Novel Flame-retardant and Thermally Stable Poly(amide-imide)s Based on Bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic Diimide and Phosphine Oxide in the Main Chain: Synthesis and Characterization

Six novel poly(amide-imide)s PAIs 5a-f were synthesized through the direct polycondensation reaction of six chiral N,N'-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-L-amino acids 3a-f with bis(3-amino phenyl) phenyl phosphine oxide 4 in a medium consisting of N-methyl-2-pyrrolidone (NMP), triphenyl phosphite (TPP), calcium chloride (CaCl2) and pyridine. The polymerization reaction produced a series of flame-retardant and thermally stable poly(amide-imide)s 5a-f with high yield and good inherent viscosity of 0.39-0.83 dLg(-1). The resultant polymers were fully characterized by means of FTIR, H-1 NMR spectroscopy, elemental analyses, inherent viscosity, specific rotation and solubility tests. Thermal properties and flame retardant behavior of the PAIs 5a-f were investigated using thermal gravimetric analysis (TGA and DTG) and limited oxygen index (LOI). Data obtained by thermal analysis (TGA and DTG) revealed that these polymers show good thermal stability. Furthermore, high char yields in TGA and good LOI values indicated that resultant polymers exhibited good flame retardant properties. N,N'-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-L-amino acids 3a-f were prepared in quantitative yields by the condensation reaction of bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride 1 with L-alanine 2a, L-valine 2b, L-leucine 2c, L-isoleucine 2d, L-phenyl alanine 2e and L-2-aminobutyric acid 2f in acetic acid solution. These polymers can be potentially utilized in flame retardant thermoplastic materials.