<i>N</i>-Methylated Nylons as a Novel Library of Degradable Hydrophilic Homopolymers

Nylon-p,q, the first synthetic fiber, is practically insoluble in water because the secondary amide group in the backbone forms a hydrogen bond network. Herein, we revisit N-methylated nylon-p,q as a novel class of degradable hydrophilic homopolymers. Although N-methylated nylons have been overlooked for over 80 years due to their unsuitability for fibers, we modernized them as hydrophilic polymers through simple N-methylation of nylons. We constructed a library of 24 types of N-methylated nylon-p,q, in which the tertiary amide group acts as a hydrophilic group, enabling fine-tuning of water solubility from soluble to insoluble by varying the carbon number (p,q). N-Methylated nylon-p,q with an optimal hydrophilic/hydrophobic balance exhibited lower critical solution temperature (LCST)-type phase separations with the formation of coacervate droplets. Furthermore, N-methylated nylons showed on-demand degradability under acidic conditions through the hydrolysis of amide groups. This research expands the potential of nylon as a hydrophilic polymer material satisfying modern societal demands.