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.

Highly transparent and organosoluble polyimides derived from 2,2′-bis[4-(5-amino-2-pyridinoxy) phenyl] propane

Two new isomers containing pyridine ring diamine monomers, 2,2′-bis[4-(5-amino-2-pyridinoxy)phenyl] propane (1b) and 2,2′-bis[4-(6-amino-3-pyridinoxy)phenyl] propane (2b), were prepared via a simple nucleophilic reaction of 2-chloro-5-nitropyridine and 5-bromo-2-nitropyridine with bisphenol A in the presence of potassium carbonate, respectively. A series of polyimides (PIs) were obtained from the heterocyclic diamine with various commercially available aromatic dianhydrides via the conventional two-step method. These obtained PIs were investigated in aspects of their solubility, thermal, mechanical, and optical properties for studying the effects of the heteroaromatic rings into the main chain. At the same time, the impact of the two isomers introduced into the PI was discussed in detail.

Synthesis and properties of highly soluble branched polyimide based on 2,4,6-triaminopyrimidine

A series of novel soluble polyimides was synthesized from commercially available 2,4,6-triaminopyrimidine (TAP), 2,2-bis(3,4-dicarboxylphenyl) hexafluoropropane dianhydride (6FDA), α,ω-aminopropylpoly(dimethylsiloxane) and 1,3-bis(3-aminophenoxy)benzene. TAP is the branched monomer, and polymerization process had been improved in three ways by using TAP to prepare soluble polyimides. The polyimides were characterized by Fourier transform infrared spectra, proton nuclear magnetic resonance, ultraviolet–visible spectrometer analysis, wide-angle X-ray diffraction, and size-exclusion chromatography with multiangle laser light-scattering detection. The branched polyimides showed excellent solubility both in strong polar solvents and in common low-boiling point solvents. Differential scanning calorimetric and thermogravimetric analyses showed high glass transition temperatures and excellent thermal stability for branched polyimides with moderate content of TAP. Polyimide membranes were formed at relatively low temperature, and the mechanical properties were tested. These results ensure that soluble polyimides with moderate content of TAP showed outstanding combined features and are desirable candidate materials for advanced applications.

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.

Intrinsically heat-sealable polyimide films derived from 2,3,3′,4′-oxydiphthalic anhydride and aromatic diamines with various ether linkages

A series of polyimides (PIs) with good heat sealability were synthesized from an asymmetric aromatic dianhydride, 2,3,3′,4′-oxydiphthalic anhydride, and aromatic ether diamines with different structures featured by ether amounts, substituted positions of ether linkages, and substituted positions of amino groups. In detail, the effects of these three substructures in the diamine were investigated on thermal resistance, thermoplasticity, and heat sealability of the PI film. It is found that the glass transition temperatures and heat-sealing strengths of the prepared PI films are influenced to different extents by the variations of the substructures, because of their different contributions to the chain mobility. These PI films are demonstrated to possess good heat sealability evidenced by completely fused heat-sealing interfaces and high heat-sealing strengths up to 580 N m−1.

Synthesis of diol monomers and organosoluble fluorinated polyimides with low dielectric

Four diimide–diol monomers were synthesized from 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride and aminophenol/aminonaphthol. The structures of the monomers were characterized by spectroscopic analysis. A series of fluorinated polyimides (FPI-1 to FPI-8) were synthesized from these new diols and 4,4′-difluorobenzophenone/4,4′-dichlorodiphenyl sulphone, through nucleophilic displacement reaction. The FPIs were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, X-ray diffraction, thermogravimetry, differential scanning calorimetry, solution viscosity, solubility test, and dielectric properties test. FPIs were amorphous and showed good solubility due to the presence of >C(CF3)2 unit and flexible groups in the polyimides backbone. These FPIs also showed good thermal stability and the 10% weight loss occurred in the range 353–505°C. The limiting oxygen index values of FPIs were in the range of 31.5–39.1 and such FPIs can be used as self-extinguishing polymers. These FPIs have a dielectric constant in the range of 3.10–4.23 and can be used as high temperature electrical insulation materials.

Synthesis and characterization of novel polyimides derived from 2,4-bis(4-aminophenoxy)pyrimidine

A novel heterocyclic diamine monomer based on pyrimidine ring, 2,4-bis(4-aminophenoxy)pyrimidine, was successfully synthesized. The obtained heterocyclic diamine was fully characterized and employed to synthesize a series of polyimides (PIs) by polycondensation with commercially available aromatic dianhydrides via the conventional two-step method. The effects of the pyrimidine rings into the main chain of the PIs were evaluated through the study of their solubility, thermal, mechanical, and optical properties. The inherent viscosities of the resulting poly(amic acid)s were in the range of 0.58–1.45 dL g−1. Meanwhile, the PIs had good thermal stability with the 5% weight loss temperatures of 445–475°C under nitrogen atmosphere as well as outstanding mechanical properties with tensile strength of 93–105 MPa and elongation at break of 3.6–4.2%. The cutoff wavelength of the PI films were in the range of 348–413 nm.

High organosolubility of novel asymmetric polyimides-containing benzimidazole rings

Two tetramethyl-substituted diphenylmethane diamines, α,α-bis(4-amino-3,5-dimethylphenyl) phenylmethane (BADP) and 3,3′,5,5′-tetramethyl-4,4′-diaminodiphenylmethane (TMDA), were synthesized. Two series of novel soluble polyimides (PIs) with high glass transition temperature ( Tg) were derived from 3,3′4,4′-benzophenone tetracarboxylic dianhydride with 6,4′-diamino-2-phenylbenzimidazole and BADP (or TMDA) via one-pot synthesis using anhydrous N-methyl-2-pyrrolidone as a solvent. Precipitation or gelation does not occur during polymerization and imidization, and the resulting products dissolve well in polar aprotic solvents and phenolic solvents. The two series of PI films have good transparency in the visible light region, with a cutoff wavelength at 365 nm and higher than 50% of the transmittance at 450 nm. Tgs are in the range of 381–431°C, and 10% weight loss in nitrogen occurs above 530°C in all cases. Upon increasing BADP (or TMDA) moieties content, the Tg values decrease, whereas the thermal stability tends to increase. Moreover, the PIs-containing TMDA units have a higher thermal stability than those containing BADP units.

Synthesis and characterization of highly soluble and optically transparent polyimides derived from novel fluorinated pyridine-containing aromatic diamine

A novel fluorinated pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[2-(4-amino-2-trifluoromethyphenoxy)phenyl]pyridine ( o, p-6FPAPP), was prepared in a three-step synthetic route. This aromatic diamine was then employed to synthesize a series of fluorinated pyridine-containing polyimides (PIs) by polycondensation with various aromatic dianhydrides via the conventional two-step method. The inherent viscosities of the resulting poly(amic acid)s (PAAs) and PIs were in the range of 0.71–0.89 and 0.62–0.84 dL/g; all the PIs obtained by chemical imidization were readily soluble in common organic solvents such as N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and so on. Meanwhile, transparent, strong and flexible PI films were obtained, which had good thermal stability, with the glass transition temperature ( Tg) of 195.2°C–232.7°C, the temperature at 10% weight loss of 530.2°C–546.0°C in nitrogen atmosphere, and good optical transparency with the cutoff wavelengths of 354–382 nm, as well as outstanding mechanical properties with tensile strengths of 96.4–105.8 MPa, tensile modulus of 1.57–1.88 GPa and elongations at break of 9.5%–13.4%. The PI films were also found to possess low water uptake of 0.52%–0.67%.