Study on the chain orientation and interdiffusion of polyimide affected by drying and curing processes

• Main Author: 조병욱
• Other Authors: 안경현, 공과대학 화학생물공학부
• Format: Thesis
• Language: English
• Published: 서울대학교 대학원 2016
• Subjects: 폴리이미드; 잔류용매; 이미드화도; 사슬 배향; 상호확산; 라만 분광법; 660; Paa; DML
• Online Access: http://hdl.handle.net/10371/119766

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 화학생물공학부, 2016. 2. 안경현. Chain orientation in polyimide (PI) film and its interdiffusional behavior influenced by the process conditions were investigated. The amount of residual solvent and the degree of imidization were proved to be the key factors that determine the final chain orientation and interdiffusion width of PIs. To observe the effect of film thickness, the films made by poly(amic acids) or PAA, the precursor of polyimide, having different thicknesses were prepared. During the drying and curing processes, the depth-wise distribution of residual solvent and imidization rate were observed. For thick PI, it showed a lower degree of in-plane chain orientation, particularly near the substrate. This non-uniform distribution of chain orientation was similar to that of a dried PAA. Fast imidization with higher solvent content for thick PI retarded the formation of a well-ordered structure and resulted in a lower degree of in-plane orientation. Chain orientation of a PI can also be changed by thermal histories. PAA began to imidize quickly with retaining more solvent as the initial drying temperature increased. The fully imidized PI showed the lowest degree of in-plane chain orientation when it was processed by the protocol of the highest drying temperature. It influenced the in-plane thermal expansion coefficient most significantly, while no significant change in crystallinity or glass transition temperature was observed. In multi-layer PI film, controlling the interdiffusion and chain orientation is essential to achieve a good adhesion performance. In the present study, bilayer PI films were made by two different drying methods, direct multi-layer (DML) and layer-by-layer (LBL). The extent of interdiffusion between two PAAs was affected by both the amount of solvent and contact time. As a result, the interdiffusion width of the cured PI made by DML was larger than that made by LBL. The chain orientation of the bottom layer, which consists of more rigid chain structure, was observed to be varied more significantly according to the drying conditions. In the bilayer PI film made by LBL method, the degree of in-plane orientation of the bottom layer became reduced compared to the single-layer when it was dried at lower temperature. The result originates from the fast diffusion of solvent in the top layer into the bottom layer. Chapter 1. Introduction 1 1.1. General introduction 2 1.2. Outline of the thesis 7 Chapter 2. Background 9 2.1. Manufacturing processes of polyimide film 10 2.1.1. Poly(amic acid) preparation 12 2.1.2. Thermal imidization of PAA 14 2.2. Drying behavior of polymer solutions 17 2.2.1. Two drying regimes of polymer solution 18 2.2.2. Stress development in polymer films 21 2.2.3. Stress development in polyimide film 22 2.3. Chain orientation of rod-shaped polymers 23 2.3.1. General introduction of polymer chain orientation 23 2.3.2. Chain orientation measurement using polarized Raman spectroscopy 24 2.4. Interdiffusion between two different polymers 30 2.4.1. Polymer/polymer interfaces 30 2.4.2. Interdiffusion at polymer interfaces 34 2.4.3. Interdiffusion between partially miscible polymers 36 2.4.4. Polymer interface and adhesion 37 2.5. Confocal Raman spectroscopy 41 2.5.1. Principles of Raman scattering 41 2.5.2. Principles of confocal Raman spectroscopy 41 Chapter 3. Experimental methods 49 3.1. Sample preparation and characterization 50 3.2. Measurement of residual solvent concentration and the degree of imidization 62 3.3. Measurement of chain orientation of polyimide 68 3.4. Experiments of polyimde interdiffusion 73 3.4.1. Measurement of PAA-PAA interdiffusion 77 3.4.2. Measurement of solvent diffusion into dried PAA film 78 3.4.3. Measurement of interdiffusion width of cured polyimide films 79 3.5. Characterization of the cured polyimide film 81 3.5.1. X-ray diffraction pattern 81 3.5.2. Glass transition temperature 81 3.5.3. Thermal expansion coefficient 81 Chapter 4. Results and discussion 83 4.1. Effect of film thickness on the polyimide chain orientation 84 4.1.1. Depth-wise residual solvent content of dried film 84 4.1.2. Depth-wise imidization degree during the curing process 87 4.1.3. Depth-wise chain orientation after curing 90 4.2. Effect of thermal history on the polyimide chain orientation 98 4.2.1. Residual solvent and imidization degree during drying 98 4.2.2. Process path and degree of in-plane orientation 103 4.2.3. Properties of cured film 107 4.3. Interdiffusion and chain orientation in the drying of bilayer polyimide film 112 4.3.1. Interdiffusion between PAA solutions having different solvent contents 112 4.3.2. Interdiffusion width of cured polyimide film 116 4.3.3. Solvent diffusion into dried PAA films 118 4.3.4. In-plane chain orientation of cured polyimide films 121 Chapter 5. Summary 125 References 131 국문 초록 141 Doctor