Synthesis of well‐defined aromatic poly(amide‐ether)s via chain‐growth condensation polymerization

Abstract

Since their advent over 50 years ago, aromatic polyamides have remained desirable for their thermal stability, mechanical strength, and overall versatility. Chain‐growth condensation (CGC) polymerization has made possible the synthesis of well‐defined polyamides with narrow molecular weight distributions for applications ranging from block copolymers to polymer brushes. However, the solubility of aromatic polyamides has always been a major obstacle to overcome due to aromatic π‐π stacking and intramolecular hydrogen bonding. In this article, we introduce an aryl ether functionality into the polyamide backbone to increase backbone flexibility and overall solubility. Through dropwise addition of the aryl ether functionalized monomer with a lithium disilazide base and a phenyl 4‐(dimethylcarbamoyl)benzoate initiator, we report the synthesis of a series of substituted poly(amide‐ether)s through CGC polymerization with low polydispersities (<1.1) and well‐defined molecular weights. Computational methods revealed that the polymerization mechanism is unlike other similar amino ester monomers bearing naphthalene and biphenyl aromatic units in that monomer self‐deactivation is weakened by the ether linkage. The self‐condensation of the amide‐ether monomer was nevertheless suppressed through reaction optimization, challenging the traditional requirement of monomer self‐deactivation to achieve a well‐defined CGC polymerization. The side‐chain on poly(amide‐ether) backbone was also modified from an octyl group to a 4‐(octyloxy)benzyl protecting group for postpolymerization removal with trifluoroacetic acid to yield the unsubstituted aromatic poly(amide‐ether), which showed a significant improvement in solubility from traditional unsubstituted aromatic polyamides, such as poly(p‐benzamide).