Kwon Hyuck-Jin, Hwang Jun, Hong Suk-Min, Lee Chil Won
Department of Chemistry, College of Science and Technology, Dankook University, Cheonan-si 31116, Republic of Korea.
Department of Foundry Engineering, Dankook University, Yongin-si 16890, Republic of Korea.
Polymers (Basel). 2025 Jul 30;17(15):2081. doi: 10.3390/polym17152081.
Transparent polyimides with excellent mechanical properties and high optical transmittance have been widely used in various optical and electrical applications. However, due to the rigidity of their aromatic structure, their flexibility is limited, making them unsuitable for applications requiring different form factors, such as flexible display cover windows. Furthermore, the refractive index of most transparent polyimides is approximately 1.57, which differs from that of the optically clear adhesives (OCAs) and window materials that have values typically around 1.5, resulting in visual distortion. This study employed 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFMB) as the base structure of polyimides (6T). Additionally, 1,3-bis(aminomethyl)cyclohexane (BAC) with a monocyclic structure and bis(aminomethyl)bicyclo[2,2,1]heptane (BBH) with a bicyclic structure were introduced as co-monomers or crosslinking agents to 6T. The mechanical, thermal, and optical properties of the obtained copolymers (6T-BAC and 6T-BBH series) and crosslinked polymers (6T-CL-BAC and 6T-CL-BBH series) were compared. Both the copolymer series (6T-BAC and 6T-BBH) and the crosslinked series (6T-CL-BAC and 6T-CL-BBH) exhibited improved optical properties compared to the conventional 6T, with maximum transmittance exceeding 90% and refractive indices ranging from approximately 1.53 to 1.55. Notably, the copolymer series achieved transmittance levels above 95% and exhibited lower refractive indices (~1.53), demonstrating superior optical performance relative not only to the 6T baseline but also to the crosslinked series. The alicyclic polyimides synthesized in this study exhibited mechanical flexibility, high optical transmittance, and a refractive index approaching 1.5, demonstrating their applicability for use as flexible display cover window materials.
具有优异机械性能和高光学透过率的透明聚酰亚胺已广泛应用于各种光学和电气应用中。然而，由于其芳香结构的刚性，其柔韧性有限，使其不适用于需要不同形状因数的应用，如柔性显示盖板窗口。此外，大多数透明聚酰亚胺的折射率约为1.57，这与光学透明粘合剂（OCA）和窗口材料的折射率不同，后者的值通常约为1.5，从而导致视觉失真。本研究采用4,4'-(六氟异丙基)二苯二甲酸酐（6FDA）和2,2'-双(三氟甲基)联苯胺（TFMB）作为聚酰亚胺（6T）的基础结构。此外，将具有单环结构的1,3-双(氨甲基)环己烷（BAC）和具有双环结构的双(氨甲基)双环[2,2,1]庚烷（BBH）作为共聚单体或交联剂引入到6T中。比较了所得共聚物（6T-BAC和6T-BBH系列）和交联聚合物（6T-CL-BAC和6T-CL-BBH系列）的机械、热和光学性能。与传统的6T相比，共聚物系列（6T-BAC和6T-BBH）和交联系列（6T-CL-BAC和6T-CL-BBH）均表现出改善的光学性能，最大透过率超过90%，折射率范围约为1.53至1.55。值得注意的是，共聚物系列的透过率水平高于95%，且折射率较低（~1.53），不仅相对于6T基线表现出优异的光学性能，而且相对于交联系列也是如此。本研究中合成的脂环族聚酰亚胺表现出机械柔韧性、高光学透过率和接近1.5的折射率，证明了它们作为柔性显示盖板窗口材料的适用性。
