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 ≤ T g ≤ 130 °C) and a remarkable thermal stability (T d > 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.

We investigate the scope of the organocatalyzed step-growth copolymerization of CO 2 -sourced exovinylene bicyclic carbonates with bio-based diols into polycarbonates. A series of regioregular poly(oxo-carbonate)s were prepared from sugar-(1,4butanediol and isosorbide) or lignin-derived (1,4-benzenedimethanol and 1,4-cyclohexanediol) diols at 25 °C with 1,8diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst, and their defect-free structure was confirmed by nuclear magnetic resonance spectroscopy studies. Their characterization by differential scanning calorimetry and wide-angle X-ray scattering showed that most of them were able to crystallize. When the polymerizations were carried out at 80 °C, some structural defects were introduced within the polycarbonate chains, which limited the polymer molar mass. Model reactions were carried out to understand the influence of the structure of alcohols, the temperature (25 or 80 °C), and the use of DBU on the rate of alcoholysis of the carbonate and on the product/linkage selectivity. A full mechanistic understanding was given by means of static-and dynamic-based density functional theory (DFT) calculations showing the determining role of DBU in the stability of intermediates, and its important role in the rate-determining steps is revealed. Furthermore, the origin of side reactions observed at 80 °C was discussed and rationalized by DFT modeling. As impressive diversified bio-based diols are accessible on a large scale and at low cost, this process of valorization of carbon dioxide gives new perspectives on the sustainable production of bioplastics under mild conditions.

The installation of both oxazolidone and thiocarbonate linkages within a single polymer backbone remains elusive by simple procedures under mild conditions. In this work, we report the construction of copolymers...

Designing easily degradable polymers has become a new challenge to overcome the post-consumer plastic waste accumulation in the environment. Polycarbonates are important polymers that can be chemically recycled; however, most often, their degradation requires high temperatures and/or the use of catalysts. In this work, we report the facile chemical recycling of regioregular polycarbonates prepared by the organocatalyzed copolymerization of CO2-sourced exovinylene biscyclic carbonates (BisαCC) with diols derived from biomass. These polymers, thanks to their pending ketone groups, are rapidly (<30 min) and totally deconstructed into the parent diol and a bis­(oxazolidinone) by catalyst-free aminolysis at 25 °C. By using 3-propanolamine for the aminolysis, a hydroxy-functionalized bis­(oxazolidinone) is recovered, which can be copolymerized with BisαCC to yield a polymer alternating carbonate and oxazolidinone linkages. Importantly, the same bis­(oxazolidinone) scaffold is recovered as the main product by aminolysis of this copolymer, offering a close-loop recycling scenario for this polymer. This work illustrates that these polycarbonates are prone to facile and complete aminolysis under mild and catalyst-free conditions, but can also be exploited to prepare new building blocks for the synthesis of novel degradable polymers. The mechanism of formation of these heterocycles is studied by model reactions and rationalized by density functional theory (DFT) calculations.