Curving and Twisting in Self-Assembly of Triblock Terpolymers Driven by a Chiral End Block

Abstract

A series of triblock terpolymers composed of a chiral end block, poly(L-lactide) (PLLA) (designated as chiral triblock terpolymers), are designed and synthesized for self-assembly. The chiral PLLA block can contribute the chirality effect for the twisting of microphase-separated domains. By attaching an asymmetric amount of the chiral block to a symmetric diblock of polyisoprene-bpolystyrene (PI-PS), compositional asymmetry can be created for the curving of microphase-separated domains. Moreover, the difference in persistence lengths of PS and PLLA blocks can give conformational asymmetry to the curving. With the combined effects of twisting and curving, the curvature at the saddle surface of microphase-separated domains might become significant to give the formation of a network phase. Consequently, a transformation from two-domain lamellae to core−shell network phases, then to a core−shell cylinder phase, and finally to a three-domain lamellar phase with undulation due to the rod−rod interaction with the chirality effect from the semiflexible PLLA, can be found in the isopleths of the triblocks. Interestingly, a core−shell double diamond phase could be found near the center of the ternary phase diagram; we speculate that the alleviation of packing frustration in the core of the self-assembled microdomain is attributed to the character of semiflexible PLLA. Accordingly, the phase window of network formation can be enlarged by the combined effects of compositional asymmetry, conformational asymmetry, and chirality.

Peculiar Transition between Chiral and Achiral Networks in Self-Assembly of Chiral Block Copolymers

“…After thermal treatment, the formation of a well-ordered phase might greatly inhibit the crystallization event due to the confinement effect. 20,23 The PLLA/PDLA in the triblock terpolymer could be removed by hydrolysis due to the degradable ester group. The PI−PS-PLLA bulk samples were soaked in a 1 M basic solution prepared by dissolving 2 g of sodium hydroxide in a 50/50 (by volume) solution of methanol/DI water.…”

“…In addition, we speculate that when the PLLA semiflexible chain reaches a certain volume fraction, it is able to exert stronger twisting and curving power, contributing to chain stretching due to the chirality effect. 20 The synergetic effects of twisting and curving driven by the spontaneous opposite curvature of the PLLA microdomain toward a preferential direction might become significant with respect to the phase transformation from the DG to the G A phase. This results in the formation of a dispersed PLLA microdomain from an achiral double network into a single chiral network.…”

“…The phase behavior of ABC triblock terpolymers is in striking contrast to that of the diblock systems. By introducing an additional block at the chain end of the diblock, the interplay between three immiscible blocks results in a notable increase in morphological diversity. − This phenomenon can be attributed to the effects of both compositional ( i,e ., f A ≠ f B ≠ f C ) and conformational asymmetry , ( i.e ., variations in the lengths of the statistical segments within each block), which create a condition that favors the formation of interfaces with a finite spontaneous curvature in triblock terpolymers during microphase separation. Nevertheless, it is worth noting that the phase window occupied by network structures is still limited by the extensive regions of lamellar structures .…”

“…Triblock terpolymers with the incorporation of a chiral end block hold promise for meeting the necessary criteria for expanding the window of network formation. The presence of chirality serves as an additional factor introducing twisting and shifting within the microphase-separated domains in the self-assembly of chiral triblock terpolymers, enabling the formation of network phases . By taking advantage of compositional asymmetry, conformational asymmetry and chirality effect, in contrast to the one from symmetric polyisoprene- block -polystyrene (PI–PS), it is expected to provide easy access for the network formation from an asymmetric PI–PS, in particular, with the nonfrustrated triblock terpolymer system having chiral end blocks.…”

Induced Circular Dichroism and Circularly Polarized Luminescence for Block Copolymers with Chiral Communications

“…[ 49 ] With the homochiral evolution from monomer to multi‐chain domain morphology through self‐assembly, the triblock terpolymer composed of a chiral end block with single‐handed helical polymer chain gives the chiral network from the chiral end block possessing particular handed network. [ 49,50 ] Accordingly, the preferred chiral sense of the network in the aDG can be formed, leading to a chiral phase.…”