Structurally Diverse and Recyclable Isocyanate-Free Polyurethane Networks from CO₂-Derived Cyclic Carbonates

Abstract

Isocyanate-free chemistry and the introduction of dynamic bonds are a promising combination toward the development of more sustainable polyurethane (PU) networks. Here, we present the synthesis of reprocessable, isocyanate-free PU networks through atom-economical reactions for both monomers and polymers, valorizing CO 2 as a building block. The monomers employed were five-membered cyclic carbonates prepared through an efficient (>99% conversion) reaction between CO 2 and epoxides with high yield (up to 97% at a 100 gram scale), catalyzed by the moisture-tolerant and easily prepared DBU•I 2 complex. The structural diversity of the monomers and the utilization of cystamine bearing the dynamic S−S motif realized PU networks with a finely tuned profile of thermal (T g from −9 to 44 °C), mechanical (E from 0.2 to 1700 MPa), and viscoelastic properties (E′ from 0.03 to 5.5 MPa at 1 Hz). Facile recycling (100 °C, 20 min) of the networks was enabled thanks to the rapidly exchanging disulfide bonds and the modulated cross-link density. Moistureinduced plasticization of the networks was identified, and its effect on the properties of the networks was elucidated. The atom economy and energy-efficiency methodology, avoiding toxic reagents and preventing waste generation, make this approach an attractive and greener pathway to PU networks taking a step toward a circular plastic economy.

Water‐Induced Self‐Blown Non‐Isocyanate Polyurethane Foams

“…For a higher content of water (1 eq vs 5CC), T g of the unloaded foam was decreased to 17 °C as the result of a lower cross-linking degree and a higher content of soft vicinal diol chain ends (resulting from 5CC hydrolysis) that increased chain segment motion. As previously observed for other PHU foams, [16a] but also coatings, [22] PHU are more hydrophilic than conventional PUs (due to the presence of the pending hydroxyl groups) and absorbed a low content of air moisture (between 2 and 3 wt % as determined by thermogravimetric analysis) that induced a strong hydroplasticization of the polymer matrix. In agreement with these reports, when the foams were fully dried and rapidly analyzed by DSC, T g 's were strongly raised from about 25 to 40 °C. The mechanical resistance of the three equilibrated foams D, F and H was assessed by compression tests (Figure 5D).…”

Mechanically Robust and Chemically Recyclable Polyhydroxyurethanes from CO2-Derived Six-Membered Cyclic Carbonates

“…By tuning the structures of CLPHUs, the values of elongation at break and tensile strength of CLPHUs can reach 452% and 65 MPa, respectively. As shown in Figure c, compared with many previous studies on PHU-based materials, our study shows a better combined performance in terms of mechanical properties. ,,,,,,,− …”

Chemically recyclable and mechanically robust non-isocyanate polyurethanes from resveratrol

“…2d). 8,10,12,15,19,20,[31][32][33][34] This was not only related to the high crosslink density of the material but also to the structure of resveratrol. The rigid aromatic ring structure of resveratrol in the main chain gave the polymer significant rigidity, which greatly increased the mechanical properties of NIPUs.…”