At a Glance
Researchers at Colorado State University have developed a novel monomer design strategy based on a bridged bicyclic thiolactone that produces stereo-disordered to perfectly stereo-ordered polythiolactones, all exhibiting high crystallinity and full chemical recyclability. These polythioesters defy aforementioned trade-offs by having an unusual set of desired properties, including intrinsic tacticity-independent crystallinity and chemical recyclability, tunable tacticities from stereo-disorder to perfect stereoregularity, as well as combined high-performance properties such as high thermal stability and crystallinity, and high mechanical strength, ductility, and toughness
Owing to their outstanding and versatile properties, synthetic polymeric materials meet the demands of end consumer products and play a key role in modern life and the global economy. However, synthetic polymers are largely based on petroleum resources, which are rapidly depleting due to ever increasing energy demands. Likewise, the tremendous growth of single-use plastics poses a threat to the environment. Therefore, modern society has inherited the responsibility of gradually replacing petroleum-based polymers with those derived from renewable resources and with built-in end-of-life solutions, such as recyclability.
Inspired by present challenges, the group set out to design high-performance circular polymers with both intrinsic chemical recyclability and crystallinity. Guided by the following working hypotheses, they arrived at a bridged bicyclic thiolactone monomer, 2-thiabicyclo[2.2.1]heptan-3-one (BTL), which can be prepared from a bio-based olefin carboxylic acid in 80% yield at a 50-g scale. First, BTL should contain higher ring strain than the parent, nonpolymerizable γ-thiobutyrolactone, which should allow the ROP to proceed at room temperature (RT) with high equilibrium monomer conversions and yield high molecular weight (MW) polymers. Second, the bridged bicyclic system should provide rigidity to the polymer backbone for enhanced thermal and mechanical properties. Third, the depolymerizability and selectivity in chemical recycling of the resulting polymer poly(2-thiabicyclo[2.2.1]heptan-3-one) (PBTL) should be high since the ring closure of the five-membered thiolactone is kinetically facile and thermodynamically favored. Furthermore, the bridged bicyclic monomer exists only in the cis configuration, thus eliminating possible isomerization. Fourth, the aforementioned PBTL that also contains the cyclopentylene units, the motif leading to atactic yet crystalline hPN, could render its tacticity-independent, thus intrinsic, crystallinity, provided the unique ability to crystalize because of pseudosymmetry and long-range order present in the pan-tactic PBTL with all degrees of tacticity.
- Robust physical and mechanical properties for common applications
- Convenient processability
- Sustainable polymer material
- Thermal stability, crystallinity, toughness and ductility
- Chemically recyclable plastics for commodity application