Emerging Reprocessable and Recyclable Biobased Cross-Linked Polyurethanes Through Diels-Alder Chemistry

Cross-linked polyurethanes (PUs) present outstanding properties and high versatility, making them ideal for use in many different applications. Nevertheless, the intersection of environmental and socioeconomic concerns regarding the recyclability of cross-linked materials presents alternative opportunities for advancing the field of cross-linked polyurethane chemistry. In this context, emerging reprocessable and recyclable biobased cross-linked PUs were synthesized within this work through Diels-Alder (DA) chemistry. Thus, a trifunctional partially biobased low-molecular-weight polyol containing the furan-maleimide Diels-Alder adduct (DA-triol) was developed to be used as a thermoreversible cross-linker in PU synthesis. First, the thermoreversibility of the cross-linker was demonstrated at temperatures as high as 160 °C (retro-DA reaction). Afterward, the DA-triol was used together with a commercial biobased macrodiol and polymeric methylene diphenyl diisocyanate (pMDI) to synthesize different formulations of PUs that ended up with properties ranging from flexible to rigid. Then, the recyclability and reprocessability of the synthesized PUs were also evaluated by compression, injection, and extrusion. Finally, the mechanical properties of the original and recycled polyurethanes were tested, obtaining recycling efficiencies higher than 80%. Thereby, these materials offer a solution to the long-standing issue of recycling of cross-linked polyurethanes, overcoming many sustainability challenges.