Improvement of tensile properties, self-healing and recycle of thermoset styrene/2-vinylfuran copolymers via thermal triggered rearrangement of covalent crosslink

Abstract

Random copolymers of 2-vinylfuran with styrene (S-co-2VFs) have been thermoreversibly cross-linked via Diels-Alder (DA) reaction with 1,1′-(methylenedi-4,1-phenylene)bismaleimide (BMI), affording recyclable and self-healable polymers with enhanced mechanical properties. The reversibility of the DA reaction was investigated in detail by solution NMR and solid state FT-IR analysis. The thermal stability and reversibility of DA cycloadducts were studied by differential scanning calorimetry (DSC) in the range of temperature 100–150 °C. The in deep knowledge of the thermodynamic and kinetic parameters governing the DA reaction allowed to design an isothermal annealing (44 min at 140 °C) or programmed temperature ramp (30–150 °C) in which the full repair of fractured polymer films or of scratches on the film surface are successfully obtained. The temperature range in which the retro-DA reaction (r-DA) is active well matches the one of the healing process, highlighting the relationship between the reorganization of the polymer network and mendable properties. A method for the evaluation of the tensile properties of thin films at the nanoscale using nanomechanical analysis based on HarmoniX-Atomic Force Microscopy was proposed and validated by comparison with the bulk properties assessed by conventional tensile testing. This study highlights the potential of the 2-vinylfuran comonomer for the design of functional recyclable polymers, having thermoreversible crosslinks, self-healing properties and tunable enhanced mechanical properties.