Spontaneous Long-Range Order and Alignment in Phase-Separated Dynamic Covalent Networks Using Discrete Siloxanes

For the first time, dynamic covalent networks are prepared that show spontaneous alignment and long-range hexagonal columnar ordering. This is a consequence of the phase-separation between the siloxane linkers and dynamic covalent acylsemicarbazide bonds that induce hydrogen bonding. The use of discrete siloxane linkers is crucial, as networks based on disperse siloxanes do not give ordered or aligned network structures. Optimization of the siloxane length is key in achieving the most pronounced effect. Interestingly, the optimized ordered networks are obtained through simple solvent evaporation, allowing to introduce near-perfect homeotropic alignment as imaged with transmission electron microscopy and corroborated with grazing incidence small angle x-ray scattering. The ordered network has improved (thermo)mechanical properties compared to the disordered networks. Additionally, order in the system slows down the network dynamics and improves creep resistance. We prepare actuators in a straightforward fashion by combining ordered and disordered networks, removing the need for any alignment step and simplifying the overall process significantly.