【Frontiers in HaiChuan Chemical Technology】Researchers from Qingdao University of Science and Technology have made new progress in the field of high-performance closed-loop thermoplastic elastomers

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Thermoplastic elastomers (TPEs) combine the high elasticity of rubber with the easy processability of plastics. They are widely used in industries such as electronics, healthcare, and aerospace. In 2023, the global market size reached $25.15 billion, and it continues to grow at a rapid pace. However, most commercial TPEs are currently produced from petroleum-based raw materials; their carbon-carbon backbones are stable and difficult to degrade, posing serious resource and environmental problems. Developing new TPEs that are green in origin, possess excellent performance, and can be chemically recycled has become key to breaking through the bottlenecks in the industry’s development. In recent years, chemically recyclable TPE materials have attracted widespread attention. Such materials can be depolymerized into monomers under specific conditions after use, and these monomers can be reused in polymerization to produce TPE, thereby achieving a closed loop of “polymer-monomer-polymer”. However, currently reported chemically recyclable TPE materials still suffer from low recycling efficiency, complex separation and purification of recycled monomers, and material properties that fail to meet the requirements of practical applications. To address these challenges, the research team led by Shen Yong and Li Zhibo from Qingdao University of Science and Technology proposed a novel type of high-performance TPEs that can be recycled in a closed loop. This material is prepared by sequential ring-opening copolymerization using bio-based β-methyl-δ-valerolactone (βMVL) and polydioxanone (PDO) as monomers in a one-pot process. It exhibits excellent overall properties while also enabling efficient closed-loop recycling. Using βMVL and PDO as raw materials, and a dual-catalyst system of organic base/urea, this study successfully prepared the well-defined ABA-type triblock copolymer PPDO-b-PβMVL-b-PPDO through sequential ring-opening copolymerization in a one-pot process (Figure 1). By controlling the molecular weight, volume fraction of hard segments, and topology, precise regulation of the material properties was achieved. The prepared TPEs exhibit excellent comprehensive properties, with mechanical properties that are superior to those of some commercial styrene-based TPEs such as SBS and SIS. Among them, TPE-6 with a three-arm star-shaped structure performs particularly well: its tensile strength reaches up to 21.1 MPa, the elongation at break is as high as 1054%, and the elastic recovery rate can attain 93.5%. TPE-6 has a glass transition temperature as low as -45.2°C, allowing it to maintain good elasticity and flexibility at low temperatures; its maximum operating temperature is 81.3 °C, which is much higher than that of previously reported recyclable TPEs (around 40 °C). This value is close to the upper operating temperatures of commercial SBS (YH-791, 79.3 °C) and SIS (YH-1209, 73.9 °C), thereby addressing the issue of poor high-temperature performance in chemically recyclable TPEs and meeting the practical application requirements in various scenarios (Figure 1). Under the catalysis of 0.5 wt% tin(II) octoate, the material undergoes bulk depolymerization at 140 °C; the mixture of original monomers can be recovered via vacuum distillation. The monomer ratio is consistent with the feed ratio, and the overall yield reaches as high as 94%. The monomer mixture can be separated by column chromatography, and the separated monomers are repolymerized to produce TPE-R with structures and properties identical to those of the original material. On the other hand, the monomer mixture can also be separated by distillation; the crude monomers obtained after secondary distillation (βMVL with a purity of 97% and PDO with a purity of 89%) can be copolymerized directly to produce gradient block copolymers (TPE-SR). The tensile strength of this material is 11.9±1.2 MPa, the elongation at break is 1070±130%, and the elastic recovery rate is 90.4±0.6%. Its maximum operating temperature is 81.7 °C, and its overall performance still meets the requirements of most application scenarios. Compared with traditional column chromatography separation and recovery methods, this approach is simpler to operate and requires less energy, making it more suitable for industrial-scale production. The relevant findings were published in ACS Sustainable Chemistry & Engineering under the title “High-Performance and Closed-Loop Recyclable Thermoplastic Elastomers from Sequential Ring-Opening Copolymerization of Biobased β-Methyl-δ-valerolactone and p-Dioxanone”. Wang Liying, a doctoral student at Qingdao University of Science and Technology, is the first author of the paper; Professors Shen Yong and Li Zhibo from Qingdao University of Science and Technology are the co-corresponding authors. This work was supported by the **Young Scientists Fund (Category B) and the Shandong Province Taishan Scholar Program.