Fig. 1. In-situ 1H NMR spectra (CDCl3, 400 MHz) of the alcoholysis reaction using the PLA-modulated depolymerization strategy (a), the methanol-modulated depolymerization strategy (b) and when PLA and TBD catalyst were added together without pre-mixing steps (c). The acquisition time per NMR spectrum used is 107 s. Conditions: 5 mg PLA, 3 mol% of TBD, 10 equivalents of MeOH, room temperature. (d) Comparison chart of the monomer yield over time with different reactant-modulated strategies at room temperature by in-situ NMR. The red line represented the methanol-modulated strategy, and the blue line represented the PLA-modulated strategy. Note: The yield of ML monomer was measured by the relative content with 1,1,2,2-tetrachloroethane as the internal standard.

Fig. 2. (a) 1H NMR spectra of the methine proton of PLA in CDCl3 with the addition of 0, 0.1, 0.2, and 0.5 equiv. TBD. (b) Characterization of PLA molecular weight changes in GPC using 0, 0.1, 0.2, and 0.5 equiv. TBD. (c) DOSY spectrum recorded on a solution of PLA and TBD in CDCl3, as well as a solution of TBD in CDCl3. Two sets of diffusion coefficients are visible, corresponding to the peaks of TBD and of the polymer, respectively. (d) High-resolution MS (the entire scan range m/z 200-1000) analyses of a mixed solution of PLA and TBD with a molar ratio of 1:1. The schematic diagram only selected two structures as representatives. The blue part in the Fig. represents the presence of acyl-TBD product forming from the combination of PLA monomer and TBD fragments, and the purple part represents the formation of the acyl-TBD oligomers with n = 11. The upper part shows the experimental mass spectrometric information, and the lower part shows the simulated mass spectrometry data.

Fig. 3. (a) FTIR spectra of chloroform solutions of TBD-methanol mixtures in the region of ν(OH). (b) 1H NMR spectra of the exchangeable proton at TBD in DMSO-d6 with the addition of 0, 0.1, 0.5, and 1 equiv. methanol. (c) The symmetrized H, H-NOESY spectrum of the equivalently mixed methanol and TBD in DMSO-d6. (d) KIE investigation on the TBD-catalyzed alcoholysis reaction.

Fig. 4. Proposed reaction mechanism. (a) The potential energy surface of the TBD-catalyzed alcoholysis reaction using ethyl acetate as the reaction substrate following the ester-modulated strategy (mixing the ester substrate with TBD before introducing methanol). (b) The potential energy surface of the TBD-catalyzed alcoholysis reaction using ethyl acetate as the reaction substrate following the methanol-modulated strategy (mixing TBD with methanol before introducing ethyl acetate). The free energy was obtained at the theoretical level of M06-2X-D3(0)/6-311+G**.

Fig. 5. (a) Schemes for the solubility of various polyester plastics in different solvents. The vertical axis showcased a variety of solvents, whereas the horizontal axis denoted different types of polyester plastics. The diagram delineated four clear-cut solubility states: soluble, partially soluble, swelling, and insoluble. As the color inclined towards red, it signified an increased solubility of the polyester plastic in that specific solvent. (b) Schemes for the impact of various solvents on the reaction rates of different types of polyester plastics. The vertical axis enumerated multiple solvents, while the horizontal axis corresponded to different types of polyester plastics. The shade of color intuitively reflected the level of reaction activity, with darker blue hues indicating faster reaction rates. The testing procedure was as follows: by measuring the mass difference of the polyester plastic before and after the reaction, and then dividing it by time, the reaction rate could be obtained, with the unit being grams per hour (g/h). Note: only the reaction rate of dissoluble plastics was tested. (c) The schematic displayed an in-situ UV-vis continuous flow reactor. (d) the UV results from the in-situ continuous amplification reaction test (T: 25 °C, 0.05 mol/L TBD in methanol at 5 mL/min, t: 240 min, wavelength range: 250-500 nm, it was added in five gradual steps, with each step involving the introduction of 20 g of plastic cups into the reaction system.). The Fig. S23 showed the purity of the alcoholysis product through 1H NMR (CDCl3, 400 MHz).