The stability of disodium tetramer of α‐methylstyrene (“living” polymer) in THF and in a THF‐α‐methylstyrene mixture has been investigated by spectrophotometry. It was found that at 25°C and at concentrations lower than the equilibrium concentration α‐methylstyrene greatly stabilizes the process leading to disappearance of the main absorption band (λmax = 340 mμ) of “living” polymer. In this case isomerization of “living” polymer is accompanied by quantitative conversion of the compound having λmax = 340 mμ into a new compound with λmax = 430 mμ. The constants of the disappearance rate D340 and the activation energies of the process were determined in THF and in a THF‐α‐methylstyrene mixture. The introduction of small amounts of α‐methylstyrene into living polymer at 25°C markedly increases its activity in the course of propagation. The experimental results are considered from the standpoint of formation of complexes of living polymer with α‐methylstyrene.
ABSTRACT:A new mechanism of anionic polymerization of butadiene is proposed.In the elementary chemical act, the "living" polymer-monomer complex is excited into the low-lying triplet state. This state has the character of charge (electron) and cation (Li ϩ or Na ϩ ) transfer from the terminal unit of the active center to the monomer molecule. In the framework of this concept, the probability of chemical bond formation is determined by spin density on radical centers of reagent molecules. Semiempirical and ab initio 6-31G** quantum-chemical calculations showed stable interaction between components of the complex in the ground electronic state (9 -11 kcal/mol) and low energy levels of triplet excited states (Ͻ14 kcal/mol). This new approach is shown to be useful in the analysis of polymerization kinetics and the microstructure of polybutadiene depending on the cation type and the ion pair state. The mechanism of cis-trans isomerization in the terminal unit of the living polymer consists in concerted rotation about the C  OC ␥ bond and the migration of Li between C ␣ and C ␥ atoms.
The kinetics of the polymerization of 3-methyl-3-chloromethyloxetane with the icatalyst system and the molecular-weight characteristics of the resulting polymer have been investigated. The main feature of this process is the ability for self-regulation of the size of the macromolecules with the formation of a polymer of high molecular weight (-10 6) and narrow molecular-weight distribution (M wl M. = 1.30 ± 0.05) which do not depend on conversion and initial monomer and catalyst concentrations. A kinetic scheme for the polymerization involves a slow initiation stage, rapid propagation via the preliminary stage of monomer complexation with active centres, spontaneous monomolecular termination as a result of intramolecular interaction of the active centre with a fragment of its own polymer chain and the inhibition stage due to the deactivation of the unconsumed catalyst by the polymer. The mathematical description of this scheme enabled us to calculate the rate constants for elementary reactions of the process at 20°C: the propagation-rate constant is (1.9 ± 0.3) x 10 3 min-I; the initiation-rate constant is (6.9 ± 0.3) x 10-4 I mol-1 min-I and the termination-rate constant is (0.16 ± 0.02) min-I. KEY WORDS Polymerization Kinetics I Molecular Characteristics I 3-Methyl-3-chloromethyloxetane I Organoaluminium Catalyst I Kinetic Scheme I Rate Constants I Elementary Reactions I
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