Mercapto-modified copolymers in polymer blends, 1. Functionalization of EPDM with mercapto groups and its use in NBR/EPDM blends

Ethylene-propylene-diene rubber (EPDM) was reacted with thioacetic acid in the presence of 2,2′-azoisobutyronitrile (AIBN), giving rise to thioacetate-modified EPDM (EPDMTA). The extent of the incorporation was studied as a function of both thioacetic acid and AIBN concentration and reaction time. The products were analyzed by FTIR spectroscopy, sulfur content, and ¹H NMR spectroscopy. The hydrolysis of EPDMTA in a NaOH methanolic solution resulted in mercapto-modified EPDM (EPDMSH). The addition of 5 wt.-% of this functionalized copolymer to a sulfur-vulcanized nitrile rubber (NBR)/EPDM (70 : 30 wt.-%) blend accelerated the vulcanization process as indicated by oscillating disk rheometer analysis. In addition, an improvement of mechanical and ageing properties was also observed.     

Curvature loci of 3-manifolds

We refine the affine classification of real nets of quadrics in order to obtain generic curvature loci of regular 3-manifolds in ${\mathbb{R}}^6$ and singular corank one 3-manifolds in ${\mathbb{R}}^5$. For this, we characterize the type of the curvature locus by the number and type of solutions of a system of equations given by four ternary cubics (which is a determinantal variety in some cases). We also study how singularities of the curvature locus of a regular 3-manifold can go to infinity when the manifold is projected orthogonally in a tangent direction.     

Tetra-tert-butyl-s-indacene is a Bond-Localized C2h Structure and a Challenge for Computational Chemistry

Whether tetra-tert-butyl-s-indacene is a symmetric D_2h structure or a bond-alternating C_2h structure remains a standing puzzle. Close agreement between experimental and computed proton chemical shifts based on minima structures optimized at the M06-2X, ωB97X-D, and M11 levels confirm a bond-localized C_2h symmetry, which is consistent with the expected strong antiaromaticity of TtB-s-indacene.     

Micro‐Raman spectroscopy and SEM/EDX applied to improve the zircon fission track method used for dating geological formations

The zircon mineral is widely studied in geochronology. In the case of the fission track method (FTM), the age is determined by the density of fission tracks at the zircon surface, which can be observed with an optical microscope after an appropriate chemical treatment (etching). The etching must be isotropic at the zircon grain surface to be used in the FTM, which leads those zircon grains whose etching is anisotropic to be discarded. The only reason for this discarding is the nonuniform morphology of the surface grain seen by optical microscopy, that is, no further physicochemical analysis is performed. In this work, combining micro‐Raman and scanning electron microscopy (SEM) to study the etching anisotropy, it was shown that zircon grains that present at least one area at the surface where the density of fission track is uniform can be used in the FTM. The micro‐Raman showed characteristic spectra of the standard zircon sample either from the areas where there are tracks or from where there are not. The only difference found was in the Raman bandwidths, which were broader for the areas with higher density of fission tracks. This suggests simply a decrease in the relative percentage of the crystalline/amorphous phases at these areas. The SEM/energy dispersive spectrometry (EDX) showed that there were no significant differences in the principal chemical composition at the areas with and without fission tracks. Copyright © 2008 John Wiley & Sons, Ltd.     

Polyethylene Made with Combinations of Single‐Site‐Type Catalysts: Monte Carlo Simulation of Long‐Chain Branch Formation

The formation of long‐chain branches (LCBs) during ethylene polymerization with a combination of catalysts was studied by Monte Carlo simulation. The model describes polymerization with a non‐branching catalyst that produces linear macromonomers, and a branching catalyst that produces linear and branched macromonomers. The LCBs are formed when the branching catalyst incorporates a macromonomer. The discussion is based on the three types of chain topology obtained during the synthesis: linear, comb‐branched, or hyperbranched. Simulation results show how the chain length distribution and the number of LCBs change according to the ratio between the two catalysts present in the reactor. The ratio hyperbranched/comb‐branched is defined to evaluate the system composition and the contribution of each catalyst.     

ChemInform Abstract: The Chemistry of Phosphorus Suboxides.

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