Study on the ratio of hydroxyl groups of B-GAP and the curing reaction rate

To quantify the ratio of hydroxyl types in branched poly(glycidylazide)(B-GAP)and its curing reaction rate, since the primary hydroxyl group in B-GAP is attached to a methylene group(—CH₂—)and the secondary hydroxyl group is attached to a methine group(—CH—). The protons of these —CH₂— and —CH— groups exhibit distinct chemical shifts in the¹H NMR spectrum due to their differing chemical environments. After reaction with isocyanate during polyurethane formation, these distinct chemical shifts persist. Therefore, the ratio of primary and secondary hydroxyl groups can be calculated from the relative signal intensities of the —CH₂— and —CH— protons in the 1H NMR spectrum. Model compounds M1 (representing the primary hydroxyl environment) and M₂(representing the secondary hydroxyl environment) of B-GAP were synthesized and their structures were confirmed by¹H NMR spectroscopy.The reaction rates of M1 and M2 with p-toluene isocyanate were measured by in-situ variable-temperature 1H NMR. The results show that the chemical shifts of the —CH₂—(M₁) and —CH—(M₂) protons are 3.74～3.58(multiplet)and 3.96～3.91 (multiplet), respectively. The reactions of both compounds with p-toluene isocyanate follow first-order reaction kinetics, with respect to the hydroxyl concentration. The reaction rate constants for M₁and M₂are 0.038, 0.009 5; 0.088, 0.014 6; 0.114, 0.021 9; 0.172, 0.027 2 at 25 ℃, 30 ℃, 35 ℃ and 40 ℃, respectively. The primary hydroxyl group has higher reactivity. These results demonstrate that the primary hydroxyl group in the model systems exhibits significantly higher reactivity than the secondary hydroxyl group. The findings can provide guidance for quality control, product selection, and structural optimization of B-GAP in practical applications.