A novel hydroxyl-containing polyimide film has been designed and fabricated as a chemosensor for the real-time visualization of F− with high selectivity and sensitivity.
A novel aromatic diamine containing pyridyl side group, 4-pyridine-4,4-bis(3,5-dimethyl-5-aminophenyl)methane (PyDPM), was successfully synthesized via electrophilic substitution reaction. The polyimides (PIs) containing pyridine were obtained via the microwave-assisted one-step polycondensation of the PyDPM with pyromellitic dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-diphenylether tetracarboxylic dianhydride (ODPA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). Contrarily to the reported similar PIs, these PIs exhibit much higher thermal stability or heat resistance, i.e. high glass transition temperatures (
T
g
s) in the range of 358–473°C, and the decomposition temperatures at 5% weight loss over 476°C under nitrogen. They can afford flexible and strong films with tensile strength of 82.1–93.3 MPa, elongation at break of 3.7%–15.2%, and Young's modulus of 3.3–3.8 GPa. Furthermore, The PI films exhibit good optical transparency with the cut-off wavelength at 313–366 nm and transmittance higher than 73% at 450 nm. The excellent thermal and optical transmittance can be attributed to synthesis method and the introduction of pyridine rings and ortho-methyl groups. The inherent viscosities of PIs via one-step method were found to be 0.58–1.12 dl g
−1
in DMAc, much higher than those via two-step method. These results indicate these PIs could be potential candidates for optical substrates of organic light emitting diodes (OLEDs).
Ladder‐like polypropylsilsesquioxane (LPSQ) with inorganic SiOSi double‐stranded skeleton in situ growth is incorporated into 18‐crown‐6‐polyimide (CE6‐PI) chains by coupling effect of aminopropyltrimethoxysilane to build ladder‐like polypropylsilsesquioxane/18‐crown‐6‐polyimide (LPSQ/CE6‐PI) nanocomposites. The dielectric constant is evidently decreased, and the strength, toughness, and thermal stability of CE6‐PI are greatly improved. A low dielectric constant of 2.71 as well as high tensile strength of 133.7 MPa and toughness of 29.7 MJ m−3 are achieved for the LPSQ/CE6‐PI nanocomposite with 23.2 wt% LPSQ. Meanwhile, its glass transition temperature and 5% weight loss temperature exhibit an increase of 23.1 °C and 68.8 °C, respectively, based on CE6‐PI. Positron annihilation lifetime spectroscopy, X‐ray diffraction patterns, dynamic mechanical analysis, and scanning electron microscope images are applied to investigate the effect of LPSQ on the structure of LPSQ/CE6‐PI nanocomposites.
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