Liquid Crystalline Functional Assemblies And Their Supramolecular Structures PDF Download

The design of novel, complex and tailored macromolecules that present and combine unique features such as stimuli responsive, self-assembly and hierarchical architectures for applications in fields ranging from healthcare, energy to engineering, is one of the major challenges that need to be addressed by a polymer chemist. One way to address this, is through the combination of monomers with desirable roles such as stimuli responsive (liquid crystalline), solubility (polar or non-polar), targeting and payload release functional monomers. Polymerization techniques such as controlled and living polymerization enables the regulation of the connectivity and composition of these diverse monomers in the synthesis of block, random or gradient copolymers. Ring-opening metathesis polymerization (ROMP) majorly employed in most of the work in this thesis, is a robust living polymerization technique which delivers highly functionalized block or random copolymers that serves as nanotemplates (chapter 2), nanoporous membranes for separation (chapter 3), photonic crystals (chapter 4), shape memory devices (chapter 5), stimuli responsive optical materials (chapter 6), drug delivery vehicles and imaging agents (chapter 7). This dissertation focuses on a new platform for the synthesis of novel liquid crystalline polymers, their architectures, morphologies, properties and applications. The control of composition and polymer architecture is key in tuning the properties of copolymers for desired applications. Side-chain Liquid Crystalline Copolymers (SCLPs) which combines the basic properties of conventional polymers and liquid crystals, exhibit low viscosity, unique self-assembly as compared to linear copolymer counterparts due to reduced entanglements. Liquid crystalline block copolymers (LCBCPs) that comprises of brush-like semicrystalline or amorphous units and comblike side chain liquid crystalline moieties will be the center of focus in this dissertation in chapter 2, chapter 4 and part of chapter 7 due to formation of hierarchical structures as a result of two competing processes: (a) microphase separation by the copolymer superstructure and (b) orientational ordering by liquid crystalline mesogens. This supramolecular cooperative assembly leads into a well-defined interface with liquid crystalline ordering in the range of 3 -10nm nanostructures and block microphase segregation of 10- 100nm microstructures. The first part of this dissertation focuses on the understanding of liquid crystalline brush-like block copolymers self-assembly, phase behavior and morphology as a function of copolymer composition and molecular weight. Here, I describe the synthesis and characterization of norbornene functionalized side chain liquid crystalline brush-like block copolymers, where one of the blocks comprises of cyanobiphenyl liquid crystalline mesogens with twelve methylene spacer and the other semi-crystalline polylactide (PLA) side chains. The self-assembly of these LC block copolymers into liquid crystalline mesophase provides the handle for magnetic alignment of the formed LCBBCs superstructures (chapter 7). The displayed morphologies such as hexagonally packed PLA cylinders in the LC matrix is put into use in the creation of functional nanoporous membranes for water purification and heavy metal sequestering (chapter 3). The high molecular weight of this LCBBCs assemble into photonic crystals of large domain sizes with different optical properties (chapter 4). In the second part of the dissertation we explore harnessing of stimuli responsive functional cholesteric random copolymers for multifunctional elastomeric platform and optical materials that cover a wide range from visible to near infrared (NIR) of electromagnetic spectrum. Overall, understanding the structure-properties of these liquid crystalline polymers leads to various applications such as membranes for separation, optics, sensors and drug delivery.