Mesomorphic and structural properties of liquid crystalline side-chain polymethacrylates: from smectic C* to columnar phases

ABSTRACT

The chiral methacrylate monomers with photosensitive azobenzene group possessing the orthogonal smectic A* and tilted smectic C* (Sm-C*) phases have been synthesised and characterised. The monomers have been used as functional side chains for the design of corresponding polymethacrylates. X-ray diffraction has been applied to elucidate the structure and phase behaviour of liquid-crystalline side-chain polymethacrylates with azobenzene-containing central core, chiral fragments and aliphatic spacers and tails of different length. X-ray patterns of polymethacrylates oriented fibres impose the tilted Sm-C* order as a basic structure of these materials. This is complemented by a regular pattern of small-angle diffuse spots, which implies complex positional order on the local scale and serves as a precursor for the formation of a columnar phase. The increase of the total length of the aliphatic tail and spacer of the side-chain fragments leads to formation of the tilted columnar phase (Col_tilt*) with two-dimensional monoclinic lattice. For the polymer containing 10 methylene units in both, spacer and aliphatic tail, the Col_tilt* precedes the formation of the Sm-C* phase. The observed structural changes are explained as due to coupling between the smectic ordering of the mesogenic side groups and the polymer backbone conformation.

Graphical Abstract

KEYWORDS:

• Liquid crystals
• methacrylate monomers
• side-chain polymers
• smectic and columnar phases
• X-ray diffraction
• small-angle diffuse scattering

Acknowledgements

The X-ray experiments at Kurchatov Synchrotron Centre and FSRC “Crystallography and Photonics” RAS were supported by the Ministry of Science and Higher Education within the corresponding State assignments. We acknowledge support from the Russian Foundation for Fundamental Research (grant 16-29-05140, X-ray data analysis, structure determination) and the Russian Science Foundation (14-13-00379, synthesis of the polymethacrylates). The work of A.B., M.C. and V.H. was supported by Czech Science Foundation grant number 16-12150S (synthesis and mesomorphic behaviour of methacrylate reactive mesogens).

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the Russian Foundation for Fundamental Research [grant 16-29-05140, X-ray data analysis, structure determination] and the Russian Science Foundation [14-13-00379, synthesis of the polymethacrylates]. The work of A.B., M.C. and V.H. was supported by Czech Science Foundation, grant number 16-12150S (synthesis and mesomorphic behaviour of methacrylate reactive mesogens).