Partially biobased processable polyimides based on aromatic diamine derived from cardanol

A partially biobased aromatic diamine – namely, 1,1-bis(4-aminophenyl)-3-pentadecylcyclohexane (BAC 15 ) – was synthesized starting from cardanol. A series of polyimides were synthesized by one-step high-temperature solution polycondensation of BAC 15 with aromatic dianhydrides. Copolyimides were also synthesized by polycondensation of various compositions of BAC 15 and 4,4′-oxydianiline with 3,3′,4,4′-biphenyl tetracarboxylic dianhydride. The inherent viscosities and number-average molecular weights of (co)polyimides were in the range of 0·33–1·4 dl/g and 14 700–31 900 g/mol, respectively, indicating formation of reasonably high-molecular-weight polymers. Polyimides were soluble in common organic solvents such as chloroform, dichloromethane and tetrahydrofuran and could be cast into transparent, flexible and tough films from their solutions in chloroform. (Co)Polyimides exhibited glass transition temperatures (T g ) in the range of 161–254°C. The lowering of T g could be attributed to the presence of flexible pentadecyl chains, which act as ‘packing-disruptive’ groups. The temperature at 10% weight loss (T 10 ) of (co)polyimides was in the range of 490–515°C, demonstrating their good thermal stability. The virtue of solubility and the large gap between T g and T 10 offers (co)polyimides opportunities of both solution and melt processability. Copolyimides containing pendent pentadecyl chains exhibited pretilt angles in the range of 2·51–2·75°, indicating their potential application as an alignment layer in liquid crystal display (LCD) devices.