Optically active and flame-retardant poly(amide-imide)s based on phosphine oxide moiety and N,N′-(pyromellitoyl)bis-l-amino acid in the main chain: Synthesis and characterization

Abstract

Six new optically active and flame-retardant poly(amide-imide)s PAIs 5a–5f containing phosphine oxide moiety as a flame-retardant unit in the main chain were synthesized from direct polycondensation reaction of six chiral N,N′-(pyromellitoyl)-bis-L-amino acid 3a–3f with bis(3-aminophenyl)phenyl phosphine oxide 4 in a medium consisting of N-methyl-2-pyrrolidone (NMP), triphenyl phosphite (TPP), calcium chloride (CaCl2) and pyridine. The polymerization reactions produced a series of optically active poly(amide-imide)s with good yield and good inherent viscosity of 0.34–0.70 dLg−1. The resulted polymers were fully characterized by means of FTIR and 1H-NMR spectroscopy, gel permeation chromatography (GPC), elemental analyses, inherent viscosity and solubility tests. Thermal properties and flame-retardant behavior of the PAIs 5a–5f were investigated using thermal gravimetric analysis (TGA and DTG) and limiting oxygen index (LOI). Data obtained by thermal analysis (TGA and DTG) revealed that these polymers showed good thermal stability. Furthermore, high char yield in TGA and good LOI values indicated that the resulting polymers were capable of exhibiting good flame retardant properties. N,N′-(pyromellitoyl)-bis-L-amino acids 3a–3f were prepared in quantitative yields by the condensation reaction of pyromellitic dianhydride (1,2,4,5-benzenetetracarboxylicacid-1,2,4,5-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.