Secondary structure and side-chain chromophore orientation of isotactic poly(methacrylamide)s in solid film

Intramolecular hydrogen bonding among the side-chain amide groups in isotac tic poly[(S)-1-(1-naphthyl)ethyl methacrylamide] (1) and poly[(S)-1-phenyle thyl methacrylamide] (2) were examined in films cast from 1,2-dichloroethan e (EDC). Curve fitting of the amide I band shows that the peaks for the ful l hydrogen bonds are broader as compared with those in EDC solution, sugges ting that the hydrogen bonds formed in film are looser and less extensive t han those in solution. X-Ray diffraction (XRD) measurements show that these polymers give hexagonal-like aggregates in film, indicating that they form rod-like helical structures as suggested by molecular mechanics calculatio ns. Isotactic 2 film shows a positive circular dichroic (CD peak at ca. 230 nm, characteristic of the fully hydrogen-bonded helical structure, which d isappears upon annealing. Isotactic 1 film shows two CD positive peaks at c a. 210 nm and at ca. 230 nm, their relative intensities changing upon annea ling, which together with the CD measurements in solution suggests that the hydrogen-bonded and non-hydrogen bonded structures of isotactic 1 give, in the B-1(6) band of the naphthyl group, exciton coupling of positive chiral ity and that of negative chirality, respectively, the overall CD being dete rmined by their relative contents.