Biodegradable Compatibilizers for Poly(hydroxyalkanoate)/Poly(ε-caprolactone) Blends through Click Reactions with End-Functionalized Microbial Poly(hydroxyalkanoate)s

Abstract

Poly(hydroxyalkanoate)s (PHAs) have gained significant attention because they readily biodegrade even under environmental conditions; however, expanding the applications of these polymers to a number of fields is hindered by their brittle nature. Blending with a soft biodegradable polymer, such as poly(ε-caprolactone) (PCL), is currently the best solution for improving the toughness of a PHA material without sacrificing biodegradability; consequently, the development of biodegradable compatibilizers is strongly desired. This Article describes a systematic investigation into the compatibilizing abilities of a number of architecturally varied block copolymers (BCPs) composed of microbially derived poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HHx); PHBH as the A block) and PCL (as the B block), including AB-, A2B-, AB2-, ABA-, and A2BA2-type BCPs. These BCPs were precisely synthesized through the click reactions of azido-functionalized PCLs with microbially produced propargyl-end-functionalized PHBH. Transmission electron microscopy and tensile-testing experiments reveal that the mechanical properties of PHBH/PCL/BCP (= 67/23/10 wt %) ternary blends are highly dependent on the choice of BCP architecture and are closely related to their morphologies. A remarkable 5–10-fold increase in elongation at break compared to that of the BCP-free blend (PHBH/PCL = 75/25) was achieved by the addition of the ABA- or A2BA2-type BCP as the compatibilizer.