Molecular Orientations in Flat-Elongated and Helical Lamellar Crystals of a Main-Chain Nonracemic Chiral Polyester

Abstract

Single flat-elongated and helical lamellar crystals have been grown thermotropically in a mainchain nonracemic chiral liquid crystalline polymer that was synthesized from (R)-(-)-4′-{ω-[2-(p-hydroxyo-nitrophenyloxy)-1-propyloxy]-1-nonyloxy}-4-biphenyl carboxylic acid, PET(R*)-9. The crystals possess the identical orthorhombic lattice dimensions of a ) 1.07 nm, b ) 0.48 nm, and c ) 5.96 nm. 1,2 Dark field (DF) image, bright field image, and selective area electron diffraction (SAED) experiments using transmission electron microscopy (TEM) provide chain orientation information in both of these crystals. In the flat-elongated lamellar crystals, the chain direction is perpendicular to the substrate surface in a center zone along the long (b) axis of the crystals. Moving away from this zone along the short (a) axis of the crystal, the chain direction continuously tilts in the ac-plane. A small tilt of approximately 0.002°per molecular layer is estimated using the SAED results. In the helical lamellar crystals, the main twist direction is parallel to the helical axis, and the rotation angle for each molecular layer is approximately 0.05°. However, specifically designed DF experiments using the entire and partial (205) and (206) diffraction arcs show that the chain orientation direction is also twisted along the short helical axis of the lamellar crystal. The rotation angle is approximately 0.01°p er molecular layer. Therefore a second twist direction with a changing molecular orientation exists in addition to the long helical axis of the crystal. Based on these experimental observations, the concept of a doubletwisted molecular orientation in the helical lamellar crystal can be established, although in principle, the macroscopic translational symmetry is broken along both of the long and short axes of the helical lamellar crystals in Euclidean space.

Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer : Synthesis, crystallization behavior and novel morphology

“…Unfortunately, reports on this field are still inadequate till now. Recently, with the comprehensive investigations on crystallization process for block copolymers, the high order structures containing crystal lamellae were frequently discovered [6,[21][22][23][24][25], where several types of spherulites with unusual morphologies such as ring banded spherulite, spherical granular aggregates and double concentric spherulites have been reported [14,15,[26][27][28][29][30][31]. Especially, the double concentric spherulites were only found in poly(ethylene oxide)/poly(!-caprolactone) PEG/PCL block copolymer up to now [14,[26][27][28][29].…”

Novel Nanostructures from Self‐Assembly of Chiral Block Copolymers

“…Mimicking nature, scientists have aimed to prepare helical morphologies from the self-assembly of synthetic molecules. A variety of origins for the formation of helical morphologies, including hydrogen bonds, [3] solvophobic interactions, [4][5][6] p-p interactions, [7][8][9][10][11] cholesteric liquid crystal formation, [12,13] relative incompatibility [14][15][16] and chirality, [17][18][19][20] have been demonstrated.…”

“…Cheng and coworkers found that polyester liquid crystal with chiral entities can self-assemble into crystalline helical superstructures with micrometer-scale pitch length. [12,13] Also,…”

Wachstumsinduziertes Biegen und Verwinden von Einkristallen

“…Dabei wird von "Ebenen der Chiralität" gesprochen. [277] Die primäre, also molekulare Ebene der Chiralität dringt in die sekundäre Ebene vor, beispielsweise die Hän-digkeit helikaler Makromoleküle. Diese kçnnen dann enantiomorphe makro-oder mesoskopische Morphologien mit entgegengesetzten Verwindungen bewirken -die tertiäre Ebene.…”