Thermomechanical properties of Diels-Alder based reversible polymer network systems

Research in the field of smart materials that exhibit self-repair mechanisms has greatly expanded over the last few years. This is especially true for polymers and polymer composite materials. One class of self-healing polymer materials is the reversible polymer network systems that use dynamic covalent bonds as a means to repair sustained damage. Currently a range of different dynamic covalent bonds is considered, of which the reversible Diels-Alder chemistry has drawn the most attention. Reversible covalent bonds have been incorporated into polymer network structures based on the Diels-Alder reaction between a furan and a maleimide [1-3]. Repair of sustained damage can be established by means of heating-used self-healing in bulk materials as well as in coating applications.
In previous work [4] the healing behaviour of these reversible polymer network systems has been studied at the microscopic scale. It was reported that it is possible to repair sustained damage at temperatures below the gel point temperature for different reversible polymer network structures. At these temperatures the polymer system still consists of an incipient network structure, maintaining its mechanical stability and properties. Close to the gel point conversion the material still behaves as an elastic solid, but the mobility has increased sufficiently to allow successful healing of microscopic damage.
The thermomechanical properties of the reversible polymer network systems are studied as a function of temperature and time using Dynamic Mechanical Analysis (DMA) and rheology. The recovery of the mechanical properties after thermal cycling is studied at different temperatures for different times. The materials are subjected to different types of damage and allowed to heal the sustained damage. The healing behaviour is evaluated by the recovery of the mechanical properties upon different healing cycles. Repeated damage and healing cycles are performed to assess the effect on the life time and durability of the materials.