Synthesis and Structure of Poly(N-propargylbenzamides) Bearing Chiral Ester Groups

N- Propargylbenzamides having chiral ester groups on the benzene ring, 1 − 6, were polymerized with (nbd)Rh + [η 6 -C 6 H 5 B - (C 6 H 5 ) 3 ] to afford soluble polymers with moderate molecular weights ( M n = 34 000−100 000) in good yield. The 1 H NMR spectra demonstrated that the polymers have stereoregular structures (cis = 91−100%). The influence of the substitution position for the chiral ester group on the secondary structure was examined. From the comparison of the CD effects of poly( 1 )−poly( 3 ), the meta-substituted polymer was proven to possess a one-handed helical conformation. When the chiral center was closer to the benzene ring or chiral ester group was bulkier, the polymers showed more intense chiroptical properties. A variable temperature CD spectroscopic study showed that the helical structure of poly( 2 ) and poly( 6 ) was thermally stable. However, the CD spectra of poly( 4 ) and poly( 5 ) were inverted in sign on temperature change in chloroform or toluene, meaning that the helix inversion took place. The temperature of helix inversion could be controlled by copolymerizing with N- propargylbenzamide ( 7 ).