded well with G' as measured macroscopically for the depletion-flocculated emulsions, but this correspondence was not found for the bridging-flocculated emulsions. The heterogeneity of bridging-flocculated emulsions was confirmed by DWS-echo measurements, indicating that their structure breaks up into large fragments upon oscillatory shear deformation larger than 1%. Depletion- and bridging-flocculated emulsions showed a different scaling of the storage modulus with the volume fraction of oil and a difference in percolation threshold volume fraction. These differences will be discussed on the basis of the two types of droplet-droplet interactions studied. Gravity-induced demixing occurred in both emulsions, but the demixing processes differed. After preparation of bridging-flocculated emulsions, serum immediately starts to separate, whereas depletion-flocculated systems at polysaccharide concentrations in the overlap regime usually showed a delay time before demixing. The delay time was found to scale with the network permeability, B; the viscosity, eta, of the aqueous phase; and the density difference between oil and water, Deltarho, as tdelay approximately B(-1)etaDeltarho(-1). The results are in line with the mechanism proposed by Starrs et al. (J. Phys.: Condens. Matter 2002, 14, 2485-2505), where erosion of the droplet network leads to widening of the channels within the droplet networks, facilitating drainage of liquid.     

Synthesis and characterization of mesoporous indium tin oxide possessing an electronically conductive framework

The new mesoporous transparent conducting oxide based on indium-tin-oxide, meso-ITO, has been synthesized by a modified sol-gel method, using CTAB as the surfactant. Critical was the employment of triethanolamine to control the rate of hydrolysis and inhibit deposition of the bulk oxides. Removal of the surfactant by calcination yielded a relatively well-ordered worm-hole motif arrangement of pores visible in the TEM and stable to 400 degrees C. BET measurements revealed no hysteresis in the absorption-desorption isotherm, consistent with a narrow pore-size distribution (between 20 and 40 A depending on the In:Sn ratio); surface areas ranged between 270 and 310 m2/g. This colorless material is the first mesoporous oxide exhibiting substantial framework conductivity, with a conductivity at 25 degrees C of 1.2 x 10-3 S/cm. This distinguishes it from mesoporous mixed-valence transition-metal oxides that exhibit weak hopping semiconductor behavior and much lower conductivity.     

Step‐by‐Step Synthesis of Monodisperse Methacrylamidoalkyl Oligolactates

Summary: This paper describes the facile step‐by‐step synthesis to graft lactic acid or lactoyl lactate onto primary as well as secondary alcohol derivatives of methacrylamides via esterification. Elongation of the chains is achieved by repeating the coupling reactions with either hydroxyl‐protected monolactate or hydroxyl‐protected dilactate, followed by mild deprotection using tetrabutylammonium fluoride. This versatile synthesis route generates, on a multi‐gram scale, monodisperse oligolactates of predetermined lengths with functional end groups. The products can be used, for example, as building blocks for biodegradable polymeric materials.

The synthesis of monodisperse oligo(lactic acids) with methacrylamide end groups and a predefined number of lactic acid units.     

A New Method for Continuous Solid-State Biaxial Orientation of Polymeric Films

A new laboratory-scale method for continuous solid-state biaxial deformation of polymer materials is introduced. The tabletop biaxial drawing tool utilizes a heated metal disc-like triangular mandrel, which allows for continuous solid-state biaxial deformation of a precursor polymer tube with a controlled drawing speed. The new biaxial drawing tool features two independent heating zones. The main mandrel sets the biaxial drawing temperature. In addition, directly after the mandrel, an annealing unit with a separate heating zone is added for better control of important process parameters, such as post-relaxation and strain-induced crystallization. As such, the new biaxial drawing tool is a tabletop analogue of the industrial triple-bubble process. Finally, a detailed theoretical model describing the deformation field and the forces needed to perform biaxial drawing as a function of the biaxial drawing ratio is presented and compared to experimental values, using isotactic polypropylene as model material. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 352-362     

Data Adaptive Ridging in Local Polynomial Regression

Abstract

When estimating a regression function or its derivatives, local polynomials are an attractive choice due to their flexibility and asymptotic performance. Seifert and Gasser proposed ridging of local polynomials to overcome problems with variance for random design while retaining their advantages. In this article we present a data-independent rule of thumb and a data-adaptive spatial choice of the ridge parameter in local linear regression. In a framework of penalized local least squares regression, the methods are generalized to higher order polynomials, to estimation of derivatives, and to multivariate designs. The main message is that ridging is a powerful tool for improving the performance of local polynomials. A rule of thumb offers drastic improvements; data-adaptive ridging brings further but modest gains in mean square error.     

Sulfide-Oxidizing Autotrophic Denitrification: an Evaluation for Nitrogen Removal from Anaerobically Pretreated Domestic Sewage

Nitrogen removal from effluents of anaerobic reactors using conventional nitrification/denitrification processes depends on the availability of electron donors for denitrification. As sulfide is normally present in such effluents, autotrophic denitrification using sulfide can be an alternative to avoid or reduce the requirements of exogenous organic carbon sources. This study evaluated the application of sulfide-oxidizing autotrophic denitrification to anaerobically pretreated domestic sewage. A denitrifying reactor was fed with a mixture, at different proportions, of anaerobically pretreated (containing sulfides and residual organic matter) and nitrified (containing nitrates) effluents produced by reactors treating synthetic domestic sewage. Autotrophic denitrification was responsible for most of the nitrogen removal and coexisted with heterotrophic activity, resulting in high denitrification efficiencies. Efficient denitrification could be attained at a molar NO₃ ^?/S^2? ratio of 2.1, higher than values reported before, and this represents an important parameter for the strategic application of the process. Under the experimental conditions studied, autotrophic denitrification showed to be an efficient and feasible alternative to conventional denitrification using exogenous electron donors.     

The transmission coefficients of a random system

We study the reflection and transmission coefficients of a strip of parallel chains with random masses. We show that the transmission coefficients decay exponentially. For this we need the applicability of a theorem by Tutubalin, which is formulated as a conjecture.