液晶高分子(Liquid crystal polymer，LCP)是一種具有廣泛應用性的材料，近年來，由於LCP薄膜具有低介電常數、低介電損失、高尺寸的穩定性、低吸濕性、不易燃燒、熱塑性及可回收等諸多優點，因而被廣泛應用於5G科技，LCP也成為應用於軟板製程中最重要的材料。LCP表現出複雜的微觀結構，包括無序型、液晶態和結晶態，他們的比例很大程度的影響高分子的性能。LCP薄膜中形成的結構受其加工條件和後熱處理的強烈影響；因此，建立LCP薄膜的製程、結構、性質的關係是其應用的重要基礎。本研究以LCP為材料，透過熱壓成膜及溶液塗佈兩種製程方法，搭配不同溶液結構及後熱處理方式來探索LCP薄膜在不同製程下，對結構與性質的影響。
研究第一部分為探索LCP薄膜在歷經不同熱處理程序上對微結構(microstructure)與性質上之影響效應，實驗中證實透過250℃以上的熱處理製程可有效使LCP薄膜內產生晶體相轉化，從動力學主導之六方晶系(hexagonal)轉變成熱力學穩定的斜方晶系(orthorhombic)，這種晶體結構轉變及以及結晶度的提高，能有效提升 LCP 薄膜的耐熱性(熔點可顯著提升約40℃) 以及薄膜的力學性能，同時降低了薄膜的熱膨脹係數，有利用LCP薄膜的應用。然而，熔融加工的薄膜具有較高的晶體取向性，這可能導致橫向機械強度較弱，不利於應用。
本研究的第二部分為探討由溶液製程所製作之LCP薄膜，使用（N-甲基吡咯烷酮）（NMP）作為溶劑，LCP溶解在NMP中沒有達到分子水平的均勻分散；相反，棒狀分子聚集（藉由氫鍵）形成微相分離的區域(microdomain)，由microdomain連接的聚合物鏈形成大小為 m的碎形結構聚集。進一步發現溶液結構受濃度、溶解溫度和老化時間的影響，溶液在室溫下長時間老化導致形成更多microdomain，這些microdomain可作為促進薄膜結晶的晶核。因此，由老化溶液塗佈的薄膜顯示出更高的結晶度和更好的晶體取向，由溶液製程的 LCP 薄膜含有較多的斜方晶體，在 250℃以上的熱退火後，這種晶體形式在薄膜中占主導地位。最後，與熔融加工薄膜相比，溶液製程薄膜顯示出較差的晶體取向和更高的結晶度，這些特徵能更突出了LCP 薄膜溶液製程的優勢。本研究已對熔融製程與溶液製程製作之LCP膜建立重要的基礎資訊，期盼對於未來更進一步解析LCP膜的性質之研發與應用將有所助益。

Liquid crystalline polymer (LCP) has been drawing considerable attention in recent years due to its wide range of applications and the need of manufacturing flexible circuit boards for the application in 5G era. LCP films have the advantages of low dielectric constant, low dielectric loss, high dimensional stability, low moisture absorption and flame retardance. LCP exhibits complex states of microstructure covering amorphous, mesomorphic and crystalline order, whose proportions strongly govern the properties of the polymer. The structure developed in the LCP film is strongly influenced by its processing condition and post-thermal treatment; consequently, establishing the processing−structure−property relationships of LCP film is an important fundamental task for its application.
This thesis investigates the structures and properties of the LCP films prepared using melt compression molding and solution casting followed by a post heat treatment. The as-prepared film was found to compose of crystallites characterized by hexagonal unit cell. The kinetically favored hexagonal phase converted into the thermodynamically stable orthorhombic phase upon thermal annealing above 250 oC. This crystal structure transformation along with the enhancement of crystallinity increased the mechanical properties and crystal melting temperature, while lowering the thermal expansivity of of the film, which are beneficial for application of the LCP films. However, the melt-processed films possessed relatively high in-plane crystal orientation, which may cause weak mechanical strength in the transverse direction, which was undesirable for application.
The structural formation mechanism and the controlling parameters became much more complex for the solution-cast film using (N-methyl-2-pyrrolidone) (NMP) as the solvent. LCP dissolved in NMP did not reach uniform dispersion at molecular level; instead, the rodlike molecules aggregated (via hydrogen bonding) to form microdomains, and the polymer chain bridged by the microdomains formed large fractal aggregates with m in size. The solution structure was further found to be influenced by concentration, dissolution temperature and aging time. Prolonged aging at room temperature led to the formation of more microdomains which could serve as the nuclei for promoting the crystallization in the cast-film. Therefore, the film cast from the aged film showed higher crystallinity and better in-plane crystal orientation. The LCP film cast from the solution contained higher amount of orthorhombic crystals and this crystal form became dominant in the film after thermal annealing above 250 oC. Finally, the solution-cast film was revealed to display poor in-plane crystal orientation and higher crystallinity compared to the melt-processed film. These features along with the easier processing highlight the advantages of solution processes for fabricating LCP films.
 

1. Steven Liu, C., PhD LCP antenna growth to explode. 19 March 2018.
2. HOSODA, T., et al., Newly Developed LCP Film Fabricated by Solvent-Casting Method. 2005.
3. Kaito, A., M. Kyotani, and K. Nakayama, Effects of annealing on the structure formation in a thermotropic liquid crystalline copolyester. Macromolecules, 1990. 23(4): p. 1035-1040.
4. Flores, A., et al., Reversible changes in the solid state of HBA/HNA liquid crystalline copolyesters studied by X-ray diffraction. Polymer, 1993. 34(14): p. 2915-2920.
5. Wilson, D.J., C. Vonk, and A. Windle, Diffraction measurements of crystalline morphology in a thermotropic random copolymer. Polymer, 1993. 34(2): p. 227-237.
6. Langelaan, H. and A.P. de Boer, Crystallization of thermotropic liquid crystalline HBA/HNA copolymers. Polymer, 1996. 37(25): p. 5667-5680.
7. Bharadwaj, R.K. and R.H. Boyd, Molecular dynamics simulation of the nematic melt of a p-hydroxybenzoic acid/2-hydroxy-6-naphthoic acid liquid crystalline copolyester. Macromolecules, 1998. 31(22): p. 7682-7690.
8. Cheng, S.Z., et al., Kinetics of mesophase transitions of thermotropic copolyesters. 2. Two transition processes. Macromolecules, 1989. 22(11): p. 4240-4246.
9. Ahmed, D., et al., Microstructural developments of poly (p-phenylene terephthalamide) fibers during heat treatment process: a review. Materials Research, 2014. 17(5): p. 1180-1200.
10. An, L., et al., Effect of thermal annealing on the microstructure of P3HT thin film investigated by RAIR spectroscopy. Vibrational Spectroscopy, 2013. 68: p. 40-44.
11. Salammal Shabi, T., et al., Enhancement in crystallinity of poly (3‐hexylthiophene) thin films prepared by low‐temperature drop casting. Journal of applied polymer science, 2012. 125(3): p. 2335-2341.
12. Lieser, G., Polymer single crystals of poly (4‐hydroxybenzoate). II. A contribution to crystal structure and polymorphism. Journal of Polymer Science: Polymer Physics Edition, 1983. 21(9): p. 1611-1633.
13. Lin, Y. and H. Winter, High-temperature recrystallization and rheology of a thermotropic liquid crystalline polymer. Macromolecules, 1991. 24(10): p. 2877-2882.
14. Biswas, A. and J. Blackwell, X-ray diffraction from liquid-crystalline copolyesters: matrix methods for intensity calculations using a one-dimensional paracrystalline model. Macromolecules, 1987. 20(12): p. 2997-3002.
15. Hanna, S., et al., Dimensions of crystallites in a thermotropic random copolyester. Polymer, 1992. 33(1): p. 3-10.
16. Reyes‐Mayer, A., et al., Nanostructure reorganization in a thermotropic copolyester. A simultaneous WAXS and SAXS study. Polymers for Advanced Technologies, 2016. 27(6): p. 748-758.
17. Hanna, S., A. Romo-Uribe, and A. Windle, Sequence segregation in molten liquid-crystalline random copolymers. Nature, 1993. 366(6455): p. 546-549.
18. Harada, M., et al., In-situ analysis of the structural formation process of liquid–crystalline epoxy thermosets by simultaneous SAXS/WAXS measurements using synchrotron radiation. Polymer journal, 2013. 45(1): p. 43-49.
19. Haraguchi, K., T. Kajiyama, and M. Takayanagi, Uniplanar orientation of poly (p‐phenylene terephthalamide) crystal in thin film and its effect on mechanical properties. Journal of Applied Polymer Science, 1979. 23(3): p. 903-914.
20. Sirringhaus, H., et al., Two-dimensional charge transport in self-organized, high-mobility conjugated polymers. Nature, 1999. 401(6754): p. 685-688.
21. Rivnay, J., et al., Drastic control of texture in a high performance n-type polymeric semiconductor and implications for charge transport. Macromolecules, 2011. 44(13): p. 5246-5255.
22. Butzbach, G., J. Wendorff, and H. Zimmermann, Structure and structure formation of a main chain thermotropic polymer. Polymer, 1986. 27(9): p. 1337-1344.
23. Lin, Y. and H. Winter, Formation of high melting crystal in a thermotropic aromatic copolyester. Macromolecules, 1988. 21(8): p. 2439-2443.
24. Murthy, N., et al., Structure of the amorphous phase in oriented polymers. Macromolecules, 1993. 26(7): p. 1712-1721.
25. Itoyama, K., Melt spinning of thermotropic liquid‐crystal polyesters to form ultrahigh‐modulus filaments. Journal of Polymer Science Part B: Polymer Physics, 1988. 26(9): p. 1845-1863.
26. Jones, R.A.L., et al., Soft condensed matter. Vol. 6. 2002: Oxford University Press.
27. Roe, R.-J., Methods of X-ray and neutron scattering in polymer science. 2000: Oxford University Press on Demand.
28. Higgins, J.S. and H.C. Benoit, Polymers and neutron scattering. 1994.
29. Zemb, T. and P. Lindner, Neutrons, X-rays and light: scattering methods applied to soft condensed matter. 2002: North-Holland.
30. Li, Y.-C., et al., Fractal aggregates of conjugated polymer in solution state. Langmuir, 2006. 22(26): p. 11009-11015.
31. Janasz, L., et al., Improved charge carrier transport in ultrathin poly (3-hexylthiophene) films via solution aggregation. Journal of Materials Chemistry C, 2016. 4(48): p. 11488-11498.
32. Horkay, F. and B. Hammouda, Small-angle neutron scattering from typical synthetic and biopolymer solutions. Colloid and Polymer Science, 2008. 286(6): p. 611-620.
33. Gandhi, K. and M.C. Williams. Solvent effects on the viscosity of moderately concentrated polymer solutions. in Journal of Polymer Science Part C: Polymer Symposia. 1971. Wiley Online Library.
34. Hua, C.C., et al., Viscometric investigation of aggregate formation in dilute conjugated polymer solutions. Journal of Rheology, 2005. 49(3): p. 641-656.
35. Murthy, N., Metastable crystalline phases in nylon 6. Polym Commun, 1991. 32(10): p. 301-305.
36. Panar, M., et al., Morphology of poly (p‐phenylene terephthalamide) fibers. Journal of Polymer Science: Polymer Physics Edition, 1983. 21(10): p. 1955-1969.
37. Dörling, B., et al., Uniaxial macroscopic alignment of conjugated polymer systems by directional crystallization during blade coating. Journal of Materials Chemistry C, 2014. 2(17): p. 3303-3310.
38. Paterson, D.A., et al., New insights into the liquid crystal behaviour of hydrogen-bonded mixtures provided by temperature-dependent FTIR spectroscopy. Liquid Crystals, 2015. 42(5-6): p. 928-939.
39. Kaito, A., M. Kyotani, and K. Nakayama, Effects of draw-down ratio and annealing treatment on structure formation in extruded strands of a thermotropic liquid crystalline copolyester. Journal of Macromolecular Science, Part B: Physics, 1995. 34(1-2): p. 105-118.
40. Yang, H., et al., Molecular Packing and Orientation Transition of Crystalline Poly (2, 5‐dihexyloxy‐p‐phenylene). Macromolecular Chemistry and Physics, 2014. 215(5): p. 405-411.
41. Yeh, I.-C., et al., Molecular dynamics simulation of the effects of layer thickness and chain tilt on tensile deformation mechanisms of semicrystalline polyethylene. Macromolecules, 2017. 50(4): p. 1700-1712.
42. Kjellander, R. and E. Florin, Water structure and changes in thermal stability of the system poly (ethylene oxide)–water. Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases, 1981. 77(9): p. 2053-2077.
43. Wang, C.-C., et al., Thermochromism of a poly (phenylene vinylene): untangling the roles of polymer aggregate and chain conformation. The Journal of Physical Chemistry B, 2009. 113(50): p. 16110-16117.
44. Lin, D.-J., et al., Strong effect of precursor preparation on the morphology of semicrystalline phase inversion poly (vinylidene fluoride) membranes. Journal of membrane science, 2006. 274(1-2): p. 64-72.
45.Persson, N.E., et al., Nucleation, growth, and alignment of poly (3-hexylthiophene) nanofibers for high-performance OFETs. Accounts of chemical research, 2017. 50(4): p. 932-942.
46.Li, Q. and Y.-S. Jun, The apparent activation energy and pre-exponential kinetic factor for heterogeneous calcium carbonate nucleation on quartz. Communications Chemistry, 2018. 1(1): p. 1-9.
47.Zhang, L., et al., Liquid crystal ordering on conjugated polymers film morphology for high performance. Journal of Polymer Science Part B: Polymer Physics, 2019. 57(23): p. 1572-1591.
48.Kobayashi, M., et al., Structural ordering on physical gelation of syndiotactic polystyrene dispersed in chloroform studied by time-resolved measurements of small angle neutron scattering (SANS) and infrared spectroscopy. Macromolecules, 1995. 28(22): p. 7376-7385.
49.Sun, Y.S., et al., WAXD and FTIR spectroscopy studies on phase behavior of syndiotactic polystyrene/1, 1, 2, 2-tetrachloroethane complexes. Polymer, 2003. 44(18): p. 5293-5302.
50.Matsumoto, T., et al., Molecular weight effect on surface and bulk structure of poly (3-hexylthiophene) thin films. Polymer, 2017. 119: p. 76-82.
51.Chu, P.-H., et al., Toward precision control of nanofiber orientation in conjugated polymer thin films: Impact on charge transport. Chemistry of Materials, 2016. 28(24): p. 9099-9109.