ABSTRACT Accessing structurally well‐defined polymer polymorphs remains extremely challenging because obtaining polymer single crystals suitable for atomic‐level structural characterization is rare. Here we report an unusual sequence of single‐crystal transformations in which a peptide monomer designed for topochemical azide–alkyne cycloaddition (TAAC) undergoes spontaneous single‐crystal‐to‐single‐crystal (SCSC) polymerization to form a 1,4‐triazolyl‐linked polymer, despite a crystal packing se