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

Abstract

Fully liquid-crystalline (LC) ABA-type triblock copolymers were synthesized by atom transfer radical polymerization; the A block was a fluorinated side-chain LC polymer, PFA-C 8 , and the B block was a main-chain LC polyester, BB-5(3-Me). The volume fraction of the A block (φ A ) was 0.11−0.70, and the B block had a constant molecular weight. Nanometer-scale segregated structures in the bulk and thin film states were investigated by synchrotron X-ray diffraction (XRD) in transmission and grazing-incidence (GI) geometries to examine the effect of competition between the LC orientation and polymer chain dimensions on the morphology. When φ A is 0.11, matching of the mesogen orientation in the A and B blocks dominates the main-chain orientation, whereas when φ A exceeds 0.28, matching of the lateral dimensions of the A and B blocks dominates the mesogen orientation, although all the polymers showed lamellar structure before isotropization of BB-5(3-Me). GI-XRD revealed that the lamellar structure in the thin film with φ A = 0.70 was completely perpendicular to the Si substrate without surface modification or solvent annealing.

Polyphilicity—An Extension of the Concept of Amphiphilicity in Polymers

“…Their organization is triggered by several external stimuli, most notably temperature, uniaxial shearing/stretching, and electric and magnetic fields. In a polymer segment, the mesogenic units are incorporated either along the backbone (main-chain liquid crystals, Figure 4( 9 )) [183], or in side groups (side-chain liquid crystals, Figure 4( 10 )) [184]. The inclusion of a mesogenic segment is expected to impart its switchability in response to external stimuli to the whole polymer.…”

LC‐Polymers and Smectic Phases with Special Substructures/Nanophase Segregation

“…[ 119–124 ] In recent years the synthesis of such block copolymers was changed to methods of controlled radical polymerization or ring‐opening‐metathesis‐polymerization. [ 125–129 ] This made a direct synthesis of many block‐copolymers possible and led to the first systems, in which both blocks are LC. [ 125,127–129 ] This can be i) polymers with two rod‐like LC‐blocks, ii) polymers with two or three blocks of LC‐side chain polymers, or iii) polymers, which combine a central block of the LC‐main chain type and two peripheral blocks of the LC‐side chain type.…”

“…[ 125–129 ] This made a direct synthesis of many block‐copolymers possible and led to the first systems, in which both blocks are LC. [ 125,127–129 ] This can be i) polymers with two rod‐like LC‐blocks, ii) polymers with two or three blocks of LC‐side chain polymers, or iii) polymers, which combine a central block of the LC‐main chain type and two peripheral blocks of the LC‐side chain type. [ 125,127,128,130,131 ]…”

“…[ 120–122 ] Thereby it turned out that the presence of a LC phase shifts—of course—the expected phase morphology to some extent. [ 121,125 ] In addition the layers of the block‐copolymer and the smectic layers can orient parallel or perpendicular to each other, depending on the connectivity of both blocks and the morphology of the two phase structure. On the molecular level the polymer chains like to cross the interface in a straight way (Figure 9).…”

Persistent Water Repellency of Syndiotactic Polymethylene with Perfluoroethyl Hexyloxycarbonyl Side Chains

“…[6,7] Such Rf groups incorporated into block copolymers help the lamellar and cylinder microdomains in films to take perpendicular orientation spontaneously on silicon wafers without substrate surface modification. [8,9] Although the smectic arrangement requires the number of fluorinated carbons (y) to be greater than 8, the oxidative degradation of long fluorinated methylene can yield perfluorooctanoic and perfluorooctanesulfonic acids that can cause potential toxicity and bioaccumulation. [10][11][12] Bioaccumulative potentials decrease markedly as y decreases to less than 6, and acute toxicity tests show that Rfs with y = 4 are significantly less toxic.…”