Pretilt angle for BTDA,PMDA and CPDA series polyimides with various side chain lengths

Polyamic acid precursors were prepared by mixing dianhydride of 3,3',4,4'-benzophenone-tetracarboxylic dianhydride (BTDA), 1,2,3,4-benzene-tetracarboxylic dianhydride (pyrromellitic dianhydride PMDA), cis-1,2,3,4-cyclopentane-tetracarboxylic dianhydride (CPDA), the diamine (alkyl 3,5-diaminobenzoate) with side chain, and 4,4'-oxydianiline (ODA) without side chain. Copolyimide films with various side chain lengths were prepared by thermal imidization of polyamic acid precursors. The roughness of rubbed polyimide surface increased with increase in the side chain length. The pretilt angle for the BTDA and PMDA series polyimide (PI) increased exponentially with increase in side chain length. Various pretilt angles were obtained on the synthesized polyimides. In the case of CPDA series PI, the pretilt angle was nearly constant at 0 until the alkyl side chain length reached 12 (C12) and then increased markedly at C18. Models of pretilt angle generation were tested.