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-tert-butylphenol) (EDBP-H₂) with ⁿBuLi in tetrahydrofuran (THF), giving [(EDBP-H)Li(THF)₃] (1) in high yield. However, the reaction of EDBP-H₂ with ⁿBuLi in the presence of benzyl alcohol (BnOH) in diethyl ether or tetrahydrofuran produces compounds [(EDBP-H)Li(BnOH)]₂ (2) and [(EDBP-H)Li(BnOH)(THF)₂] (3), respectively. Further reaction of 2 with excess of THF produces 3. Alternatively, 3 can also be prepared by the reaction of benzyl alcohol with 1 in toluene. Experimental results show that 2 and 3 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-b-poly(l-lactide), have also been prepared from the ring-opening polymerization of l-latide catalyzed by 3 using polystyrene as a macroinitiator.