Synthesis of Highly Transparent Semi-aromatic Poly(amide–imide)s from Alicyclic Diamines and Dicarboxylic Acids Derived from 2,2'-Di(trifluoromethyl)benzidine with Trimellitic Anhydride

Highly transparent thermally stable semi-aromatic poly(amide–imide)s (PAI)s were successfully prepared utilizing a diimide-dicarboxylic acid monomer, 2,2’-bis(trifluoromethyl)-4,4’-bis(trimellitimidophenyl)biphenyl (BTFTB), by direct polycondensation with aromatic, semi-aromatic, aliphatic, and alicyclic diamines in N-methyl-2-pyrrolidinone (NMP) with diphenyl (2,3-dihydro-2-thioxo-3-benzoxazolyl) phosphonate (DBOP) as a condensation agent in good yield (68 – 96%). The resulting PAIs, whose number-average molecular weights were up to 85,000 Da, showed good solubility in various organic solvents such as NMP, N,N-dimethylacetamide (DMAc), and tetrahydrofuran depending on the structure. The prepared films showed the good thermal stability (glass transition temperature (Tg) 236 – 314 °C), good mechanical properties (tensile strength up to 148 MPa, elongation at break 1.2 – 7.2%, and tensile modulus 1.7 – 4.3 GPa), and excellent optical transparency (cut-off wavelength (λcut) 322 – 405 nm). While these PAIs showed comparable thermal and mechanical properties and solubility with wholly aromatic PAIs such as poly(BTFTB-ODA) and poly(BTFTB-BAFL), they showed superior optical properties.