Copolymerization of chiral propargylethers and N-propargylamide and conformational control of the copolymers

Abstract

The novel acetylene monomers, L-proline-derived chiral propargylether (PA, PC, PL, and PM) were synthesized. The copolymerization of L-proline-based propargylether having amide group (PR) with N-(tert-butoxycarbonyl)-L-alanine-Npropargylamide (LA) by different unit ratio and the control of conformation of poly(LA-co-PR) were discussed. The copolymerization catalyzed by (nbd)Rh + [η 6 -C 6 H 5 B À (C 6 H 5 ) 3 ] afforded copolymers with medium M n . The specific rotation of poly(LA 88 -co-PA 12 ), poly(LA 88 -co-PC 12 ), and poly(LA 88 -co-PL 12 ) was 250°, 967°, and 1117°, respectively. The specific rotation of poly(LA-co-PC) ranged from À967°to À167°. Conformation change of poly(LA 88 -co-PR 12 ) and poly(LA-co-PC) in different solvents was studied and it was found that the intramolecular hydrogen bonding in the side chain significantly contribute to the stabilization of helical conformation of the copolymers and that solvent polarity strongly affected the stability of helical conformation. The helical structure of poly(LA 88 -co-PL 12 ) was affected by temperature change.