이온성 고분자 및 복합물질의 광학 ∙ 전기촉매 특성 연구

Abstract

Numerous kinds of polymers have been adopted in different fields due to their useful advantages such as flexibility, stability, and processability. Besides, to accomplish the advanced properties from the polymeric materials, ionic polymers have been widely used in different applications since they contain ionic functional groups that can assign their own unique characteristics or participate in chemical process by specific interactions with ionic or charged molecules. Over the past decade, many researchers have focused on the investigation of ionic polymer in order to secure their uses in variety of application fields including fuel cells, secondary battey, composite matrices, and chemical sensors. Among the various features of ionic polymers, fluorescence and hybridization with inorganic species have attracted much interest from fundamental and applied perspectives due to their limitless utilization. Conventional strategies of ionic polymers for the improvement of their features are relied on modification of functional groups, molecular weight, and composition of polymers. Along with these approaches, introduction of self-assembled morphology nature within nanometer scale into ionic polymer has been taking center stage to obtain extraordinary performances. Herein, in this thesis, investigation of fluorescence and electrocatalytic properties of ionic polymers and ionic polymer/metal nanoparticle composites having self-assembled nature are described in the perspective of fundamental and application researches such as chemical sensor and electrocatalytic electrode materials. Chapter 1 gives a brief overview of ionic polymers and their uses. Since the ionic polymers possess a lot of ionic sites within their molecular structures, they exhibit specific characteristics and can be processed to organic/inorganic composites. In terms of application study, fluorescence phenomenon or electrocatalytic feature are considered as the one of the representative properties of ionic polymers and their composite derivatives since they can be directly adopted as chemical sensor systems and electrocatalytic materials. Currently, I devoted many efforts to improve these two kinds of properties by the introduction of morphology behavior to the ionic polymer and ionic polymer/metal nanoparticle composites. This strategy was a effective way to develop their properties and that can be successfully applied to the different application researches. In Chapter 2, I investigated the fluorescence properties of non-conjugated ionic polymers that contain partially sulfonated polystyrene (PSS) chains. Additionally, Relationship between the morphologies and fluorescence properties of block copolymer micelles possessing PSS chains has been studied. Significantly enhanced fluorescence intensities were observed for PSS-containing block copolymer micelles upon stabilizing the light-emitting PSS chains within nanosized micellar core phases, which is in sharp contrast to the weak fluorescent PSS homopolymer solutions. Notably, the fluorescence properties of PSS-containing block copolymer micelles were highly sensitive and selective to Cu2+ ions with a rapid quenching response time within 1 min. The spatial matching derived from morphological factors and fast collision kinetics for Cu2+ through high binding affinity with –SO3- were found out to be an origin for the observation. These results were not observed in case of PSS homopolymer owing to the lack of morphology effects. In chapter 3, I described emission behaviors of non-conjugated engineering plastic, poly(N-phenylmaleimide) (PPMI), and developed a tricolor luminescent pH sensor based on this polymer. PPMI and its substituted analogues exhibited strong solvatochromism and tautomerism allowing the precise measurement of pH values by emission color changes from green to yellow and yellow to orange. In particular, the synthesis of a PPMI-based block copolymer containing water soluble poly(ethylene oxide) (PEO) units enabled me to develop ratiometric pH sensors covering wide pH range 1-13. Key to success stemmed from the self-assembly characteristics of the PEO-PPMI block copolymer, which regulate fluorescence properties while avoiding the self-quenching behavior. Finally, this system can be used as a fast responsive pH sensor in versatile device forms. In chapter 4, I investigated the synthesis of polymer-metal nanoparticle composites based on nanostructures for the catalytically active materials. I developed the precise and controlled gold nanoparticle (AuNPs) synthesis with partially sulfonated poly(styrene-b-methylbutylene) (PSS-PMB) ionic block copolymers as a nanoreactor. PSS-PMB copolymers contain 3 – 5 nm sized ionic domains which is hierarchically located within self-assembled microstructures with periodicity of 21 – 43 nm. Isolation of Au ions in the ionic domains and sequential reduction by photochemcal method process (UV-irradiaion) can produce the AuNPs. I was able to control the the size of AuNPs from 2.0 ± 0.3 to 3.9 ± 0.5 nm by adjusting sulfonation levels of PSS-PMB copolymers. Furthermore, significantly improved electrocatalytic activity toward methanol oxidation reaction were achieved due to the ion conducting –SO3H groups and the interconnected network of AuNPs confined within self-assembled microstructures, which provides electronic conductivity