Avance 3 400 nmr

¹H NMR (400 MHz) was attempted on all synthesized compounds
using a Bruker AVANCE III 400 NMR spectrometer with a tetramethylsilane
(TMS) internal standard in deuterated solvents. Chemical shift (δ)
values were recorded in parts per million (ppm), and the peaks were
labeled as singlet (s), doublet (d), triplet (t), quartet (q), or
multiplet (m) where possible.

The chemical modifications were also determined using proton nuclear magnetic resonance (¹H-NMR) spectroscopy. The imaging was performed using Bruker Avance III 400 NMR spectrometer (Bruker, Karlsruhe, Germany). The polymers were dissolved, at the same concentration described above, in deuterium oxide (D₂O) to stabilize the magnetic field and eliminate any perturbation in the spectrum. Hydrogels were introduced into 2 mm tubes and measured with a stable temperature of 37 °C. The results were recorded with a chemical shift in hydrogen ranging from −4 to 16 ppm and treated with an ACD/NMR processor program.

Time Domain ¹H Double Quantum DQ measurements were carried out on a Bruker Avance III 400 NMR equipped with a 5 mm ¹H solenoid static probe. DQ measurements were based on Baum-Pines pulse sequences [38 (link)] optimized by Saalwächter [39 (link)]. For these experiments to be able to access the network structure, they had to be conducted at a temperature where the molecular motions probed by this technique must be effective in the fast motion regime as has been previously described [42 (link)]. For most polymers this truly elastic domain is found at temperatures equal or above T_g + 90 °C, and, as such, all of the samples were studied at this temperature, ensuring that they were all tested at the same state of molecular dynamics in the temperature-independent regime of ¹H DQ NMR measurements. Samples were finely cut then put in glass tubes and inserted in the 5 mm ¹H solenoid static probe, where they were gradually heated up to T = T_g + 90 °C. The temperature was stabilized for one hour before conducting the measurements. The NMR spectra were then treated to obtain a DQ build-up normalized signal I_nDQ for each sample following the same approach that has been detailed in previous works [42 (link)].