Chelate type polymerization

While the types of MCMs described earlier have already received comparatively wide popularity in polymerization practice, polymers based on metal-containing monomers of the chelate type have only been prepared more recently. The methods of assembly of such MCMs, i.e. the simultaneous formation of the ligand and the corresponding complex, have been substantially developed. The synthesis of MCMs from /7-aminostyrene, 2-formylpyrrole and Cu(II) or Co(III) salts is an example of such a method. The last approach is especially characteristic of the preparation of MCMs with macrocyclic chelate nodes, in particular, from porphyrins, phthalocyanines and other macrocycles with exocyclic multiple bonds. It is worth noting that traditional methods of chelation are used for preparing MCMs when scientists want to ensure strong multicenter fixation of metals into monomer molecules, and, thus, into (co)polymers. 

These are the same chelate-type MCMs, but with tetradentate coordination (Table 4-1). Moreover, MCMs with a small strained structure (vinylimine, epoxide) have already been considered above. By considering MCMs with macrocycles in a separate section, we wish to focus attention on monomers of this type because of their widespread use in polymerization practice, especially, porphyrin and phthalocyanine derivatives. As we know, such macrocycles are n-conjugated planar tetradentate ligands and capable of forming rather stable chelates with almost all metals. A basic method of MCM synthesis is based on the incorporation of metal ions into a window of macrocycles completed by an exocyclic multiple bond [45 8]. Examples are 74-76. 

The most widely used method for chemical initiation for graft copolymerization on polysaccharides has been with ceric salts such as CAN or ceric ammonium sulfate. Free radical sites are generated on a polymeric backbone by direct oxidation through ceric metal ions (e.g., Ce "). The ceric ion with low oxidation potential is the proper choice for the reaction. The proposed mechanism for such processes has been depicted by an intermediate formation of metal ion polymer complex (chelate type) [17, 21-24]. Such a complex formation is not restricted to all polymers. The plausible mechanism for ceric ion induced graft copolymerization by direct oxidation method is shown in Scheme 3.1. A series of four grades of Ag-g-PAM copolymers have been synthesized by the conventional method. 

Ion-exchange resins are categorized by the nature of functional groups attached to a polymeric matrix, by the chemistry of the particular polymer in the matrix, and by the porosity of the polymeric matrix. There are four primary types of functionaHty strong acid, weak acid, strong base, and weak base. Another type consists of less common stmctures in specialty resins such as those which have chelating characteristics. 

A typical recipe for batch emulsion polymerization is shown in Table 13. A reaction time of 7—8 h at 30°C is requited for 95—98% conversion. A latex is produced with an average particle diameter of 100—150 nm. Other modifying ingredients may be present, eg, other colloidal protective agents such as gelatin or carboxymethylcellulose, initiator activators such as redox types, chelates, plasticizers, stabilizers, and chain-transfer agents. 

Calcium Chelates (Salicylates). Several successhil dental cements which use the formation of a calcium chelate system (96) were developed based on the reaction of calcium hydroxide [1305-62-0] and various phenohc esters of sahcyhc acid [69-72-7]. The calcium sahcylate [824-35-1] system offers certain advantages over the more widely used zinc oxide—eugenol system. These products are completely bland, antibacterial (97), facihtate the formation of reparative dentin, and do not retard the free-radical polymerization reaction of acryhc monomer systems. The principal deficiencies of this type of cement are its relatively high solubihty, relatively low strength, and low modulus. Less soluble and higher strength calcium-based cements based on dimer and trimer acid have been reported (82). 

Macromolecular metal complexes can be classified into three main categories, taking into consideration the manner of binding of a metal compound to suitable macroligands [33] (Fig. 1). Type 1 metal complexes are those with the metal ion or metal chelate at a macromolecular chain, network, or surface. One possible approach to synthesize such polymers is using the polymerization of vinyl-substituted metal complexes. 

In the search for a reactive functional group which could be substituted on the acetylacetonate ring, chloromethylation of these chelates was attempted. The initially formed products were too reactive to be characterized directly. Treatment of rhodium acetylacetonate with chloromethyl methyl ether in the presence of boron trifluoride etherate afforded a solution of a very reactive species, apparently the chloromethyl chelate (XXX) (26). Hydrolytic workup of this intermediate yielded a polymeric mixture of rhodium chelates, but these did not contain chlorine On the basis of evidence discussed later on electrophilic cleavage of carbon from metal chelate rings and on the basis of their NMR spectra, these polymers may be of the type shown below. Reaction of the intermediate with dry ethanol afforded an impure chelate which is apparently the trisethyl ether (XXXI). Treatment of the reactive intermediate with other nucleophiles gave intractable mixtures. 

Hydrazine and substituted-hydrazine complexes of the type ZrOX2(NH2NHR)4 (R = H, Me or Ph X = Cl, Br, I, NCS or N03) have been synthesized by addition of six equivalents of the hydrazine to an ethanol solution of the appropriate zirconyl salt. An IR band at —970 cm-1 assigned to v(N—N) indicates the presence of bidentate chelating or bridging hydrazine ligands these complexes may be polymeric since they are insoluble in common organic solvents.56... 

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