Synthesis of New Acryl-Based Functional Liquid Crystalline Monomers and Corresponding Polymers, and Their Applications

Abstract

Liquid crystalline (LC) polymers have been received much attention, due to their unique characteristics in molecular ordering, the multiple internal reflection of light, and good electrical properties. Based on these characteristics, LC polymers have been studied extensively in many applications such as display, thermal and optical mapping, photonic device, and holographic memory. In this research, eight kinds of novel LC polymers were synthesized. PDAEMAs containing pendant azobenzene moieties, n-dodecyl substituents and ethyleneoxy spacers of different lengths showed their selective detection behaviors to alkali metal ions. The new azopolymers produced homogeneous smectic phases with a typical fan-shaped texture on both heating and cooling scans (enantiotropism). Both the ethyleneoxy spacer and azobenzene units participated in binding to Li+ and Na+ cations in solution. Interestingly, after formation of the complexed structure, the ratio of the cis to trans conformer was considerably increased suggesting ii stronger interactions of the cis conformer with alkali metal ions. Homopolymers (PDOPBAMs) with side-chain LC units were prepared by RAFT polymerization of a LC monomer, DOPBAM. The resulting PDOPBAMs had low polydispersity, Mw/Mn < 1.2. Optical and thermal investigations confirmed that both the DOPBAM and PDOPBAM have smectic structures. New diblock copolymers (PMMA-b-PDOPBAM) with different ratios of the hard block containing the LC monomer moiety and PMMA as a soft segment were successfully prepared using RAFT polymerization. The block copolymerizations were proceeded on controlled/living characteristics. The morphologies of thin films of the block copolymers prepared via a simple solvent annealing showed nanographic patterns (in-plane cylinder and spherical domain) with long range ordering along the surface of substrate. The observed morphologies were dependent on the composition ratio of the LC hard block to the soft PMMA segment. In addition, the LC azoacrylamide polymers (PDDABAM, PTDABAM, and PHDABAM) with different long alkyl chain lengths (n=12,14,16) were synthesized by radical polymerization. The azoacrylamide monomers (DDABAM, TDABAM, and HDABAM) produced smectic B phase showing dendritic or mosaic textures on both heating and cooling scans. With increasing alkyl chain lengths, smectic B texture becomes more clear. Alignment of azoacrylamide monomers and their homopolymers show layered smectic structures. On the basis of the above results, the newly designed acryl-based functional LC polymers may pave the way for various applications such as new selective sensor and next generation nano-lithography and liquid crystalline display (LCD) industry.