Synthesis and Characterization of Novel Processable and Flexible Polyimides Containing 3,6-Di(4-carboxyphenyl)pyromellitic Dianhydride

Table 1

FTIR, ¹H NMR of polyimides (PI-1–PI-6).

Compound	IR (KBr)/cm^−1	^1H NMR (DMSO-d6, , ppm); (s; singlet, m; multiplet)
PI-1	1725, (CO)sym, 1788 (CO)asym; 1665 (C=N)	13.01 (s, 2H, COOH); 6.78–7.90 (m, aromatic protons); 8.65 (s, 1H, azomethine)
PI-2	1718, (CO)sym, 1772 (CO)asym; 1650 (C=N)	13.21 (s, 2H, COOH); 6.65–7.89 (m, aromatic protons); 8.15 (s, 1H, azomethine)
PI-3	1725, (CO)sym, 1778 (CO)asym; 1664 (C=N)	13.12 (s, 2H, COOH); 6.41–7.90 (m, aromatic protons); 8.52 (s, 1H, azomethine)
PI-4	1715 (CO)sym, 1782 (CO)asym; 1657 (C=N)	12.98 (s, 2H, COOH); 6.75–7.97 (m, aromatic protons); 8.15 (s, 1H, azomethine)
PI-5	1725 (CO)sym, 1775 (CO)asym; 1665 (C=N)	12.99 (s, 2H, COOH); 6.45–7.78 (m, aromatic protons); 8.62 (s, 1H, azomethine);
PI-6	1717 (CO)sym, 1780 (CO)asym; 1638 (C=N)	13.08 (s, 2H, COOH); 6.35–7.88 (m, aromatic protons); 8.25 (s, 1H, azomethine)

In DMSO-d₆ at 295 K.