Process for the Preparation of Polymers of Dimeric Cyclic Esters
Polylactic acid (PLA) is growing rapidly in popularity as an alternative to petroleum-derived plastics. It is biodegradable, thermoplastic, and derived from renewable resources. Presently, the preparation of crystalline materials requires enantiopure L-lactide, where lactic acid is produced by microbial fermentation, and the cyclic lactide monomer is made by oligomerization and catalytic dimerization. PLA is then produced from the lactide monomer by ring-opening polymerization. This process is costly, weakening PLA's position as an alternative to less costly petroleum-derived plastics. Less costly production methods for preparing crystalline PLA are needed to reduce the cost of the material. Low costs would broaden PLA use as an alternative to petroleum-derived polymers.
Description of Technology
This invention provides a process that eliminates the need to prepare enantiopure D and L-lactic acid as a precursor for making PLA. The process involves direct synthesis of PLA from racemic lactide or polymendelide, and the use of a racemic metal organic ligand polymer to catalyze the polymerization of racemic dimeric cyclic monomers to a polylactide sterocomplex. PLA made from this process is potentially less costly and has a higher melting temperature than PLA made from precursor enantiopure L-lactide.
- Lower cost production process for PLA : One of the challenges for biodegradable replacement polymers has been the lower cost of commodity polymers like polyethylene, polypropylene and PVC. Technologies that contribute to reducing the cost of PLA will increase its competitiveness with petroleum-derived polymers. This process eliminates the need for enantioselective processes.
- Process produces stereocomplex PLA: This mixture of D and L-PLA has a significantly higher meting point than PLA produced by the standard process. This higher melting temperature allows the materials to be used for high temperature applications.
- Environmentally advantageous: The technology enables broader use of PLA as both green replacements for petroleum-derived polymers and bioresorbable polymers used for implanted medical devices.
This invention is useful for providing less costly crystalline PLA for bioplastics applications where PLA is already employed. Materials made from PLA produced by this process are ideal for biomedical implants and high temperature polymer applications.
US 6469133 (issued Oct 22, 2002)
Gregory Baker, Milton Smith III
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Michigan State University