Formation Mechanism of Helical Polyacetylene with Spiral Morphology in Asymmetric Reaction Field Consisting of Chiral Nematic Liquid Crystal

Abstract

The formation mechanism of helical polyacetylene (H-PA) in chiral nematic liquid crystal (N*-LC) used as an asymmetric reaction field was investigated by taking into account the relationship in morphology between the H-PA and N*-LC. The spiral texture characteristic of N*-LC observed in polarized optical microscopy was examined and compared with the spiral morphology of the resultant H-PA. The distance between the fibril bundles of H-PA was determined to be half of a helical pitch of N*-LC; in addition, the helical axis of H-PA is orthogonal to that of N*-LC. Interestingly, the screw direction of the H-PA fibrils was found to be opposite to that of N*-LC. On the basis of these experimental facts, we propose a chemically graspable formation mechanism of H-PA in N*-LC.

Chiral Reaction Field with Thermally Invertible Helical Sense that Controls the Helicities of Conjugated Polymers

“…Interfacial polymerization of acetylene was achieved using a Ziegler–Natta catalyst dissolved in the N*‐LC. The H‐PAs that were synthesized at low (−12 °C) and high (28 °C) temperatures exhibited right‐ and left‐screwed helical senses, respectively, that opposed those of the N*‐LCs required by the polymerization mechanism 37,38. Therefore, the current N*‐LC can produce hierarchically controlled helical structures consisting of the primary to higher‐order structure of H‐PA under thermal stimulus 17–23,39.…”

“…At 28 °C, the bundles of fibrils and the spiral morphology were left‐handed. The helical sense of H‐PA opposed that of the N*‐LC due to the polymerization mechanism of acetylene in the N*‐LC 37,38…”

“…The relationship between the helical pitch ( p ) of the N*‐LCs and the distance ( d ) between the fibril bundles of H‐PA can be described as p /2 = d 4–6,37,41,42. Figure 5b shows the correlation between the distance between the fibril bundles of H‐PA and the helical pitch of the temperature‐dependent N*‐LC and the actual polymerization temperature rather than the applied temperature for polymerization.…”

Synthesis of Conjugated Polymers in Chiral Nematic Liquid Crystal Fields

“…This allows the regulation of the helical sense and helical power (helical pitch) of the N*‐LC by selecting the chirality and helical twisting power (HTP; β M ) of the chiral dopant 38. Therefore, the induction of chirality in N‐LC with a chiral dopant is a type of chiral amplification 27k. 38, 39 The director of a N*‐LC, defined as the averaged direction for the LC molecules within the domain, rotates gradually in one screw direction to form a helical structure.…”

“…The H‐PA chains with a screw direction opposite to the N*‐LC smoothly propagate along the LC molecules, as shown in Figure 7. When the H‐PA chains with the same screw direction as the N*‐LC encounter the LC molecules, a sterically unfavorable polymerization results 27k…”