CO2-sourced (activated) cyclic carbonates: from their synthesis to their valorization for the preparation of non-isocyanate polyurethanes and polycarbonates

Polyurethanes (PUs) are versatile materials finding applications in several sectors, such as automotive, building and construction, household or medicine. Due to the toxicity of isocyanates used in the conventional PU chemistry, there has been an increasing interest to develop more environmentally-friendly/safer alternatives. The synthesis of poly(hydroxyurethanes) (PHUs) by polyaddition of diamines with CO2-sourced bis(cyclic carbonate)s has emerged as one of the most promising alternatives. However, this strategy does not compete with the conventional synthesis of PU yet due to the low reactivity of the cyclic carbonates with amines, and to some side reactions occurring during the polymerization.
The aim of this thesis is to develop novel conceptual routes for the synthesis of isocyanate-free PUs by valorizing different CO2-sourced building blocks, ideally under mild conditions in order to disfavor the occurrence of side reactions.
The work starts with the development of organocatalysts that facilitate the synthesis of 5-membered cyclic carbonates (5CC) by coupling CO2 with various epoxides, including epoxidized vegetable oils. We demonstrate that some of these CO2-sourced cyclic carbonates can be converted into PHU hydrogels under solvent-free conditions by reaction with a diamine and a crosslinker, followed by swelling in water. In order to avoid some important drawbacks associated to the synthesis of PHU (low reactivity of 5CCs, side reactions, lack of regioselectivity in the ring-opening, etc.), we then consider the synthesis of novel activated CO2-sourced bis(5CC)s bearing exocyclic olefinic bonds (bis-αCCs). We illustrate that these monomers provide new families of functional and regioregular polyurethanes and polycarbonates, under unusual ambient conditions, by polyaddition with amines or diols, respectively. Finally, we report the first synthesis of isocyanate-free PUs bearing pH-sensitive imine moieties within the polymer backbone, named poly(urethane-co-imine)s (PUIs), by polycondensation of novel CO2-sourced bis(oxo-carbamate)s with secondary diamines. Preliminary hydrolysis tests demonstrate the pH-responsive behavior of PUIs induced by the presence of reversible imine linkages.
Overall, this work demonstrates that CO2 is a realistic renewable C1-feedstock for the production of a new generation of polyurethanes but also of polycarbonates under mild experimental conditions. Multiple variants of this chemistry should drastically broaden the polymer structures available, and therefore the application fields of these two polymer classes.