Lithium naphthalenides in non-polar or in low-polarity media: some insights regarding their use as initiators in anionic polymerizations

Abstract

The synthesis of bidirectional anionic initiators by the reaction between metallic lithium (Li) and naphthalene (Naph), under mild conditions, in non-polar (benzene) or low-polarity media (benzene/THF mixtures) is reported. The efficiency of these initiators to provide macromolecules with well-defined structures was demonstrated. Model linear homopolymers from styrene (S) or hexamethyl(ciclotrisiloxane) (D3) monomers were synthesized using classical anionic polymerization (high-vacuum techniques). The model polymers obtained were analyzed using the conventional analytical techniques, and showed narrow molar mass distributions, a broad range of molar masses (from 3000 to 1,000,000 g/mol) and polydispersity indexes (Mw/Mn) lower than 1.1. High molar mass polymers were obtained using pure benzene as solvent, whereas lower molar masses were obtained in benzene/THF mixtures in which the concentration of THF was lower than 10 % v/v. The ratio [Li]/[Naph] and the nature of the reaction medium are the experimental parameters to be controlled to obtain the desired lithium naphthalenides.