The chemistry of piperidines—I : 3-Azabicyclo[3.3.1]nonanes

The reaction of pyrrolidine, piperidine and morpholine enamines of 1-methyl-4-piperidone with acraldehyde is found to be a convenient route to 3-aza-3-methyl-6-cycloalkylaminobicyclo[3.3.1]-nonan-9-ones. In each case two difficultly separable ketones are obtained which on reduction give mixtures of isomeric alcohols. The alcohols are separated and their stereochemistries are determined from their physical and chemical properties.     

Chain Orientation in Polyethylene Fibers Prepared by Ethylene Nanoextrusion Polymerization

Summary: Ethylene nanoextrusion polymerization has been demonstrated to be a novel nanofabrication concept for the preparation of polyethylene (PE) fibers directly from ethylene monomers without any post‐processing procedures. For PE fibers, chain orientation is a critical parameter that affects performance and application of the fibrous materials. In this communication, we report an investigation on chain orientation in PE fibrous samples prepared through nanoextrusion polymerization using a two‐dimensional wide angle X‐ray diffraction (2D WAXRD) technique. Two types of fibrous samples, including individual microfibers and microfiber aggregates, were sampled randomly and studied. For individual PE microfibers, anisotropic diffraction patterns were observed, suggesting chain orientation along the microfiber axial direction. Some microfibers showed the most desired diffraction pattern often found in high‐modulus high‐strength PE fibers. These samples possessed a very high degree of chain orientation along the fiber axis. Owing to a random aggregation of anisotropic microfibers, microfiber aggregates exhibited isotropic diffraction patterns. This work provided further experimental evidence for the proposed nanoextrusion polymerization concept.

2D WAXRD diffraction pattern of a PE microfiber.     

Laser smoothing of sub-micron grooves in hydroxyl-rich fused silica

Nano- to micrometer-sized surface defects on UV-grade fused silica surfaces are known to be effectively smoothed through the use of high-temperature localized CO₂ laser heating, thereby enhancing optical properties. However, the details of the mass transport and the effect of hydroxyl content on the laser smoothing of defective silica at sub-micron length scales are still not completely understood. In this study, we examine the morphological evolution of sub-micron, dry-etched periodic surface structures on type II and type III SiO₂ substrates under 10.6 μm CO₂ laser irradiation using atomic force microscopy (AFM). In situ thermal imaging was used to map the transient temperature field across the heated region, allowing assessment of the T-dependent mass transport mechanisms under different laser-heating conditions. Computational fluid dynamics simulations correlated well with experimental results, and showed that for large effective capillary numbers (N_c > 2), surface diffusion is negligible and smoothing is dictated by capillary action, despite the relatively small spatial scales studied here. Extracted viscosity values over 1700-2000 K were higher than the predicted bulk values, but were consistent with the surface depletion of OH groups, which was confirmed using confocal Raman microscopy.     

Metal complexes of bridging neutral radical ligands: pymDTDA and pymDSDA

Metal complexes of the 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl (pymDTDA) neutral radical ligand and its selenium analogue (pymDSDA) are presented. The following series of metal ions has been studied using M(hfac)(2) as the coordination fragment of choice (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato): Mn(II), Co(II), Ni(II), and Zn(II). The binuclear cobalt and nickel complexes of pymDTDA both exhibit ferromagnetic (FM) coupling between the unpaired electrons on the ligand and the metal ion, while the binuclear zinc complex of pymDTDA is presented as a comparative example incorporating a diamagnetic metal ion. The binuclear manganese complex of pymDTDA, reported in a preliminary communication, is compared to the pymDSDA analogue, and new insight into the magnetic behavior reveals that intermolecular magnetic coupling, mediated by chalcogen-oxygen contacts, gives rise to a significant increase in the χT product at low temperature. Surprisingly, the binuclear nickel complex of pymDSDA forms dimers in the solid state, as do the mononuclear complexes of cobalt and nickel with pymDTDA. In addition, mixed mononuclear/binuclear complexes of Mn- and Zn(pymDTDA) have been identified.