Diels-Alder-based thermo-reversibly crosslinked polymers: Interplay of crosslinking density, network mobility, kinetics and stereoisomerism
Polymers crosslinked through thermo-reversible furan / maleimide Diels-Alder chemistry have been widely explored, since they stand as an ingenious design for reprocessable and self-healing thermosets and elastomers. For these polymeric products, crosslinking density plays a key role on the polymer thermo-reversibility. However, how this degree of network interconnectivity influences the kinetics of thermal reversibility has not yet been addressed. In order to tackle this problem, furan-grafted polyketones crosslinked by a bi-functional maleimide were prepared with different ratios between maleimide and furan groups. The thermo-reversible dynamics of the prepared polymers were then studied by rheology and differential scanning calorimetry. Here we show that, the thermo-reversible process occurs faster and at lower temperatures in polymers with lower crosslinking densities. Network mobility is responsible for such effect. It allows the formulations to rearrange their polymer network differently through the heating-cooling cycles. The results also point out that the crosslinking density is more relevant on the system reversible behavior than the stereoisomerism of the Diels-Alder adducts. Additionally, the polymer thermo-reversible features were shown to be dependent on its thermal history. This work impacts the development of reprocessable and self-healing crosslinked polymers, and the design of the corresponding reprocessing and healing procedures.