Synthesis via Chain-Growth Condensation Polymerization and Gelating Properties of a Variety of Block Copolymers of Meta- and Para-Substituted Aromatic Polyamides

Abstract

Well-defined diblock copolymers consisting of poly(m-benzamide)s with different N-alkyl groups and of poly(m-benzamide)s and poly(p-benzamide)s with different N-alkyl groups were synthesized by means of sequential chain-growth condensation polymerization. The polymerization of 3-(alkylamino)benzoic acid alkyl ester 1 was carried out with phenyl 4-methylbenzoate (3) as an initiator in the presence of 2.2 equiv of lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) as a base, followed by addition of another kind of 1 or 4-(alkylamino)benzoic acid alkyl ester 2 to the reaction mixture to yield the block copolymer. The 4-octyloxybenzyl groups on the amide nitrogen in the obtained block copolymers were removed with trifluoroacetic acid (TFA) to give block copolymers containing an N−H polyamide segment. These block copolymers showed gelating properties at low concentration in various solvents ranging from aromatic to aprotic polar solvents. Scanning electron microscopic (SEM) images of the CH2Cl2 gel revealed that the block copolymers self-assembled to form three-dimensional network structures, in which the solvent was confined to afford a gel. The gelating properties were dependent on both the orientation of the monomer substituents (meta or para) and the composition ratio of the N−H poly(benzamide) segment in the block copolymers.