Simultaneously Improving the Optical, Dielectric, and Solubility Properties of Fluorene-Based Polyimide with Silyl Ether Side Groups

Abstract

Three fluorene-based polyimides with silyl ether groups (Si–PIs) were successfully synthesized by a simple and efficient silicon etherification reaction of hydroxyl-containing polyimides (OH–PIs) and tert -butylchlorodiphenylsilane (TBDPSCl), and their structures were confirmed by 1 H NMR and IR spectra. The bulky nonpolar tert -butyldiphenylsilyl (TBDPS) side groups in the modified PI unit instead of the strong electron donor −OH group is conducive to decreasing electronic conjugation and charge transfer (CT) interaction along the PI chain. Accordingly, the optical, dielectric, and solubility properties of the modified Si–PI films are simultaneously improved compared with the precursor OH–PI films. The modified Si–PI films demonstrate a meaningful enhancement in the transmittances at a wavelength of 400 nm ( T 400 ) to 74–81% from 42 to 55% of OH–PI films and the regeneration of fluorescence characteristics. The dielectric constant and loss of Si–PI films are also obviously reduced to 2.63–2.75 and 0.0024–0.0091 at 1 kHz from 4.19 to 4.78 and 0.0173–0.0295 of OH–PI films, respectively, due to substituted with the bulky nonpolar TBDPS groups to increase the free volume and hydrophobicity of Si–PI films. The solubility of Si–PIs in low- or nonpolar solvents (such as CHCl 3 , CH 2 Cl 2 , acetone, and toluene) is significantly improved. Furthermore, Si–PI films still maintain relatively good thermal properties with the 5% weight loss temperature ( T 5% ) in the range 470–491 °C under a nitrogen atmosphere and the glass transition temperature ( T g ) in the range 245–308 °C.

Structural Designs of Transparent Polyimide Films with Low Dielectric Properties and Low Water Absorption: A Review

“…8) [75], which also led to enhanced thermal properties (Tg > 311 °C; Td 5% > 469 °C). The same group also reported similar results using tert-butyldiphenylsilylchloride (Figure 8) [76]. 8) [75], which also led to enhanced thermal properties (T g > 311 • C; T d 5% > 469 • C).…”

“…To further reduce the D k (up to 2.44) value, Wu et al modified the fluorene moieties of ODPA-and FDA-based polyimides by directly silylating the pendant hydroxy groups of 9,9-bis(4-aminophenyl)-2,7-dihydroxy-fluorene (Fn1) and 9,9-bis(3-methyl-4-aminophenyl)-2,7-dihydroxy-fluorene (Fn2) with tert-butyldimethylsilylchloride (Figure8)[75], which also led to enhanced thermal properties (T g > 311 • C; T d 5% > 469 • C). The same group also reported similar results using tert-butyldiphenylsilylchloride (Figure8)[76].…”

“…8) [75], which also led to enhanced thermal properties (T g > 311 • C; T d 5% > 469 • C). The same group also reported similar results using tert-butyldiphenylsilylchloride (Figure 8) [76]. With the aim of developing 5G/6G communication materials, Zhang et al synthesized liquid-crystal poly(ester-imide) (LCPEI) PEI films based on various fluorinated imide dicarboxylic acids by copolymerizing different moieties containing carboxylic and phenolic functionalities using the direct-esterification method reported by Higashi (Figure 9) [81,82].…”

Preparation and Properties of Low-Dielectric Polyimide Films Containing Tert-Butyl

“…In addition, Zuo and co-workers [28] developed a new strategy to construct low-dielectric-constant PI films by the introduction of meta-substituted and trifluoromethyl structures into the main chains of PI films, in which the meta-substituted structure and trifluoromethyl units could inhibit the transfer of charge transfer complex effects and increase the free volume of PI films, thereby resulting in a lower dielectric constant. Recently, Wu et al [29] reported three fluorene-based PI films with silyl ether structures that delivered a low dielectric constant and high hydrophobicity. The reason is that the bulky nonpolar tert-butyldiphenylsilyl side groups in the PI films are able to decrease the charge transfer interaction and electronic conjugation along the PI chain, and increase the free volume and hydrophobicity of Si-PI films.…”

Synthesis and Characterization of Organo-Soluble Polyimides Based on Polycondensation Chemistry of Fluorene-Containing Dianhydride and Amide-Bridged Diamines with Good Optical Transparency and Glass Transition Temperatures over 400 °C

“…In the current work, such PI films were endeavored to be developed based on the fluorene-containing dianhydride, 9,9-bis(3,4dicarboxyphenyl)fluorene dianhydride (FDAn) and the amide-containing diamines. Fluorene groups represent a class of rigid and fused-ring structure with high thermal resistance and bulky molecular volumes [37]. As for the optical and dielectric features, the fluorene groups can usually endow the derived polymer films with good optical transparency, high refractive indices, low birefringence, low optical retardation, and low dielectric constants [38][39][40].…”