Synthesis and behavior of responsive biobased polyurethane networks cross-linked by click chemistry: Effect of the cross-linkers and backbone structures

Distinct bismaleimides (BMIs) of differing molar masses and chemical architectures were studied as cross-linkers of different polyurethane (PU) backbones containing pendant furan rings to form responsive biobased networks via the Diels-Alder (DA) reaction. The pendant furan rings were introduced during PU synthesis by the inclusion of a specific diol structure with furan groups and derived from oleic acid. The diol is denoted as the Furan Oligomer (FO) and its synthesis can respect green chemistry principles. The effects of varying the proportions of FO in cross-linked systems as well as the type of BMIs (aliphatic vs. aromatic) were particularly studied. The corresponding materials were fully analyzed through several complementary approaches to evaluate their physical, chemical and thermal properties and behaviors. PUs cross-linked by an aromatic BMI yield superior mechanical properties, whereas the chain length and structure clearly influenced the swelling, reprocessability and heat-induced healing of the networks. The introduction of hard segments (HS) into the PU backbone was also examined in terms of micro-segregation. The effect of hydrogen bonding linked to HS in combination with the cross-links by DA would yield superior mechanical properties with good thermal recyclability and self-healing behaviors, to develop materials for advanced applications.