Synthesis and characterization of novel thermally stable and optically active poly(amide-imide)s derived from N,N'-(4,4'-diphthaloyl)-bis-L-leucine diacid and aromatic diamines

A new diacid containing optically active functional groups, N,N'-(4,4'-diphthaloyl)-bis-L-leucine diacid (3), was synthesized and used in a preparation of a series of poly(amide-imide)s (PAIs) by direct polycondensation with various aromatic diamines in N-methyl-2-pyrrolidinone (NMP). All polymers derived from diacid (3) were highly organosoluble in the solvents like N-methyl-2-pyrrolidinone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, γ-butyrolactone, cyclohexanone, and chloroform at room temperature or upon heating. Inherent viscosities of the PAIs were found to range between 0.34 and 0.61-dL g^-1. All the PAIs afforded flexible and tough films. The glass-transition temperatures of these PAIs were recorded between 212 and 237°C by differential scanning calorimetry, and the 10% weight loss temperatures were ranging from 372 to 393°C and 336-372°C under nitrogen and air, respectively. The polyimide films had a tensile strength in the range of 63-88 MPa and a tensile modulus in the range of 1.2-1.7 GPa. Optically active PAIs exhibited specific rotations in the range of -10.58° to -38.70°.