Thermomechanical Properties of Hybrid Imine and Silica Based Vitrimers

The limited recyclability of thermosets poses a significant challenge for end-of-life disposal of these materials. Covalent adaptable network (CAN) materials, such as vitrimers possess reversible crosslinker chemistries. The mechanical properties of vitrimers at room temperature are comparable to those of thermosets. Vitrimers become malleable upon thermal or photonic stimulation, so they can be reshaped and recycled. However, vitrimers can exhibit undesirable creep or fatigue, especially at elevated temperatures. Therefore, we are pursuing a hybrid chemistry approach, where a portion of the organic dynamic crosslinkers is replaced with inorganic static crosslinkers to provide the desired thermomechanical stability. Catalyst-free polyimine vitrimer is synthesized from glutaraldehyde (GA) and bis[2-(3-aminopropoxy)ethyl] Ether (Di-Amine). The dynamic crosslinker is tris(2-aminoethyl)amine (Tris-Amine), of which various fractions are replaced with (3-Aminopropyl)triethoxysilane (APTES). Depending on its concentration, APTES can undergo polycondensation to form different-sized silica network fragments, but is always able to compatibly bridge between polyimine matrix segments by forming imine bonds, thus substituting permanent Si-O-Si bonds for dynamic bonds. Here we report on how the relative proportions of static and dynamic crosslinkers affect the hybrid vitrimers’ viscoelastic properties, mechanical stability, shifts in the glass transition and topology freezing temperatures. We specifically focus on evaluating the tradeoff between weldability or self-healing capabilities and creep resistance as a function of the crosslinker type concentrations.