Tetraquinoxaline cavitand-crosslinked polymers as potential molecular auxetics Alessandro Pedrini 1 , Francesca Portone 1 , Matteo Montanari 2 , Roberta Pinalli 1 , Roberto Brighenti 2 , Enrico Dalcanale 1 1 Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy 2 Department of Engineering and Architecture, University of Parma, Parco Area delle Scienze 181/A, 43124 Parma, Italy Auxetics are functional materials with negative Poisson’s ratio (NPR) that expand in the transversal direction upon longitudinal stretching. Tetraquinoxaline cavitands (QxCav) are ideal platforms for the development of molecular auxetic materials, as they are capable to switch between a close ( vase ) and an open ( kite ) conformation. The vase - kite interconversion can be triggered in solution by different stimuli, such as pH, temperature, metal coordination and redox. 2 We have recently demonstrated that mechanical stimulation (tensile stress) is effective in inducing the expansion/contraction of these dimensionally variable units in cavitand-crosslinked polyurethanes. 3 To achieve NPR behaviour upon mechanical elongation, QxCav are introduced as crosslinkers in highly oriented main-chain liquid crystal elastomers (LCE). In our design the preorganization of polymer chains maximizes cavitand opening effect when the material is stretched in the same direction of the alignment.For this purpose, the four quinoxaline walls are decorated with terminal alkenes and the resulting cavitand is reacted via metathesis with a mesogenic unit to obtain a monodomain LCE.
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