GoKawiilMaterials
PE (M n = 1,700 Da, M w = 4,700 Da by GPC) was purchased from Sigma-Aldrich. PP (M n = 5,000 Da), UHMWPE (M n = 6,000,000 Da) and 3,3′,5,5′-TMB were purchased from Macklin. (Trimethylsilyl)diazomethane (TMS-CHN 2 ), PBD and all of the standard diacids were purchased from Aladdin. 4-Carboxyphenylboronic acid (4-CPB) was purchased from Shanghai Meryer Scientific. CH 3 OH (as received), ether (as received) and 30% H 2 O 2 (as received) were purchased from Sinopharm Chemical Reagent. PS (as received) was purchased from Shanghai Titan Scientific. H 2 18O (97% 18O) was purchased from Shanghai Xinbo Industrial. Deionized water with the specific resistance of 18.2 MΩ cm was used in all experiments.
Characterization
The molecular weight of the polymers was recorded using an Agilent PL-GPC 220 system. 1,2,4-trichlorobenzene (TCB) was used as mobile phase at 150 °C. High-temperature gel permeation chromatography (HT-GPC) measurements were calibrated using narrow PS standards. The effective calibration range of the system spans approximately 500 to 1 × 107 g mol−1. 1H-NMR, 13C-NMR and HSQC were performed on a Bruker AVANCE III 500. Fourier transform infrared (FT-IR) spectra were recorded on a Nicolet Nexus 470 in the spectral range 400–4,000 cm−1 using the KBr disc method. Ultraviolet–visible (UV–Vis) spectra were recorded on a Hitachi UH5300 in the spectral range 190–1,100 nm. EPR signals were carried out on a Bruker A300 X-band EPR spectrometer. The radical scavenger used was 5,5-dimethylpyrroline-N-oxide (DMPO). The H 2 O 2 concentration was measured by a catalase assay kit (Beyotime Biotech) on a microplate reader (Thermo Fisher Scientific Varioskan LUX). Confocal fluorescence detection was performed on a Zeiss LSM 980 with Airyscan. We conducted thermal analysis using a METTLER-TOLEDO TGA/DSC 1 or an equivalent synchronous thermal analyser. All measurements were performed under a nitrogen atmosphere with a heating rate of 10 K min−1. We carried out proximate analysis using a 5E-MAG6700 Fully Automatic Industrial Analyzer. Before testing, the commercial PE samples were cooled with liquid nitrogen and ground into powder.
Catalyst-free PE oxidation
This one-pot reaction was performed in the Parr autoclave (Anhui CHEMN Instrument) equipped with an electronic pressure gauge. PE (0.2 g) and 5 ml of deionized water were loaded into the autoclave. The sealed reactor was purged using alternating vacuum and oxygen cycles (3×), then charged to 2 MPa with oxygen and heated to 125 °C at a heating rate of 5 °C min−1 under stirring at 600 rpm. After the reaction, gas products were collected by a 0.5-l Teflon bag. Then, the liquid products were collected and the autoclave was washed using 5 ml of methanol. Finally, the product dissolved in liquid phase and unreacted solid residue is separated by centrifugation. Unless otherwise specified, all other reaction conditions are based on this. We noted a similar work during our revision. Although both studies share the same phenomenon of catalyst-free oxidative upcycling of PE, the reaction mechanisms and conclusions differ substantially51.
Applicability of other polymers oxidation
The post-consumer plastics were derived from PE gloves, LDPE bags, HDPE caps, LDPE packaging and tyres, which were cut into small pieces without any other operation. Then, 0.2 g of post-consumer polyolefin and 5 ml of deionized water were loaded into the autoclave. The sealed reactor was charged to 2 MPa with oxygen and heated to 125 °C at a heating rate of 5 °C min−1 under stirring at 600 rpm.
Measurements for •OH detection
4-CPB generates 4-hydroxybenzoic acid (4-HB) under the action of •OH/H 2 O 2 . 0.60 g of 4-CPB and 5 ml of H 2 O were added in the reactor. The sealed reactor was charged to 2 MPa with oxygen and heated to 125 °C at a heating rate of 5 °C min−1 under stirring at 600 rpm. The cooled solution was detected by liquid chromatography–mass spectrometry (LC–MS).
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