Structure–Property Relationships of Elastomeric Vinylogous Urethane Thermosets and Their Application as Closed-Loop Recyclable Strain Sensors
Youwei Ma, Francesco Stellacci
Abstract
High Resolution Image Download MS PowerPoint Slide Developing closed-loop recyclable thermosets and understanding their structure–property relationships are essential steps in advancing a circular materials economy. Here, we present a vinylogous urethane ( VU ) thermoset with closed-loop recyclability, synthesized through the reaction of polytetrahydrofuran bisacetoacetate ( aPTHF ) and tris(2-aminoethyl)amine ( TREN ). These VU polymers exhibit high elasticity, with only a 3–9% residual strain observed after cyclic tensile testing at a maximum strain of 100%, depending on the molecular weight of aPTHF and network cross-link density. The two structural parameters also allow modulation of the mechanical and stress-relaxation properties of VU elastomers. To investigate the hydrolysis of the VU linkages within the hydrophobic aPTHF matrix, we employed a heterogeneous system using a biphasic mixture of HCl and CDCl 3 . Our findings show that the hydrophobic VU s remain stable in pure water but can be dissociated under acidic conditions, with the dissociation rate accelerated at higher temperatures and/or in the presence of higher HCl concentrations. These detailed investigations indicate the potential of VU elastomers as sustainable substrates for wearable sensors. We therefore conduct a case study of synthesizing a strain sensor through the incorporation of multiwalled carbon nanotubes ( MCN s) into the VU elastomer matrix. The sensor can robustly detect various movements. Moreover, acidic treatment of both the neat polymer and the sensor composite using a HCl and diethyl ether solvent mixture allows for the excellent recovery of aPTHF (>90%) and TREN (86%), without discernible damage to the MCN s reclaimed from the latter.