文摘
We report the preparation, structural characterization, and detailed lactide polymerization behaviorof a new Zn(II) alkoxide complex, (L1ZnOEt)2 (L1 = 2,4-di-tert-butyl-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenolate). While an X-ray crystal structure revealed the complex to be dimeric in the solid state,nuclear magnetic resonance and mass spectrometric analyses showed that the monomeric form L1ZnOEtpredominates in solution. The polymerization of lactide using this complex proceeded with good molecularweight control and gave relatively narrow molecular weight distribution polylactide, even at catalyst loadingsof <0.1% that yielded Mn as high as 130 kg mol-1. The effect of impurities on the molecular weight of theproduct polymers was accounted for using a simple model. Detailed kinetic studies of the polymerizationreaction enabled integral and nonintegral orders in L1ZnOEt to be distinguished and the empirical rate lawto be elucidated, -d[LA]/dt = kp[L1ZnOEt][LA]. These studies also showed that L1ZnOEt polymerizes lactideat a rate faster than any other Zn-containing system reported previously. This work provides importantmechanistic information pertaining to the polymerization of lactide and other cyclic esters by discrete metalalkoxide complexes.
