Thermally bisignate supramolecular polymerization

One of the enticing characteristics of supramolecular polymers is their thermodynamic reversibility, which is attractive, in particular, for stimuli-responsive applications. These polymers usually disassemble upon heating, but here we report a supramolecular polymerization that occurs upon heating as well as cooling. This behaviour arises from the use of a metalloporphyrin-based tailored monomer bearing eight amide-containing side chains, which assembles into a highly thermostable one-dimensional polymer through pi-stacking and multivalent hydrogen-bonding interactions, and a scavenger, 1-hexanol, in a dodecane-based solvent. At around 50 degrees C, the scavenger locks the monomer into a non-polymerizable form through competing hydrogen bonding. On cooling, the scavenger preferentially self-aggregates, unlocking the monomer for polymerization. Heating also results in unlocking the monomer for polymerization, by disrupting the dipole and hydrogen-bonding interactions with the scavenger. Analogous to 'upper and lower critical solution temperature phenomena' for covalently bonded polymers, such a thermally bisignate feature may lead to supramolecular polymers with tailored complex thermoresponsive properties.