Synthesis and characterization of poly(amide-imide)s and their precursors as materials for membranes

Water soluble diamine amic acids (DAAs) were synthesized by reacting alipha tic diamines with pyromellitic dianhydride. Poly(amide-amic acid)s (PAAs) w ere prepared by interfacial polycondensation of DAAs in aqueous sodium hydr oxide solution with isophthaloyl chloride in dichloromethane. Poly(amide-im ide)s (PAIs) containing alternating (amide-amide)-(imide-imide) sequences w ere obtained by thermal cycloimidization of the PAA films at 175 degrees C for 4 h in a forced air woven. The PAIs were readily soluble in polar aprot ic solvents such as dimethylformamide, dimethylacetamide, dimethylsulfoxide , and N-methyl-2-pyrrolidone. The inherent viscosities of the polymers are in the range of 0.97-1.7 dL/g. The polymers were characterized by IR, H-1 n uclear magnetic resonance (NMR), and thermogravimetric analysis (TGA). Thin film composite membranes containing PAA ultrathin barrier layer were prepa red by in situ interfacial polycondensation of DAA in water with trimesoyl chloride or isophthaloyl chloride in hexane on the surface of a porous poly sulfone membrane. The membranes were characterized for water permeability a nd for the separation of NaCl and Na2SO4. (C) 2000 John Wiley & Sons, Inc.