Z. M. Sabirov

Lanthanide compounds—Catalysts of stereospecific polymerization of diene monomers. Review☆

The results of investigations in the field of polymerization of conjugated dienes on cis-regulating lanthanide-containing catalysts of the ion-coordination type are reviewed. The influence of the composition of the catalysts, the structure of the monomer and the conditions of polymerization on their activity and stereo-specificity is examined. The factors influencing the molecular mass characteristics of the polymers and procedures for regulating the latter are analysed. From the results of study of the plasto-elastic, physicomechanical and use characteristics of “lanthanide” polydienes and vulcanizates the authors look at the prospects for their use.

Relationship between the Stereospecificity of Lanthanide Catalysts and the Structures of Active Sites and Dienes, the Nature of a Cocatalyst, and Preparation Conditions

Several types of active sites can be formed during the polymerization of dienes in the presence of lanthanide catalytic systems. These sites differ in the nearest environment of a lanthanide atom (the numbers of chlorine and carbon atoms) and in the number of lanthanide–carbon bonds involved in chain growth. Quantum-chemical calculation shows that the π-allyl binding of the terminal unit of a growing polymeric chain with the lanthanide atom of an active site may be the reason for the cis-stereospecificity of the site. Therefore, the active sites containing electron-acceptor chlorine atoms that favor π-allyl binding can form cis-polydienes. Depending on the conditions of catalytic system preparation, primarily on the nature of an organic compound of a nontransition metal, one or another set of active sites is formed that can affect its stereospecificity. The quantitative analysis of kinetic data for diene polymerization shows that the anti-synisomerization of terminal units of growing polymeric chains made a certain contribution to the formation of trans-1,4 units in the presence of cis-regulating active sites.

Kinetic stereocontrol of polydiene microstructures during polymerization of Nd―Al bimetallic systems

Abstract Quantum chemical calculations (EHM) have been carried out for models of the active centres involved in butadiene polymerization in the presence of Nd-Al catalytic systems. The kinetics of the propagation reaction and the polybutadiene microstructure have been investigated using a low initial concentration of the monomer. From analysis of the data, an expression has been derived connecting the ratio of the formation rates for 1,4-cis and 1,4-trans units to the current monomer concentration. This relationship has been confirmed experimentally, thus leading to the conclusion that kinetic stereocontrol of the polybutadiene microstructure occurs during the process.

Reactivity indices of adamantane-containing diamines in the synthesis of polyimides

The reactivity of adamantane-containing diamines in the reactions with dianhydrides of 3,4,3′, 4′-tetracarboxydiphenyl oxide was studied as a function of the parameters of their electronic structures. It was found that the reactivity changes in parallel with the charges on the N atoms, the energy of homolytic cleavage of the N-H bond, and the basicity of diamines.

Diene polymerizations with the lanthanide coordination catalysts IV. Quantochemical studies of active centre models

Abstract Quantochemical studies have been carried out for the models of active centres of butadiene polymerization on the Nd-Al catalytic system. The syn -isomeric forms of active centres have been found energetically preferable over the anti -isomeric forms; Nd 4f orbitals have been observed as relatively inactive participants in the formation of Nd-C bonds. On the whole, the obtained results provide support to the mechanism of kinetic stereocontrol of the polymer microstructure upon diene polymerizations on lanthanide catalytic systems.

Basic Stages of Microstructures Formation in Polydienes upon Lanthanide Catalytic Systems

Abstract This review systematizes the studies on the various aspects of the stereoregulation mechanism in diene polymerization by the lanthanide catalytic systems. Quantum-chemical investigations of electronic and geometric structure of active centers and their complexes with monomers, and the analysis of the structural-kinetic scheme of propagation reaction were examined more thoroughly.

Diene polymerizations with lanthanide coordination catalysts. III. Kinetic stereocontrol of polybutadiene microstructure

Abstract Butadiene polymerization has been investigated with the NdAl catalytic system with a low monomer concentration. By theoretically analyzing the data, an equation has been derived to connect the ratio of formation rates of 1,4-cis- and 1,4-trans-units to the current monomer concentration, that being in good conformity with the experiment. On the basis of the results obtained, the mechanism of kinetic stereocontrol of polybutadiene microstructure has been determined in the system under consideration.

Experimental and quantum-chemical investigation of thermolysis of adamantyl-substituted organosilicon peroxides

The kinetics and mechanism of thermal decomposition of adamantyl-containing organosilicon peroxides in a solution inn-nonane were studied. The relationship between the structure of the peroxide and the rate and mechanism of thermolysis was established. The effect of the peroxide structure on the electronic characteristics of the peroxide bond was studied by the MNDO method. The heterolytic rearrangement occurring during the decomposition of peroxides was analyzed.

Electronic structure of active centers and kinetic stereocontrol in polymerization of butadiene under the influence of a catalytic system based on neodymium chloride

On the basis of quantum-chemical calculations of models of active centers, a suggested mechanism of kinetic stereocontrol of the microsctructure in polymerization of butadiene under the influence of the catalytic system NdCl3 · 3TBP-HA1 (i-C4H9)2 has been verified experimentally.

Nature of the active centres of the catalytic system VOCl3TiCl4Al(iso-C4H9)3 on polymerization of piperilene☆

Abstract The polymerization of piperilene has been studied on exposure to the catalytic system VOCl 3 TiCl 4 Al( iso -C 4 H 9 ) 3 prepared with a fractionated supply of the organoaluminium component. It is known that the stereospecificity of the action and reactivity of the active centres and the molecular mass of the polymer obtained depend in a complex fashion on the relative concentration of the first portion of the organoaluminium compound. It was found that change in the content of V 3+ and Ti 3+ in the catalytic system correlates with the activity and stereospecificity of the action. It is assumed that in conditions of formation of the catalyst active centres form including, simultaneously, V and Ti atoms in trivalent forms.