Liquid crystalline polymers: development trends and photocontrollable materials

The results of studies on thermotropic liquid crystalline polymers containing mesogenic groups in the main chains of linear macromolecules or in pendant side-chain branches of comb-shaped polymers are analyzed and summarized. The concept for the preparation of liquid crystalline polymers via introduction of molecules of low-molecular-mass liquid crystals into the macromolecules is outlined. The presence of rodlike anisometric fragments of liquid crystals in the main chains of macromolecules is shown to control the high level of orientational order in melts and solutions of liquid crystalline polymers. The structure and photooptical properties of photochromic comb-shaped liquid crystalline polymers are considered. The mechanism of light-induced structural chemical transformations in photoactive liquid crystalline compounds is addressed. Examples illustrating the development of photo controllable liquid crystalline polymers and related composites are discussed. Structural optical properties of binary and ternary liquid crystalline photochromic block copolymers with independent modulation of photoalignment of photochromic and non-photochromic subblocks are analyzed. The feasibility of preparation of light-controlled liquid crystalline gels is considered. Special attention is given to mass transfer processes in liquid crystalline polymers, which allow the development of nanostructured surfaces and formation of diffraction gratings as well as enable preparation of diverse supramolecular structures. This review covers the challenges concerning the preparation of light-controlled liquid crystalline dendrimers and holographic media as well as the problems related to the nonlinear optical properties of liquid crystalline polymers. The roadmap for the practical applications of liquid crystalline polymers and their composites as photoactive media in photonics, optics, display technology, and in the systems for data recording and storage is outlined. The bibliography includes 240 references.