Optically active polyethers. 3. On the relationship between main-chain chirality and the lamellar morphology of solution-grown single crystals

The morphology of chiral (R)- and (S)-poly(epichlorohydrin) (PECH) single c rystals grown from solution was studied to obtain insight into the mechanis m by which the chiral character of the main chain can be transmitted to hig her organizational levels, such as the lamellar twisting orientation in ban ded spherulites. Poor solvents were selected so that the crystallization fr om solution occurred at high temperatures, where the resulting lamellar hab its simulate most closely those obtained in crystallization from the melt. Interestingly, the TEM examination of folded-chain single-crystal lamellae showed no morphological evidence that could be related to the chiral charac ter, R or S, of the polyenantiomer. In addition, it was established that th e handedness (or sense) of screw dislocations in these lamellae is not cont rolled by the main-chain chirality; This result supports previous evidence which shows that, although the screw dislocations may contribute to the ban ding through lamellar branching, they appear not to be primary determinants of either the handedness or magnitude of the twist of lamellae in banded s pherulites. Similar morphology patterns were obtained for lamellar single c rystals of chiral (R)- and (S)-poly(propylene oxide) and of the optically a ctive biopolyester, (R)-poly(3-hydroxyvalerate), supporting the generality of these features. In searching further for chiral effects, the examination of lamellar morphology in large PECH aggregates, e.g., highly dendritic cr ystals and hedrites, grown from solution indicated that some of the lamella e are nonplanar while in solution. Some considerations pertaining to the fa ctors that may contribute to the nonplanar habits observed in the morpholog y of these large aggregates are discussed as well.