Coordination polymerization, templating

Emulsion droplets can also serve as soft templates to produce capsules. A range of cross-linking chemistries on the interface of oil-in-water emulsion droplets, whereby introducing various polymer functionalities in the resulting capsules has been employed. These are ring-opening metathesis polymerization [59], interfacial step-growth polymerization [60], metal coordination polymerization also termed miniemulsion periphery polymerization [61], surface-initiated miniemulsion ATRP [62, 63], and inverse miniemulsion periphery RAFT polymerization [64, 65]. 

Since the coordination almost certainly involves the transition metal atom, there is a resemblance here to anionic polymerization. The coordination is an important aspect of the present picture, since it is this feature which allows the catalyst to serve as a template for stereoregulation. 

Application of classical type of kinetic equations to the template polymerization was demonstrated by Kabanov at al It was shown that 4-vinylpyridine, in the presence of poly(methacrylic acid), poly(acrylic acid), poly(l-glutamic acid), and polyphosphate, polymerizes according to the classical equation and the order of reaction with respect to the monomer is 2 as demonstrated in the Figure 8.1. In log-log coordinates, for the all sets of polymerizations, experimental points fit straight lines. In the same paper dependence of the initial rate on the molar ratio of acid to monomer was examined. This relationship is shown on the Figure 8.2. The rate of polymerization in the presence of the poly(acrylic acid) is much higher than that for the low molecular analogue (acetic acid). The polymerization rate riches its maximum for the molar ratio [acid]/[monomer] 2. The authors found kinetic equation for template polymerization of 4-vinylpyridine in the presence of different polyacids in the form ... 

Other important methods of synthesis of coordination compounds are discussed in detail [1,3,10,11,53,201,202,206,207,316,318,322,690]. In this respect, we emphasize the synthesis of metal-polymers [690,691] and preparation of complexes in the solid phase (mechano- or tribosynthesis) [10,201,202,206]. Additionally to the above-described techniques, the general methods and principles of synthesis of coordination compounds are used to obtain metal-polymers (immediate interaction of polymer ligands and metal salts, template electrosynthesis, polymer-analogous transformations). The last method consists of the polymerization of metal-monomers (metal-containing monomers) and fixation of metal complexes on the polymer... 

A number of mixed macrocycles have been prepared. A template requirement has not been established unless the sodium ion serves to coordinate to sulfur and oxygen in the reaction of cyclic vicinal mercaptophenols or dithiols with equivalent proportions of terminal-substituted ether dichlorides in the presence of sodium hydroxide (109) and in the reaction of 1,2-dibromoethane with the disodium salt of 3-oxapentane-1,5-dithiol at high dilution (15). Macrocycles XCVI-XCVIII were prepared by the former route, and XCIX, in low yield due to extensive polymerization, by the latter. 

Myriad polydentate aza-macrocycles have been reported 41. The extent of the subject forces limitation of this discussion to only macrocycles containing a pyridine or dipyridine subunit. Most of these coronands have been synthesized by a SchifF base condensation of an aldehyde or ketone with a hfc-primary amine in the presence of a metal ion. The metal ion acts as a template, resulting in dramatic increases in yield of the desired cyclic product over linear polymerization products42 46. Lindoy and Busch45 have described this effect in two ways, kinetic and thermodynamic. If the metal ion controls the steric course of a series of stepwise reactions, the template effect is considered to be kinetic. If the metal ion influences an equilibrium in an organic reaction sequence by coordination with one of the reactants, the template effect is termed thermodynamic. It is the kinetic effect that is believed to be operative in most metal ion-assisted (in situ) syntheses of... 

The low affinity of sulfur for alkali metal ions, however, renders template effects of less consequence in the synthesis of polythia macrocycles. Thus, the competition between cycli-zation and linear polymerization is more statistically defined, with cyclization kinetically favored only at high dilution 64,65,66). Consequently, most of the synthetic methods for the synthesis of polythia rings involve high-dilution techniques coupled with relatively long reaction times. Historically, the study of the coordination chemistry of macrocyclic thioethers has been hindered by difficulties in the synthesis of the free ligands. The synthesis of [BJaneSa, first reported by Ochrymowycz and co-workers in 1977 101), illustrates this well. 

Molecularly imprinted polymers (MIPs) may 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 (Table 5.1) (see Chapter 4). Thus, the template can be linked and subsequently recognised by virtually any combination of cleavable covalent bonds, metal ion coordination or non-covalent bonds. The first example of molecular imprinting of organic network polymers introduced by Wulff (see Chapter 4) was based on a covalent attachment strategy, i.e. covalent monomer-template, covalent polymer template [1]... 

The paramagnetic nature of Cu ion was utilised to characterise these polymeric receptors by studying the interaction between the Cu centres and imidazole groups using ESR spectroscopy [17]. Results from the ESR experiments indicate that Cu -imidazole coordination bonds formed during the assembly of the monomer and template are conserved upon polymerisation. Furthermore, analysis of the ESR data obtained for different polymers suggested a defined arrangement of metal ion sites in the templated materials, which is absent in the non-templated control polymers. 

The many beneficial features of metal-coordination interaction, combined with the attractiveness of template polymerisation, make these metal-complexing polymeric receptors a class of potentially useful materials. These functional polymers have been investigated for their usefulness in different analytical applications. 

Mosbach et al. also attempted to use metal-coordination interaction to prepare polymeric adsorbents for selective recognition of proteins [27]. Using the monomer (3), they polymerised the protein-monomer complex on methacrylate-derived silica particles in the presence of ribonuclease A as the template protein. After removing the template, the imprinted functionalised silica particles were used as packing... 

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