Studies on functional diene oligomers with an amino end group, 2. Reaction mechanism of the isoprene oligomerization

Abstract

AbstractLithium diisopropylamide, in the presence of diisopropylamine, initiates the polymerization of isoprene to form oligomers having one diisopropylamino end group. These oligomers 1 a, formed in the early stages of the reaction, are considered to carry out the chain termination (or metalation) reaction. Results of mechanistic studies of the chain termination (or metalation) reaction in isoprene oligomerization in the presence of various types of allylamine homologues, as low molecular weight model compounds for 1 a are presented. The presence of a cis‐methyl group with respect to the amino methylene group was found to be essential for the low molecular weight model compounds to exhibit large reactivity in the chain transfer reaction. Oligomers with amino end groups neither have to possess a cis‐methyl group nor an allylamine structure to be active. A number of results showed that the driving force for the metalation reaction of oligomers with amino end groups is different in nature from that of the lowmolecular‐weight allylamine homologues. A possible mechanism for the metalation reaction of these oligomers is discussed in terms of a hydrophobic interaction with the growing chain.