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

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 CH 2 Cl 2 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.