Syndiotactic poly(lactic acid)

• US 6,608,170 B1
• Filed: 01/24/2000
• Issued: 08/19/2003
• Est. Priority Date: 03/31/1999
• Status: Expired due to Fees

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: Coates, Geoffrey W.
• Primary Examiner(s): Zalukaeva, Tatyana
• Application Number:
  US09/490,449
• Time in Patent Office: 1,303 Days
• Field of Search: 528/297, 528/354, 528/357, 528/361, 528/355, 525/437, 525/450
• US Class Current: 528/355
• CPC Class Codes: C08G 63/08 Lactones or lactides
• CPC Class Codes: C08G 63/823 for the preparation of polylactones or polylactides

Abstract

Syndiotactic poly(lactic acid) is formed by polymerization involving a cleavage of the same oxygen-acyl bond in a series of meso-lactide molecules to form polymer containing a series of units with stereocenters wherein adjacent stereocenters are of the opposite stereochemistry. The mechanism is catalyzed by chiral metal alkoxides that afford stereocontrol such as those formed by reacting

or the opposite enantiomer with Al(OR)₃ where R is straight chain or branched alkyl containing 1 to 20 carbon atoms, e.g., methyl or isopropyl, in solvent, with subsequent evaporation of solvent in vacuo.

Claims

1. Syndiotactic poly(lactic acid) comprising the structure:

where n ranges from 20 to 5,000 and containing enantiotopic selectivity greater than 60%.

8. The syndiotactic poly(lactic acid) of claim 1 containing enantiotopic selectivity greater than 85%.

9. The syndiotactic poly(lactic acid) of claim 1 containing an enantiotopic selectivity of 96%.

2. A process for preparing syndiotactic poly(lactic acid) comprising the structure:

where n ranges from 20 to 5,000 and containing enantiotopic selectivity greater than 50%, said process comprising ring opening polymerization of meso-lactide in the presence of a chiral metal alkoxide catalyst, where the same oxygen-acyl bond in a series of meso-lactide molecules is cleaved, whereby a polymer is formed containing a series of units containing stereocenters where adjacent stereocenters are of opposite stereochemistry.

3. The process according to claim 2, wherein the metal of the chiral metal alkoxide catalyst is not yttrium.

4. The process according to claim 2, wherein the chiral metal alkoxide catalyst is prepared by reacting a chiral ligand with Al(OR)₃ where R is straight chain or branched alkyl containing 1 to 20 carbon atoms in solvent, and then evaporating the solvent in vacuo.

5. The method of claim 4, wherein the chiral ligand is

or the opposite enantiomer.

6. The method of claim 5, wherein R in Al(OR)₃ is isopropyl.

7. The method of claim 6, wherein R in Al(OR)₃ is methyl.