Tröger’s Base (TB)-Based Polyimides as Promising Heat-Insulating and Low‑K Dielectric Materials

The correlations between the molecular structures of four Tröger’s base (TB)-based polyimides (PIs) and two non-TB containing analogues and physical properties including thermal conductivity (λ) and dielectric properties both at low and high frequencies were investigated in detail. The TB-based PI films exhibited low dielectric constants (D_k = 2.25–2.80) at 10 GHz. They possessed much lower λ values (0.035–0.145 W/mK) compared to the commercial PI Kapton (0.240 W/mK). The influences of incorporating TB units into chain backbones on aggregation structures and physical properties of PIs were identified. Incorporating TB units into chain backbones effectively reduced the degree of chain orientation and increased fractional free volume, leading to both low D_k and low λ values for the resulting PI films. Also, introducing TB units enhanced molecular weights, toughness, and glass-transition temperature (T_g) of the resulting PIs. Therefore, the TB-based PIs can be promising heat-insulating and low-k dielectric materials.