Hierarchical Chirality in Polycarbodiimides

Non-linear or helical polycarbodiimides feature a nitrogen-rich fully substituted guanidine-like backbone repeat unit with two synthetically selective pendant groups. As a result of a complex ballet of bond rotations within steric proximity of the backbone, these polymers can adopt multiple tiers of asymmetry. Primary locales of chiral influence incorporated onto the polymer or on the catalyst during polymerization permit amplification to secondary levels of chirality through a backbone with an excess helical sense. In turn, the conformational chirality of the helix promotes hierarchical orders of tertiary chirality around this chiral scaffolding. These higher levels of asymmetry have shown static and dynamic attributes and can be obtained from monomers containing no predominant chirality. Tailoring these properties with the selection of spatially constricting pendant groups such as substituted arenes, polyarenes, and enantiopure configurationally chiral alkanes has exemplified this behavior. This manuscript will focus on some of the highlights of dynamic and static asymmetry observed for these polycarbodiimide systems.