X-ray Reflectivity and Scattering Studies on Nanostructures of Brush Polymers Bearing Functional Moieties

Abstract

Polymer materials are big part of modern material science. Simply put, almost every plastic material around us is composed of polymer materials. When compared with other material, polymers have better mechanical strength and processability, even though it is light in weight. Polymers can be applied to various different fields by mixing or adding various functional chemical groups. Because of these kinds of functional groups, polymer can be applied in nanotechnology, microelectronics, information technology, and biological systems. Research into the nanostructures of polymers has become increasingly important. Why is this kind of work important? For example, we have to think about house we live in. this house has so many different shapes, materials, and structures. Different houses are not made uniformly for the same reason and purpose, but they are closely related to the life style, emotion and environment of the occupants. Similarly, the structure of each polymers represents and is related to its properties and functions. Therefore characteristics and use are decided by their structure and properties. Contrary to the past, polymers are no longer simply synthesized and commercially produced and used if they have good mechanical strength or properties. Future science wants new materials which have more detailed and developed application, nanomaterials, biocompatible materials and other fields. In this situation, it has become more important to understand the nature of the substance and subsequently apply it. In Chapter II, self-assembly characteristics of a well-defined brush polymer, poly(oxy(n-dodecyl-thiomethyl)ethylene) were in detail investigated at the air-water interface with surface–area isotherm, X-ray reflectivity, and infrared spectroscopy analyses. The brush polymer self-assembled at the air-water interface as a fully-extended chain via favorable lateral packing of the bristles in a fully extended conformation, forming highly ordered, oriented Langmuir monolayer. This well-ordered monolayer was produced via a five-regime structure formation with varying surface pressure. These Langmuir film formations and their ordering and orientation might be driven by the well-defined chemical architecture and the lateral orderings of the polymer backbones and the bristles in fully extended conformations. In Chapter III, self-assembly characteristics of poly(oxy(11-phosphorylcholineundecylthiomethyl)ethylene) (PECH-C11-PC), a lipid-mimicking brush polymer, were investigated for the first time in nanoscale thin films as well as at the air-water interface using synchrotron grazing incidence X-ray scattering, X-ray reflectivity, and infrared spectroscopy. In thin films, the PECH-C11-PC molecules were found to form a well-ordered, inplane-oriented molecular multibilayer structure in which the bristles made partial interdigitation in the neighbored layers via the favorable interactions of the PC end groups. The brush polymer molecules were further found to favorably form molecular assemblies at the water interface. This phase underwent a surface pressure-driven structural transformation path way, ultimately forming a canonical bilayer structure similar to that commonly observed among natural lipids. These remarkable self-assembly behaviors were comprehended with consideration of the hydrophilic backbone, zwitterionic PC end, hydrophobic alkylenyl linker, and their selective interactions. In Chapter IV, self-assembling characteristics of a series of amphiphilic zwitterionic brush random copolymers (PECH-DMAPSm where m is the mol% of DMAPS end group), were investigated at an air–water interface by using surface pressure–area isotherms, infrared spectroscopy, and X-ray reflectivity analysis. The random polymers (m: 20–60 mol%) always formed Langmuir monolayer structures only rather than any other structures, regardless of the surface pressures. The Langmuir monolayers possessed enhanced lateral ordering together with conformational changes of the backbone and bristles through increasing the surface pressure. The monolayer structures were basically composed of a hydrophobic bristle phase in the air side and a hydrophilic backbone and bristle phase in the water side. The highly ordered Langmuir monolayer structures could be realized by positive, cooperative efforts of several factors such as the compositional balance of hydrophobic and hydrophilic zwitterionic bristles. In Chapter V, block copolymers were synthesized by Sequential living anionic polymerization and selective post-modification: PVPK–P2VP (43/57 in volume) and PVPK–QP2VP (31/69) including each blocks homopolymers. PVPK block corresponds to electrically active part and P2VP and QP2VP blocks are dielectric part. The blocks in the copolymers were found to undergo phase-separation. Nanoscale thin film morphology details were investigated by quantitative synchrotron grazing incidence X-ray scattering (GIXS) analysis. A horizontal lamellar structure was developed in the CS2-annealed PVPK–P2VP (43/57) films while a vertically lamellar structure was formed in the CHCl3-annealed PVPK–QP2VP (31/69) films. This study nicely demonstrated a well-defined lamellar structure and its preferential orientation control along the in-plane or out-of-plane direction in the block copolymer films by the surface modification of substrates without and with piranha solution treatment and the optimizations of thermal- and solvent-annealing conditions in various conditions. In Chapter VI, block copolymers of poly(4,4'-Vinylphenyl-N,N-bis(4-tert-butylphenyl)benzenamine) (PTPA) and poly(2-vinylpyridine) (P2VP), including homopolymers, were synthesized by sequential living anionic polymerization: PTPA–P2VP (50.9/49.1 in volume). Nanoscale thin film morphology details were investigated by quantitative synchrotron grazing incidence X-ray scattering (GIXS) analysis. The PTPA-b-P2VP make well-ordered hexagonal packing cylinder structure after solvent annealing. Furthermore, the horizontally oriented cylinder structure was clearly observed in the nanoscale thin films that were selectively annealed with tetrahydrofuran (THF). The vertically oriented cylinder structure of this block copolymer was also clearly formed in the films that were selectively annealed with carbon disulfide (CS2). Furthermore, the structural orientation is dominated by a particular solvent and the reversible transition between two different structures occurs completely. These different morphologies depending on the annealing conditions influenced the electrical memory characteristics of the devices