Ultra-high Tg and ultra-low CTE polyimide films based on tunable interchain crosslinking

A novel interchain crosslinking system was designed to improve the thermal performance of PI films. A diamine containing Cl atom (Cl-DAXBA) was prepared and polycondensed with pyromellitic dianhydride and 3,3′,4,4′-biphenyl tetracarboxylic dianhydride, respectively. Two series of PI films (PM and BP) were prepared under different curing temperatures in the range of 320–380 °C. The crosslinking of free radicals produced by Cl-DAXBA decomposition occurred between the molecular chains, and the crosslinking degree increased with raising the curing temperature. The network structure formed by crosslinking effectively inhibited the movement of molecular chains and promoted their close packing. The glass transition temperature (Tg) of PM films increased from 378 °C to >450 °C, and the coefficient of thermal expansion (CTE) decreased from 66.3 ppm·K−1 to 4.9 ppm·K−1. The Tg of BP films increased from 349 °C to >450 °C, and the CTE decreased from 50.4 ppm·K−1 to 17.7 ppm·K−1. Definitely, the tunable interchain crosslinking provides an effective strategy to improve both Tg and CTE simultaneously. © 2022