Syntheses and properties of novel polyimides derived from 2‐(4‐Aminophenyl)‐5‐aminopyrimidine

Abstract

2-(4-Aminophenyl)-5-aminopyrimidine (4) is synthesized via a condensation reaction of vinamidium salts and amidine chloride salts, followed by hydrazine palladium catalyzed reduction. A series of novel homo-and copolyimides containing pyrimidine unit are prepared from the diamine and 1,4-phenylenediamine (PDA) with pyromellitic dianhydride (PMDA) or 3,3 0 ,4,4 0 -biphenyl tertracarboxylic dianhydride (BPDA) via a conventional two-step thermal imidization method. The poly(amic acid) precursors had inherent viscosities of 0.97-4.38 dL/g (c ¼ 0.5 g/dL, in DMAc, 308C) and all of them could be cast and thermally converted into flexible and tough polyimide films. All of the polyimides showed excellent thermal stability and mechanical properties. The glass transition temperatures of the resulting polyimides are in the range of 307-4348C and the 10% weight loss temperature is in the range of 556-6098C under air. The polyimide films possess strength at break in the range of 185-271 MPa, elongations at break in the range of 6.8-51%, and tensile modulus in the range of 3.5-6.46 GPa. The polymer films are insoluble in common organic solvents, exhibiting high chemical resistance.

Enhancing mechanical properties of aromatic polyamide fibers containing benzimidazole units via temporarily suppressing hydrogen bonding and crystallization

“…The NH stretching bands of amide and benzimidazole units are observed in the wavenumber interval from 3200 to 3500 cm −1 . The peak located between 1480 and 1490 cm −1 can be assigned to the stretching vibration of C=N in the benzimidazole ring . The peak centered at 3415 cm −1 can be attributed to the stretching vibration of the isolated, non‐hydrogen bonded NH groups in benzimidazole units and the peak centered approximately at 3300 cm −1 is related to the hydrogen bonded NH group .…”

“…Due to the PABZ units contained in PBIA fibers, the PBIA fibers can also complex with HCl. In addition, from the FTIR spectra shown in Figure 3, bands can be seen at 3415 and 1490 cm 21 , which have been attributed to isolated, non-hydrogen bonded NH groups in PABZ units 14 and C5N stretching vibrations in PABZ units, 15,16 respectively. The ratio of I 3415 /I 3300 is used to characterize the change of non-hydrogen bonded NH group in benzimidazole units.…”

“…The peak located between 1480 and 1490 cm 21 can be assigned to the stretching vibration of C5N in the benzimidazole ring. 15,16,19 The peak centered at 3415 cm 21 can be attributed to the stretching vibration of the isolated, non-hydrogen bonded NH groups in benzimidazole units 14 and the peak centered approximately at 3300 cm 21 is related to the hydrogen bonded NH group. 14 In order to study the change of non-hydrogen bonded NH group in benzimidazole units during drawing process, the internal standard of hydrogen bonded NH stretching bands was introduced, and the ratio of I 3415 to I 3300 was used to characterize the change of non-hydrogen bonded NH group in the benzimidazole units.…”

Structure and properties of aromatic poly(benzimidazole‐imide) copolymer fibers

“…To reduce the CTE value and maintain the thermal and mechanical properties of PI fibers in the meantime, one attempted approach is structural modification. So far, many efforts on chemical modification of PI structures have been done, including the introduction of heterocyclic rings like both benzoxazole and benxadiazole, pyridine, pyrimidine, furan,and phthalazinone in polymer backbone, which led to good thermal and mechanical properties of these PIs. Polybenzimidazoles (PBIs) are another class of high‐performance polymer that containing recurrent benzimidazole rings, which have been used extensively in the aerospace industry recent years due to their high‐strength, high‐modulus and sufficient thermal stability to withstand extreme conditions .…”

Synthesis and characterization of high‐performance polyimides based on 6,4′‐diamino‐2‐phenylbenzimidazole

“…A series of novel polyimides containing heterocylic units in the main chains were reported over past decades. Homo-and copolyimides containing pyrimidine units were prepared by Xia et.al., 9 show-ing excellent thermal stability and mechanical properties. A series of polyimide-benzbithiazole prepared via a two-step method by Kimura 7 exhibited poor solubility and good thermal stability.…”