Phase Behavior of Acid-tethered Block Copolymers Comprising Various Ionic Additives

다국어 초록 (Multilingual Abstract)

Block copolymers, consisting of two or more polymer chains covalently bonded together, exhibit phase behavior due to the incompatibility between the different polymer chains. The phase behavior of block copolymers, which form various morphologies on the nanometer scale, has been theoretically and experimentally shown to be influenced by various factors such as the Flory-Huggins interaction parameter and conformational asymmetry. Recently, research has extended to the phase behavior of block copolymers including electrostatic interactions, which affect a long-range in the polymer matrix. Many studies have reported that block copolymers containing ions show complicated phase behavior compared to the neutral block copolymers. However, due to the challenges in synthesizing ion-containing block copolymers, there is a lack of experimental data, necessitating systematic studies to precisely control electrostatic interactions within block copolymers and analyze their relationship with phase behavior. In this study, I systematically control the intermolecular interactions within block copolymers by introducing various ionic additives into acid-tethered block copolymers, such as non-stoichiometric ionic liquids, mixed ionic liquids with various ratios of two different types of ionic liquids, and zwitterions. I discuss on the resulting phase behaviors of acid-tethered block copolymer comprising various ionic additives in the point of intermolecular interaction. Furthermore, since ion-containing block copolymers can be applied as electrolytes in energy storage and conversion technologies, I investigate the relationship between phase behavior and ion transport property in it. Through this, I aim to provide insights into the design of next-generation block copolymer electrolytes from the perspective of phase separation behavior.
In Chapter 1, I provide an overview of the phase behavior of ion-containing block copolymers and the relationship between morphology and ionic conductivity have been studied. This chapter discusses the impact of interactions between ionic additives and block copolymers on phase separation behavior.
In Chapter 2, I investigate the phase behavior of block copolymers with non-stoichiometric ionic liquids. To precisely control intermolecular interactions, non-stoichiometric ionic liquids were introduced to two distinct block copolymers tethering different acid functional moieties. Depending on the acid functional groups, interactions with the ionic liquid were different, leading to different phase behaviors and phase transitions that are difficult to explain with general phase diagrams. Consequently, the phase diagram for ion-containing block copolymers was redefined by introducing the new variable of ionic liquid composition. Through precise control of intermolecular interactions, I stabilized the A15 phase, a Frank-Kasper phase rarely reported in soft materials. The A15 phase, with its low symmetry, was stabilized by forming interfacial layers through strong interactions between acid-functional group in block copolymers and the cations of the ionic liquid. It demonstrated that the interface morphology varied with the type of acid group due to different interactions with the ionic liquid cations. The stabilized A15 phase exhibited higher ion transport property than the lamellar structure with two-dimensional connectivity, due to the three-dimensional connectivity of the ionic domains. This approach provides an insight about how controlling interactions between ionic additives and block copolymers can stabilize complicated morphology and enhance ionic conductivity.
In Chapter 3, I investigate the phase behavior and ion distribution in block copolymers comprising mixed ionic liquids. By introducing ionic liquids with varying compositions, I controlled the intermolecular interactions within the block copolymer electrolytes, mediated by the interactions with acid functional groups on the block copolymers. I analyzed the resulting phase behavior and ionic conductivity. It indicates that block copolymers with strong acid group interacting with the ionic liquids exhibited higher ionic conductivity when mixed ionic liquids were introduced, compared to when a single ionic liquid was introduced. Phase behavior and dynamic secondary ion mass spectroscopy revealed that each ionic liquid preferred to localize in the center of the ionic domains or at the block copolymer interfaces. The introduction of mixed ionic liquids alleviated the formation of dead zones at the interfaces, which otherwise hinder ionic conduction. This study provides an approach to precisely control phase behavior and interfacial properties of block copolymer electrolytes by incorporating mixed ionic liquids, thereby maximizing ionic conductivity.
In Chapter 4, I study the phase behavior of acid-tethered block copolymers containing zwitterions. Particularly, when zwitterions were introduced into block copolymers with specific ratio, a rarely reported superlattice morphology was obserbed. Transmission electron microscopy revealed the distribution of zwitterions within the ionic domains of the block copolymer, and infrared spectroscopy demonstrated the intermolecular interactions between the zwitterions and the acid-functional groups in the block copolymers. These results inferred that the unique phase behavior of it was originated from the interactions between the zwitterions and the acid functional groups within ionic domain of the block copolymers. Additionally, to control the interactions between the acidic functional groups of the block copolymers and the zwitterions, imidazole additives were introduced into polymer matrix. The addition of imidazole facilitated the formation of stable interaction network even at high temperature, leading to enhanced ion conduction properties and affect mechanical properties. This study presents an approach to control the complicated phase behavior of block copolymers and improve ion transport properties through the introduction of zwitterions.

목차 (Table of Contents)

• Abstract ………………………………………………………………………………........ ⅰ
• Contents ………………………………………………………………………………….. ⅴ
• List of Figures ………………………………………………………………………….. ⅷ
• List of Tables and Schemes …………………………………………………………….. ⅹⅵ
• Chapter 1. Introduction ……….……….…………….……….……….….………. 1
• I. Phase behavior of ion-containing block copolymer ………………………………. 2
• II. Morphology and ion transport relationship in ion-containing block copolymer ….. 5
• III. References ….…………………………………………………………………..…. 8
• Chapter 2. Phase behavior of acid-tethered block copolymers containing ionic liquids ………………………………………………………….. 11
• 1. Introduction ….…………………………………………………………………... 12
• 2. Experimental section ….…………………………………………………………. 15
• 2.1 Synthesis of a PS-b-PMB block copolymer ………………………………… 15
• 2.2 Synthesis of a PSS-b-PMB block copolymer ………………………………...15
• 2.3 Synthesis of a PSTFSI-b-PMB block copolymer ……………………........... 16
• 2.4 Preparation of ionic liquid-containing polymers ………………………….... 19
• 2.5 Small angle X-ray scattering (SAXS) ……………………………………… 20
• 2.6 Electron density reconstruction ……………………………………………... 20
• 2.7 Ionic conductivity measurements …………………………………………… 21
• 2.8 Simulation Methods ………………………………………………………… 21
• 3. Results and discussion …………………………………………………………… 25
• 3.1 Phase diagrams of acid-tethered block copolymers with ionic liquids…….…25
• 3.2 Stabilization of low symmetry morphology in block copolymer with nonstoichiometric ionic liquids …………………………………………………. 36
• 3.3 Ion transport properties in block copolymer electrolytes with low symmetry morphology ……………………………………………………………………... 47
• 4. Conclusions ….…………………………………………………………………... 51
• 5. References ….……………………………………………………………………. 52
• Chapter 3. Interfacial structures of acid-tethered block copolymers containing mixed ionic liquids ……………………………………………….. 57
• 1. Introduction ….…………………………………………………………………... 58
• 2. Experimental section ….………………………………………………………..... 61
• 2.1 Synthesis of acid-tethered block copolymers ………….…………………… 61
• 2.2 Preparation of block copolymer electrolytes………………………………… 61
• 2.3 Small angle X-ray scattering (SAXS) ………………………………............. 62
• 2.4 Ionic conductivity and fluorine-19 nuclear magnetic resonance spectroscopy (19F NMR) measurements ……………………………………………………… 62
• 2.5 Dynamic secondary ion mass spectroscopy (DSIMS)…..…………………... 63
• 3. Results and discussion …………………………………………………………… 64
• 3.1 Morphology of block copolymers containing mixed ionic liquids ………..... 64
• 3.2 Formation of passivation layer at the interfaces of block copolymer electrolytes …………………………………………………………………………………... 71
• 3.3 Ion transport properties in block copolymer containing mixed ionic liquids .. 80
• 4. Conclusions ….…………………………………………………………………... 85
• 5. References ….…………………………………………………………………..... 86
• Chapter 4. Morphology of acid-tethered block copolymers containing zwitterions …………………………………………………….…...… 90
• 1. Introduction ….…………………………………………………………………... 91
• 2. Experimental section ….…………………………………………………………. 94
• 2.1 Synthesis of acid-tethered block copolymer ……………………………….... 94
• 2.2 Synthesis of ZPyB zwitterion…………………………………………….. 94
• 2.3 Preparation of acid-tethered block copolymer comprising zwitterions …...... 95
• 2.4 X-ray scattering………………………………………………………......... 95
• 2.5 Transmission electron microscopy (TEM) ……………………………… 96
• 2.6 Temperature-dependent Fourier transform infrared spectroscopy ........ 96
• 2.7 Ionic conductivity measurements………………………………………........ 96
• 2.8 Rheology ……………………………………………………………….….... 97
• 3. Results and discussion …………………………………………………………… 98
• 3.1 Superlattice formation in acid-tethered block copolymers through the incorporation of zwitterions ………………………………………………... 98
• 3.2 Modulating intermolecular interactions between acid-functional groups and zwitterions to improve ion transport properties of acid-tethered block copolymers ………………………………………………………………... 110
• 4. Conclusions ….…………………………………………………………………. 118
• 5. References ….…………………………………………………………………... 119
• Abstract (in Korean) ….…..……………………………………………………………... 122
• Acknowledgement (in Korean) …...…………………………………………………….. 126
• Curriculum Vitae ….…………………………………………………………………….. 130

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