Development of a mechanically tunable triblock copolyester with partial chemical recyclability

Triblock copolymers can significantly enhance material properties due to their unique microphase separation structures and have become important candidates for the development of sustainable polymers. However, research reports on recyclable block copolyesters remain relatively limited. 3,4-Dihydro-2H-benzo [b][1,4]dioxepin-2-one (BDXO) is a renewable monomer derived from lactones, and its homopolymer exhibits excellent thermal properties and tensile strength but low flexibility. Copolymerizing various cyclic esters and leveraging their respective advantages for modification has emerged as a highly promising strategy to address this issue. In this study, a partially chemically recyclable triblock copolyesters was designed and synthesized using poly(trimethylene carbonate) (PTMC) as the soft chain and poly(3,4-dihydro-2H-benzo[b][1,4]dioxepin-2-one) (PBDXO) as the hard segment. The synthesized triblock copolyesters were characterized for their chemical structure, molecular weight, and thermal properties using proton nuclear magnetic resonance (¹H NMR), size exclusive chromatography (SEC), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Mechanical tests revealed that the mechanical strength the copolyesters can be tuned by the proportion of the soft and hard segments as well as the total molecular weight. Leveraging the disparity in ceiling temperature (T_c) between the hard and soft segments enables efficient selective chemical recycling of the PBDXO hard segment, with the PTMC soft segment being substantially remained. This offers a facile and sustainable approach to the design of recyclable block copolyesters.