One-step High-temperature Polycondensation Procedure Research Articles

Methylethynyl-Terminated Polyimide Nanofibrous Membranes: High-Temperature-Resistant Adhesives with Low-Temperature Processability.

As an alternative to traditional riveting and welding materials, high-temperature-resistant adhesives, with their unique advantages, have been widely used in aviation, aerospace, and other fields. Among them, polyimide (PI) adhesives have been one of the most studied species both from basic and practical application aspects. However, in the main applications of solvent-type PI adhesives, pinholes or bubbles often exist in the cured PI adhesive layers due to the solvent volatilization and dehydration reaction, which directly affect the adhesive performance. To address this issue, electrospun PI nanofibrous membranes (NFMs) were employed as solvent-free or solvent-less adhesives for stainless steel in the current work. To enhance the adhesion of PI adhesives to the metal substrates, phenolphthalein groups and flexible ether bonds were introduced into the main chain of PIs via the monomers of 4,4′-oxydiphthalic anhydride (ODPA) and 3,3-bis[4-(4-aminophenoxy)phenyl] phthalide (BAPPT). At the same time, the methylethynyl group was used as the end-capping component, and the crosslinking reaction of the alkynyl group at high temperature further increased the adhesive strength of the PI adhesives. Three kinds of methylethynyl-terminated PI (METI) NFMs with the set molecular weights of 5000, 10,000, and 20,000 g/mol were first prepared via the one-step high-temperature polycondensation procedure. Then, the PI NFMs were fabricated via the standard electrospinning procedure from the soluble METI solutions. The afforded METI NFMs showed excellent melt-flowing behaviors at high temperature. Incorporation of the methylethynyl end-capping achieved a crosslinking reaction at 280−310 °C for the NFMs, which was about 70 °C lower than those of the phenylacetylene end-capping counterparts. Using the METI NFMs as adhesive, stainless steel adherends were successfully bonded, and the single-lap shear strength (LSS) was higher than 20.0 MPa at both room temperature (25 °C) and high temperature (200 °C).

Electrospun Polyphenylquinoxaline Ultraline Non-woven Fibrous Membranes with Excellent Thermal and Alkaline Resistance: Preparation and Characterization

A series of polyphenylquinoxaline (PPQ) ultrafine non-woven fibrous membranes have been first successfully prepared via the electrospinning procedure with the soluble PPQ solutions as the starting materials. For this purpose, various organo-soluble PPQ resins were synthesized via the one-step high temperature polycondensation procedure from the aromatic ether-bridged bis(α-diketone) and bis(o-diamine) monomers. Flexible ether linkages and pendant bulky phenyl substituents endowed the PPQ resins good solubility in polar aprotic solvents. The high-molecular-weight PPQ resins were dissolved in N-methyl-2-pyrrolidone (NMP) to afford the PPQ electrospinning solution except PPQ-Ia derived from 4,4′-oxydibenzil (ODB) and 3,3′-diaminobenzidine (DAB) due to the limited solubility in the solvent. All the derived PPQ ultrafine non-woven fibrous membranes maintained good structure integrity after hydrolysis aging either at room temperature (25 °C) for 72 h or at refluxing temperature (100 °C) for 24 h in an aqueous sodium hydroxide (NaOH) solution at a solid content of 20 wt%. Comparatively, the polyimide (PI) reference electrospun membrane (PI-ref) derived from 1,2,4,5-pyrromellitic anhydride (PMDA) and 4,4′-oxydianiline (ODA) lost its original structure only after boiling in the same NaOH solution within 3 h. In addition, the developed PPQ ultrafine non-woven fibrous membranes exhibited good thermal stability with the 5 % weight loss temperatures (T5%) higher than 555.0 °C in nitrogen and glass transition temperatures (Tg) in the range of 248.1–266.1 °C, respectively.

Synthesis and characterization of thianthrene-containing preimidized soluble polyimide resins and the derived films with high refractive indices and good optical transparency

A series of organo-soluble polyimide (PI) resins were prepared from a newly designed and synthesized aromatic thianthrene-containing diamine, 2,7-bis(3-aminophenoxy)thianthrene (APOT) and various aromatic dianhydrides via a one-step high temperature polycondensation procedure with N-methyl-2-pyrrolidone (NMP) as the solvent. The derived PI resins were soluble in polar aprotic solvents, including NMP and N,N- dimethylacetamide (DMAc). For comparison, several unsoluble sulfur-containing PIs were prepared from anotherpara-substituted thianthrene-containing diamine, 2,7-bis(4-aminophenylenesulfanyl)thianthrene (APTT) and aromatic dianhydrides by a two-step polycondensation procedure via poly(amic acid) (PAA) precursors at elevated temperatures as high as 300 °C. Flexible and tough PI films with the tensile strength higher than 88 MPa were successfully cast from the APOT-PI resin solution at a relatively low curing temperature of 250 °C. The meta-substituted molecular skeleton in the APOT- PIs endowed the films good optical transparency with the transmittance higher than 83% at a thickness around 10 um, which was apparently higher than those of the para-substituted APTT-PI analogues. The sulfur-rich thianthrene moiety with high molar refraction endowed the APOT-PI films high refractive indices up to 1.7147 at 632.8 nm and low birefringence in the range of 0.0064–0.0133. In addition, the PI films showed good thermal stability with the glass transition temperatures (Tg) higher than 198.3 °C and 5% weight loss temperatures higher than 510 °C in nitrogen.

Synthesis and Properties of New Fluorinated Polyimides Derived from an Unsymmetrical and Noncoplanar Diamine

AbstractA new unsymmetrical and noncoplanar diamine containing trifluoromethyl and trimethyl groups, 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐2,3,5‐trimethylbenzene (2), was synthesized using 2,3,5‐trimethylhydroquinone and 2‐chloro‐5‐nitrobenzotrifluoride as starting materials. A series of fluorinated poly(ether imide)s (PEIs) (4a–4d) were prepared from diamine 2 with four aromatic dianhydrides via a one‐step high‐temperature polycondensation procedure. The obtained PEIs were readily soluble in most organic solvents and could be solution‐cast into flexible and strong films. The resulting thin films exhibited light color and good optical transparency with a cutoff wavelength of 356–376 nm. They also displayed good thermal stability with glass transition temperatures (Tg) above 281°C, 10% weight loss temperatures in the range of 482–486°C, and the weight residue more than 55% at 800°C in nitrogen. Moreover, they revealed low dielectric constants (2.77–2.93 at 1 MHz) and low moisture absorptions (0.41%–0.57%).

Synthesis and characterization of novel semi-alicyclic polyimides from methyl-substituted tetralin dianhydride and aromatic diamines

The asymmetrical alicyclic dianhydride 3,4-dicarboxy-1,2,3,4-tetrahydro-6-methyl-1-naphthalene succinic dianhydride (MTDA, II) was synthesized from 4-methylstyrene and maleic anhydride under nitric oxide catalysis with a yield >70%. A series of semi-alicyclic polyimides (PIs) (PI–IIa∼PI–IId) were prepared by a one-step high temperature polycondensation procedure from MTDA and various aromatic diamines. For comparison, another series of PIs (PI–Ia∼PI–Id) were prepared from the analogous dianhydride 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride (TDA, I) and the same diamines. The asymmetrical molecular structure of MTDA endowed the derived PIs with good solubilities in common solvents and high optical transparencies in the ultraviolet and visible light regions by decreasing the intramolecular or intermolecular interactions of the polymer chains. The flexible and tough PI films exhibited good thermal stability up to 400 °C and showed glass transition temperatures in the range of 204–271 °C. The PI films exhibited good optical transparency with transmittances >80% at 400 nm, a cut-off wavelength <300 nm and a refractive index <1.54. A series of semi-alicyclic PIs have been synthesized from an alicyclic dianhydride MTDA and various aromatic diamines by a one-step high temperature polycondensation procedure. Flexible and tough PI films have been cast from their solution in common solvents. The PI films exhibited good thermal stability and good transparency in the ultraviolet-visible (UV-vis) light region.

High optical transparency and low dielectric constant of novel soluble polyimides containing fluorine and trifluoromethyl groups

A novel aromatic diamine containing fluorine and trifluoromethyl groups, α-bis(4-amino-3,5-difluorophenyl)-4-(trifluoromethyl)phenylmethane (1), was synthesized. Based on diamine 1 and four aromatic dianhydrides, a series of polyimides (PI) with high fluorine content were prepared via a one-step high-temperature polycondensation procedure. These obtained PIs were readily soluble in a variety of organic solvents, and they could afford flexible and strong films with low dielectric constants (2.57–2.84 at 1 MHz) and low moisture absorptions (0.23–0.45%). Thin films of these PIs exhibited high optical transparency and light color, with the cutoff wavelength at 311–354 nm and transmittance higher than 83% at 450 nm. Moreover, these PIs possessed eminent thermal stability and good mechanical properties.

Highly transparent and organosoluble polyimides derived from 2,2′-disubstituted-4,4′-oxydianilines

To improve the optical transparency and organosolubility of aromatic polyimides derived from 4,4′-oxydianiline (4,4′-ODA), two new aromatic diamines, 2,2′-diiodo-4,4′-oxydianiline (DI-ODA) and 2,2′-bis[(p-trifluoromethyl)phenyl]-4,4′-oxydianiline (BTFP-ODA) were synthesized by using 4,4′-ODA as a starting material. Novel polyimides were prepared from these two diamines with various commercially available aromatic dianhydrides via a one-step high-temperature polycondensation procedure. Most of these polyimides showed enhanced solubility in common organic solvents compared with those corresponding polyimides derived from 4,4′-ODA. Especially, polyimide derived from BTFP-ODA and rigid pyromellitic dianhydride (PMDA) was also soluble in DMF, DMAc, DMSO, NMP, and m-cresol at room temperature. These polyimides had inherent viscosities from 0.41 to 1.26 dLg−1 in NMP or m-cresol at 30°C. Transparent, flexible, and tough films can be obtained by casting from their DMAc or m-cresol solutions. These films had the UV onset wavelengths in the range of 347–391 nm and the wavelengths at 80% transmission of 445–544 nm, indicating high optical transparency. They also exhibited good thermal stability with glass transition temperatures in the range of 260–327°C. The decomposition temperatures of these polyimides at 5% weight loss under nitrogen were 429–609°C. Because of the weak carbon-iodine bond, polyimides derived from DI-ODA decomposed at lower temperatures than polyimides derived from BTFP-ODA. The effects of the substituents at the 2 and 2′ positions of 4,4′-ODA on the properties of polyimides are also discussed. High optical transparency and good solubility combined with high thermal stability make these polyimides potential candidates for soft electronics applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Novel fluorinated polyimides derived from 9,9-bis(4-amino-3,5-difluorophenyl)fluorene and aromatic dianhydrides

Novel fluorinated polyimides (PIs) were prepared from 9,9-bis(4-amino-3,5-difluorophenyl)fluorene with three aromatic dianhydrides via a one-step high-temperature polycondensation procedure. These obtained PIs showed excellent solubility and could be readily soluble in a variety of organic solvents such as NMP, DMAc, DMF, CHCl 3, CH 2Cl 2 and THF. All the PIs could afford flexible and strong films with low dielectric constants (2.62–2.79 at 1 MHz) and low moisture absorptions (0.18–0.41%). Thin films of these PIs exhibited high optical transparency and light color, with the cutoff wavelength at 341–355 nm and transmittance higher than 80% at 450 nm. Meanwhile, these PIs possessed eminent thermal stability, with decomposition temperatures ( T d) above 570 °C in both air and nitrogen atmospheres and glass transition temperatures ( T g) beyond 376 °C. Moreover, these fluorinated PI films showed low surface free energy and hydro -oleophobic character. The contact angles on the films for water and glycerol were in the range of 102.3–107.9° and 94.0–100.3°, respectively. In comparison with the analogous PI non-containing fluorine group, these fluorinated PIs showed better solubility, higher optical transparency, lower dielectric constants and lower surface free energy.

High solubility and optical transparency of novel polyimides containing 3,3′,5,5′-tetramethyl pendant groups and 4- tert-butyltoluene moiety

A series of novel polyimides ( 3a– d) were prepared from 3,3′,5,5′-tetramethyl-4,4′-diaminodiphenyl-4”- tert-butyltoluene ( 1) with four aromatic dianhydrides via a one-step high-temperature polycondensation procedure. The obtained polyimides showed excellent solubility, with the dissolvability at a concentration of 10 wt% in most amide polar solvents and chlorinated solvents. Their films were nearly colorless and exhibited high optical transparency, with the UV cutoff wavelength in the range of 322–350 nm and the wavelength of 80% transparency in the range of 395–414 nm. They also showed low dielectric constant (2.72–2.91 at 1 MHz) and low water absorptions (0.37–0.62%). Moreover, these polyimides possessed high glass transition temperatures ( T g) (above 321 °C) and good thermal stability with 10% weight loss temperatures in the range of 526–547 °C in nitrogen atmosphere. In comparison with the analogous polyimides non-containing 3,3′,5,5′ -tetramethyl pendant groups, the resultant polyimides 3a– d showed better solubility, higher optical transparency and lower dielectric constant.

Synthesis and properties of fluorinated poly(ether ketone imide)s based on a new unsymmetrical and concoplanar diamine: 3,5-Dimethyl-4-(4-amino-2-trifluoromethylphenoxy)-4′-aminobenzophenone

A new unsymmetrical and concoplanar aromatic diamine monomer containing trifluoromethyl and dimethyl groups, 3,5-dimethyl-4-(4-amino-2-trifluoromethylphenoxy)-4′-aminobenzophenone (3), was synthesized in a three-step reaction using 2,6-dimethylphenol and 4-nitrobenzoyl chloride as starting materials. A series of fluorinated poly(ether ketone imide)s (PEKIs) (5a–d) were prepared from diamine 3 with four aromatic dianhydrides via a one-step high-temperature polycondensation procedure. The obtained PEKIs were readily soluble in some organic solvents and could be solution cast into flexible and tough films. These PEKI films exhibited high optical transparency with a cutoff wavelength of 354–375 nm and low dielectric constants (2.26–2.45 at 1 MHz). They also showed good thermal stability with glass-transition temperatures (Tgs) above 289 °C, 10% weight loss temperatures in the range of 518–531 °C, and the weight residue more than 52% at 800 °C in nitrogen. Moreover, the PEKI films possessed tensile strengths and initial modulus ranged from 91 to −128 MPa and 1.7 to 2.4 GPa, respectively. Due to their properties, these fluorinated PEKIs could be considered as photoelectric and microelectronic materials.

Novel polyfluorinated polyimides derived from α,α-bis(4-amino-3,5-difluorophenyl)phenylmethane and aromatic dianhydrides: Synthesis and characterization

A novel aromatic diamine containing bulky lateral phenyl unit and fluorine groups ortho-substituted to the amino groups in the structure, α,α-bis(4-amino-3,5-difluorophenyl)phenylmethane (4FMA) was synthesized and characterized. 4FMA was polymerized with four aromatic dianhydrides to afford a series of polyimides (PIs) via a one-step high-temperature polycondensation procedure. All the PIs were amorphous and showed good solubility not only in polar aprotic solvents, but in many common solvents, such as cyclopentanone and tetrahydrofuran. The soluble polymers formed flexible, tough and transparent films. The films had a tensile strength, elongation at break, and tensile modulus in the ranges 85–107MPa, 4–7%, 1.7–2.8GPa, respectively. The polyimides also exhibited high-Tg (292–338°C), good thermal stability, good dielectric strength, low dielectric constants, and low water uptakes due to the introduction of the polyfluorinated substituents in the polymer backbone. As expected, the PI films showed good transparency in the UV–Vis light region with cutoff wavelength as low as 318nm and transmittance higher than 60% at 450nm. PI-4 derived from 4FMA and fluorinated dianhydride 6FDA exhibited low light-absorption in the near-infrared region, especially at the optocommunication wavelength of 1310nm and 1550nm. The remarkable combined properties indicate their potential applications in microelectronic and optoelectronic fabrications.