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Study on the mechanism of anionic polymerization with mixed RLi–R′OK initiators, 1. Polymerization of butadiene
Author(s) -
Nakhmanovich Boris I.,
Zolotareva Irina V.,
ArestYakubovich Alexander A.
Publication year - 1999
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/(sici)1521-3935(19990901)200:9<2015::aid-macp2015>3.0.co;2-i
Subject(s) - polymerization , chemistry , polymer chemistry , chain transfer , dispersity , toluene , molar mass , metal , polymer , molar mass distribution , anionic addition polymerization , reaction rate constant , living polymerization , molar ratio , kinetics , radical polymerization , organic chemistry , catalysis , physics , quantum mechanics
Butadiene polymerization in toluene with n‐ BuLi/ t‐ AmOK mixed initiator at K/Li molar ratio, x , from 0 to 6 has been studied. The results observed substantially depend on the composition of the initiator. The usual scheme assuming the accumulation of highly reactive organopotassium species due to a metal‐metal exchange between the initiator components is qualitatively applicable only at 0 < x < 1, although its quantitative agreement with the experiment still remains disputable. In the overstoichiometric region ( x > 1), the general pattern is completely inconsistent with this scheme. At x = 2, the relative constant of chain transfer to toluene is 30 times higher than that with potassium alkyls (RK), and only low‐molecular‐weight polymer ( M n ≈ 500) is formed, the polymerization rate being 10 times lower than the rate observed at x = 1. At even higher excess of t‐ AmOK, x ≥ 5, M n remains very low but M w greatly increases. As a result, the polydispersity of the polymer is unusually high, M w / M n ≥ 50, indicating the participation of at least two new types of growing species with a fairly slow exchange between them. The study of several model mixed initiators suggests that these new species are complex aggregates containing simultaneously K, Li, and OR moieties rather than single‐metal species. Surprisingly, it was found that neither free RK nor its complexes with excess t‐ AmOK play any important role in the overstoichiometric region.