A new class of tuneable crystalline solid supports for metal complexes have been synthesised and used for ethylene polymerization. We have developed a family of high surface area, highly dispersible layered double hydroxides (AMO-LDHs) which, on treatment with alkyl aluminum activators, are able to support metallocene and non-metallocene complexes to make active catalyst systems for the slurry polymerization of ethylene. We show that the chemical composition of the AMO-LDH support can dramatically affect catalyst activity, polymer morphology, and polymer microstructure. A Zr K-edge EXAFS study of these active catalysts has enabled us to observe a metallocene-derived single-center catalytic species in close proximity to the support.
We report the synthesis of two zirconocenes, dimethylsilylbis(hexamethylindenyl) zirconium dichloride, rac-(SBI*)ZrCl2 and n butyldimethylsilyl(hexamethylindenyl) zirconium trichloride [(Ind*SiMe2 n Bu)Zr(µ-Cl)Cl2]2. The complexes were characterised by NMR spectroscopy and X-ray crystallography, and the bonding was evaluated using density functional theory. rac-(SBI*)ZrCl2 demonstrated a very high activity for solution phase polymerisation of ethylene (ca. 22500 kgPE/molZr/h/bar). Both rac-(SBI*)ZrCl2 and rac-(EBI*)ZrCl2 (EBI* = ethylenebis(hexamethylindenyl) have been supported on MAO modified silica and AMOST layered double hydroxides (AMO-LDHs), and evaluated as catalysts in the slurry-phase polymerisation of ethylene. The highest catalytic polymerisation activities for rac-(SBI*)ZrCl2 and rac-(EBI*)ZrCl2 on the layered double hydroxides were 9657 and 4325 kgPE/molZr/h/bar respectively for MAO modified Mg2Al-SO4 LDH. However, rac-(EBI*)ZrCl2 was a three times more active catalyst than rac-(SBI*)ZrCl2 when supported on silica.
A series of frustrated Lewis pairs (FLPs) based on the Lewis acids tris(perchloroaryl)borane (BAr(Cl)), and tris(2,2',2''-perfluorobiphenyl)borane (PBB) and trialkylphosphines were prepared; their ability to effect the heterolytic cleavage of dihydrogen, insert carbon dioxide into the borohydride, and reduce the resulting formatoborate to methanol were studied. Additionally, the insertion of CO(2) into a B-OH bond is explored with the ultimate aim of developing a homogeneous, catalytic preparation of carbonates. The compound [PBB-OH][H-P((t)Bu)(3)] was characterised by single crystal X-ray crystallography.
BackgroundRoot phenotyping aims to characterize root system architecture because of its functional role in resource acquisition. RGB imaging and analysis procedures measure root system traits via colour contrasts between roots and growth media or artificial backgrounds. In the case of plants grown in soil-filled rhizoboxes, where the colour contrast can be poor, it is hypothesized that root imaging based on spectral signatures improves segmentation and provides additional knowledge on physico-chemical root properties.ResultsRoot systems of Triticum durum grown in soil-filled rhizoboxes were scanned in a spectral range of 1000–1700 nm with 222 narrow bands and a spatial resolution of 0.1 mm. A data processing pipeline was developed for automatic root segmentation and analysis of spectral root signatures. Spectral- and RGB-based root segmentation did not significantly differ in accuracy even for a bright soil background. Best spectral segmentation was obtained from log-linearized and asymptotic least squares corrected images via fuzzy clustering and multilevel thresholding. Root axes revealed major spectral distinction between center and border regions. Root decay was captured by an exponential function of the difference spectra between water and structural carbon absorption regions.ConclusionsFundamentals for root phenotyping using hyperspectral imaging have been established by means of an image processing pipeline for automated segmentation of soil-grown plant roots at a high spatial resolution and for the exploration of spectral signatures encoding physico-chemical root zone properties.Electronic supplementary materialThe online version of this article (10.1186/s13007-018-0352-1) contains supplementary material, which is available to authorized users.
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