High Thermally Stable Anthracene-Based Polyimides with Low Dielectric Constants and Dissipation Factors

At present, high-performance polymers with low dielectric constants (D_k) and low dissipation factors (D_f) have gained much attention with the rapid evolution of microelectronic and 5G communication technologies. Due to their excellent thermal stabilities, heat resistances, mechanical strengths, and dielectric properties, polyimides (PIs) have attracted a lot of attention. Herein, a series of anthracene (An)-based PIs are synthesized from an ester-functionalized anthracene diamine (An-NH₂) monomer and four kinds of commercial dianhydrides such as keto (3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA)), sulfone (3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride (DSDA)), fluoro (4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)), and ether (4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) and 4,4-oxydiphthalic anhydride (ODPA)) functional groups by a two-step process, i.e., the chemical polyaddition followed by thermal imidization. The resulting An-NH₂/BTDA, An-NH₂/DSDA, An-NH₂/6FDA, An-NH₂/BPADA, and An-NH₂/ODPA PIs are denoted as AnBT-PI, AnDS-PI, An6F-PI, AnBPA-PI, and AnOD-PI, respectively. As a result, all An-based PI films display excellent thermal properties, with thermal decomposition temperatures of 450-530 °C (T_d5% weight loss) and glass transition temperatures (T_g) of 270-410 °C. In addition, these PI films exhibit decent optical transparency, flexibility, coefficient of thermal expansion (CTE), and mechanical properties. Remarkably, all An-based PI films show excellent dielectric properties with a low D_k of 2.540-3.388 and a D_f of 0.0059-0.0240 at high frequency (10 GHz). In particular, the An-based PI films with ether linkages (AnOD-PI and AnBPA-PI) and a high fluorine content (An6F-PI) show low D_k and D_f values compared with those with keto (AnBT-PI) and sulfone (AnDS-PI) linkages. These results indicate that the An-based PIs are promising candidates for achieving low D_k and D_f values at higher frequencies.