Semi-aromatic Polyimides Research Articles

Dual-processable semi-aromatic fluorinated polyimides with outstanding optical transparency and low dielectric constants prepared from in situ [2 + 2] thermal polymerization

A facile strategy has been developed to produce semi-aromatic polyimides through direct in situ thermo-polymerization. The obtained polyimides exhibit favorable performances and are presented as potential candidates applied in microelectronics.

Synthesis and characterization of optically transparent semi-aromatic polyimide films with low fluorine content

A series of novel semi-aromatic polyimides with low fluorine content were prepared from alicyclic dianhydrides, i.e. 1,2,4,5-cyclohexane-tetracarboxylic dianhydride (CHDA) and bicyclo[2.2.2]octa-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA), and three aromatic diamines containing ortho-substituted methyl and pendent phenyl groups, respectively. These polyimides exhibited excellent solubility even though their fluorine content lower than 10 wt%. Chemical resistance to MEK and aqueous alkali of films was also satisfied for application as flexible substrates. The semi-aromatic polyimides showed outstanding heat resistance with Tg values up to 387 °C and good mechanical strength. These films had excellent optical transparency with cutoff wavelengths of 282–286 nm, transmittance >89% at 500 nm and yellowness indices <14.8. Especially, PIBF-3 and PIBF-6 were extremely transparent and very light color with thickness of 70 μm. Their improved optical transparency and elimination of coloration was mainly attributed to weakened electrophilicity of alicyclic dianhydrides, steric hindrance and distorted non-coplanar caused by ortho-substituted and bulky pendent groups.

Towards solution-processable, thermally robust, transparent polyimide-chain-end tethered organosilicate nanohybrids

The main challenge to developing future display substrates is to synthesize flexible substrate materials that also have excellent optical and thermal properties, and low thermal expansion number. In this study, a novel trifluoromethylated asymmetric aromatic diamine, 4-[[4-(4-amino-2-trifluoromethylphenoxy)phenyl]sulfonyl-3-(trifluoromethyl)]benzenamine (AFPSFB), was synthesized through nucleophilic substitution. Conventional two-step polycondensation of AFPSFB with commercially available tetracarboxylic dianhydrides enabled the fabrication of fully or semi-aromatic polyimides (PIs). The resulting PIs were highly soluble in polar aprotic solvents with good optical and thermal properties. Next, polyhedral oligomeric silsesquioxane containing an amine group (NH2-POSS) was reacted with the resulting soluble PI. All the PI-POSS nanohybrids displayed excellent optical properties, including high transparency (>91% at 400 nm), low refractive index (<1.5589), and very small birefringence (<0.0025 at 637 nm). End-capping of the POSS and chemical bonding between the POSS and PIs significantly enhanced the thermal and electrical properties. The results provide useful information for designing molecular architectures for manufacturing high-performance flexible substrates in future display devices.

Understanding the Effect of the Dianhydride Structure on the Properties of Semiaromatic Polyimides Containing a Biobased Fatty Diamine.

In this work we report the effect of the hard block dianhydride structure on the overall properties of partially biobased semiaromatic polyimides. For the study, four polyimides were synthesized using aliphatic fatty dimer diamine (DD1) as the soft block and four different commercially available aromatic dianhydrides as the hard block: 4,4′-(4,4′-isopropylidenediphenoxy) bis(phthalic anhydride) (BPADA), 4,4′-oxidiphthalic anhydride (ODPA), 4,4′-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA), and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). The polymers synthesized were fully organo-soluble thermoplastic branched polyimides with glass transition temperatures close to room temperature. The detailed analysis took into account several aspects of the dianhydrides structure (planarity, rigidity, bridging group between the phtalimides, and electronic properties) and related them to the results obtained by differential scanning calorimetry, rheology, fluorescence and broadband dielectric spectroscopy. Moreover, the effects of physical parameters (crystallization and electronic interactions) on the relaxation behavior are discussed. Despite the presence of the bulky branched soft block given by the dimer diamine, all polyimides showed intermolecular charge transfer complexes, whose extent depends on the electronic properties of the dianhydride hard block. Furthermore, the results showed that polyimides containing flexible and bulky hard blocks turned out fully amorphous while the more rigid dianhydride (BPDA) led to a nanophase separated morphology with low degree of crystallinity resulting in constrained segmental relaxation with high effect on its mechanical response with the annealing time. This work represents the first detailed report on the development and characterization of polyimides based on a biobased fatty dimer diamine. The results highlight the potential of polymer property design by controlled engineering of the aromatic dianhydride blocks.

Polyimides with Heavy Halogens Exhibiting Room-Temperature Phosphorescence with Very Large Stokes Shifts.

Semiaromatic polyimides (PIs) and imide compounds containing heavy halogens (Br, I) in pyromellitic moieties were designed and synthesized to examine their photoluminescence properties. Solutions of imides and PI films exhibited reddish-color room-temperature phosphorescence (RTP) with very large Stokes shifts (ca. 10000 cm-1). In addition, the PI films showed small-Stokes-shifted fluorescence emissions at around 540 nm with absorption bands arising from aggregated PI chains at 400-500 nm. Enhanced phosphorescence observed for the PI films under vacuum indicates that the RTP lifetime is significantly influenced by the triplet-triplet energy transfer to atmospheric oxygen. These PIs with very-large-Stokes-shifted RTP are applicable as spectral conversion materials in displays, photovoltaic devices, and crop cultivators, as well as to oxygen/air sensors.

Synthesis of new autophotosensitive semiaromatic hyperbranched polyimides with excellent mechanical properties and low birefringences

A series of autophotosensitive semiaromatic hyperbranched polyimides (PIs) were prepared by (A2 + B3)-type method and endcapped with 2,6-dimethylaniline. The photosensitive hyperbranched PIs (PHBPIs) showed excellent solubility, excellent optical properties, and low birefringences in the range of 0.0022–0.0042 caused by their special hyperbranched structures and alicyclic chain segments reduced both intramolecular and intermolecular charge transfer complex effect. It also showed excellent mechanical properties with tensile modulus in the range of 1.37–1.60 GPa and good thermal stabilities. Photolithographic property of the polymer was examined by ultraviolet exposure. Scanning electron microscopic analysis revealed a highly resolved pattern with a line width of 8 μm.

Synthesis and characterization of novel optically transparent and organosoluble polyimides based on diamines containing cyclohexane moiety

Two new aliphatic diamine monomers, one containing cyclohexane moiety and the other containing both cyclohexane and trifluoromethyl moieties, were synthesized. Two series of semi-aromatic polyimides (PIs) derived from the two diamines were prepared by one-step solution polycondensation using m-cresol as solvent. These PIs had inherent viscosities between 0.32 and 1.20 dL/g and could be processed to colorless, flexible and tough films. Compared with the PIs without trifluoromethyl group, the PIs with trifluoromethyl group showed better solubility in many solvents such as DMAc, NMP and m-cresol. It was also found that all the PI films had high optical transparency in the visible region with the cut-off wavelength of 291–379 nm. However, compared with the non-fluorinated PI 5 series, the PI 4 series showed lighter color. Furthermore, thermal analysis showed that the synthesized PIs had 5 % weight lost temperature (T 5%) in N2 of 372–425 °C, and the glass transition temperature (T g) of 221–270 °C. Moreover, all the PIs showed good mechanical properties with the tensile strengths of 80–114 MPa, tensile moduli of 2.7–3.5 GPa, and elongation at breaks of 5.1–26.5 %.

Aggregation behavior of organic-soluble semi-aromatic polyimides in N -methylpyrrolidone systems

Aggregation behavior of the organic-soluble semi-aromatic polyimides, whose degrees of imidization range from 69 to 96%, obtained using 4,4′-oxydianiline, 4,4′-diamino-3,3′dihydroxybiphenyl, and bicyclo[2.2.2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA) in N-methylpyrrolidone (NMP), NMP/cyclohexanone, and NMP/γ-butyrolactone (BCDA-based polyimides) were studied by static light scattering (SLS) and dynamic light scattering (DLS). The DLS analyses for the multirelaxation modes demonstrated the specific character unlike flexible polymers that the single BCDA-based polyimide chains first associate with each other to form small clusters in the dilute region, and then expand to large aggregates by the entanglements between the small clusters with an increasing concentration into the semi-dilute region. Given the semi-aromatic structure of BCDA-based polyimides weakening the charge transfer (CT) interaction between the diamine and the dianhydride unit, it is concluded that the unique aggregation behavior of BCDA-based polyimides is dominated by the balance between the driving force for the “organic solubility” given by both the increase in bulkiness and the decrease in the CT interaction, and that for the “organic insolubility” derived from both the hydrogen-bonded interaction of the phenolic hydroxyl groups and the π–π interaction of the phenyl rings. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Preparation and characterization of highly transparent and colorless semi-aromatic polyimide films derived from alicyclic dianhydride and aromatic diamines

A novel meta-substituted aromatic diamine containing trifluoromethyl and sulfonyl groups in the backbone, i.e., 2,2′-bis[4-(3-amino-5-trifluoromethylphenoxy)phenyl]sulfone (m-6FBAPS), was synthesized and characterized. A series of semi-aromatic polyimides were prepared from 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA) and various aromatic diamines. These polymers exhibited excellent solubility, high thermal stabilities and good mechanical properties. All semi-aromatic polyimide films showed considerably improved optical transparency as comparing with traditional aromatic ones due to the incorporation of alicyclic moieties. They gave the UV cutoff wavelengths of 292–314 nm, transmittance at 450 nm > 91% and yellowness indices <3.8. The extremely transparent and entirely colorless films were obtained from the polymers incorporated with bulky electron-withdrawing trifluoromethyl and sulfonyl groups in diamine moieties, such as PI-2, PI-5 and PI-6. Their excellent optical properties are attributed to the distorted molecular conformation combined with the weakened electron-accepting and electron-donating properties of dianydride and diamines, which significantly restrained the formation of inter-/intra-molecular charge transfer interactions.

Preparation and Characterization of Polyimide/ZnO Nano-hybrid Films Exhibiting High Refractive Indices

A series of polyimides (PIs) / zincoxide (ZnO) nano-hybrid materials exhibiting high transparency, high refractive indices, and low wavelength dispersions were prepared by the in situ thermal decomposition method. First, the optical properties of six kinds of matrix PIs were investigated, and a fully aromatic PI derived from 4,4'-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA) and 9,9-bis (4-aminophenyl) fluorene (BAFL) and a semi-aromatic PI derived from 3,3';4,4'-biphenyl tetracarboxylic dianhydride (BPDA) and 4,4'-diaminodicyclohexylmethane (DCHM) were chosen as transparent matrices. Secondly, two types of ZnO precursors, which are thermally decomposed into ZnO, were chosen, and the thermal decomposition behaviors of the ZnO precursors dissolved in PI films was examined by far-infrared (Far-IR) and variable temperature mid-infrared (IR) spectra. The PI/ZnO hybrid films prepared from Zn(NO3)26H2O as a ZnO precursor exhibit yellowish coloration, though the transparency of the hybrid films was significantly improved by using a preheated Zn(NO3)26H2O at 110 °C as a ZnO precursor or using a soluble PI solutions in place of poly(amic acid) solutions. The PI/ZnO hybrid films exhibited high thermal degradation temperatures, and 6FDA-BAFL and BPDA-DCHM/ZnO hybrid films exhibited higher refractive indices by up to +0.0037 (+0.25 %) and +0.0130 (+1.10 %), respectively, compared with the pristine PIs. In the case of BPDA-DCHM, the effect of hybridization with ZnO on the increase in the refractive index at infinite wavelength (n∞) relative to the coefficient of wavelength dispersion (D) is more significant than that of modifying the chemical structures of PIs.

Alicyclic polyimides – a colorless and thermally stable polymer for opto-electronic devices

Alicyclic polyimides were prepared from polyalicyclic monomers using a two-step method. Light absorption of polyimides was elucidated from quantum chemistry. The alicyclic polyimide films were colorless, and the transparencies in the visible region were over 85%. The semi-aromatic polyimide films had an average refractive index range of 1.599 to 1.617, and that of a full-alicyclic polyimide was 1.522. The birefringencies were nearly zero. Semi-aromatic polyimides were soluble in aprotic polar solvents like DMAc. However, the non-aromatic (full-alicyclic) polyimides were insoluble except sulfuric acid. All the alicyclic polyimides have the 5% weight loss temperatures in nitrogen over 450 °C, and 400 °C in air. They possess glass transition temperatures over 280 °C. The alicyclic polyimide films have a tensile modulus range of 1.3–3.0 GPa, and a tensile strength range of 38–145 MPa. Especially semi-aromatic polyimide films display high strength. They have an elongation at break range 5–30%. All the polyimides exhibited amorphous patterns and broad dispersive peaks of diffraction around at 16° (2θ).

Optical Measurements of Polyimide Films in UV and VUV Regions

Absorption and reflection measurements of polyimides (PIs) PMDA-BAPP, BTDA-BAPP, and CBDA-BAPP were performed using synchrotron radiation as a light source in UV and VUV regions. Absorption spectra were obtained by Kramers-Kronig analyses from reflection spectra. Molecular orbital calculations were performed for model PI compounds. Optical transitions at the absorption tails of aromatic PIs (PMDA-BAPP and BTDA-BAPP) are characteristic of localized electronic transitions of dianhydride units while those at the absorption tail of semi-aromatic PI (CBDA-BAPP) are characteristic of charge transfer transitions. At high-energy regions, phenyl-group π-π* transitions are observed at about 6.2 eV. Very strong absorption peaks are also observed at about 16.0 eV for aromatic PIs and at about 15.0 eV for semi-aromatic PI. These results are characteristic of optical transitions from HOMO-level C 2p orbitals to high-energy region C 2p orbitals above LUMO levels.

Synthesis and Characterization of Semiaromatic Polyimides Containing POSS in Main Chain Derived from Double-Decker-Shaped Silsesquioxane

Synthesis and Characterization of Semiaromatic Polyimides Containing POSS in Main Chain Derived from Double-Decker-Shaped Silsesquioxane

Cycloaliphatic–aromatic polyimides based on diamines with azobenzene unit

A new family of functionalized semiaromatic polyimides has been developed. Cycloaliphatic–aromatic polyimides, derived from the polycondensation of 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA) with various diamines bearing azobenzene group, have been prepared and characterized. Molecular structural characterization for the resulting polymers has been achieved by 13C NMR, 1H NMR, FTIR and UV–visible spectroscopies. Light-induced optical anisotropy, in novel azobenzene functionalized polyimides, has been studied by holographic polarization grating recording performed at 514.5 nm line of Ar + laser. Two-wave mixing technique has been employed to inscribe the gratings in these polymers. Formation of gratings has been investigated with two s–s and s–p polarized writing beams. The kinetics of grating recording observed within the studied polymers is discussed in relation to their structure.

New Negative-type Photosensitive Alkaline-developable Semi-aromatic Polyimides with Low Dielectric Constants Based on Poly(amic acid) from Aromatic Diamine Containing Adamantyl Units and Alicyclic Dianhydrides, A Cross-linker, and A Photoacid Generator

A new negative-working and alkaline-developable photosensitive polyimide precursor based on semi-aromatic poly(amic acid)s (4), 4,4′-methylenebis[2,6-bis(hydroxymethyl)]phenol (MBHP) as a cross-linker, and a photoacid generator (5-propylsulfonyloxyimino-5H-thiophen-2-ylidene)-2-(methylphenyl)acetonitrile (PTMA) has been developed. Novel polymers 4 were prepared by ring-opening polyadditions of alicyclic dianhydrides (1), 1,2,3,4-cyclobutanetetracarboxylic dianhydride (1a), bicyclo[2.2.2]oct-7-ene-2,3;5,6-tetracarboxylic dianhydride (1b), and bicyclo[2.2.1]heptane-2-methanecarboxylic-3,5,6-tricarboxylic-2,3:5,6-dianhydride (1c) with 1,3-bis(4-aminophenoxy)adamantane (3). Polymers 4 were converted to corresponding poly(imide)s (5) by thermal treatment. The dielectric constants (ε) of 5 estimated from the refractive indices were 2.72–2.74. The photosensitive polyimide precursor containing 4 (60 wt %), MBHP (30 wt %), and PTMA (10 wt %) cast from 2-methoxyethanol solution showed a clear negative image featuring 15 μm line and space patterns when it was exposed to 436 nm light, post-exposure baked at 110 °C for 3 min, followed by developing with 2.38 wt % aqueous tetramethylammonium hydroxide (TMAH) solution at 25 °C for 40 s.

Synthesis of semiaromatic polyimides from aromatic diamines containing adamantyl units and alicyclic dianhydrides

AbstractWe prepared new semiaromatic polyimides from alicyclic dianhydrides and aromatic diamines containing adamantyl and biadamantyl units. Polycondensations were performed in 1‐methyl‐2‐pyrrolidinone at room temperature for 7 h and then 80 °C for 23 h, giving poly(amic acid)s with inherent viscosities up to 0.58 dL/g. Poly(amic acid)s were converted to corresponding poly(imide)s by thermal treatment. Poly(imide)s showed relatively high thermal stability (5% weight loss around 450 °C) and low dielectric constants (2.69–2.79). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 144–150, 2004

Semi-Aromatic Polyimides with Low Dielectric Constant and Low CTE

Semi-aromatic polyimides (PIs) possessing simultaneously a low dielectric constant ( K) and low linear coefficient of thermal expansion ( CTE) were molecularly-designed. Two PI systems were focused on, i.e. the s-BPDA/CHDA polyimide derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride with trans-1,4-cyclohexanediamine and CBDA/TFMB derived from 1,2,3,4-cyclobutanetetracarboxylic dianhydride and bis(2,2′-trifluoromethyl)benzidine. In the s-BPDA/CHDA system, poly(amic) acid (PAA) polymerization using the common procedure was prevented by strong salt formation at the initial stage. However, heating the salt-forming reaction mixture at a selected temperature for a short period allowed the system to polymerize and resulted in a high-molecular-weight PAA (reduced viscosity ηred &gt; 2 dl g−1). On the other hand, in the CBDA/TFMB system, a high-molecular-weight PAA ( ηred &gt; 3 dl g−1) was readily obtained by choosing the solid content without any salt formation. The chosen PIs almost achieved the current goal; CTE &lt; 20 ppm K−1, K &lt; 3.0, and Tg &gt; 300°C concurrently with adequate film flexibility. In particular, CBDA/TFMB accomplished a very low K (∼2.6). Although these PIs have a much lower thermo-oxidative stability than wholly aromatic PIs, the results suggested that there is no serious problem for the short-term thermal stability required for soldering processes.

Aliphatic Polyimides Derived from Polyalicyclic Monomers

Tetracarboxylic dianhydrides bearing a polyalicyclic structure, bicyclo[2.2.1]-heptane-2,3,5,6-tetracarboxylic 2,3:5,6-dianhydrides (BHDA), bicyclo[2.2.2]-octane-2,3,5,6-tetracarboxylic 2,3:5,6-dianhydrides (BODA), (4arH,8acH)decahydro-1t,4t:5c,8c-dimethanonaphthalene-2,3,6,7-tetracarboxylic 2,3:6,7-dianhydrides (DNDA), and bicyclo[2.2.1]heptane-2-exo,3-exo,5-exo-tricarboxyl-5-endo-acetic 2,3:5,5-dianhydride (BSDA) were synthesized and polycondensated with aromatic diamines or a polyalicyclic diamine, bis(aminomethyl)bicyclo[2.2.1]heptane (BBH), in DMAc, NMP, DMI or HMPA at room temperature or 60–105°C under nitrogen. The polymerization solutions gave the flexible and free-standing polyimide films after being cast on glass plates and then cured. The films were soluble in aprotic polar solvents such as DMAc and NMP at room temperature. Among the films, some dissolved in CHCl3 or 1,4-dioxane. The polyimides showed good thermal stability and the 5% weight loss temperatures in N2 were over 450°C. The polyimide films exhibited Tg values in the range of 280–400°C. The cutoff wavelengths of the non-aromatic polyimides such as PI(DNDAdx-BBH) and PI(BHDAdx-BBH) were shorter than 235 nm, and around 290–330 nm for the semi-aromatic polyimides. The transparencies in the visible region (400–780 nm) were over 85%. The flexible polyimide films possessed an average refractive index range of 1.522–1.617, and the optical anisotropies were 0.000–0.017. The dielectric constant ε values that were estimated from the refractive indices according to the modified Maxwell’s equation were 2.55–2.87.

Semiaromatic Polyimides based on Bis(Aminomethyl)Bicyclo[2.2.1]Heptane

Semiaromatic polyimides with a polyalicyclic structure were prepared by the polycondensation of bis(aminomethyl)bicyclo[2.2.1]heptane (BBH) with aromatic dianhydrides. The corresponding poly(amic acid)s possessed an inherent viscosity range of 0.60–1.00 dl g−1. The polyimides were soluble in organic polar solvents and most of them formed flexible, free-standing films. The polyimides had good thermal stability with no significant weight loss up to approximately 400 °C and possessed a 5% weight loss temperature range of 428–465 °C. These polyimide films showed a tensile modulus range of 1.4–3.0 GPa, a tensile strength range of 62–115 MPa, and an elongation at break range of 5.4–6.1%. The semiaromatic polyimide films exhibit a cut-off wavelength around 322–362 nm and are entirely colourless, while the cut-off wavelengths of PI(PMDA-DDE) and PI(BPDA-DDE) films were 426 and 376 nm respectively. The origin of coloration in the aromatic polyimides and the lack of colour in the semiaromatic polyimides were elucidated from the standpoint of molecular orbital (MO) calculations of the model compounds using semiempirical AM1 and INDO/S methods. The calculated λmaxof the M(PMDA-BBH) was 371 nm, and the first excited state is mainly characterized by an n−π* transition. Based on both the MOs and the difference in electron density between the ground and the first excited states, the first excited state is attributable to light-induced polarization in the five-membered imide ring. The λmaxof the M(PMDA-DDE) model for a representative aromatic polyimide was calculated to be 392 nm. From the charge difference map, it is theoretically evident that the coloration in the aromatic polyimides caused intramolecular charge transfer between the diamine and dianhydride moieties.