Superheat-resistant polymers with low coefficients of thermal expansion

Abstract

Here, we report superheat-resistant polymers, poly(benzoxazole imide)s (PBOI), with very low coefficients of thermal expansion (CTE) and sufficient ductility for applications as the plastic substrates of organic light-emitting diode (OLED) displays. Diamines incorporating benzoxazole (BO) units were synthesized for this purpose. A PBOI derived from a BO-containing diamine and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) has excellent properties that are superior to those of s-BPDA/p-phenylenediamine (p-PDA) polyimide such as an undetectable Tg, a very low CTE (9.6 ppm K−1), a very high the 5% weight loss temperature (Td5 = 592 °C) in N2, and good ductility while remaining the highest level of non-flammability (UL-94, V-0). The use of another BO-incorporating diamine permitted further improvement in the target properties: an extremely high Td5 (609 °C) in N2 and a considerably low CTE (3.3 ppm K−1) close to that of a silicon wafer. These results show that the PBOIs examined in this work are promising candidates for use as the plastic substrates in OLED displays.