Anionic polymerization of isoprene at low concentrations of polyisoprenyllithium

Abstract

The kinetics of polymerization of isoprene with n-butyUithium initiator was investigated in n-hexane solution over an extended concentration range of poly-organolithium. The propagation reaction was found to be first-order with r egard to monomer a nd half-order with respect to chain anion concentration. The degree of chain anion aggregation, in the associa tion equilibrium between active single chains and inactive associated cha ins, was concurrently scrutinized. The evidence acc!'ued from the studies indicates t hat the associated chains exist only as binary a ggregates. These experimental findings are in concert with those results obtained at higher concentrations of polyorga nolithium .

Kinetics of Anionic Polymerization of Polybutadienyl Lithium in Benzene: An Osmotic Effect on Propagation Process

“…Furthermore, in the top panels of Figures 4-7, the data points in a range of ðtÞ ! 0:1 are well described by the solid lines representing the single-exponential decay for these points, which is in harmony with the previous studies for polydienes [1][2][3][4][5][6][7][8] that mostly examined the propagation kinetics in this range of ðtÞ.…”

“…15 ) If this additional route contributes to the propagation process, no single-exponential decay is expected for the residual fraction of the monomer, ðtÞ ¼ ½M=½M 0 . This expectation is not necessarily contradicting to the single-exponential decay seen in the previous studies for the polymerization of dienes, [1][2][3][4][5][6][7][8] because most of those studies traced the decay of ðtÞ only down to ðtÞ ¼ 0:1{0:2 (to 0.05 at the lowest 8 ): The fusion-aided mechanism should contribute to the propagation process less significantly with decreasing ðtÞ because the corresponding increases of M and C in the polymerizing system enhance the osmotic barrier for the fusion, but this change of the contribution is not necessarily resolved well in the limited ranges of ðtÞ.…”

“…This type of single-exponential decay should be observed irrespective of the details of the initiation step and a distribution of the aggregation number f , as long as all aggregates are inert for the propagation step. Indeed, most of the kinetic experiments [1][2][3][4][5][6][7][8] lent support to the single-exponential decay (though in limited ranges of time, as explained later in more details).…”

“…In particular, the polymerization reaction utilizing organolithium (RLi) compounds as the initiator in nonpolar solvents offers a route of synthesizing polydienes (rubbers) of well-controlled microstructures and thus its kinetics has been extensively studied. [1][2][3][4][5][6][7][8][9][10] These studies indicated that the initiation process of this reaction does not obey the simplest kinetics (RLi þ M ! RM À Li þ ; M = monomer) for which the initiation rate is proportional to the initiator concentration.…”

Kinetics of Living Anionic Polymerization of Polystyrenyl Lithium in Cyclohexane

“…Most of the kinetic experiments [1][2][3][4][5]8,9,13,14 lent support to this single-exponential decay, though only in an early stage of the propagation (at short t).…”