Toughening Biodegradable Isotactic Poly(3-hydroxybutyrate) via Stereoselective Copolymerization of a Diolide and Lactones

Poly(3-hydroxyburtyrate) (P3HB) is the simplest but most important member of the large biodegradable polyhydroxyalkanoate family. However, bacterial P3HB, a pure isotactic crystalline material, is brittle, thus limiting its broad applications. Considering that biodegradable poly(epsilon-caprolactone ) (PCL) and poly(4-hydroxybutyrate) (P4HB) are much more ductile than P3HB, here we utilize metal-catalyzed stereoselective copolymerization of racemic eight-membered dimethyl diolide (rac-8DL(Me)) with epsilon-caprolactone (epsilon-CL) and gamma-butyrolactone (gamma-BL) to toughen P3HB through the formation of isotactic P3HB-based synthetic copolyesters. Notably, catalyst's strong kinetic preference for polymerizing rac-8DL(Me) over epsilon-CL enables one-pot copolymerization of the 1/1 comonomer mixture to afford diblock copolymer P3HB-b-PCL with two crystalline domains (T-m1 similar to 55 degrees C, T-m2 similar to 164 degrees C). Semicrystalline random copolymers, P(3HB-co-CL) and P(3HB-co-4HB), can also be obtained by simply adjusting the comonomer feed ratio and other polymerization conditions. Mechanical testing showed that P3HB-b-PCL is a hard and tough plastic that synergistically combines isotactic P3HB's high modulus with PCL's high ductility.

Automated summary

By utilizing metal-catalyzed copolymerization, the toughness of P3HB has been enhanced, resulting in a hard and tough plastic P3HB-b-PCL with distinct crystalline domains.