Ultra‐highT_gand ultra‐low coefficient of thermal expansion polyimide films based on hydrogen bond interaction

Abstract

To tolerate high processing temperature during the fabrication of low-temperature polycrystalline silicon thin-film transistors (LTPS-TFT) in flexible OLED devices, the polyimide (PI) films, which are used as substrate, should have ultra-high glass transition temperature (T g > 450 C) and ultra-low coefficient of thermal expansion (CTE at 0-5 ppm K À1 ). In this paper, two novel heterocyclic monomers, namely, N,N'-(xanthone-2,7-diyl)bis(4-aminobenzamide) (p-DAXBA) and N,N'-(xanthone-2,7-diyl)bis(3-aminobenzamide) (m-DAXBA), which contain a xanthone moiety, are prepared and polycondensed with pyromellitic dianhydride (PMDA), respectively. PI films (PIa and PIb) with intrinsic high T g and low CTE are designed from the perspective of rigid conjugate xanthone structure and hydrogen bonding interaction. It is found that the PIa films prepared by p-DAXBA have better linear structure of molecular chains and show relatively higher T g and lower CTE. The T g of PIa-40 is greater than 450 C, and CTE can reach as low as 2.7 ppm K À1 , tensile strength of 179 MPa, modulus of 5.67 GPa, indicating potential application prospect as a flexible OLED substrate.

Comprehensive Performance of Polyimide Reinforced by Multiple Hydrogen Bonds for Flexible Electronics Application

“…Intermolecular interaction can be tested by DMA by determining the tan δ value, which reflects the energy loss during motion of the polymeric chain; the larger the tan δ value, the greater the internal friction of the polymeric chain or segments, restricting their movement . In Figure b, it can be seen that the peak of tan δ increased with increasing amount of DAPyBA, which indicated that the co-polymerization of DAPyBA effectively increased intermolecular interactions due to the presence of inter-HBs. , Therefore, we conclude that multiple inter-HBs in co-PIs arising from DAPyBA units increase the interaction between molecules, resulting in closer molecular packing. The smaller chain spacing means that a greater force is required for slippage between molecular chains, such that the tensile strength and initial modulus of the PI are significantly enhanced.…”

“…The results show that the co-PI films had good thermal decomposition stability, meeting the needs of the vast majority of applications. However, compared with Kapton PI, co-PIs have slightly lower T d values due to the presence of relatively unstable amide groups containing single bonds. , In order to further understand the thermogravimetric process of PI films, the first-order derivative of the thermal weight loss curve was performed to obtain the thermal weight loss rate curve (DTG), as shown in Figure b. PI-0 had only one thermal weight loss peak, which was located roughly at 550–650 °C.…”

Biaxially curved ultra-thin, light ambient dimming LC films for AR headsets

“…It is generally straightforward to wrap films such as flexible LC cells around uniaxially curved surfaces because no stretching is required. However, in order to take an initially planar flexible LC optical film and wrap it around a biaxially curved surface it must be stretched [1,2]. This paper reports on how TAC-film based active LC optics can be biaxially curved around surfaces while also enabling ambient dimming.…”

High glass transition temperature and ultra‐low thermal expansion coefficient polyimide films containing rigid pyridine and bisbenzoxazole units

“…They found that films obtained through polymerization of diamine DAR-4AB containing benzobisoxazazole and rigid dianhydride 2,3,6,7-naphthalenetetracarboxylic dianhydride exhibited excellent thermal properties, including a CTE of 3.3 ppm K À1 and 5% weight-loss temperature (T d5% ) exceeding 600 C. The authors attributed this result to diamine DAR-4AB improving linearity and stiffness of molecule. Jiao et al [37][38][39] prepared a range of PI films with stiff xanthone, T g and CTE of best result were >450 C and 2.7 ppm K À1 , respectively. Yang et al 40 prepared diamines 2,5-bis(4-aminophenyl)pyridine (PRD) and 2,5-bis(4-aminophenyl)pyrimidine (PRM) containing pyridine and pyrimidine structures.…”