Synthesis of stereospecific and atactic poly(lactic acid)s

• US 6,316,590 B1
• Filed: 11/08/2000
• Issued: 11/13/2001
• Est. Priority Date: 11/10/1999
• Status: Active Grant

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: Cheng, Ming, Chamberlain, Bradley M., Coates, Geoffrey W.
• Primary Examiner(s): Acquah, Samuel A.
• Application Number:
  US09/707,980
• Time in Patent Office: 370 Days
• Field of Search: 528/357, 528/358, 528/359, 502/155, 502/159, 502/200, 502/324, 502/340
• US Class Current: 528/357
• CPC Class Codes: B01J 2531/22 Magnesium
• CPC Class Codes: B01J 2531/26 Zinc
• CPC Class Codes: B01J 31/1608 the ligands containing silicon
• CPC Class Codes: B01J 31/1805 the ligands containing nitrogen
• CPC Class Codes: B01J 31/2226 Anionic ligands, i.e. the overall ligand carries at least one formal negative charge
• CPC Class Codes: C08G 63/08 Lactones or lactides
• CPC Class Codes: C08G 63/823 for the preparation of polylactones or polylactides

Abstract

Isotactic poly ((R)-lactic acid) or isotactic poly (S)-lactic acid are respectively 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 and the preferred catalyst contains as the ligand which is not a propagating group diiminate substituted with isopropyl substituted phenyl and 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.

Claims

1. A method for preparing isotactic poly ((R)-lactic acid) or isotactic poly ((S)-lactic acid) which comprises polymerizing respectively (R,R)-lactide or (S,S)-lactide in the presence of 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, or is dimer thereof.

2. The method of claim 1 where the catalyst has the structure

where M is selected from the group consisting of zinc and magnesium, R is selected from the group consisting of OAc, OR² where R² is selected from the group consisting of C₆-C₂₀ aryl and C₁-C₂₀ alkyl, N(SiMe₃)₂ and C₁-C₂₀ alkyl and R₁ is selected from the group consisting of ethyl and isopropyl, or is dimer thereof.

3. The method of claim 2 wherein the catalyst has the structure (I) wherein M is magnesium, R₁ is ethyl and R is OMe or is dimer thereof.

4. Heterotactic poly(lactic acid).

5. A method for preparing heterotactic poly(lactic acid) which comprises polymerizing rac-lactide in the presence of 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.

6. The method of claim 5 where the catalyst has the structure

where M is zinc, R is selected from the group consisting of OAc, OR² where R² is selected from the group consisting of C₆-C₂₀ aryl and C₁-C₂₀ alkyl, N(SiMe₃)₂ and C₁-C₂₀ alkyl and R₁ is selected from the group consisting of ethyl and isopropyl, or is dimer thereof.

8. The method of claim 6 wherein the catalyst has the structure (I) where R is OR² where R² is isopropyl and R¹ is isopropyl.

7. A single-site catalyst for lactide polymerization containing a β

-diiminate ligand which remains bound to a zinc center which is joined to a ligand which initiates polymerization.

10. The method of claim 7 wherein the catalyst has the structure (I) wherein R is N(SiMe₃)₂ and R₁ is isopropyl.

11. The catalyst of claim 7 having the structure:

where M is zinc, R is OR² where R² is isopropyl and R₁ is isopropyl, or is dimer thereof.

12. The catalyst of claim 11 which is a dimer.

9. Catalyst having the structure

where M is magnesium, R is selected from the group consisting of OAc, OR² where R² is selected from the group consisting of C₆-C₂₀ aryl and C₁-C₂₀ alkyl, N(SiMe₃)₂ and C₁-C₂₀ alkyl and R₁ is selected from the group consisting of ethyl and isopropyl, or is dimer thereof.

13. A method for preparing syndiotactic poly(lactic acid) which comprises polymerizing meso-lactide in the presence of 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.

14. The method of claim 13 where the catalyst has the structure:

where M is zinc, R is selected from the group consisting of OAc, OR² where R² is selected from the group consisting of C₆-C₂₀ aryl and C₁-C₂₀ alkyl, N(SiMe₃)₂ and C₁-C₂₀ alkyl and R₁ is isopropyl, or is dimer thereof.

15. The method of claim 14 where the catalyst has the structure (I) where R is OR² where R² is isopropyl.

16. The method of claim 15 where the catalyst is a dimer.

17. A method for preparing atactic poly(lactic acid) with polydispersity M_w/M_n ranging from 1.15 to 1.40 as determined by gel permeation chromatography versus monodispersed polystyrene standards, said method comprising polymerizing rac-lactide in the presence of a catalyst which has 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, said polymerization being carried out in the presence of 0.5 to 2 equivalents of C₁-C₄ alcohol per mole of magnesium.

18. The method of claim 17 where the catalyst has the structure:

where M is magnesium, R is selected from the group consisting of OAc, OR² where R² is selected from the group consisting of C₆-C₂₀ aryl and C₁-C₂₀ alkyl, N(SiMe₃)₂ and C₁-C₂₀ alkyl and R₁ is selected from the group consisting of ethyl and isopropyl, or is dimer thereof.

19. The method of claim 18 where the catalyst has the structure (I) where R is OR² where R² is isopropyl and R₁ is isopropyl and is dimer, and the alcohol is isopropanol.