Abstract
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 (Tgs) 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).
Highlights
With the rapid development of the optoelectronic field and microelectronics manufacturing industry, substrates with high& 2019 The Authors
Conventional aromatic polyimide (PI) films exhibit dark colours and poor transparency in the visible region arising from the charge –transfer (CT) interactions, and they cannot be used as the plastic substrates in organic light emitting devices (OLEDs) displays and so on
The aromatic diamines with pendent pyridyl group was successfully synthesized by electrophilic reaction between pyridine-4-aldehyde and 2,6-dimethylaniline catalysed by HCl, as shown in scheme 2
Summary
With the rapid development of the optoelectronic field and microelectronics manufacturing industry, substrates with high. Amutha & Sarojadevi [35] have synthesized several PIs with side pyridine groups (m-PyDPM, as shown in scheme 1) and obtained polymers exhibited relatively low Tgs of less than 3178C. It is still a question whether the introduction of pendent pyridine groups would sacrifice the thermal properties of polymers. PyDPM, a novel pyridine containing TPM derivative bearing dimethyl groups at R2 and R3 positions, was prepared considering that the introduction of ortho-methyl substituents can effectively enhance the Tgs of the final polymers. The cut-off wavelength of PI films except PyDPM-PMDA is in the range of 313–366 nm, and the transmittance at 450 nm is higher than 82%, indicating that these almost colourless PI films except PyDPM-PMDA can be potential candidates for optical substrates of OLEDs
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