Synthesis And Property Studies Of Single-Layer Dual-Phase Liquid Crystalline Elastomers

Over the past few decades, liquid crystalline elastomers (LCEs) have attracted increasing global interest for their wide applications in artificial muscles, actuators, electro-optic or nonlinear optic materials, micropumps, etc. LCEs are materials that combine the self-organization of liquid crystals and the entropy elasticity of the polymeric elastomers. LCEs are among the most promising materials because their property of stimuli-responsive changes, such as reversible changes of shapes and dimensions, can be triggered by environmental variations such as temperature, electric field, UV light, or light with other wavelengths. In this thesis, photopatterned LCE technique is used to prepare single-layer dual-phase nematic-elastomer films. Under heat stimulus, the synthesized LCE films exhibit bending, accordion-folding, curling or buckling motions. Meanwhile, the ring-opening metathesis polymerization technique is used to prepare a series of side-on and end-on side-chain liquid crystalline polymers (SCLCPs) with an optically active polynorbornene main chain and achiral mesogens. Their mesomorphic properties are further studied by analytical and testing techniques. This thesis can be divided into two parts:1. Liquid crystalline monomer A444 is mixed with radical initiator and crosslinker, and then the mixture is filled into an antiparallel surface-rubbed cell. A photopatteming technique is used to prepare a LCE film comprised of periodic patterned nematic and isotropic stripes. Since these two different regions mismatch in shrinkage ratios at the nematic-to-isotropic transition temperature (TNI), these novel single-layer dual-phase nematic-elastomer materials have the potentials to perform under thermal stimulus versatile 3D motions, including, bending, accordion-like folding/shrinkage, curling and buckling. The single-layer dual-phase nematic-elastomer materials are regarded as a unique shape-memory polymers and have a certain application prospects.2. In this thesis, several enantiomerically pure norbornene monomers functionalized with achiral mesogenic units are asymmetrically synthesized. The monomers are further applied a ring-opening metathesis polymerization technique to prepare a series of side-on and end-on SCLCPs with an optically active polynorbornene main chain and achiral mesogens. Their physical properties are fully characterized by NMR, UV, CD, GPC, TGA, DSC, polarimetry, polarized optical microscopy and small-angle X-ray scattering. The obtained side-on SCLCPs display the tendency to form nematic mesophases, in strong contrast to the chiral nematic (cholesteric) mesophase exhibited by their comparative end-on analogues. The proposed explanation for this phenomenon is that the chiral backbones and the laterally attached mesogens of side-on SCLCPs can concurrently exist in a parallel arrangement so that the mesogenic directors might not be affected by the chirality information, while the mesogenic directors of end-on SCLCPs always tilt to the backbone orientation so that the twisting power of chiral main chains might force the terminally attached mesogens to form helical structures.