Novel Non-Coplanar and Tertbutyl-Substituted Polyimides: Solubility, Optical, Thermal and Dielectric Properties

Versatile Landscape of Low-k Polyimide: Theories, Synthesis, Synergistic Properties, and Industrial Integration

The development of microelectronics and large-scale intelligence nowadays promotes the integration, miniaturization, and multifunctionality of electronic and devices but also leads to the increment of signal transmission delays, crosstalk, and energy consumption. The exploitation of materials with low permittivity (low-k) is crucial for realizing innovations in microelectronics. However, due to the high permittivity of conventional interlayer dielectric material (k ∼ 4.0), it is difficult to meet the demands of current microelectronic technology development (k < 3.0). Organic dielectric materials have attracted much attention because of their relatively low permittivity owing to their low material density and low single bond polarization. Polyimide (PI) exhibits better application potential based on its well permittivity tunability (k = 1.1-3.2), high thermal stability (>500 °C), and mechanical property (modulus of elasticity up to 3.0-4.0 GPa). In this review, based on the synergistic relationship of dielectric parameters of materials, the development of nearly 20 years on low-k PI is thoroughly summarized. Moreover, process strategies for modifying low-k PI at the molecular level, multiphase recombination, and interface engineering are discussed exhaustively. The industrial application, technological challenges, and future development of low-k PI are also analyzed, which will provide meaningful guidance for the design and practical application of multifunctional low-k materials.

Synthesis and characterization of an adamantane-based copolyimides with high transparency

In this work, a copolyimide (Co-PI) film with high transparency was prepared by the copolymerization of hexafluoroisopropylidene)diphthalic anhydride (6FDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2,2′-Bis(trifluoromethyl)benzidine (TFMB) and adamantane-1,3-diamine (DAA). The effects of DAA monomers on the optical, thermal, and mechanical properties of the co-PIs were discussed in detail. We found that the preparation of polyimide (PI) based on the combination of two dianhydrides and two diamines could obtain the co-PI film with excellent comprehensive performance due to the synergy between the -CF3 group, the aliphatic ring and the aromatic structure. Through the structure and composition optimization, the co-PI film with 1.30% DAA (Q3) has a Tg of 374oC, T5 higher than 530oC, T430 of 82% and the tensile strength higher than 145 MPa. These results indicate that the Co-PI films can be successfully utilized in the development of novel heat-resistant plastic substrates for the optoelectronic engineering applications.

Soluble copolyimides containing 4,4′-isopropylidenedicyclohexanol (HBPA) isomer units: Synthesis, characterization, thermal, mechanical, and optical properties

In this work, 4,4′-isopropylidenedicyclohexanol (HBPA)-based dinitro isomers mixture (H″BPBN and H′BPBN) was synthesized and separated, and the structures of dinitro isomers were confirmed by differential scanning calorimetry and proton nuclear magnetic resonance spectroscopy. A series of copolyimides were prepared from diamino monomers with different percentages of novel diamine H″BPDA and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride via a conventional two-step procedure. All the copolyimides could afford flexible, tough, and transparent films with transmittance no less than 73% at 450 nm, which was attributed to the fact that nonplanar alicyclic diamine and the bulky and weakly polarizable trifluoromethyl hampered the formation of charge-transfer complex. Moreover, all the copolyimides were soluble not only in polar solvents such as N,N-dimethylformamide but also in low-boiling-point solvents such as dichloromethane, which was related to the fact that the existence of alicyclic diamine and bulky trifluoromethyl decreased the intermolecular force. In addition, the conformation effects of H″BPDA and H′BPDA on the aspects of thermal, mechanical, optical, and soluble performance of copolyimides were investigated and their structure–property relationships were discussed in detail.

Colorless Semi-Alicyclic Copolyimides with High Thermal Stability and Solubility

A series of colorless copolyimide films with high thermal stability and good solubility are synthesized from (trifluoromethyl)biphenyl-4,4’-diamine (TFMB) with different 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) to 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropane (6FDA) dianhydride mole ratios through one-pot solution polycondensation. These copolyimide films exhibit excellent optical transparency (T₄₀₀ > 90% and λ₀ ~305–333 nm) with a thickness of 15 μm and good solubility in most organic solvents. The excellent optical properties are mainly attributed to the low inter- and intra-molecular charge transfer interactions due to the alicyclic structure and the strong electronegative CF₃ groups. The glass transition temperature increases from 332 to 352 °C with increasing HPMDA content in the copolymers, while the thermal decomposition temperature is improved with increasing 6FDA content. These results indicate that the copolyimide films can be successfully utilized in the development of novel heat-resistant plastic substrates for the optoelectronic engineering applications.

Investigation of thermal and fluorescent properties of benzoxazole-linked triphenylamine-based co-polyimides

A series of novel fluorescent co-polyimides are obtained by combining N 1-(4-aminophenyl)- N 1-(4-(benzo[ d]oxazol-2-yl) phenyl) benzene-1,4-diamine and 4,4′-oxydianiline with four aromatic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 4,4′-oxydiphthalic anhydride, and 4,4 ′-(hexafluoroisopropylidene)diphthalic anhydride following conventional polycondensation method. The resultant co-polyimides are characterized by elemental, Fourier transform infrared spectral analysis and gel permeation chromatography. All newly prepared polyimides (PIs) exhibit shallow highest occupied molecular orbital energy levels in the range of −4.47 to −4.98 eV and have reasonable optical bandgaps. The photoluminescence spectral analysis shows blue to green emission in solution form. Thermal and solubility properties reveal that the PIs with pendant 4-(benzo[ d]oxazol-2-yl group linked to triphenylamine unit in polymer backbone impart not only good thermal stability but also appreciable solubility making these new co-polyimides versatile for multipurpose usage.

Novel hyperbranched poly(urethane–imide)s with enhanced thermal, mechanical, and UV-shielding properties

A series of novel hyperbranched poly(urethane–imide)s (HBPUIs) was synthesized and derived from as-prepared imide-containing glycol and commercial materials via an A2 + B2 + B3 approach. The chemical and morphological structures of the resulting polymers were evaluated by infrared attenuated total reflection and X-ray diffraction techniques, respectively. Compared with pure HBPU, HBPUIs exhibited better thermal stability with the 10% weight loss temperature of 282–298°C under nitrogen atmosphere, good mechanical property with the tensile strength of 2–19 MPa, and elongation at breaks of 461–896%. Moreover, optical transmissivity of all films was measured and the results showed that they had excellent transparency in the scope of visible light. Meanwhile, the cutoff wavelengths of as-prepared HBPUI films were at around 350 nm, which can block the whole ultraviolet (UV)-C (200–280 nm) and UV-B (280–320 nm), as well as a part of UV-A (320–400 nm). Furthermore, the designed photocatalytic degradation experiment of the methylene blue (MB) confirmed that HBPUI films had good UV-shielding performance with 70% degradation of MB after intense UV irradiation (400 W) for 50 min under the protection of HBPUI film with 14% imide-containing glycol. This endowed HBPUIs with potential applications prospect in UV-shielding materials.

Enhancement of dielectric constant of polyimide by doping with modified silicon dioxide@titanium carbide nanoparticles

PI/SiO₂@TiC composites with enhanced dielectric constant are synthesized by hydrolysis of TEOS into microspheres forming a thin SiO₂layer on the TiC surface followed by mechanical blending of ODA and PMDA.

Design and synthesis of high heat-resistant, soluble, and hydrophobic fluorinated polyimides containing pyridine and trifluoromethylthiophenyl units

In this study, a novel diamine monomer, 4-(4-trifluoromethylthiophenyl)-2,6-bis(4-aminophenyl)pyridine (FTPAP) was synthesized through two-step reaction from 4-trifluoromethylthiobenzaldehyde and 4-nitroacetophenone as raw materials, and then the structure of FTPAP was characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance, and mass spectrometry. A series of fluorinated polyimides were prepared from FTPAP with five commercial dianhydrides, namely, pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, oxydiphtahalic anhydride, benzophenone tetracarboxylic dianhydride, and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride. The structure and performance of the fluorinated polymers were fully characterized by FTIR, differential scanning calorimetry, thermogravimetric analysis, and wide-angle X-ray diffraction (WAXD). The inherent viscosity of polymers ranged from 0.41 to 1.45 dL g−1. These polymers displayed good solubility in polar aprotic solvents, such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone, at room temperature or on heating. Furthermore, they exhibited outstanding thermal stability with glass transition temperatures beyond 305°C, and the temperature of 10% weight loss was in the range of 514–573°C with more than 56% residue at 800°C under nitrogen. Moreover, they showed high optical transparency with the cutoff wavelengths in the range of 385–457 nm and excellent hydrophobic property with contact angle in the range of 82.8–97.6°. In addition, the results of WAXD indicated that all of the polymers presented amorphous structure.

Novel fluorinated hyperbranched polyimides with excellent thermal stability, UV-shielding property, organosolubility, and low dielectric constants

A novel fluorinated aromatic triamine, named 1,3,5-tris (4-(2-trifluoromethyl-4-aminophenoxy)phenyl) benzene (TTFAPOPB), with several –CF3 groups, prolonged chain segments, and ether bonds was first successfully synthesized via a three-step reaction. Then a series of fluorinated hyperbranched polyimides (FHBPIs) with terminal amino or anhydride groups were prepared by condensation polymerization, which were derived from three commercial dianhydrides and the obtained triamine. The prepared FHBPIs showed excellent optical properties with the transmittance reaching 94.5% at 800 nm, favorable ultraviolet (UV)-shielding property with only 27% photodegradation of methylene blue solution after intense UV irradiation for 50 min, good thermal stability with glass transition temperature between 225°C and 264°C, and 10% weight loss temperature of 520–555°C and 509–541°C, respectively, in nitrogen and air atmosphere. They also exhibited relatively good mechanical properties with tensile strength, tensile modulus, and elongation at break values of 64.2–84.2 MPa, 1.2–1.5 GPa, and 6–10%, respectively. Moreover, the introduction of –CF3 and hyperbranched architecture reduced the dielectric constants of the FHBPIs to 2.69–2.92 and increased the surface contact angles to more than 98°. Thus, the FHBPIs are promising dielectric or UV-shielding materials.

Colorless polyimides derived from 2R,5R,7S,10S-naphthanetetracarboxylic dianhydride

Colorless polyimides with excellent thermal and mechanical properties were developed from 2R,5R,7S,10S-naphthanetetracarboxylic dianhydride, and their properties were systematically compared with those based on 1S,2R,4S,5R-cyclohexanetetracarboxylic dianhydride.

High performance polyimides with good solubility and optical transparency formed by the introduction of alkyl and naphthalene groups into diamine monomers

Highly soluble and optically transparent polyimides with excellent thermal stability were prepared by the introduction of alkyl and naphthalene groups into a single diamine monomer under microwave-assisted polymerization.

Synthesis and characterization of organosoluble, transparent, and hydrophobic fluorinated polyimides derived from 3,3′-diisopropyl-4,4′-diaminodiphenyl-4′′-trifluoromethyltoluene

A novel aromatic fluorinated diamine monomer, 3,3′-diisopropyl-4,4′-diaminodiphenyl-4′′-trifluoromethyltoluene, was synthesized by coupling of 2-isopropylaniline and 4-(trifluoromethyl)benzaldehyde and its structure was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, elemental analysis, and mass spectrometry, and then used to prepare a series of fluorinated polyimides (FPIs) by polycondensation reaction with various commercial dianhydrides via conventional one-step method. The obtained FPIs present excellent solubility in most organic solvents and enough to cast into tough and flexible films. All the FPI films show good optical transparency and light color with the cutoff wavelengths in range of 307–362 nm and the average transmittance above 86%. These polymer films also exhibit high glass transition temperature in range of 261–331°C and thermal stability with 10% weigh loss above 463°C under nitrogen atmosphere. Furthermore, they exhibit outstanding mechanical properties with tensile strengths of 65.9–94.3 MPa, elongation at break of 11.4–13.8%, Young’s modulus of 1.6–1.9 GPa, and low dielectric constants in range of 2.75–3.10 at 1 MHz as well as prominent hydrophobicity with the contact angle in the range of 87.3–93.9°.

Synthesis and characterization of blue light emitting redox-active polyimides bearing a noncoplanar fused carbazole–triphenylamine unit

Photoactive organosoluble polyimides containing a fused triphenylamine–carbazole group were synthesized. These polyimides demonstrated significant potential for optoelectronic devices.