NEW LIGANDS FOR THE LIVING ISOTACTIC ANIONIC-POLYMERIZATION OF METHYL-METHACRYLATE IN TOLUENE AT 0-DEGREES-C - 2 - LI-7 NMR ANALYSIS OF SEC-BUTYLLITHIUM LIGATED BY LITHIUM SILANOLATES

The mixed associated species {xsBuLi, (y - x)sBuMe(2)SiOLi} formed by reaction of sec-Butyllithium (sBuLi) with octamethylcyclotetrasiloxane (MeaSiO)(4) in toluene have been used to initiate the anionic polymer ization of methyl methacrylate (MMA) in that solvent at 0 degrees C. T he active species generated by this new type of initiator have been ch aracterized by Li-7 NMR at 0 degrees C. The Li-7 NMR spectra of sBuLi and sBuMe(2)SiOLi mixtures in toluene show that only one single type o f {sBuLi, 5sBuMe(2)SiOLi} mixed species prevails at [sBuMe(2)SiOLi]/[s BuLi] molar ratios higher than ca. 21, as result of a large excess of {6sBuMe(2)SiOLi} species. The Li-7 NMR has also concluded to the forma tion of {PMMALi, 5sBuMe(2)SiOLi} species upon the addition of MMA to t hat initiator solution, supporting the theory that only one type of io nic species is active during the MMA conversion. These active centers are stable for at least 1 h at 0 degrees C as confirmed by Li-7 NMR.