Description:
A new polymerization method that produces poly(γ-butyrolactone) from bioderivable succinic acid. Possible applications in biomedical, biodegradable polyesters, and thermally recyclable plastics industries.
At a Glance
- Catalytic ring-opening polymerization reaction for γ-butyrolactone.
- Very high conversion rates at ambient pressure, excellent control over molecular weight and topology.
- Product is derived from biorenewable succinic acid, is biocompatible and biodegradable.
- Polymer may be recycled via thermal treatment back to starting material in virtually 100% yield.
Detailed Description
Aliphatic polyesters, a class of biopolymers conveniently prepared by ring-opening polymerization (ROP) of certain cyclic esters or lactones, have received ever-growing interest for use in a wide range of applications, due to their biodegradability and biocompatibility. Gamma-butyrolactone (γ-BL) is an attractive starting material for the synthesis of the corresponding biopolymer because it is biorenewable from succinic acid, which is produced chiefly from bacterial fermentation of glucose or chemical oxidation of 1,4-butanediol and was recently ranked first in DOE’s top 12 biomass-derived compounds best suited to replace petroleum-derived chemicals. However, in sharp contrast to other lactones, γ-BL is commonly regarded as "non-polymerizable" via ROP.
This invention provides for the polymerization of γ-BL in a reaction that proceeds smoothly to high conversions of starting material (up to 90%) under ambient pressure with a suitable catalyst and/or initiator. The most effective systems produce poly(y-BL) in a multi-gram scale (or larger) using either an earth-abundant lanthanum complex or a discrete, single-site molecular yttrium complex. Excitingly, this technology has recently been demonstrated without the need for metal catalysts. Use of organic superbases affords similar control and opens the way for medical applications where polymers must be without trace levels of metals, such as biomedical applications.
Impressively, both metal-based and organic catalytic systems afford a high degree of control over the final product. Not only can the length of the polymer product be controlled (with molecular weights up to 30 kg/mol), but it the topology of the resulting PγBL can be controlled to result in either linear or cyclic structures (or both). This unprecedented synthetic capability provides for the tuning of a variety of materials properties, including degree of crystallinity, melting-transition temperature, and thermal stability.
Remarkably, both linear and cyclic PγBL materials can be readily recycled back to the monomer γ-BL in 100% yield by simply heating the bulk materials at 220 °C or 300 °C (respectively) for 1 h, therefore demonstrating complete recyclability of PγBL.
Considering γ-BL as a biorenewable monomer and poly(γBL) as a recyclable and biodegradable polymer, this invention, which provides for facile access to this new class of materials, will undoubtedly catalyze further major advances in the field. The product is a structural equivalent of poly(4-hydroxybutyrate) (P4HB), which is incorporated in the commercial product Biopol (widely used as internal sutures). The products of this invention are expected to have potential commercial applications in the biomaterials, biomedical, biodegradable polyester, and thermally recyclable plastics industries.
