Preparation, characterization and fluorimetric studies of novel photoactive poly(amide-imide) from 1-naphthaldehyde and 2,6-diaminopyridine by microwave-irradiation

Trimellitic anhydride acid chloride (2) was obtained by the reaction of trimellitic anhydride (1) and excess amount of thionyl chloride. The acid chloride was reacted with 2,6-diamino pyridine (3), and produced the monomer 4. 1-Naphthaldehyde (5) was reacted with sulfuryl chloride to produce 1-naphthoyl chloride (6) in a quantitative yield. Through the reaction of 6 and 1,3,5-triazine-2,4,6-triamine (7), the monomer 8 was produced in high yield. Two monomers were characterized by 1H NMR and FT-IR spectroscopy, and then were used in the polymerization reaction. A new facile and rapid polycondensation reaction of the two monomers was performed by using a domestic microwave oven. The polymerization reaction proceeded rapidly, compared with the conventional solution polycondensation and was completed within 8 min, producing a photoactive poly(amide-imide) in a quantitative yield. The resulting polymer was characterized by IR, 1H NMR and thermal gravimetric analysis (TGA) techniques. Thermogravimetric analysis indicated that polymer 9 was thermally stable in nitrogen atmosphere. In addition the initial decomposition temperature (IDT), 5 and 10% weight loss (T5, T10) were 265.85 and 292.85 °C. The residual weight percent at 500 °C was 50%, which shows it is moderately thermally stable. Fluorescence properties of polymer 9 were investigated in several solvents. The ideal concentration of each case was determined by fluorescence self-quenching phenomena. Also the self-quenching mechanism was studied according to the specific behavior of the polymer in different solvents.