KES1-0331
Synthesis of high-performance polymers for transparent and flexible displays: colorless poly(amide-imide)s with high glass transition temperature and low coefficient of thermal expansion
Topic
S1. Polymer Synthesis
When and Where
Sep 29, 2026
17:05 - 17:30
Room 101
Session Chairs
Chang-Geun CHAE
Presenter(s)
Sang Youl Kim (KAIST)
Co-Author(s)
Abstract
Among high-performance polymers with high thermal and mechanical properties, polyimides (PI) exhibit a high glass transition temperature and low thermal expansion behavior. However, the highly aromatic and rigid nature of polyimide chains tends to form charge-transfer (CT) complexes, resulting in a yellowish-to-brown color. Removing this color to make PIs transparent without deteriorating their thermal properties remains very challenging. To overcome color and transparency issues in polyimides, various structural modifications have been explored, including incorporating flexible or unsymmetric linkages into the main chain and introducing noncoplanar or alicyclic units. However, many structural modifications in aromatic polyimides exhibit a trade-off between transparency and thermal properties. Poly(amide-imide)s (PAIs), a class of copolyimides, exhibit high thermal stability, good mechanical properties, and good processability. Hydrogen bonds between PAI chains enhance both thermal properties and processability without compromising the thermal characteristics of polyimides. PAIs offer advantages for structural modification through more versatile synthetic pathways. Leveraging these characteristics to achieve high transparency and low coefficient of thermal expansion (CTE), we synthesized aromatic poly(amide-imide)s with a biphenylene backbone bearing sterically bulky trifluoromethyl groups that could form a complex hydrogen-bonding network in two distinct directions. This approach yielded polymers with approximately 90% transparency and CTE values as low as 4 ppm/°C. We found that by controlling the fraction of asymmetrically positioned trifluoromethyl groups in the polymer backbone, the CTE could be precisely adjusted in the range of 4-20 ppm/°C without sacrificing high transparency. The glass transition temperature of aromatic poly(amide-imide)s was further improved to over 400 °C by introducing a multicyclic structure.
