Co-ordination polymerization

The polydispersity with heterogeneous Ziegler-Natta polymerization may range from 5 to 30. High-density polyethylene (HDPE) produced by co-ordination polymerization has a degree of branching of about 1-5 per 1000 monomer units, compared with 25-50 for... 

Co-ordination Processes.— The general field of co-ordination polymerization has been reviewed. Hirai examines the relationship between the structure and reactivity of metal complexes in co-ordination polymerization and Yamamoto and Yamamoto give particular attention to transition-metal alkyls and hydrides as catalysts. Oligomerization is the main concern of Reichert. ... 

Co-ordination polymerization processes will not be discussed further here. 

Molecularly imprinted polymers (MIPs) can be prepared according to a number of approaches that are different in the way the template is linked to the functional monomer and subsequently to the polymeric binding sites (Fig. 6-1). Thus, the template can be linked and subsequently recognized by virtually any combination of cleavable covalent bonds, metal ion co-ordination or noncovalent bonds. The first example of molecular imprinting of organic network polymers introduced by Wulff was based on a covalent attachment strategy i.e. covalent monomer-template, covalent polymer-template [12]. 

The oxide surfaces prepared by condensation and polymerization of hydroxo metal ions (see Schneider, 1988 on iron(HI) hydrolysis) usually have lower coordination numbers than bulk oxide ions of the surface hydroxyles. Often the co-ordinatively unsaturated Mn+ site behaves like a Lewis acid and the coordina-tively unsaturated O2 ion is more basic than the bulk ions ... 

It was indeed found necessary to have excess antimony pentafluoride present in order to obtain stable alkylcarbonium hexafluoroantimonate complexes. Antimony pentafluoride is a liquid Lewis acid fluoride (b.p. 148-150°) of low dielectric constant (e 3), which has been shown by fluorine N.M.R. studies in the pure liquid state and in solution to exist in both cyclic and acyclic polymeric forms involving fluorine bridges. The antimony is in approximately octahedral co-ordination with predominant bridging by coordinating fluorines (Gillespie and Rothenbury, 1963). As fluorine generally does not show bridging properties, the structure of antimony pentafluoride itself indicates the very... 

The reaction of Zr(OPr ) with the Schiff bases acetylacetone-2-hydroxy-alkylimine, N-[(3-hydroxy-2-naphthyl)methylene]-2-hydroxyalkylamine, and o-hydroxyacetophenone-2-hydroxyalkylimine (HL) affords the polymeric Zr(OPr )2L and ZrL2 compounds. N.m.r. and i.r. spectral studies indicated that the N atom of the Schiff base is co-ordinated in these compounds. 

S- and Se-donor ligands. The e.s.r. and electronic spectra of [Co(sacsac)2] and [Co(sacsac)2L] (sacsac = dithioacetylacetonate, L = py or piperidine) have been studied, and a polarographic study of [Co(sacsac)J (n = 2 or 3) in acetone has shown the complexes to have a well-defined capacity to accept one or two electrons in a reversible stepwise manner. The magnitude of the potentials and their reversible nature suggest that isolation of cobalt-sacsac complexes of low formal oxidation states should be possible." Co complexes of l,5-bis-(2-methylmercaptoethylthio)pentane are both hydrated and polymeric, and thermal decomposition in air or nitrogen leads to oxida tion to Co . Ethylenethiourea (etu) and tetramethylthiourea (tmtu) form the complexes [Co(etu) ](N03)2 and [Co(tmtu) ](C10 )2, which are tetrahedral, and [Co(etu)2(N03)2] and [Co(tmtu)2(N03)2] which have distorted octahedral co-ordination. 3-Diphenylphosphinothioyl-l-phenylthiourea, -1,1-diethyl-thiourea, and -1,1-dimethylthiourea form complexes with Co in which the ligands are bidentate. ... 

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