Advancing the Synthesis of Isocyanate-Free Poly(oxazolidones)s: Scope and Limitations

Poly(oxazolidone) is an emerging class of polyurethanes (PUs) that is easily accessible by an isocyanate-free pathway via the step-growth copolymerization of CO₂-based monomers (bis(α-alkylidene cyclic carbonate)s) with primary diamines at room temperature. Here, we explore the scope and limitation of this process by investigating the influence of the diamine and the reaction conditions on the structure and macromolecular parameters of the polymer. Less hindered diamines (aliphatic and benzylic) provide selectively poly(hydroxyoxazolidone)s, whereas the bulkier ones (cycloaliphatic) furnish polymer chains bearing two types of linkages, oxo-urethane and hydroxyoxazolidone ones. The increase of the reaction temperature or the addition of DBU as a catalyst enables to accelerate the polymerizations. The quantitative polymer dehydration is also achieved by refluxing in acetic acid, providing a new class of unsaturated poly(oxazolidone)s composed of α-alkylidene oxazolidone linkages (for hindered polymers) or a mixture of α- and β-alkylidene oxazolidone linkages (for the less hindered ones). These unsaturated poly(oxazolidone)s present a high glass transition temperature (90 °C ≤ Tg ≤ 130 °C) and a remarkable thermal stability (Td > 360 °C), rendering these polymers attractive for applications requiring high temperatures. This work is therefore opening an avenue to novel functional isocyanate-free PUs, with the pendant hydroxyl or olefin groups that are expected to be easily derivatized.