Synthesis of thermally stable polyureas containing zinc and nickel schiff base complexes

Abstract

Hexadentate Schiff base zinc (II) and nickel (II) complexes were synthesized from the reaction between salicylaldehyde or salicylaldehyde derivatives, metal (II) acetate and triethylenetetramine at the mole ratio of 2:1 :1. The reaction between Schiff base zinc complexes and isocyanates to yield zinc-complexes ureas were carried out to studied the reactivity of amine group in Schiff base zinc complexes. The liquid crystalline property of Schiff base metal-complexes and metal-complexes ureas were investigated by differential scanning calorimetry (DSC). It was found that these complexes did not show liquid crystalline property. They exhibited good thermal stability and therefore used in the synthesis of metal-containing polyureas which were done by the polymerization reaction between Schiff base metal-complexes and hexamethylene diisocyayanate (HDI) or 4,4'-methylenebis(phenyl isocyanate) (MDI) at a 1:1 mole ratio. The progress of polymerization reaction was followed by using infrared spectroscopy. The disappearance of isocyanate peak at 2270 cm-1 was observed when the polymerization was completed. Metal-containing polyureas were characterized by FTIR, NMR, elemental analysis, solubility and viscometry. Heat resistance of polymers was investigated by thermogravimetric analysis (TGA) and measuring limiting oxygen index (LOI) values. It was found that the polymers showed good thermal stability.