Metal-free Catalytic Reactions to Improve Industrial
Production of Isotactic Polylactides (PLA)
At A Glance
- Two novel reactions that, when paired, yield an effective, metal-free, one-pot process to produce isotactic poly(L-lactide) from the meso-lactide waste product of conventional poly(lactide), or PLA, production.
- May be utilized to either improve i-PLLA yield or to produce value-added side product (racemic mixture of L- and D- lactide).
- Potential commercial applications include the packaging, microelectronics, and biomedical fields
Poly(lactide) (PLA) is one of the most commercially important biodegradable and biocompatible polymers, with a wide array of applications in packaging, microelectronics, and biomedical fields. Its utility will only increase as the field of organopolymerization of lactide (LA) is opening up the possibility of metal-free alternatives to traditional PLA. The physical properties of PLA are highly dependent on the optical purity of the lactic acid monomer and/or specificity of the catalytic polymerization reaction .
Isotactic poly(L-lactide), or i-PLLA is an important type of PLA whose current industrial production relies on the large-scale production of optically pure L-LA. Unfortunately, the process to produce L-LA also produces a considerable amount of meso-LA that, if not removed, contaminates the final i-PLLA product and significantly alters or deteriorates its properties, for example its crystallinity and biodegradation rate. The removal of meso-LA seriously decreases the economy of i-PLLA production.
Researchers in Colorado State University’s Department of Chemistry have developed a method that converts the waste meso-LA to a racemic mixture of L-LA and D-LA (Figure 1 Below). This mixture is itself valuable, but additionally they have developed a second method that uses a novel organic catalyst to selectively polymerize the L-LA into i-PLLA without previously removing the D-LA. These two steps may be combined in a “one pot” process that effectively converts a large portion of the meso-LA waste product into the desired i-PLLA product, thereby improving the efficiency of the overall i-PLLA production process.
This technology offers the potential to improve the i-PLLA production process by converting a waste product into additional i-PLLA product and/or into a useful racemic mixture of LA. Both reactions utilize novel, organic (metal-free) catalytic systems and are very effective. The racemization reaction is quantitative (nearly 100% yield) and the polymerization to i-PLLA proceeds with high enantioselectivity (91% ee at 51% monomer conversion).
- Two step process to produce isotactic poly(L-lactide) from meso-lactide waste product.
- First step produces racemic lactide from meso-lactide quantitatively (nearly 100% yield).
- Second step (optional) utilizes kinetic resolution polymerization to selectively produce isotactic PLLA from racemic mixture.
- Both reactions are metal-free catalytic reactions that proceed in high yield and enantioselectivity.
- Utilization of waste meso-lactide improves efficiency of the overall PLA synthesis process.
Last updated: October 2019
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