The aminolysis of five-membered cyclic carbonates, which results in polyhydroxyurethanes (PHUs), is one of the most promising synthetic pathways to achieve isocyanate-free polyurethanes (NIPUs), one of the main industrial challenges over the coming years. This study highlights the higher reactivity of β-hydroxylamines toward cyclic carbonates compared to classical alkylamines through the determination of their reaction rate constants. The key role of the β-OH substituent in the aminolysis was revealed by DFT investigation. Polyfunctional alkylamine and β-hydroxyamine were then used for the synthesis of fully biobased PHU thermosets. The higher reactivity of β-hydroxylamines was confirmed by the gelation time gap between the two formulations studied. After curing, the thermal and thermo-mechanical properties of the thermosets were compared.