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Various elastomeric polypropylenes (PPs) are synthesized through homogeneous propylene polymerization with metallocene catalyst (2-PhInd)2ZrCl2 in the presence of different cocatalyst mixtures: triethylaluminum (TEA)/methylaluminoxane (MAO) or triisobutylaluminum (TIBA)/MAO in the range of AlAlR3/AlMAO = 0.0-0.9. The cocatalyst formulation impacts the resultant polymer microstructure and the thermal and dynamic mechanical properties of the produced PPs. 13C NMR analysis of the polymers reveals essentially atactic PP, with mmmm = 7.9% , when AlAlR3/AlMAO = 0.0. The mmmm pentad content is maximized when AlAlR3/AlMAO = 0.8; for TIBA, mmmm = 23.5%; and for TEA, mmmm = 17.6%. Differential scanning calorimetry analysis and dynamic mechanical thermal analysis corroborate these findings. Specifically, Tm, Δ Hm, and Tg are essentially maximized under these conditions, and the minimum damping is observed for AlAlR3/AlMAO = 0.6-0.8. 1H NMR analysis of the mixtures of catalyst and cocatalysts (without monomer) shows very minor differences for [Zr]:AlAlR3 in the range of 1:1-1:5. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 [ABSTRACT FROM AUTHOR]

The effect of adding various aluminum alkyls (R = Et, i-Bu) on the polymerization of propylene is studied using a (2-PhInd)2ZrCl2 pre-catalyst. A mild deactivating effect is found upon addition of TIBA, whereas TEA shows a sharp deactivating effect. Increasing amounts of AlR3 results in a significant activity increase for TIBA, but an activity plateau for TEA. AlR3 imposes remarkably different effects on the molecular weight and stereochemical microstructure of polymers. As the TIBA concentration increases, $\overline {M} _{{\rm v}} $ increases at first, growing from 49 000 to 72 000, but subsequently drops to 40 000. For TEA, $\overline {M} _{{\rm v}} $ decreases sharply, plummeting from 49 000 to 17 000. Both TIBA and TEA increase the mmmm pentad content from 7.9 to 23.5% and 17.6%, respectively. [ABSTRACT FROM AUTHOR]

Abstract: This note shows that some of the results, interpretations and discussions presented by Dong et al. [X. Dong, L. Wang, J. Zhou, H. Yu, T. Sun, Catalysis Communications 7 (2006) 1–5] may not be correct. Here by comparing the internal diameter of beta-cyclodextrin pore and the external diameter of MCM-41 particles it is shown that a single MCM-41 particle can not be located in the pore of beta-cyclodextrin and even it can be concluded that beta-cyclodextrin may be located in the pores of MCM-41 and therefore the interpretations presented in the article mentioned above are not correct. Even more the Scheme presented in the said article is incorrect and a better demonstration of the facts is proposed here. [Copyright &y& Elsevier]

Physically cross-linked collagen hydrogel is a desirable scaffold for tissue engineering applications especially where 3D cell encapsulation is considered. To overcome its shortcomings such as weak mechanical properties and also provide additional benefits, nanofiller reinforcement could be applied. This study was conducted to compare physical properties and cellular performance of physically cross-linked collagen hydrogel reinforced with cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). Addition of both nanofillers drastically changed the hydrogel properties depending on the type and concentration. As a general trend, both CNCs and CNFs resulted in reduction in gelation time, enhancement in compressive strength, increase in swelling ratio, decrease in weight loss and improvement of injectability. The highest impact for CNCs was achieved when 5 % was applied, while the maximum impact for CNFs was observed for 3 % content (related to the collagen solid weight). By comparing two types of nanocellulose, CNCs showed higher impact on all properties. In-vitro cell compatibility with fibroblasts showed that CNFs did not adversely affected the viability and morphology of the cells while the CNCs improved cell viability and developed more elongated cell morphology. [Display omitted] [ABSTRACT FROM AUTHOR]

Several polypropylene (PP) reactor blends were synthesized using homogenous binary metallocene catalytic systems composed of isospecific (I): rac-MeSi(2-Me-4-Ph In)ZrCl and oscillating (II): (2-Ph In)ZrCl catalysts. The reactor blends were analyzed using gel permeation chromatography and differential scanning calorimetry. All the blends showed bimodal molecular weight distribution, and the MWs were shifted toward higher values compared with PPs synthesized with each of individual catalysts showing some probable interactions between the two active sites. Self-nucleation and annealing treatment on hexane-insoluble-heptane-soluble parts of the PP reactor blends showed that as the II/I molar ratio increases from 0 to 40 in the binary system, multiplicity of the endotherm peaks increases from 1 to 7, which is indicative of the presence of various lamellar thicknesses in the samples. Wide-angle X-ray scattering studies on the PP reactor blends confirmed that the blends have isotacticities and crystallinities between those of polymers obtained by the individual catalysts. [ABSTRACT FROM AUTHOR]

Polyethylene reactor alloys are synthesized through heterogeneous ethylene polymerization with a new type of Ziegler-Natta (ZN)/late transition metal (LTM) hybrid catalyst. The effect of various parameters including catalyst composition (LTM/ZN = 0.01, 0.02, 0.04), polymerization temperature (TP = 30, 30-60, 60 °C) and loading temperature (TL = 30, 60 °C) on catalyst activity, chain's vinyl content, viscosity average molecular weight ( Mv) and thermal properties are investigated. Two distinct melting peaks were observed in the ranges of 110-140 °C and 60-90 °C, indicating presence of two different lamellar structures. LTM/ZN ratio shifted melting peaks toward lower values. Rheological properties confirmed homogeneity of polymer blend's microstructure as they follow time temperature superposition. [ABSTRACT FROM AUTHOR]

A very simple and efficient solvent-free method for the direct conversion of carboxylic acids to primary, secondary, tertiary alkyl, and aromatic amides in the presence of the corresponding ammonium salts, silica-supported 2,4,6-trichloro-1,3,5-triazine, and triethylamine is described. The reactions proceed rapidly at room temperature, and the products are obtained in moderate to excellent yields. [ABSTRACT FROM AUTHOR]

An efficient procedure for the synthesis of some N-nitroaryl derivatives of nucleobases via microwave-assisted N-nitroarylation of nucleobases in the presence of SiO2 and Cs2CO3 in DMSO, as the homogenizing solvent, is described. In this method, some pyrimidine and purine nucleobases are nitroarylated regioselectively in moderate to high yields and short reaction times. [ABSTRACT FROM AUTHOR]