| 摘要 |
<p>Isotactic poly ((R)-lactic acid) or isotactic poly (S)-lactic arerespectively prepared from (R,R)-lactide and (S,S)-lactide using a catalyst which has a zinc center or a magnesium center and two ligands where one of the ligands is a propagating group and the other of the ligands is not a propagating group. Heterotactic poly(lactic acid) is prepared from rac-lactide using a catalyst which has a zinc center and two ligands where one of the ligands is a propagating group and the other of the ligands is not a propagating group; heterotactic poly(lactic acid) is a novel composition. The catalyst with a magnesium center is a novel catalyst. Syndiotactic poly(lactic acid) is prepared from meso-lactide using a syndiotactic poly(lactic acid) effecting catalyst which has a zinc center and two ligands where one of the ligands is a propagating group and the other of the ligands is not a propagating group diiminate substituted with isopropyl substituted pheny and the ligand which is not a propagating group and the preferred catalyst contains as the propagating group is isopropoxide. Atactic poly(lactic acid) of polydispersity ranging from 1.15 to 1.40 is prepared in less than 10 minutes by polymerizing rac-lactide in the presence of C1-C4 alcohol and a catalyst with a magnesium center and two ligands where one of the ligands is a propagating group and the other of the ligands is not a propagating group.</p> |
