Polymeric metal ions, formation

Two possible reasons may be noted by which just the coordinatively insufficient ions of the low oxidation state are necessary to provide the catalytic activity in olefin polymerization. First, the formation of the transition metal-carbon bond in the case of one-component catalysts seems to be realized through the oxidative addition of olefin to the transition metal ion that should possess the ability for a concurrent increase of degree of oxidation and coordination number (177). Second, a strong enough interaction of the monomer with the propagation center resulting in monomer activation is possible by 7r-back-donation of electrons into the antibonding orbitals of olefin that may take place only with the participation of low-valency ions of the transition metal in the formation of intermediate 71-complexes. 

The activation of olefins through the formation of the ir-complex with the transition metal ion at polymerization was postulated as one of the stages of the propagation reaction in many works, beginning with those of Ludlum el at. 184) and Carrick (185) ... 

Penicillamine is known to form complexes of varying stability with several metal ions. In neutral solution, penicillamine complexes with mercury, lead, nickel, and copper are relatively more stable than those of zinc, iron, and manganese. The three functional groups of penicillamine may be engaged in the formation of metal complex, and the resultant compounds may be polymeric in structure. 

These iniferter sites containing an N-H group can be easily transformed into the corresponding thiol which leads to disulfide by oxidative coupling and can form chelation with metal ions (Eq. 47) [171,172]. Poly(St) prepared for polymerization with 44 and 45 was applied to the chain-extension reaction by the S-S bond or chelation bond formations. 

The reaction rate of cyanate ester resins can be increased by using catalysts such as carboxylate salts or chelates of transition metal ions. The role of transition metal ions in the polymerization reaction consists of facilitating the cycli-zation reaction of three cyanate monomer functionalities by the formation of... 

RNA and the synthetic polynucleotides can be cleaved in the absence of divalent metal ions by basic hydrolysis as shown in Figure C, in which the formation of small oligonucleotides from highly polymeric nucleotide chains is followed. In the absence of divalent metal, the reaction rates are approximately the same for RNA, Poly I, and Poly A. 

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