Title Page
Abstract
Contents
Chapter 1. Introduction 23
1. Introduction 24
1.1. Acrylic Pressure Sensitive Adhesives 24
1.2. Photopolymerization 31
1.3. Application of Photocatalyst-mediated Photopolymerization 46
2. Objectives 58
2.1. Driving the Catalytic Cycle by Typical Monomers for General PSA 61
2.2. Driving the Catalytic Cycle by Additives for OCA 62
2.3. Optimization of the Catalytic Cycle with Various Photocatalysts and Additives for UV-blocking OCA 63
Chapter 2. Experimental Section 65
1. Materials 66
1.1. Photocatalysts 66
1.2. Acrylic Monomers 67
1.3. Others 68
2. Preparation of Acrylic PSAs 70
2.1. Bulk Polymerization 70
2.2. Film Curing 75
3. Characterization of Acrylic PSAs 77
3.1. Gel Content 77
3.2. UV/Vis Spectroscopy 77
3.3. Adhesive Performances 78
3.4. Viscoelasticity 82
3.5. Folding Stability 85
Chapter 3. Results and Discussion 89
1. Driving the Catalytic Cycle by Typical Monomer for General PSA 90
1.1. Strategy 90
1.2. Preparation of Visible-Light-Curable Acrylic PSAs 91
1.3. Characterization of Visible-Light-Curable Acrylic PSAs 103
1.4. Conclusions 116
2. Driving the Catalytic Cycle by Additives for OCA 117
2.1. Strategy 117
2.2. Preparation of Visible-Light-Curable Acrylic OCAs 121
2.3. Characterization of Visible-Light-Curable Acrylic OCAs 132
2.4. Conclusions 142
3. Optimization of the Catalytic Cycle with Various Photocatalysts and Additives for UV-blocking OCA 143
3.1. Strategy 143
3.2. Preparation of Visible-Light-Curable Acrylic OCAs 151
3.3. Characterization of Visible-Light-Curable Acrylic OCAs 165
3.4. Preparation and Characterization of UV-blocking OCAs 186
3.5. Conclusions 196
Chapter 4. Conclusions 197
1. Conclusions 198
1.1. Driving the Catalytic Cycle by Typical Monomer for General PSA 198
1.2. Driving the Catalytic Cycle by Additives for OCA 199
1.3. Optimization of the Catalytic Cycle with Various Photocatalysts and Additives for UV-blocking OCA 200
References 201
List of Publications 215
초록 216
Table 3-1. Results of the bulk polymerization (Back, et al., 2020). The total conversion of bulk polymerization (αt) was characterized by ¹H-NMR (see...[이미지참조] 94
Table 3-2. Reproducibility test results of Table 3-1. 95
Table 3-3. Bulk polymerization results in different monomer compositions (Back, et al., 2020). The total conversion of bulk polymerization (αt) was...[이미지참조] 104
Table 3-4. Reproducibility test results of Table 3-3. 105
Table 3-5. Lap shear strength, elongation at break, peel strength, loop tack, gel fraction, and film conversion of various PSAs (entries 1-6 in Table 3-3). The irradiation time of blue LED for film curing was set as 60 min for all PSAs. 113
Table 3-6. Lap shear strength, elongation at break, peel strength, and loop tack of various PSAs (entries 2, 4, 5, 6, and 7 in Table 3-1). The irradiation time of... 114
Table 3-7. Bulk polymerization results (Back, et al., 2021). Mole ratio ([M]) was set as follows; [BA]:[IBOA]:[HBA]=80:10:10. Ð means dispersity. 122
Table 3-8. Reproducibility results of Table 3-7. 123
Table 3-9. Bulk polymerization results in different content of 4DP-IPN and DBM (Back, et al., 2021). Mole ratio ([M]) was set as follows;... 125
Table 3-10. Reproducibility results of Table 3-9. 126
Table 3-11. References for PSAs/OCAs for flexible/stretchable displays. 147
Table 3-12. Peel strength of the prepared PSAs with different monomer compositions. 150
Table 3-13. Bulk polymerization results of negative control experiments. 152
Table 3-14. Bulk polymerization results with various photocatalysts and reductants (Back, et al., 2022). Irradiation time was set as 30 s. 153
Table 3-15. Reproducibility results of Table 3-14 (entries 1~8). 154
Table 3-16. Reproducibility results of Table 3-14 (entries 9~16). 155
Table 3-17. Bulk polymerization results in different DMAEAc content (Back, et al., 2022). 4Cz-IPN content and irradiation time were set as 10 ppm and 30... 157
Table 3-18. Bulk polymerization results in different 4Cz-IPN content (Back, et al., 2022). DMAEAc content and irradiation time were set as 0.5 mol% and 30... 157
Table 3-19. Bulk polymerization results in different visible-light-active photocatalyst-based systems (Back, et al., 2022). The contents of photocatalyst... 160
Table 3-20. Conversion and gel contents as a function of irradiation time (Back, et al., 2022). The contents of 4Cz-IPN and DMAEA were set as 10 ppm and... 161
Table 3-21. Bulk polymerization and gel content results in different monomer/hybrid reductant compositions (Back, et al., 2022). The film curing... 168
Table 3-22. Peel strength of the prepared OCAs with different hybrid reductant compositions. 171
Table 3-23. Viscoelastic properties of the prepared OCAs with different monomer/hybrid reductant compositions. 176
Table 3-24. Strain recovery and stress relaxation of the prepared OCAs with different monomer/hybrid reductant compositions. 178
Table 3-25. Physical properties and adhesive performances of the prepared UV-blocking OCAs (Back, et al., 2022). 0.3 phr of UV absorber 1 and 1 phr of UV... 190
Table 3-26. Viscoelastic properties of the prepared UV-blocking OCAs (Back, et al., 2022). Detailed conditions for preparing UV-blocking OCAs were the... 191
Table 3-27. Strain recovery and stress relaxation of the prepared UV-blocking OCAs (Back, et al., 2022). Detailed conditions for preparing UV-blocking... 192
Figure 1-1. Classification of monomers used for acrylic PSAs. 25
Figure 1-2. Radical polymerization of acrylate monomers. 28
Figure 1-3. Example of the mobile display structure: expected structure of "Galaxy Z Fold3". 30
Figure 1-4. Radical generation mechanism of PI. 31
Figure 1-5. Examples of visible light-active or UV-active PI. 33
Figure 1-6. Various PIs for light curable acrylic PSAs. 35
Figure 1-7. Examples of visible light-curable PSA in medical tapes. 36
Figure 1-8. Light switchable PSA using visible light active PI. 36
Figure 1-9. Example of generating reactive species using camphorquinone. 37
Figure 1-10. Oxidative quenching cycle and reductive quenching cycle of photocatalyst. PC, EA, and ED mean photocatalyst, electron acceptor, and... 39
Figure 1-11. Photophysical processes and ground state/excited state redox potentials of photocatalyst. 41
Figure 1-12. Common organic photocatalysts. 43
Figure 1-13. Strategies to reduce oxygen inhibition in photopolymerization. 45
Figure 1-14. Eosin Y-mediated photopolymerization mechanism. 47
Figure 1-15. a) Photo-induced FRP for 3D printing using various photocatalyst; b) electron acceptor (A), electron donor (D), and c) opaquing agent (OA). d)... 49
Figure 1-16. a) Strategy to reduce oxygen inhibition in light-driven 3D printing. Proposed mechanism for oxygen tolerance induced by b) thiol and c) reductive... 51
Figure 1-17. a) Schematic illustration of the crosslinked polymer network induced by FRP and RAFT. b) Various RAFT agents used for tests. c)... 53
Figure 1-18. Advantages of visible light curing: polymerization under UV-blocked conditions. 54
Figure 1-19. The schematic illustration of battery cell assembly uses visible light-curable adhesive. 55
Figure 1-20. The device structure of foldable smartphones with a conventional display (left) and an advanced display (right). 57
Figure 1-21. Schematic illustration of research objectives. 60
Figure 1-22. Driving catalytic cycle by typical monomers. 61
Figure 1-23. Driving catalytic cycle by additives. 62
Figure 1-24. Optimization of the catalytic cycle with various photocatalysts/additives and preparation of UV-blocking OCA for foldable displays. 64
Figure 2-1. Various visible-light-active photocatalysts we used. 66
Figure 2-2. Various acrylic monomers and N-vinyl-based monomers we used. 67
Figure 2-3. ¹H NMR result of UV absorber 1 (DMSO-d6).[이미지참조] 69
Figure 2-4. Example of the PSA manufacturing process using visible-light-active photocatalyst-mediated photopolymerization: Bulk polymerization (left)... 70
Figure 2-5. ¹H-NMR result of monomers we used (a-e). 73
Figure 2-6. Example of ¹H-NMR: a) before and b) after bulk polymerization. 74
Figure 2-7. Example of evaluating film curing conversion by FT-IR. 76
Figure 2-8. Schematic illustration for 180˚ peel test. 78
Figure 2-9. Schematic illustration for loop tack test. 79
Figure 2-10. Schematic illustration for lap shear test. 80
Figure 2-11. Picture of holding test. 81
Figure 2-12. The viscoelastic window of PSAs. 82
Figure 2-13. The shear sandwich clamp of DMA. 83
Figure 2-14. Examples of a) strain recovery curve and b) stress relaxation curve. 84
Figure 2-15. Structure of a) actual foldable display and b) test specimen we used. 86
Figure 2-16. a) Outside and b) inside view of the equipment for the dynamic folding test. c) Scheme for the in-fold test procedure. d) Pictures of the folding... 87
Figure 2-17. a) Schematic illustration for the dynamic folding test. b) Quantitative evaluation of the folding stability by the change in surface texture... 88
Figure 3-1. Procedure for preparing visible-light-curable acrylic PSAs using photocatalyst and N-vinyl-based monomer. 92
Figure 3-2. Proposed mechanism for initiation via NVP and 4DP-IPN. 96
Figure 3-3. a) Molecular orbital diagram of photocatalyst (4DP-IPN) and monomer (NVP and MA). b) Chemical structures of monomer (NVP and MA).... 98
Figure 3-4. UV/Vis spectra of the monomer solution (before and after bulk polymerization. 99
Figure 3-5. Conversion of film curing as a function of irradiation time for different NVP content (entries 2 and 4-7 in Table 3-1). 100
Figure 3-6. Conversion of film curing as a function of irradiation time for different 4DP-IPN content (entries 5, 10, and 11 in Table 3-1). 101
Figure 3-7. a) Schematic illustration for the film curing using UV-active PI (Irgacure 184). Conversion of the film curing using b) low-intensity UV light... 102
Figure 3-8. Examples of heat flow curves obtained by differential scanning calorimetry (Back, et al., 2020). Test conditions; sample (entries 1, 4, and 6 in... 106
Figure 3-9. a) Frequency-storage modulus curve and b) viscoelastic window of various PSAs (entries 1-6 in Table 3-3). c) Frequency-storage modulus curve... 108
Figure 3-10. a) Strain-stress curve of lap shear test, b) extension-force curve from 180˚ peel test (substrate: stainless steel), and c) extension-force curve... 110
Figure 3-11. a) Strain-stress curve of lap shear test, b) extension-force curve of 180˚ peel test, and c) extension-force curve of loop tack test of PSAs with... 112
Figure 3-12. Picture of the prepared PSAs using 50 ppm of 4DP-IPN. 115
Figure 3-13. a) The mechanism for photocatalyst-mediated ATRP initiated by DBM (Singh, et al., 2018). b) Procedure for manufacturing visible-light-... 118
Figure 3-14. Chemical structures and experimental/compunational redox potentials of the 4DP-IPN and α-haloesters (DBM, EBiB, and EBP). 120
Figure 3-15. Evaluation of remaining DBM after bulk polymerization using gas chromatography (Back, et al., 2021). The content of DBM was set as 0.1 mol%. 127
Figure 3-16. UV/Vis spectra of the monomer mixture with 2 ppm of 4DP-IPN and 0.1 mol% of DBM (before/after bulk polymerization). 128
Figure 3-17. Characterization of the pre-polymer obtained by bulk polymerization (entry 6 in Table 3-7); a) ¹H-NMR result and b) differential... 129
Figure 3-18. Conversion of the film curing as a function of irradiation time: a) 4-DP-IPN was set as 50 ppm, and b) DBM was set as 0.1 mol%. 131
Figure 3-19. The gel content of the prepared PSAs with different a) DBM and b) 4DP-IPN content. The curing time was fixed as 30 min. 133
Figure 3-20. a) Mp (molecular weight at the peak of the curve) obtained from SEC curve and b) remaining DBM obtained from gas chromatography.[이미지참조] 134
Figure 3-21. a) Structure of the test specimens for evaluating transparency and pictures of the specimens. b) UV/Vis spectra of the prepared PSAs with... 136
Figure 3-22. UV/Vis spectra of traditional UV-curable acrylic PSA. 137
Figure 3-23. Example strain-stress curve for the single lap shear test and the obtained lap shear strength of the prepared PSA. 138
Figure 3-24. Peel strength, loop tack, and holding time of the prepared PSAs with different a) DBM content (4DP-IPN: 50 ppm) and b) 4DP-IPN content... 140
Figure 3-25. Chemical structures of photocatalysts and sacrificial reductants with different HOMO levels. 145
Figure 3-26. Illustration for the hybrid reductant using DMAEAc and DMAEA. 149
Figure 3-27. Photographs of monomer mixtures with 10 ppm of photocatalyst. 156
Figure 3-28. The proposed mechanism for visible-light-photocatalyst-based polymerization uses sacrificial reductants. 159
Figure 3-29. Film curing conversion with a) different DMAEAc contents and b) reductant types. The content of 4Cz-IPN was fixed as 10 ppm. 163
Figure 3-30. Film curing conversion with different 4Cz-IPN content. The content DMAEAc was fixed as 0.5 mol%. 164
Figure 3-31. a) UV/Vis spectra of the prepared visible-light-curable OCA. b) photographs of the pre-polymer (left) and the cured OCA (right). The content... 166
Figure 3-32. Proposed mechanism for crosslinking by a) HBA and b) DMAEA or DMAEMA. 169
Figure 3-33. Peel strength of the prepared OCA (black, entry 3 in Table 3-22) and commercial foldable OCA (green, entry 7 in Table 3-22) as a function of... 172
Figure 3-34. a) Schematic illustration for evaluating the peel strength of the curing-type adhesive. b) UV/Vis spectra of PETf and CPI film. c) Peel strength...[이미지참조] 174
Figure 3-35. Temperature sweep test results: before/after light exposure (irradiating light for 14 days by a typical display). 179
Figure 3-36. Dynamic folding test results (entry 5 in Table 3-24). 181
Figure 3-37. Dynamic folding test results (entry 6 in Table 3-24). 182
Figure 3-38. Dynamic folding test results (entry 7 in Table 3-24). 183
Figure 3-39. Dynamic folding test results (entry 8 in Table 3-24). 184
Figure 3-40. Dynamic folding test results (entry 9 in Table 3-24). 185
Figure 3-41. UV/Vis spectra of the UV absorbers we used. 187
Figure 3-42. UV/Vis spectra of the cured UV-blocking OCAs incorporating a) one UV absorber and b) two UV absorbers (Back, et al., 2022). The monomer,... 188
Figure 3-43. Conversion of the film curing using different light sources (Back, et al., 2022). The monomer, reductant, and photocatalyst content were the same... 189
Figure 3-44. Dynamic folding test results (entry 1 in Table 3-27). 194
Figure 3-45. Dynamic folding test results (entry 2 in Table 3-27). 195