Polyimides have attracted increasing attention due to
being promising
candidate materials for flexible display substrates. However, to meet
the rigorous demands of thin-film transistor processing, the heat
resistance and dimensional stability of polyimides need to be further
improved. In this work, we designed a series of terphenyl diamines
with small side methyl groups. This rodlike linear molecular terphenyl
structure provides the self-orientation ability to achieve the purpose
of reducing the coefficient of thermal expansion (CTE), while the
methyl group restricts the molecular chain rotation, thus further
increasing the glass-transition temperature (T
g) of the polyimides. The terphenyl diamines with different
quantities of methyl groups were polymerized with commercial 3,3′,4,4′-biphenyltetracarboxylic
dianhydride (BPDA) and pyromellitic dianhydride (PMDA), and the obtained
polyimides showed outstanding performance, with high T
gs ranging from 399 to 439 °C, remarkable thermal
decomposition temperature at a 5% weight loss (T
d5) exceeding 500 °C, and extremely low CTEs ranging from
−0.76 to 11.92 ppm·K–1. The regulation
of the methyl groups on the performance of polyimides was investigated
and explained by the analysis of their condensed structures and theoretical
simulation. This strategy provides an approach for preparing polyimides
with excellent comprehensive performance.