Synthesis and Properties of Glutamic Acid-Derived Optically Active Phenyleneethynylene-Based Helical Polymers

Di(iodophenyl)-substituted l -glutamic acid-derived benzenetetracarboxylic diimide ( 1 ) was synthesized, and the polycondensation of 1 with p -/ m -diethynylbenzenes ( 2p / 2m ) was carried out to obtain optically active phenyleneethynylene-based polymers carrying ester-protected carboxy groups [poly( 1 - 2p ) and poly( 1 - 2m )] with M n ’s in the range from 6500 to 37 600 in 84−96% yields. The polymers were satisfactorily converted into the corresponding polymers [poly( 1 - 2p )′ and poly( 1 - 2m )′] with free carboxy groups by alkaline hydrolysis. The polymer structures were characterized by IR, NMR, UV, and CD spectroscopies. All the polymers exhibited intense CD signals, indicating that they formed helices with predominantly one-handed screw sense. The helical structures of the polymers were stable against heat. Para -linked poly( 1 - 2p ) carrying ester-protected carboxy groups and poly( 1 - 2p )′ carrying free carboxy groups formed helices with opposite predominant helical senses each other, while their meta -linked counterparts [poly( 1 - 2m ) and poly( 1 - 2m )′] formed helices with the same screw sense. Poly( 1 - 2p )′ lost the one-handed helicity by the addition of KOH, and the resultant polymer recovered the original conformation upon HCl addition. On the other hand, poly( 1 - 2m )′ kept stable by KOH addition.