Advance 3 500 mhz

¹H NMR spectra were recorded on a Bruker ADVANCE III 500 MHz, (Bruker, Santa Barbara, CA, USA), in 5 mm sample tubes at 298 K (digital resolution of ±0.01 ppm) in DMSO-d₆ using TMS as internal reference, with a spectrometer frequency for ¹H at 500.23 MHz. The number-average molecular weight of each chain on the block copolymer was determined by ¹H NMR. Sample temperature was kept constant for all measurements at 25 °C. The NMR peak of DMSO (δ = 2.54) was used as the reference in determining the chemical shifts of ¹H in PEG-b-PLA.

A Bruker Advance III 500 MHz wide-bore NMR spectrometer operating at room temperature was used, with a 4 mm double resonance (1H/X) MAS probe. The material was packed in 4 mm zirconia rotors, and the solid-state ¹³C and ¹⁵N NMR spectra were recorded at 125.73 and 50.66 MHz Larmor frequencies. Standard RAMP ¹³C/¹⁵N CP-MAS spectra were acquired at 14/7 kHz spinning frequencies, 2/4 ms contact times, and proton decoupling under TPPM. For ¹³C spectra, the acquisition parameters were optimized to the following values of relaxation delay and number of transients: 2 s/30,000 transients for PBAAA and CHIT, and 2 s/50,000 transients for sample CHIT-PAAA. For ¹⁵N spectra the relaxation delay and number of transients were: 2 s/31,000 transients for CHIT and 2 s/60,000 transients for CHIT-PAAA. The recorded spectra were calibrated relative to the CH₃ line in tetramethylsilane (TMS) and the ¹⁵NO₂ line in nitromethane, through an indirect procedure that used L-Glycine as an external reference (C=O of glycine at 176.5 ppm for ¹³C and −347.6 ppm for ¹⁵N), and line broadening was applied at 20 Hz (for ¹³C spectra) and 150 Hz (for ¹⁴N spectra).

Analytical methods for product characterization here have been outlined previously³⁷ . Gaseous products were evaluated using gas chromatography (GC, Agilent 7890B). The GC was equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) in series. The TCD was for H₂ and CO detection, and the FID was for CH₄ and C₂H₄ detection. As for those products in liquid phase, gas chromatography-mass spectrometry (GC-MS, 5977A) was adopted to detect ethanol and propanol, and nuclear magnetic resonance (NMR, Bruker Advance III 500 MHz) was used for the detection of formic acid. The faradaic efficiency (F.E.) of each product was calculated by Eq. (4): $\mathrm{FE}\left(\%\right)=\frac{\mathrm{moles}\mathrm{of}\mathrm{target}\mathrm{products}\times n\times F}{C}\times 100\%$ where n is the number of electrons transferred, F stands for Faraday’s constant (96485 C mol⁻¹), and C represents the total amount of charge passed through a working electrode.