Structure-property relationships to direct the dynamic properties of acylsemicarbazide-based materials

Secondary interactions, such as hydrogen bonding or phase separation, can enhance the stability of dynamic covalent materials without compromising on desired dynamic properties. Here, we investigate the combination of multiple secondary interactions in dynamic covalent materials based on acylsemicarbazides (ASCs), with the aim of achieving tunable material properties. The effects of different ASC substituents on the dynamic covalent and hydrogen bonding capabilities were investigated in a small molecule study using a combined experimental and theoretical approach, and revealed the presence of cooperative hydrogen-bonding interactions in 2 directions in one of the derivatives. The different motifs were subsequently incorporated into polymeric materials. Combining ASC motifs capable of strong, multiple hydrogen bonding with a polydimethylsiloxane backbone introduces structure-dependent, ordered nanophase separation in polymeric materials. The thermo-mechanical properties of the materials reveal a strong dependance on the hydrogen-bonding structure and exact nature of the ASC bond. The dynamic behavior in bulk shows that bond exchange depends on the dissociation rate obtained from ASC model compounds, as well as the strength of the secondary interactions in these materials. Differences in hydrogen-bonding structures of the ASC motifs also cause differences in creep resistance of the materials. Interestingly, the materials with strong, ordered and cooperative hydrogen-bonded clusters show the highest creep resistance. Our results demonstrate that tuning both the dissociation rate and the secondary interactions by molecular design in dynamic covalent materials is important for controlling their thermal stability and creep resistance.