Poly(lactic acid) (PLA) as a biodegradable and bio-derived polyester has limited application due to its brittleness. In an effort to increase the flexibility, a redox-switchable catalytic system was developed to make A-B-A’ triblock copolymers containing stiff PLA end blocks and a flexible poly(tetrahydrofuran) (PTHF) midblock. A cationic iron(III) catalyst that was previously reported to be active for epoxide polymerization was found to form elastomeric materials when copolymerized with THF. The incorporation of THF into the polyether was controlled by varying the monomer ratio such that the resulting polyether obtained was predominately PTHF. Redox-switchable polymerization was achieved by reducing the catalyst to an Fe(II) species, which arrested the THF/epoxide copolymerization and activated the complex for lactide polymerization. The orthogonal reactivity demonstrated by the iron-based catalyst was used to make A-B-A’ triblock copolymers. Mechanical characterization of the triblock copolymers demonstrated improved flexibility compared to PLA and behavior that makes them suitable as thermoplastic elastomers. In addition to providing access to these new thermoplastic elastomers, the redox-switchable polymerization method used to access these materials provides distinct advantages compared to more traditional routes to synthesize thermoplastic elastomers. These advantages will be highlighted throughout the talk.

Synthesis of biodegradable thermoplastic elastomers using redox switchable polymerization

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ACS Fall 2022

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