Synthesis, Characterization, and Catalytic Studies of Lithium Complexes:  Efficient Initiators for Ring-Opening Polymerization of l-Lactide

The reaction of 2,2‘-ethylidenebis(4,6-di-<i>tert</i>-butylphenol) (EDBP-H<sub>2</sub>) with <i><sup>n</sup></i><sup></sup>BuLi in tetrahydrofuran (THF), giving [(EDBP-H)Li(THF)<sub>3</sub>] (<b>1</b>) in high yield. However, the reaction of EDBP-H<sub>2</sub> with <i><sup>n</sup></i><sup></sup>BuLi in the presence of benzyl alcohol (BnOH) in diethyl ether or tetrahydrofuran produces compounds [(EDBP-H)Li(BnOH)]<sub>2</sub> (<b>2</b>) and [(EDBP-H)Li(BnOH)(THF)<sub>2</sub>] (<b>3</b>), respectively. Further reaction of <b>2 </b>with excess of THF produces <b>3</b>. Alternatively, <b>3 </b>can also be prepared by the reaction of benzyl alcohol with <b>1</b> in toluene. Experimental results show that <b>2 </b>and<b> 3 </b>efficiently initiate the ring-opening polymerization (ROP) of l-lactide in a controlled fashion, yielding polymers with very narrow polydispersity indexes in a wide range of monomer-to-initiator ratios. Block copolymers, polystyrene-<i>b</i>-poly(l-lactide), have also been prepared from the ring-opening polymerization of l-latide catalyzed by <b>3</b> using polystyrene as a macroinitiator.