Directed crystallization of isotactic poly(2-vinylpyridine) for preferred lamellar twisting by chiral dopants
TaoWen, Hsiao-Fang Wang, Yung-Cheng Mao, Wei-Tsung Chuang, Jing-Cherng Tsai, Rong-Ming Ho
As reported in our previous work, banded spherulites of isotactic poly(2-vinylpyridine) (iP2VP) with preferred handedness of twisted lamellae can be formed by the inducement of chiral dopants, i.e., (R)- or (S)-hexahydromandelic acids (HMAs). In the present work, we systematically studied the behaviors of chirality transfer in the crystallization of iP2VP associated with the chiral dopant. As evidenced by the signatures of the split-type Cotton effect of circular dichroism (CD) spectra, the chains of iP2VP exhibit exclusive conformational chirality, i.e., induced circular dichroism (ICD), due to the complexation of chiral dopants (configurational chirality) with the lone-pair electron of the iP2VP. With the same growth axis along the radial direction of the banded spherulites, as indicated by selected area electron diffraction (SAED), the helical sense of the twisted lamellae of the iP2VP with ICD can be driven by the chiral dopants. The handedness of the helical chains remains after crystallization with intrinsic crystalline structure of iP2VP, which was revealed by the corresponding results of CD spectroscopy. As a result, a homochiral evolution from the configurational chirality of chiral dopant to the hierarchical chirality of crystallized iP2VP can be developed through directed crystallization of the iP2VP by chiral HMAs.
Vibrational circular dichroism. ChiralitySpherulitePoly(2-vinylpyridine)