A Syndiotactic Polymer\nvia Spontaneous Exoselective\nSingle-Crystal-To-Single-Crystal Topochemical Diels–Alder Cycloaddition\nReaction

We designed and synthesized an amide-based monomer decorated\nwith\nfuran as the diene unit and maleimide as the dienophile unit at its\ntermini. Single-crystal X-ray diffraction (SCXRD) analysis of its\ncrystal revealed a head-to-tail arrangement of molecules with furan\nand maleimide groups of neighboring molecules proximally placed in\nan arrangement suitable for their topochemical Diels–Alder\ncycloaddition (TDAC) to form a linear polymer. The monomer underwent\na spontaneous single-crystal-to-single-crystal (SCSC) polymerization\nat room temperature, yielding a linear polymer with oxa-bicyclic linkage.\nSCXRD analysis revealed that the cycloaddition occurred in an exoselective\nmanner, and the absolute stereochemistry of the oxa-bicyclic linkage\nalternated in successive repeat units, leading to a syndiotactic linear\npolymer. The polymerization can be accelerated by heating the powder\nat 120 °C; the topochemical nature of the high-temperature reaction\nwas established by time dependent differential scanning calorimetry\n(DSC), time-dependent powder X-ray diffraction (PXRD), and UV–visible\nspectroscopic analysis; the polymer was characterized using solid-state\nNMR spectroscopy and MALDI-TOF mass spectrometry.