Iterative Click-Addition Process for Urethane-based 1st-5th Dendrons

Dendrimers and dendrons are widely studied in the industrial and academic fields, but their efficient synthesis remains challenging. We herein report the synthesis of a type of urethane-based dendron through a facile, tailor-made, iterative click-addition process (iCAP). Hydroxyl-group-terminated first–5th generation dendrons were synthesized through iCAP, in which nucleophilic urethane and thiol–ene addition reactions were repeated alternately. ¹H NMR spectroscopic and SEC measurements showed that each reaction progressed quantitatively at all stages. Because iCAP involves only two types of addition reactions, it is different from conventional polyurethane-type dendrimer and dendron syntheses in that it has high atom utilization efficiency. In addition to the iCAP to first–5th generation dendrons, the urethane-forming addition reaction to the terminal hydroxyl group also proceeded quantitatively, giving dendrons having long alkyl chain termini. Differential scanning calorimetry measurements showed that the thermophysical properties of the dendrons changed as the number of generations increased. Additionally, when we investigated the aggregation of the dendrons by scanning electron microscopy images of the solution-growth solids, unique morphologies were observed. It is expected that by expanding this synthetic process, we will be able to design and synthesize a variety of topological sequence-defined polymers and impart them with a wide variety of polymer functionalities.