Synthesis and properties of novel colorless and thermostable polyimides containing cross‐linkable bulky tetrafluorostyrol pendant group and organosoluble triphenylmethane backbone structure

Abstract

A colorless and high temperature resistant fluorinated polyimide (PI) film based on a novel cross‐linkable diamine monomer 4,4′‐diamino‐4″‐(2,3,5,6‐tetrafluoro‐4‐ethylenephenoxy) triphenylmethane (DFPTM) was successfully prepared. The special triphenylmethane backbone and the bulky tetrafluorostyrol pendant group in DFPTM gave the PI material eximious solubility in organic solvents, high tensile properties, good thermal stability, and excellent optical transparency (cutoff wavelength for 331 nm and light transmittance above 94% at 450 nm). Furthermore, the styryl could initiate self‐crosslinking reaction to form a dense three‐dimensional network structure by thermal curing. Hence, the cross‐linked PI film showed superior combination property (including excellent resistance to solvents). It's Tg increased by 57.1–306.0°C, the 5% thermal weight‐loss temperature improved by 10.2% to 500.0°C, and the tensile strength enhanced by 17.5% to 39.7 MPa. Moreover, after thermal curing, the cross‐linked PI attained a lower elongation at break from 8.1 to 3.9%, and the thermal expansion coefficient reduced from 82.2 to 68.8 ppm/°C without obvious loss of optical transparency (cutoff wavelength for 347 nm and light transmittance remained 93.0% at 450 nm).

Ultralow Coefficient of Thermal Expansion and a High Colorless Transparent Polyimide Film Realized Through a Reinforced Hydrogen-Bond Network by In Situ Polymerization of Aromatic Polyamide in Colorless Polyimide

“…That is, it should appear in the top right corner of Figure b. Compared with recent reports, the comprehensive performance of CPI-PA 4 obtained in this work is outstanding. ,− ,− The strategy of PA by in situ polymerization in CPI has significant advantages in improving the dimensional stability and thermal properties while maintaining the optical transparency of CPI films …”

Cooperative synergistic effects of multiple functional groups in amide‐containing polyimides with pyridine ring and pendent tert‐butyl

“…There are effective methods aiming at improving the transparency and solubility of PIs, mainly including copolymerization, 14 and introduction of nonaromatic structure, 15–17 cardo structure, 18–20 flexible structure such as ether linkage and siloxane segments, 21 and pendent groups such as bulky alkyl, 22,23 and nonpolarized fluoroalkyl, 24,25 and so forth. These methods aim to depress the polymer chain packing, disrupt the conjugation structure of the polymer backbone to reduce the formation of CTC, thereby increasing the solubility and the optical transmittance of the PIs 26–28 . Large tert‐butyl pendant groups enlarge the intermolecular spacing, and weaken the polymer chain interaction, resulting in higher solubility and optical transparency of PIs 29 …”

“…These methods aim to depress the polymer chain packing, disrupt the conjugation structure of the polymer backbone to reduce the formation of CTC, thereby increasing the solubility and the optical transmittance of the PIs. [26][27][28] Large tert-butyl pendant groups enlarge the intermolecular spacing, and weaken the polymer chain interaction, resulting in higher solubility and optical transparency of PIs. 29 However, the thermal and mechanical properties were unfavorably decreased as the result of chain rigidity reduction and inter-chain space enlargement.…”

Novel cardo‐type heat‐resistant polyimides bearing 9H‐xanthene and polymer‐based nanocomposite consisting of NH2‐terminated TiO2: Synthetic strategies, extraction of methylene blue dye, and biological activities

“…22,23 Abundant efforts have been made to improve processing virtues of PIs, especially, by enhancing their fusibility and solubility, while keeping thermal constancy. Incorporation of ring-shaped structures, 24 nonplanar structures, 25 bulky side groups, 26,27 flexibilitie s linkages, 28 cardo groups, 29,30 and heterocyclic ring [31][32][33] are among modification methods used for improving properties of PIs.…”