Synthesis and characterization of novel polyimides derived from 4,4'-bis(5-amino-2-pyridinoxy)benzophenone: effect of pyridine and ketone units in the main

A diamine monomer, 4,4’-bis(5-amino-2-pyridinoxy)benzophenone, was designed and synthesized, and used to react with commercially different kinds of aromatic dianhydrides to prepare a series of polyimides containing pyridine and ketone units via the classical two-step procedure. Glass transition temperatures (T_g) of the resultant polyimides PI-(1–5) derived from 4,4’-bis(5-amino-2-pyridinoxy) benzophenone with various dianhydrides ranged from 201 to 310 °C measured by differential scanning calorimetry. The temperatures for 5%wt loss of the resultant polyimides in nitrogen atmosphere obtained from the thermogravimetric analysis curves fell in the range of 472–501 °C. The temperatures for 10%wt loss of the resultant polyimides in nitrogen atmosphere fell in the range of 491–537 °C. Meanwhile, the char yields at 800 °C were in the range of 55.3–60.8%. Moreover, the moisture absorption of polyimide films was measured in the range of 0.37–2.09%. The thin films showed outstanding mechanical properties with tensile strengths of 103–145 MPa, an elongation at break of 12.9–15.2%, and a tensile modulus of 1.20–1.88 Gpa, respectively. The coefficients of thermal expansion of the resultant polyimides were obtained among 26–62 ppm °C⁻¹. To sum up, this series of polyimides had a good combination of properties applied for high-performance materials and showed promising potential applications in the fields of optoelectronic devices.

Poly(ether–imide)s with flexible linkages and kinks

Four new aromatic diimide–diol monomers were synthesized from bisphenol A dianhydride and hydroxyamines. The poly(ether–imide)s (PEI-1 to PEI-4) were synthesized from these diols and 4,4′-difluorobenzophenone-IV via carbonyl-activated aromatic nucleophilic fluoro displacement reaction. The chemical structures of the monomers and PEIs were confirmed by Fourier transform infrared spectrometer and proton nuclear magnetic resonance spectroscopies. The PEIs synthesized here were amorphous and soluble in polar aprotic solvents and low-boiling organic solvents. The PEIs had good thermal stability, 10% weight loss occurred in the temperatures range of 400–448°C, and char yields at 800°C under nitrogen atmosphere was in the range of 14–22%. The limiting oxygen index values of PEIs were in the range of 23.1–26.3, and such PEIs can be used as self-extinguishing polymers. The dielectric constants of the PEIs were in the range of 3.30–4.00, and such PEIs can be used as electrical insulation materials for systems operating at high temperature for long time.

Synthesis and properties of electroactive aromatic polyimides with methyl- or trifluoromethyl-protecting triphenylamine units

Two series of new redox-active aromatic polyimides with methyl- (–CH3) or trifluoromethyl (–CF3)-protecting triphenylamine moieties were prepared from 4,4′-diamino-4″-methyltriphenylamine and 4,4′-diamino-4″-(trifluoromethyl)triphenylamine with aromatic tetracarboxylic dianhydrides via the conventional two-step polycondensation technique. Flexible and strong polyimide films could be obtained via the thermal curing of their precursor poly(amic acid) films or direct solution cast from some organosoluble polyimides. The polyimides showed high glass-transition temperatures between 269°C and 312°C, and they did not show significant decomposition before 500°C in air or under nitrogen atmosphere. Cyclic voltammograms of the polyimide films on the indium–tin oxide-coated glass substrate exhibited a pair of reversible redox waves with half-wave oxidation potentials of 1.08–1.10 V (for the –CH3 series) and 1.23–1.26 V (vs. silver/silver chloride; for the –CF3 series) in acetonitrile solution. The polyimide films showed anodic electrochromism from pale yellow neutral state to purplish blue (for the –CH3 series) and chrome yellow (for the –CF3 series) when oxidized.

Synthesis and crosslinking study of isomeric poly(thioether ether imide)s containing pendant nitrile and terminal phthalonitrile groups

Upon crosslinking, phthalonitrile-terminated polyimide PN-PI (a–d) films exhibited better solvent resistance, and greater thermal and mechanical properties than PI (a–d) films.

Preparation, characterization, and properties of poly(thioether imide)s from isomeric bis(chlorophthalimide)s and bisthiophenols

A series of isomeric poly(thioether imide)s (PTIs) containing thioether linkages were prepared by aromatic nucleophilic substitution reaction of isomeric bis(chlorophthalimide)s (BCPIs) and bisthiophenols. The glass transition temperatures ( Tgs) of the isomeric PTIs were 190–264°C, the 5% weight loss temperature ( T5%) reached up to 441–508°C under nitrogen and 472–520°C in air atmospheres, respectively. It was found that the Tg values of the PTIs from three isomeric BCPIs with the same bisthiophenol increased in the order of 4,4′-BCPI < 3,4′-BCPI < 3,3′-BCPI, while the T5% values gradually decreased in the order of 4,4′-BCPI > 3,4′-BCPI > 3,3′-BCPI. Flexible films that could be cast from the polymer solutions exhibited good mechanical properties with tensile strengths of 91–121 MPa, elongations at break of 8–12%, and tensile moduli of 2.2–2.6 GPa. The minimum melt viscosity of isomeric PTIs decreased with increasing the content of asymmetric 3,4′-substituted phthalimide unit, and the PTI (2c) showed the lowest melt viscosity about 760 Pa·s at 264°C among these isomeric polymers.