Preparation of Block Copolymers by a Sequential Transesterification Strategy: A Feasible Route for Upcycling End-of-Life Polyester Plastics to Elastomers

Developing a new approach for synthesizing block polymers is highly demanded. Herein, we propose a sequential transesterification strategy to synthesize block polymers in a "polymer to polymer" mode, such as PLA-PCL-PLA triblock copolymers, by exploiting differences in transesterification rates between different polymers. Poly(epsilon-caprolactone) (PCL) was first controllably cleaved to an alpha,omega-hydroxyl-terminated macroinitiator (HO-PCL-OH) with defined molecular weights by employing 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) as a transesterification organocatalyst and diols as a transesterification reagent, after which PLA was added to conduct sequential transesterification with HO-PCL-OH, thus affording a triblock copolyester. The structure of copolyesters was identified by gel permeation chromatography (GPC), H-1, DOSY, and C-13 NMR. Besides, chemical upcycling of end-of-life PLA and PCL plastics into PLA-PCL-PLA triblock polyester was also explored. This sequential transesterification strategy might provide a new approach for synthesizing useful block copolymers and chemical upcycling of polyester plastics.