Polymerization chelate type monomers

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. 

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). 

The dissociation of the dimer [Cp 2Y(/i-H)]2 to the Cp 2YH monomer is an important process in the reactions of the dimer with alkenes. The kinetics and formation of yttrium alkyl complexes from [Cp 2Y(//-I I)]2 and alkenes have been investigated.587 In situ prepared dimeric bis(pentamethylcyclopentadienyl)yttrium hydride reacted rapidly with 3,3-dimethyl-l,4-pentadiene in methylcylohexane-r/ at — 78 °C and formed a bright yellow solution of the t/°-yttrium(m)pentenyl chelate complex Cp 2Y[7/,7/2-CI I2CI I2CMc2CI I=CH2] in 98% yield (Scheme 130). This pentenyl chelate complex was also prepared in toluene-// in 84% yield. The chelate complex was stable for about 2 weeks at — 78 °C but decomposed after a few hours at —50 °C. The complex was characterized without isolation by 1H and 13C NMR spectroscopy at —100 °C such complexes can be regarded as models for the coordination of alkenes to lanthanide and isoelectronic grouop 4 polymerization catalysts.588 Agostic interactions in yttrium alkyls of the type... 

The efficiency that this set of initiators showed for both types of polymerization reactions, and the displayed influence of the bound A,0-chelating ligand, led to testing for copolymerization of the two monomers. Impressively, the titanium pyridonate complexes led to a random copolymer with a nearly 1 1 ratio of monomers. These random copolymers have average molecular weights of 1.8-2.2X 10 g/mol with PDl values of 1.29-1.41. 

Hacroporous-type crossllnked chloromethylated or lodomethylated polystyrene was used to initiate the polymerization of monomer 1. The product poly(styrene-g-phenyltrlmethylenphosphlne oxide) jU, is a white bead-like resin (n-4.1-10.5), fdilch showed efficient chelating properties toward heavy metal ions such as UOo , Th " ",... 

Kaufman suggested (97d) that silica polymerization is inhibited in regions where the hormone gibberellic acid causes a lowering of the pH from 6.5 to 5.0 or less, as noted in elongating cells, for example (97e). It may be significant that such a drop in pH would stabilize the tropolone-type chelates of silicon and thus inhibit release of monomer (see Weiss, in Ref. 127). 

Type I A metal ion, a metal complex or metal chelate is connected with a linear or crosslinked macromolecule by covalent, coordinative, chelate, ionic or Ti-type bonds (Figure 1). This type I is realized by binding of the metal part at a linear, crosslinked polymer or at the outer or interior surface of an inorganic support. Another possibility uses the polymerization or copolymerization of metal containing monomers. 

Free Radical Polymerization. In situ polymerization reactions of the monomers added to metal salt solution other than Pechini process were proposed. They utilize free radical polymerization of acrylamide (Gotor, 1993 Rao, 1995 Sin, 2000, 2002) or acryUc add (Mani, 1992). The gelation in a usual synthesis occurs due to the reaction between acrylamide and N- N= methylene-bis-acrylamide. Free radicals initiating the polymerization are created by hydrogen peroxide or azobisisobutyronitrile. Just solvated copper ions strongly inhibit polymerization and sufficient amount of EDTA (Sin, 2000) or dtric add (Gotor, 1993 Rao, 1995) should be added to chelate copper and possibly other metals. The clear advantage of this method is that in contrast to Pechini-type process, which enploys reversible polyesterification reaction, the polymer formation by free radical mechanism is irreversible process that can be conducted, in addition, at low temperatures. 

Even more complicated processes occur in the case of ligands that isomerize during the formation and polymerization of MCMs. For example, methacryloylace-tone (5-methylhex-5-ene-2,4-dione), which is the initial monomer for the synthesis of dicarbonyl type chelates, is susceptible to keto-enol tautomerism (scheme 24). ... 

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