Influence of tertiary aromatic diamines on the n-buLi-initiated polymerization of isoprene in hexane solution

The influence of three aromatic tertiary diamines, bis(4-dimethylamino phenyl) methane (DMAPM), N,N,N′,N′-tetramethyl-p-phenylenediamine (p-TMPDA), and N,N,N′,N′-tetramethyl-o-phenylenediamine (o-TMPDA), on the kinetics of polymerization of isoprene in hexane solution, with n-BuLi as initiator, was studied for different values of ratio r = [amine]/[n-BuLi]. It is shown that added amine increases initiation rate according to its complexing ability (DMAPM < p-TMPDA « o-TMPDA); this result is explained by the formation of complexes between amine A and n-BuLi, (n-BuLi, A)x, where x = 6, 4, and 1 for the three amines, respectively. The propagation rate and the structure of polyisoprene are modified with o-TMPDA only; the decrease in propagation rate and the increase in 3,4 units in the polymer obtained when r increases are assigned to the formation of solvated ion pairs PI−Li+, o-TMPDA.