Isoprenyllithium

All the experiments were carried out at 18 C under high vacuum (10 mm of mercury) in sealed glass vessel supplied with an ultra-violet cell. Before polymerization the apparatus is care -fully and successively washed with a cyclohexane solution of butyllithium and cyclohexane. The stability of complexed poly-isoprenyllithium has been verified by protonic nuclear magnetic resonance and ultra violet spectroscopy (18)... 

In analogous fashion, an uncapped polybutadienyllithium or poly-isoprenyllithium anion may attack an unreacted pendant vinyl group of another polymer chain (Reaction 4) to give the alkylbenzyl anion (III). 

A more detailed description of the mechanism of isoprene polymerization by lithium compounds has been given (99, 104). The poly-isoprenyllithium first complexes with isoprene in the cis-form. The complex subsequently rearranges to form a transition state in the form of a six-membered ring. H CH... 

However, a series of such experiments showed that ku is not constant but is inversely proportional to the square root of the total organolithium concentration. This behavior can be contrasted to that of isoprene adding to styryllithium and styrene adding to isoprenyllithium in cyclohexane 263) where the apparent rate constants were constant. 

Anionic Synthesis of Hydroxyl-Functionalized Polymers Using Protected, Functionalized Alkyllithium and Isoprenyllithium Initiators... 

FIGURE 2. U.V. Spectra of Isoprenyllithium in Cyclopentane solution at 21 , 10 + and 10 2 m, in presence of various DlPIP/lithium ratios. 

FIGURE 3. Percentage trans isomer in active chain end models for butadienyllithium and isoprenyllithium. DIPIP is 1,2-dipiperidinoethane and TMEDA is tetramethylethylene-diamine. 

FIGURE 4. a) Influence of DIPIP/Li ratio on chemical shifts of the y carbon in isoprenyllithium in cyclopentane at 20°. Major peak-cis isomer, minor peak-trans isomer. 

This lack of copolymerization reactivity of DPE was also observed for the copolymerization of 1,1-diphenylethylene and isoprene [125, 134]. As shown in Table 7, when isoprene was copolymerized with DPE in benzene using n-butyllithium as initiator, the monomer reactivity ratio was 37, which indicates that the addition of isoprene to the isoprenyllithium chain end is 37 times faster than the addition of 1,1-diphenylethylene. The unreactivity of isoprenyl carbanions toward DPE is unique to lithium the monomer reactivity ratios for isoprene in benzene were 0.38 and 0.05 with sodium and potassium as the counterions [125, 134]. When THE was used as the solvent at 0°C, ri decreased to 0.11 with lithium as counterion. 

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