Topochemical Synthesis of a Syndiotactic Polymer from a Racemic Monomer

Tacticity critically governs polymer properties, yet achieving precise stereoregularity from racemic monomers remains an enduring challenge. The equal reactivity of enantiomers under isotropic conditions typically leads to atactic polymers with limited order, while conventional approaches rely on intricately engineered catalysts to enforce stereocontrol during chain growth. Herein, we present a catalyst-free strategy that harnesses supramolecular preorganization and topochemical polymerization to achieve precise alternation of enantiomers, yielding a perfectly syndiotactic polymer. A racemic alanine-squaramide-based monomer, bearing azide and alkyne termini, self-assembles in the crystal into an alternating heterochiral arrangement guided by complementary hydrogen bonding of the squaramide scaffold. Upon thermal activation, a topochemical click reaction covalently locks this architecture, producing a perfect syndiotactic polymer through a single-crystal-to-single-crystal transformation. Single-crystal X-ray diffraction unambiguously confirms the polymer structure at atomic resolution, representing the first crystallographically characterized syndiotactic polymer derived from a racemic precursor. This proof-of-concept demonstrates a strategically simple route to otherwise inaccessible polymer microstructures and architectures.