Anionic polymerization of acrylic monomers. 17. Ligated anionic living polymerization of 2-ethylhexyl acrylate as promoted by polydentate lithium alkoxides

Different initiators combined with a new family of mu/sigma dual ligands, i.e., polydentate alkoxides, were used to initiate the anionic polymerization of 2-ethylhexyl acrylate (2EtHA) at low temperatures. It has been found that lithium 2(2-methoxyethoxy) ethoxide (LiOEEM) is the most efficient mu/sigma ligand in promoting a living polymerization of that monomer. Although LiOEEM gives rise to a molecularly well-controlled P2EtHA at -78 degrees C in a 9/1 toluene/THF mixture, i.e., quantitative yield, high initiator efficiency (>90%), and narrow molecular weight distribution (M(w)/M(n) down to 1.05), two-step monomer resumption experiments always lead to a bimodal distribution, suggesting that the LiOEEM-complexed P2EtHA anions are not stable. Nevertheless, a perfectly living 2EtHA anionic polymerization process has been obtained at -100 degrees C, keeping other conditions unchanged. In comparison with other types of ligands, such as LiCl and LiOtBu (both mu-ligands) and DB18CE6 and K222 (both sigma-ligands), it has been further demonstrated that the formation of a stable and bulky active complex is at the origin of the anionic living polymerization of 2EtHA, in agreement with our findings in the case of anionic statistical copolymerization of methacrylate and acrylate.