New polyimides containing aliphatic segments and thin films based on them

A series of polyimides (PI) based on two dianhydrides, namely 5-(2,5-dioxotetra-hydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride (DOCDA) and benzophenonetetracarboxylicdianhydride (BTDA), and an aliphatic diamine, namely 1,6 diaminohexane (DAH), have been obtained by solution polycondensation reaction, followed by thermal ring closure of the resulting polyamic acids. The chemical structures were identified by infrared and ¹H-NMR spectroscopy and their thermal and electrical properties (dielectric constant and dielectric loss at different frequencies) were investigated. The polymers showed good thermal stability, with no significant weight loss up to 340°C, with 5% weight loss temperature in the range of 345-430°C and glass transition temperatures (Tg_s) between 122-190°C. The resulting polyimides gave flexible films by thermal imdization of poly (amic acid) precursors. The AFM analysis revealed a smooth topography of their surfaces, with root-mean-square (Sq) roughness between 0.42-6.32 nm and average roughness (Sa) in the range of 0.33-2.39 nm. The dielectric constants of the PI films varied between 3.05 and 2.68 at 1 MHz frequency. The correlation between the polymers structure and their properties has been discussed.