Helical phase from blending of chiral block copolymer and homopolymer

Abstract

The phase behavior of the binary blends of polystyrene-b-poly(L-lactide) chiral block copolymer (BCP*) and polystyrene homopolymer (HS) is found to be strongly dependent on the molecular weight (M(n)) of the HS. A helical phase is formed in the blends with low-M(n) HS due to an enhancement of helical steric hindrance.

Chiral transfer‐dictated self‐assembly of chiral block copolymers

“…[54] Given the relatively well-established understanding on the synthesis, physical properties, good degradability, and biocompatibility of PLLA/PDLA, there has been a litany of studies on the self-assembly of PLLA-/PDLA-based BCPs*. [35,38,[55][56][57][58] Besides, α-amino acids were also widely employed for the preparation of BCPs*. [37] For instance, PBLG-/PBDG-based BCPs* (PBLG: poly(γ-benzyl-L-glutamate), PBDG: poly(γ-benzyl-D-glutamate)) attracted a large number of studies.…”

“…Some of the key elements in this elucidation were extensively studied and manifested, that is, the intramolecular chiral interaction between PS and PLLA/PDLA, and the chiral steric hindrances. [55,57,80] The crystallization of PLLA/PDLA was demonstrated as another key factor to the self-assembly of PS-b-PLLA/PSb-PDLA BCPs* in bulk/films. By taking advantage of real time in situ SAXS and wide-angle X-ray diffraction, Grason and Russell et al indicated that the self-assembly of PS-b-PLLA/PS-b-PDLA entailed a sophisticated competition between incompatibility-driven microphase separation and the crystallization of PLLA/PDLA.…”

“…The most studied BCPs* in bulk/films belonged to PS-b-PLLA, where single helixes*, networks, core-shell cylinders, and concentric/roll cake-like spiral lamellae were obtained from a manipulation on the volume fraction of PLLA (f PLLA ) and the overall molecular mass. [75,76] The helix* phase from PS-b-PLLA/PS-b-PDLA BCPs* were systemically characterized by Ho et al [35,38,[55][56][57][58] In a combination of transmission electron microscopy images (TEM) and small-angle X-ray scattering (SAXS) results, it was evidenced that this intriguing helix* phase contained PLLA/PDLA spring-like single helixes* embedded in a PS matrix, with an interdigitated and hexagonal fashion (Figure 3A). [35] This unique feature was verified by 3D TEM tomography, as well as the morphological chirality.…”

Tuning the Chirality of Block Copolymers: From Twisted Morphologies to Nanospheres by Self‐Assembly

“…For instance, Nolte and co‐workers used charged chiral BCPs to generate hierarchical superstructures with helical sense8a and, more recently, Ho et al. reported the formation of different helical textures by the self‐assembly of poly(styrene)‐ b ‐poly( L ‐lactide) BCPs 8e–i. In these works, the presence of chiral centres in the main chain of the BCPs has been postulated as the main factor to induce the formation of helical morphologies.…”

“…In these works, the presence of chiral centres in the main chain of the BCPs has been postulated as the main factor to induce the formation of helical morphologies. Indeed, these chiral centres can induce helical conformations in one of the segments of the BCP, which can be transferred to a nanostructure (helical aggregate) during the self‐assembly in the so‐called “chirality effect” 8e–i. New fundamental insight into the chirality effect on the self‐assembly of BCPs can be provided by means of systematic modification (i.e., tuning) of the helicity of one of the blocks (e.g., by controlling the number of chiral centres), without altering other parameters, such as molecular weight, block ratio, or solubility.…”