High-Performance Polyimides with High Tg and Excellent Dimensional Stability at High Temperature Prepared via a Cooperative Action of Hydrogen-Bond Interaction and Cross-Linking Reaction

Although the development of flexible display technology urgently needs the high-performance polyimides (PIs) with high glass transition temperature (Tg) and low coefficient of thermal expansion (CTE) at high temperature (up to 400 °C), rare satisfactory materials are reported. Here, we report a new way to greatly enhance the dimensional stability of PIs at high temperature via a cooperative action of hydrogen-bond interaction and cross-linking reaction between molecular chains. First, a novel aromatic diamine monomer (called BCTA) was designed and synthesized, which contained H-bond donor units and a thermally cross-linkable benzocyclobutene (BCB) group. This monomer was used as a comonomer to synthesize high-performance PIs, which included other diamine monomers (called PABA and AAPA) containing H-bond donor units and a mixture of commercial dianhydrides (called BPDA and PMDA). Second, two types of new PIs with/without diamines BCTA were synthesized. The results indicated that a PI displayed a CTE of 6.0 ppm/°C by varying the temperature from 30 to 400 °C when the molar ratio of BCTA/PABA/BPDA/PMDA was 0.1:0.9:0.85:0.15, whereas the CTE values was −1.9 ppm/°C for other kind of PI with the molar ratio of BCTA/AAPA/BPDA/PMDA of 0.1:0.9:0.85:0.15. Moreover, the two new PIs also exhibited Tg of more than 400 °C. These thermal properties are better than those of conventional PIs as well as PIs without BCTA comonomer. Moreover, the two PIs having BCTA comonomer exhibited tensile strengths of 178 and 197 MPa as well as tensile moduli of 10.2 and 11.1 GPa. Such excellent dimensional stability and good mechanical properties indicate that the new PIs are desirable for the fabrication of flexible substrates in the panel display industry. This study also suggests that a cooperative interaction of a hydrogen bond and cross-linking can effectively improve the thermostability of PIs at high temperature.