Lamellar Morphology of an ABA Triblock Copolymer with a Main‐Chain Nematic Polyester Central Block

Abstract

A liquid crystal (LC) ABA triblock copolymer with poly(styrene) (PS) A blocks and a main‐chain nematic LC polyester B block is synthesized by atom‐transfer radical polymerization of styrene with an LC polyester macro‐initiator. The nematic LC and PS amorphous phases are segregated from each other to form lamellae with a spacing of 27 nm. The 16 nm‐thick nematic LC lamellae are significantly smaller than the contour length of the LC segment (63 nm), and the nematic director is parallel to the lamellae. The central LC segment is primarily more extended in the lamellar direction, but folds so as to meander through the LC lamella and bridges adjacent PS domains. The lamellar microstructure exhibits a reversible spacing increase of up to 31 nm with increasing temperature, suggesting a corresponding increase in the probability of the chain folding.

Influence of Smectic Liquid Crystallinity on Lamellar Microdomain Structure in a Main‐Chain Liquid Crystal Block Copolymer Fiber

“…The LC segment is mainly extended perpendicular to the lamellar boundary due to the repulsive interaction with the PEMA segment. In contrast, the mesogens in a main‐chain nematic LC block copolymer, the mesogen exhibits homogeneous anchoring at the lamellar boundary . The mesogens in main‐chain LC block copolymers do not always exhibit homeotropic anchoring at the microdomain boundary.…”

Synthesis of Block Copolymers of Polyester and Polystyrene by Means of Cross-Metathesis of Cyclic Unsaturated Polyester and Atom Transfer Radical Polymerization

“…Block copolymers composed of two or more different polymer segments self-assemble in films and/or in solvents including water, and this self-assembly behavior is dependent on the molecular weight and the composition ratio of each segment. − Block copolymers with controlled morphology are used in nanolithography, − nanotemplating, , storage media, , and so on. The most general synthetic method for block copolymers , is sequential polymerization of different monomers in one pot by using living polymerization methodology, such as addition polymerization − and ring-opening polymerization. − In addition, unique block copolymers have recently been obtained by means of postpolymerization modification of the polymer end groups. − For example, many block copolymers of crystalline polyester (PEs) and noncrystalline polystyrene (PSt) have been synthesized by living ring-opening polymerization of lactone or lactide and living addition polymerization of styrene (St) via postpolymerization modification. − However, there are only three reports about block copolymers of PEs and PSt, in which the PEs segment was synthesized by polycondensation: (i) radical polymerization of St, initiated from the end groups of PEs, (ii) coupling reaction of telechelic PEs and monofunctionalized PSt, and (iii) copolymerization of hydroxyl-terminated PSt, diol, and dicarboxylic acid chloride . The telechelic PEs in (i) and (ii) were prepared by the use of an excess of one of the two monomers in polycondensation, but the possibility of contamination with cyclic polymers cannot be ruled out because intramolecular reaction of both chain ends occurs in competition with propagation, as described by Kricheldorf …”

“…23−25 For example, many block copolymers of crystalline polyester (PEs) and noncrystalline polystyrene (PSt) have been synthesized by living ring-opening polymerization of lactone or lactide and living addition polymerization of styrene (St) via postpolymerization modification. 26−40 However, there are only three reports about block copolymers of PEs and PSt, in which the PEs segment was synthesized by polycondensation: (i) radical polymerization of St, initiated from the end groups of PEs, 41 (ii) coupling reaction of telechelic PEs and monofunctionalized PSt, 42 and (iii) copolymerization of hydroxyl-terminated PSt, diol, and dicarboxylic acid chloride. 43 The telechelic PEs in (i) and (ii) were prepared by the use of an excess of one of the two monomers in polycondensation, but the possibility of contamination with cyclic polymers cannot be ruled out because intramolecular reaction of both chain ends occurs in competition with propagation, as described by Kricheldorf.…”

Fully Liquid-Crystalline ABA Triblock Copolymer of Fluorinated Side-Chain Liquid-Crystalline A Block and Main-Chain Liquid-Crystalline B Block: Higher Order Structure in Bulk and Thin Film States

“…11,12,14,18 This phenomenon is known as the anchoring effect. 11,14,18,19 When the SCLCP block in a BCP forms a smectic phase, two different orientations are observed depending on the degree of decoupling between the mobility of mesogens and the main-chain (backbone) conformation: main chains of the SCLCP are aligned perpendicular to the interface of the domains for a shorter spacer, that is, a lower degree of decoupling, whereas the main chains are aligned parallel to the interface for a longer spacer, that is, a higher degree of decoupling. 20 If a main-chain LC polymer (MCLCP) is incorporated into a BCP and segregated from an amorphous block, two different orientations are also observed depending on the type of LC phase.…”

“…When the MCLCP forms a nematic phase, the main chain and mesogen are aligned parallel to the interface, in an effect similar to the anchoring effect in SCLCPs. 19 When the MCLCP forms a smectic phase, a lamellar morphology is observed over a wide range of volume fractions, and the main chain is aligned perpendicular to the interface. 21−24 Note that the distributions of the lamellar thickness and long period were very narrow, even though the MCLCP block was polymerized by a traditional polycondensation method and had a large polydispersity of close to 2.…”