PMDT

The influence of two tertiary polyamines on the a-nionic polymerization of isoprene in cyclohexane has been studied. TMEDA (N,N,N, N -tetramethyl-ethylenediamine) and PMDT (pentamethyIdiethylene-triamine) can increase or decrease the propagation rate, depending on the concentration range. The results are discussed on the basis of the nature of the living species. 

The purpose of this paper is to present some kinetic results relative to the propagation reaction in the polymerization of isoprene by oligoisoprenyllithium complexed with TMEDA or PMDT (pen-tamethyldiethylenetriamine) in cyclohexane. 

After 4 or 5 hours the reaction is complete and a sigmoidal living ends formation curve is observed (1 ). The degree of polymerization of the oligoisoprenyllithium equals about ten. By addition of catalytic amounts of complexing agent (TMEDA or PMDT) the remarkable increase of the initiation rate is not measurable by ultra violet spectroscopy. Also, only the propagation step was studied. 

We have followed the propagation rate of the polymerization of isoprene initiated by cyclohexane solutions of the complexes oli-goisoprenyllithium/TMEDA and oligoisoprenyllithium/PMDT in two very different ranges of living ends concentration. In each case we have determined the order of the reaction with respect to the living ends concentration. 

Complexation with PMDT. The study developed above has been repeated using a tertiary triamine (PMDT). 

For "high" concentrations of polyisoprenyllithium (10 mole.l ), PMDT affects the propagation rate like TMEDA. Respectively a low and a high increase are observed for r values less than 0.5 and r values included between 0.5 and 1 (figure 5). 

Figure 4. Influence of PMDT on the propagation rate in the polymerization of isoprene in cyclohexane at low PILi concentration [A/] = 034 mol 1 [PILi] = 4.5 X 10 mol L1 18°C.

Complexation with PMDT. The study developed above has been repeated using the tertiary triamine PMDT. The results are analogous to those found in presence of TMEDA (figure 6). A first order reaction with respect to the complexe PILi/PMDT is evidenced so it seems that the active propagating species is the 1 1 chelate. 

PMDT (figure 6) show a critical point at 2.5 x 10 mole.l... 

Moreover, it is possible to determine from figure 6 the values of vR corresponding to the complexes PILi/TMEDA and PILi/PMDT. Such investigation evidences the higher reactivity of the 1 1 chelate PILi/TMEDA toward the 1 1 complexe PILi/PMDT. 

Using the same scheme, PMDT leads to a complexe in which three nitrogen atoms surround the lithium atom. In step 1 occurs a precomplexation of the monomer which is then inserted in the propagating chain (step 2). 

It seems also reasonable to think that substituting TMEDA by PMDT provokes a steric hindrance in the monomer insertion, involving a diminution of reactivity this point is more developed in a coming paper about the polymerization of isoprene with the complexe oligoisoprenyllithium/hexamethyltriethylenetetrami-... 

The dimethylaurate(I) anion was more readily isolated (9) when the lithium ion was complexed with pentamethyldiethylenetriamine (PMDT) [Eq. (2)]. The greater thermal stability of these complexes compared with their phosphine analogs was explained in terms of less-ready ligand dissociation and complexation of the lithium ion, preventing its attack at the gold center. 

AuMe(PPh3)] + MeLi + PMDT —> [Li(PMDT) [AuMea + PPh,... 

Crassous et al.177) studied the polymerization of ethylene using n-butyllithium in conjunction with the tertiary diamines TMEDA, TEEDA (tetraethylethylenedi-amine) and PMDT (pentamethyldiethylenetriamine). In contrast to the situation with TMEDA the rate of polymerization was found to show a first order dependence upon the complexed chain end concentration. Steric hindrance seems to prevent the dimerization of the chain ends. Examination of the n-BuLi. TEEDA complex by -NMR shows that the displacement to high field of the protons a to the lithium induced by complexation is much smaller with TEEDA than with TMEDA or PMDT. With [TEEDA] < [RLi] time-averaged signals were obtained showing that the exchange process... 

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