(385o) Recyclable Non-Isocyanate Polyurethane Network Foams from Renewable Biobased Precursors

Polyhydroxyurethane (PHU), made by the aminolysis of cyclic carbonates, is a non-isocyanate polyurethane material with promising potential as a benign, recyclable alternative to isocyanate-based polyurethane. Recently, thiols were shown to react with cyclic carbonates to liberate CO₂, presenting a pathway to produce self-blowing PHU foams. We have developed a rheology-guided, rapid preparation of self-blowing PHU network foams, allowing for dramatic reduction of reaction times to achieve foams. Furthermore, because PHU networks exhibit covalent adaptable network (CAN) nature, the waste PHU foams synthesized by this method show excellent reprocessability to the bulk with full recovery of cross-link density and associated properties. Additionally, the use of our rheology-guided foaming strategy unlocks the potential to employ renewable biobased monomers that are less reactive, such as those derived from dimer acid and cashew nutshell liquid (CNSL). To understand further the structure-property relationships in recyclable biobased PHU network foams made with dimer-acid- and CNSL-based cyclic carbonates, we studied the effects of thiol concentration as well as functionality. We observed that morphology depends on thiol concentration but is independent of thiol functionality, whereas compressive mechanical properties depend greatly on both thiol concentration and functionality. To address further the sustainability challenges, the biobased PHU CAN foams were melt-reprocessed into bulk films with full recovery of cross-link density. We characterized the elevated-temperature stress relaxation of these bulk biobased PHU CANs, observing how the presence of permanent bonds (originating from the thiol-cyclic carbonate reaction) affects the relaxation dynamics. Moreover, the recycled bulk biobased PHU CANs function as elastomers with high dimensional stability and excellent elevated-temperature resistance to creep deformation.