Abstract
Upcycling plastic waste into reprocessable materials with performance-advantaged properties would contribute to the development of a circular plastics economy. Here, we modify branched polyolefins and postconsumer polyethylene through a versatile C-H functionalization approach using thiosulfonates as a privileged radical group transfer functionality. Cross-linking the functionalized polyolefins with polytopic amines provided dynamically cross-linked polyolefin networks enabled by associative bond exchange of diketoenamine functionality. A combination of resonant soft X-ray scattering and grazing incidence X-ray scattering revealed hierarchical phase morphology in which diketoenamine-rich microdomains phase-separate within amorphous regions between polyolefin crystallites. The combination of dynamic covalent cross-links and microphase separation results in useful and improved mechanical properties, including a ∼4.5-fold increase in toughness, a reduction in creep deformation at temperatures relevant to use, and high-temperature structural stability compared to the parent polyolefin. The dynamic nature of diketoenamine cross-links provides stress relaxation at elevated temperatures, which enabled iterative reprocessing of the dynamic covalent polymer network with little cycle-to-cycle property fade. The ability to convert polyolefin waste into a reprocessable thermoformable material with attractive thermomechanical properties provides additional optionality for upcycling to enable future circularity.
| Original language | English |
|---|---|
| Pages (from-to) | 27450-27458 |
| Number of pages | 9 |
| Journal | Journal of the American Chemical Society |
| Volume | 145 |
| Issue number | 50 |
| DOIs | |
| State | Published - Dec 20 2023 |
Funding
Polymer functionalization, network synthesis, sample preparation, stress relaxation, scattering, DMTA, reprocessing, thermal property characterization, and evaluation of structure–property relationships by E.N., V.B., and F.A.L. was supported by the Air Force Office of Scientific Research under Award Number 1-22RT0214. Scattering, creep, and stress relaxation by M.H., Z.P., and B.A.H. was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231 Unlocking Chemical Circularity in Recycling by Controlling Polymer Reactivity Across Scales program CUP-LBL-Helms. Additional scattering measurements and analysis by L.T.K. were performed under support from DOE BES MSED FWP ERKCK60. Rheological instrumentation, rheological training, stress relaxation, and technical expertise by F.V. and S.S.S was supported by the National Science Foundation (DMR 2324167 and DMR 2004048). The UNC Department of Chemistry’s NMR Core Laboratory is acknowledged for the instrumentation that enabled this work through support from the National Science Foundation (CHE-1828183 and CHE-0922858). Portions of this work, including synthesis of DCPN-P2 and spin coating of polymer thin films, were carried out as a User Project at the Molecular Foundry, which is supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. DOE under contract no. DE-AC02-05CH11231. RSoXS and GIWAXS characterization was carried out at the Advanced Light Source, which is a DOE Office of Science User Facility operating under the same contract.