Structural resins have historically found ubiquitous use across various industries as lightweight adhesives. As the automotive, aerospace and electronics industries continue to look to increase performance to weight ratios, the need for improved resin designs becomes apparent. One main focus here is the improvement of ductility in glassy materials. Polycarbonate has proven to be the “gold standard” for an engineering thermoplastic (Tg ~150 °C) with ductile behavior at temperatures deep in the glassy state (where T-Tg &gt; 150 °C). However, PC’s limited resistance to solvent-induced cracking and crazing prevents its use in many applications. Crosslinked polymer networks, such as epoxy-amines, provide an encouraging alternative for enhanced solvent resistance, but suffer from brittle-like behavior well below the Tg. Over the last decade, several efforts from our group have systematically probed the influence of the ‘static’ network structure on the performance of crosslinked glasses. However, responsive, or adaptive, glasses provide a relatively unexplored avenue for an on-demand mechanical response. Many challenges still remain in achieving responses deep in the glassy state, in addition to the often extreme operational environments. Three response mechanisms are outlined to provide a range of mechanical behaviors on demand: (i) shape-changing functionalities which locally yield or soften the material to stimulate chain mobility; (ii) bond forming (or breaking) chemistries which increase (or decrease) the stiffness of the material; and (iii) energy absorbing groups which convert the incoming stimuli into a spatially controlled heating and result in a designed softening of the material.

Engineering structural adhesives: Complementary efforts of adaptive and static networks

ACS Fall 2021

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