Controlled incorporation
of nitrogen into macromolecular skeletons
is a long-standing challenge whose resolution would enable the preparation
of soft materials with the scalability of man-made plastics and functionality
of Nature’s proteins. Nylons and polyurethanes notwithstanding,
nitrogen-rich polymer backbones remain scarce, and their synthesis
typically lacks precision. Here we report a strategy that begins to
address this limitation founded on a mechanistic discovery: ring-opening
metathesis polymerization (ROMP) of carbodiimides followed by carbodiimide
derivatization. An iridium guanidinate complex was found to initiate
and catalyze ROMP ofN-aryl andN-alkyl cyclic carbodiimides. Nucleophilic addition to the resulting
polycarbodiimides enabled the preparation of polyureas, polythioureas,
and polyguanidinates with varied architectures. This work advances
the foundations of metathesis chemistry and opens the door to systematic
investigations of structure-folding-property relationships in nitrogen-rich
macromolecules.