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[Display omitted] • The effect of coordination bond and chain rigidity on the crystalline structure was discussed. • Novel polyimide films with low linear thermal expansion coefficients were made. • Mechanical Properties of polyimides were enhanced by introducing coordination bonds. Coordination bonds and chain rigidities play severe roles in crystalline structure and property of polyimides (PIs). This study developed various polyimides with metal-diimine coordination bonds and varying chain rigidities. How coordination bonds and chain stiffness affect the semi-crystalline structure of polyimide films was investigated. Results from Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra confirmed the successful synthesis of coordinated polyimide films. Wide-angle diffraction (WAXD) results revealed that the crystallization behavior of PIs with flexible chains is significantly affected by additional coordination bonds, while the crystallization of PIs with rigid structures is primarily influenced by the chain rigidities. Compared to coordinated PIs with amorphous structure, PIs with both coordination bonds and semi-crystalline structures exhibited enhanced heat resistance, crystallinity, and dimensional stability. Notably, the coordinated PI-BP-Cu film with the highest chain rigidity in this study demonstrated excellent mechanical properties, with a tensile strength of 280 MPa, initial modulus of 5.7 GPa, and outstanding dimensional stability, characterized by a linear thermal expansion coefficient of 8.9 ppm/K (40–300 °C). These findings significantly enhance its suitability for use in metal/non-metal bonding composite materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two series films were prepared using APBIA and TFMB as diamine, PMDA and ODPA as dianhydride, TAPOB as crosslinking agent. • The addition of TAPOB maked for the adverse effects caused by adding fluorinated groups and lowering imidization temperature. • The XTTOP5-0.15 film with suitable monomer ratios and imidization temperature showed excellent comprehensive performance. • In molecular simulation, TAPOB content of PBII model is controlled by a TAPOB connecting chains of different lengths. In order to solve the problem of high-water absorption and low transparency of benzimidazole polyimide (PBII) films, this study introduced fluorine-containing groups into the benzimidazole polyimide molecule chains, and a series of benzimidazole polyimide films with different fluorine-containing ratios were prepared. In addition, a micro-branched crosslinking structure was established by adding triamino compounds to the system, and the effect of the micro-branched crosslinking structure on the film properties was investigated. The research showed that adding a certain amount of fluorine-containing groups could effectively improve the optical properties and decrease water absorption of polyimide films while having a small effect on the heat resistance and thermal dimensional stability. The incorporation of a small amount of triamino compounds effectively compensated for the adverse effects on the mechanical properties, heat resistance, and thermal dimensional stability caused by the addition of fluorine-containing groups and lowering the imidization temperature. In addition, the water absorption could be further reduced by establishing a cross-linked structure. In this study, a new design idea was provided to achieve the balance of heat resistance, thermal dimensional stability, water absorption, transparency, and mechanical properties of benzimidazole polyimide films. [ABSTRACT FROM AUTHOR]

[Display omitted] • The transparent, flexible, semi-aliphatic CPI films were elaborately prepared. • CPI-55 film has excellent thermal stability and high transparency. • The outstanding dielectric and mechanical properties are given to CPI-55 film. • CPI-55 film has an excellent prospect for application in the display technology. A set of colorless polyimide (CPI) films with norbornene-aliphatic ring structures has here been prepared through polycondensation reactions by using cyclopentanone bis-spironorbornane tetracarboxylic dianhydride (CpODA), 4,4′-(hexafluoroisopropyl)diphthalic anhydride (6FDA) and 4,4′-diaminodiphenyl ether (ODA) monomers as raw materials. The transmissivities, dielectric properties and thermal stabilities of CPI films are optimized by adjusting the CpODA-to-6FDA molar ratios. Compared with the aromatic and aliphatic PI films, the thermal stabilities and transmissivities of CPI films are well balanced. Moreover, the CPI films possessed low dielectric constants and low dielectric losses. The thermal expansion coefficients, temperatures at a 5% weight loss and glass-transition temperatures are maintained at 31–41 ppm K−1, 461–484 °C and 348–362 °C, respectively. In addition, the transmittances (86–89%), dielectric constants (2.15–2.47) and dielectric losses (<0.023) are all prominent. In short, the CPI films have been shown to have a high potential for use in the display technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ester groups were introduced the molecular chain of PI to enhance its crystallinity. • The PI films with multiple ester groups exhibited low dielectric loss at high frequency. • The PI films possessed low moisture rate and maintained low dielectric loss even in water. • The introduction of ester groups enhanced the thermal stability and mechanical properties of PI. Polyimides are ideal candidates for 5G high-frequency communications due to their good thermal stability, mechanical properties and processability. However, the exploration of how to reduce their high-frequency dissipation factor (D f) remains an urgent and alluring challenge. Inspired by the molecular structure of liquid crystal polyester, which is insensitive to high-frequency electric fields, here we design two series of polyimides derived from diamines with multiple ester groups (AXEB, X = 1, 2 or 3) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) or p-phenylene bis (trimellitate anhydride) (TA2EB). We investigated the effects of ester number on the aggregation structure, water absorption, dielectric properties, heat resistance and mechanical properties of the polyimides and find that the D f of the multiple ester-containing polyimides decreases rapidly with increasing frequency and number of ester groups. Wide-angle X-ray diffraction analysis, polarized optical microscopy observations and molecular dynamics simulations show that the unique properties of these polyimides benefit from the tight packing of the molecular chain and the strong intermolecular interaction force caused by the ester group, as well as the resulting prolonged dipole relaxation time and the greatly reduced water absorption. Therefore, the polyimide films show extremely low D f values of 0.0030 for AXEB-6FDA and 0.0013 for AXEB-TA2EB. Furthermore, AXEB-TA2EB also shows excellent thermal stability, mechanical properties, electrical properties and permittivity. More importantly, their ultralow moisture rate (<0.83 %) ensures that the high-frequency D f remains stable in different humid environments, even after soaking in water. This method can also be extended to other polymers, thus providing a new strategy for the design of low dielectric loss materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The organic filler fluoroelastomers were introduced into polyimide, which realized controllable preparation of ultra-low permittivity (ε = 1.21) all-organic polyimide composite films for the first time. • The FEM/PI composite films exhibited excellent thermal stability, outstanding mechanical properties and high hydrophobicity. • The preparation process of FEM/PI composite films is simple and the developed films presented excellent practical application potential. Dielectric materials with low permittivity are urgently needed in the field of microelectronics due to the development of integration and miniaturization of integrated circuits. In this work, a series of all-organic polyimide (PI) films with ultra-low-permittivity and high hydrophobicity were successfully synthesized by introducing a kind of fluoroelastomer (FEM). And the significant permittivity reduction phenomenon was discussed through molecular dynamics simulations and practical tests. It was assumed that the hydrogen bond significantly inhibited the dipolar polarization of the FEM/PI composite system, which played an important role in determining the dielectric properties of FEM/PI composite films. At a low filler content of 7 wt%, FEM/PI composites exhibited the optimum permittivity (ε) of 1.21 at 106 Hz, which was the lowest permittivity of the PI films, while a low water absorption of 0.44 % and high thermal stability with a 10 % decomposition temperature (T d 10 %) of 548 °C were also observed. This simple and effective strategy of fabricating ultra-low-permittivity PI film is a potential way to realize commercial process. [ABSTRACT FROM AUTHOR]

A novel highly transparent polyimide film with reduced CTE value was synthesized by introducing bulky pendent group and amide unit and the effects of designed structures on the optical transparency and dimensional stability of polyimide film were studied in detail. [Display omitted] • Several PI films were fabricated by introducing bulky pendent group and amide unit. • The effects of introduced groups on the properties of PI films were studied. • The film possesses good optical properties with λ cutoff of 384 nm and T 450 nm of 81%. • The film with designed structure displays reduced CTE value of 45 ppm/℃. Monomers of 4,4′-((4-(trifluoromethyl)phenyl)methylene)bis(2,6-dimethylaniline) (3FTMDT) and N,N'-(2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diyl)bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxamide) (TA-TFMB) were synthesized and designed to fabricate polyimide film with simultaneously designed bulky pendent group and amide unit in polymer chains and their effects on the optical transparency and dimensional stability of films were investigated in detail. The prepared polyimide (3FTMDT/TA-TFMB) film possesses highly optical transparency (λ cutoff = 384 nm, T 450 nm = 81%, Haze = 0.86) and lighter color (L *=95.09, a *=-2.14, b *=6.44) with the in-plane coefficient of linear thermal expansion of 45 ppm/oC. Meanwhile, the film presents good thermal stability and mechanical properties, with a glass transition temperature (T g) of 337 °C and 5 wt% decomposition temperature of 459 °C under N 2 , the fracture strength and tensile modulus of the film are 105 MPa and 2.2 GPa, respectively. The film also exhibits low dielectric performances with intrinsic dielectric constant of 2.29 and dielectric loss of 8 × 10-3 at 10 KHz, and which could keep stable up to 280 °C. In addition, the film shows good solubility in common solvents and is easy to be processed. The highly transparent polyimide film with reduced coefficient of linear thermal expansion is expected to be used as substrate material for flexible display or other photoelectric fields. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two series of novel aromatic polyimide films containing xanthone moiety and amide groups were prepared through a two-step procedure. • The maximum T g of the PI film is 400 °C. • The minimum CTE of the PI film is 2.3 ppm·K−1. • The PI films has fluorescence properties and the highest absolute fluorescence quantum efficiency is 2.9%. In recent years, an increasing amount of attention has been paid to polyimide (PI) substrate materials with high glass transition temperature (T g) and low coefficient of thermal expansion (CTE) due to the rapid development of the flexible OLED field. To improve T g and CTE, rigid conjugated structure and hydrogen bonds are designed. Two diamines containing amide and rigid xanthone groups were synthesized (p -DAXBA and m -DAXBA). Two series of PI films, PIa and PIb, were prepared by polymerization of DAXBA with different dianhydrides, i.e., pyromellitic dianhydride (PMDA), 3,3′,4,4′-biphenyl tetracarboxylic diandhydride (BPDA), 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and 4,4′-oxydiphthalic anhydride (ODPA). PIa films prepared by p -DAXBA have more hydrogen bonding, closer molecular chain packing, and stronger molecular charge transfer (CT) effect, as well as better heat resistance, dimensional stability, and mechanical properties than PIb films prepared by m -DAXBA. However, their absolute fluorescence quantum efficiency and transparency are weaker than those of PIb films. A PIa-1 film prepared by p -DAXBA/PMDA has a T g of 400 °C, tensile strength of 192 MPa, modulus of 6.14 GPa, and CTE as low as 2.3 ppm·K−1. Both PIa-4 and PIb-4 films prepared by ODPA show fluorescent property with maximum emission wavelengths at 509 and 508 nm, and their absolute fluorescence quantum efficiencies are 1.5% and 2.9%, respectively. The as-prepared PI films exhibit potential application in the flexible OLED field. [ABSTRACT FROM AUTHOR]

[Display omitted] • Clean fabrication of elastomer with improved adhesion capability is proposed. • A combination of dual-function azide-containing crosslinkers is attempted. • Noncatalytic C-H insertion capabilities of azide groups are utilized. • Triethoxysilane group affords adhesion capability on OH-containing substrates. The utilization of the noncatalytic C-H insertion capability of the nitrene intermediate of azide-containing compounds is proposed in this study for the clean fabrication of polymer-inorganic functional hybrid materials with elasticity and adhesion capabilities. For this purpose, a combination of dual-function azide-based crosslinkers composed of azidosilane (6-azidosulfonylhexyltriethoxysilane, AS) and diazide-based crosslinkers [tri(ethylene glycol)diazidoformate, GDAF] is attempted. AS affords good adhesion capability of polymer materials to OH-containing inorganic substrate/fillers, while GDAF undergoes a simultaneous C-H insertion reaction with polymer chains in bulk, affording enough crosslinking sites to improve elasticity. Through adjustments of the compositions and curing conditions, the styrene butadiene rubber compound with the proposed combination of crosslinkers exhibits good mechanical properties and excellent elasticity, as demonstrated by the low tension set value. The compound also exhibits improved adhesion capability on OH-containing silica, quartz and polyimide films, providing functional hybrid materials with an ideal combination of elasticity and adhesion capabilities suitable possibly for cutting-edge applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • The diphenylpyridine and diphenylpyrimidine moiety were introduced into PI chains. • The ultralow CTE (< 5 ppm K−1), high T g (> 450 °C) and good flexibility were achieved. • Effect of chain rigidity, chain packing and in-plane orientation on CTE was studied. • The impact of hydrogen bonds formed at the PAAs stage on CTE was discussed. The flexibility of organic light-emitting diode (OLED) displays highly depends on the properties of the flexible substrates. In this paper, a series of aromatic polyimides have been fabricated via the copolycondensation of pyromellitic dianhydride (PMDA), the two different rigid heterocyclic diamines, 2,5-bis(4-aminophenyl)pyrimidine (PRM) or 2,5-bis(4-aminophenyl)pyridine (PRD), and another flexible diamine, 4,4′-oxydianiline (ODA). The performance of the polyimide films could be systematically tailored by means of adjusting the main-chain rigidity, as well as the close packing and orientation of polymer chains by the formation of the intermolecular hydrogen bonds between poly(amic acid)s. The optimal results (PIb-4, PIb-5, PIc-2) showed that the polyimides were endowed with ultra-high glass transition temperature (T g) exceeding 450 °C, low coefficient of thermal expansion (CTE) at 0–5 ppm K−1 and excellent thermal stability (T d5% = 570–590 °C). Meanwhile, all of them exhibited sufficient flexibility, the elongation at break at of 40–60%, extremely high tensile strength of 250–380 MPa and modulus of 4.1–6.1 GPa. Hence, the polyimide films should be the promising candidates for application as the polymer substrates for flexible OLED displays. [ABSTRACT FROM AUTHOR]

• Transparent polyimides containing different methyl side groups were synthesized. • The effects of methyl were discussed with assistant of density functional theory. • Polyimide exhibits the best optical transmittance of 82% at 400 nm, T g of 407 °C. • Polyimides show excellent solubility in common solvents. Highly transparent polyimides (PIs) with excellent combined properties are in great demand for flexible optical devices. In this work, transparent PIs were synthesized by fluorinated aromatic dianhydride (6FDA) and three aromatic diamines containing methyl side groups with different amount and position. These PIs possessed moderate to great optical transparency and excellent solubility. With four methyl groups at 2,2′,5,5′-position in diamine, 2255TMB–PI exhibited the best transmittance up to 82% at 400 nm. In all cases, PIs were determined to have low dielectric constants (2.84–2.99) and high glass transition temperature (above 390 °C, even up to 407 °C for 2255TMB–PI). In addition, the toughness of these PI films was also proven by a tensile strength of 130 – 156 MPa. In spite of the electron donating character of methyl groups, their steric hindrance was found to have significant effect on the combination properties of PIs. Spatial structures and packing morphology are thought to be the main contribution. Therefore, this work provided an easy way to prepare highly transparent polyimides with excellent combined properties by controlling steric hindrance through methyl side groups. [ABSTRACT FROM AUTHOR]