Polyurethane Synthesized with Mixtures of Polycarbonate Polyols of Different Molecular Weights Showing Intrinsic Self-Healing at 20 °C and Relevant Adhesion Properties

Polyurethanes (PUs) with self-healing at 20 °C, acceptable mechanical properties and high adhesion were synthesized by using blends of polycarbonate polyols of molecular weights 1000 and 2000 Da (CD1000 + CD2000). The structural, thermal, rheological, mechanical and adhesion (single lap-shear tests) properties of the PUs were assessed. The length of the polycarbonate soft segments and the interactions between them determined the self-healing ability, the mechanical properties and the adhesion of the PUs. PUs with higher CD1000 polyol content exhibited shorter self-healing times and dominant viscous properties due to a higher amount of free carbonate groups, significant carbonate-carbonate interactions and low micro-phase separation. As the CD2000 polyol content increased in the PUs, slower kinetics and longer self-healing times were obtained, and higher mechanical and adhesion properties as well, due to a dominant rheological elastic behavior, higher crystallinity of the soft segments and greater micro-phase separation. All PUs synthesized with CD1000 +CD2000 blends exhibited a mixed phase due to interactions between the polycarbonate soft segments of different lengths which favored self-healing and mobility of the polymer chains leading to an increase of the mechanical properties. The adhesion properties of the PUs were similar to the highest ones reported in the literature.