This study investigated the effect produced by the preparation procedure of a 2‐component lanthanide catalytic system and by the nature of organoaluminium compound on 1) the molecular characteristics of 1,4‐cis‐polybutadiene (PB), 2) the regularities of its average molecular weight (MW), and 3) molecular weight distribution (MWD). The kinetic parameters of the polymerization process were calculated. The principal regularities of variations in PB molecular characteristics with respect to the polymerization conditions, i.e., OAC and monomer concentrations and temperature, are retained with different procedures of the lanthanide catalytic system, and those present distinctive features of the catalytic complexes studied in this article. But as for differences in MW and its patterns of dependence on monomer conversion rate and OAC nature, these are due to changes in kinetic parameters of the polymerization, which occur with the use of the catalyst prepared by a different procedure. © 1994 John Wiley & Sons, Inc.

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The initiation of radical polymerization of methyl methacrylate in the presence of benzoyl perox ide-metallocene (Cp 2 Fe, Cp 2 ZrCl 2 , and Cp 2 TiCl 2 ; (C 5 Me 5 ) 2 Fe, (C 5 Me 5 ) 2 ZrCl 2 , and (AcC 5 H 4 )(C 5 H 5 )Fe) systems is studied. It is shown that a metallocene affects the rate of initiation and the initial rate of polymer ization. On the basis of quantum chemical calculations, a new mechanism of the initiation reaction may be advanced: Namely, the decomposition of benzoyl peroxide proceeds via the stage of complexation with a metallocene, while the nature of a metallocene determines the probability of complexation and decomposi tion.

ABSTRACT:The influence of organoaluminum compound on kinetic heterogeneity of active sites in lanthanidebased diene polymerization was investigated. It was shown that heterogeneity of investigated catalytic systems was displayed in the existence of four types of active centers. They are formed at the beginning of the polymerization process and produce macromolecules with lengths that are definite for each type of active centers. The organoaluminum compound's nature greatly influences the kinetic activity of polymerization centers. The method of analysis of the curves' maximum distribution on kinetic activity and the change of kinetic activity of every active centers' type were proposed, which permits the calculation of values of concentration for each type of active center separately.

The polymerization of methyl methacrylate in the presence of metallocenes and radical initiators has been shown to proceed as radical coordination polymerization, with the propagation of some chains fol lowing a coordination mechanism involving metallocenes. The polymerization products are capable of initi ating monomer polymerization in the absence of an initiator. The catalytic activities of "metallocene" poly mers are determined by the history of their synthesis.