Polyimide Precursor Research Articles

Anomalous Polyimide Nanoparticles Prepared from Blending of Unlike Polymers

Anomalous polyimide (PI) nanoparticles with controllable morphology, i.e., porous hollow structures, hollow structures, or bowl-like structures, were fabricated by blending a second polymer with poly(amic acid) (PAA, the precursor of PI) through the reprecipitation method and subsequent imidization. The phase separation between PAA and the porogen induced the formation of various hollow PI nanoparticles. The hollow morphology was mainly affected by the compatibility/interaction between PAA and the porogen. Hollow PI nanoparticles with superficial pores (ca. 30 nm), smooth surface, or holes in their surfaces can be obtained by selecting a suitable porogen, respectively.

Printed Nonvolatile Memory for a Sheet-Type Communication System

By using state-of-the-art printing technologies and functional inks, we have demonstrated organic nonvolatile flexible random-access-memory matrices with a nondestructive read-out capability and a time-continuous current output; these functionalities have not been simultaneously achieved even by silicon-based conventional memory. A memory cell comprising three transistors becomes possible with inkjet printing and other solution-based processes, which can use ferroelectric copolymer ink comprising poly(vinylidenefluoride-co-trifluoroethylene) and insulating ink comprising polyimide precursors properly within the planer plastic substrate. A large ldquo1 : 0rdquo current ratio of 105 is observed in air when it is annealed at 135degC , which is sufficiently low to be compatible with many plastic substrates. When stored in air, the ldquo1 : 0rdquo ratio was still 104 after 15 days and 103 after 5 months, which is sufficient for practical applications. Furthermore, human-scale communication sheets were manufactured as the first demonstration utilizing large-area organic memories.

Preparation and characterization of carbon molecular sieve membranes for gas separation—the effect of incorporated multi-wall carbon nanotubes

A new class of multi-wall carbon nanotubes (MWCNTs)/carbon nanocomposite thin films was successfully prepared by incorporating (MWCNTs) into polyimide (PI) precursor solution. The carbon films were obtained in only one coating step by spin-coating technique on a macroporous alumina substrate and were pyrolyzed at 773 K. The structure and single gas permeation properties of PI-based carbon membranes incorporated with or without MWCNTs were investigated. From the FE-SEM images, the pure carbon membranes have a thin dense permselective layer with few closed pores while the permselective layer of the MWCNTs/carbon nanocomposite thin films are porous due to the structure of nanotubes. The MWCNTs/carbon nanocomposite thin films exhibited that the ideal carbon dioxide flux was 866.6 Barrer (1 Barrer = 1×10 −10 cm 3 (STP) cm cm −2 s −1 cm Hg −1) and the separation factor of CO 2/N 2 was 4.1 at room temperature and 1 atm, which was 2–4 times of magnitude higher than that of pure carbon membrane prepared by the same procedures and conditions.

Preparation of vertical alignment layers by blending polyimide precursors with and without side chains

A series of polyimides (PIs) were prepared from the precursors, blends of a poly(amic acid) and a side-chain poly(amic acid), based on a diamine 4′-(tert-butyldimethylsiloxy)biphenyl-4-yl 3,5-diaminobenzoate (DPA). The blended polyimide (bl-PI) films were relatively tough. The surface properties of the bl-PI films were characterised by surface energy measurement, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-IR). The results showed that the non-polar side chains were highly enriched on the surface and 90° pretilt angles of liquid crystal molecules were generated regardless of side chain content. For comparison, the copolyimides (co-PI) with different DPA contents were synthesised. It was found that the enrichment of the side chain on the surface increased with increasing DPA content and the pretilt angles of liquid crystal molecules rose from 3° to above 20° when DPA content increased from 10% to 30%. For the polyimides based on a diamine without a non-polar end group, 4′-biphenyl-4-yl 3,5-diaminobenzoate (DABBE), both bl-PIs and co-PIs could only generate the same low pretilt angles. In conclusion, by blending poly(amic acids) based on DPA, tough vertical alignment layers could be prepared.

Preparation and properties of conductive silver/photosensitive polyimide nanocomposites

AbstractA new electrically conductive photoresist has been developed. It is based on the dispersion of silver nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 2‐Mercaptopropionic acid was used as the surfactant to modify the silver nanoflake surface for the dispersion of silver nanoflakes in the polymer. The silver/PSPI nanocomposites showed electrical conductivity at a low silver content of 10 wt %. The electrical conductivity of the silver/PSPI nanocomposites ranged from 10 to 104 S/cm, which was dependent on the silver weight fraction in the resist formulation. Patterns with a resolution of 30 μm were obtained from the silver/PSPI nanocomposites. The silver/PSPI nanocomposites had excellent thermal properties. Their glass transition temperatures were above 360 °C and thermal decomposition temperatures were over 420 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1575–1583, 2009

Novel Partial Esterification Reaction in Poly(amic acid) and Its Application for Positive-Tone Photosensitive Polyimide Precursor

We found novel quantitative esterification in poly(amic acid) (PAA) by reacting with N,N-dimethylformamide dialkyl acetals (DFAs). Different alkyl ester was obtained by changing the alkyl group in DFAs. The esterification ratio was determined by amount of DFAs. The reaction proceeds under mild condition without any catalysis. It has not been reported such a kind of quantitative partial esterification before. The partial esterification allowed us to control the solubility of PAA to alkaline solutions. The strict solubility rate control to alkaline solution of PAA was quite important for positive tone photosensitive polyimide (posi PSPI). The partial esterification of PAA gave us a way to strict dissolution control. By using it, we could obtain posi PSPI just mixing with diazonaphthoquinone compound.

Colorless Polyimides Derived from Cycloaliphatic Tetracarboxylic Dianhydrides with Controlled Steric Structures (4). Applications to Positive-type Photosensitive Polyimide Systems with Controlled Extents of Imidization.

Novel colorless polyimides (PIs) derived from 1R, 2S, 4S, 5R-cyclohexane tetracarboxylic dianhydride (a new hydrogenated pyromellitic dianhydride (PMDA) with a controlled steric structure, H"-PMDA) with various aromatic diamines were applied to positive-type photosensitive PI systems. The H"-based PI precursors, poly(amic acid)s (PAAs), were partially imidized with controlled extents of imidization (χI) by adding established amounts of a cyclodehydration reagent (acetic anhydride/pyridine) into the PAA solutions and stirring at room temperature for 24 h while keeping the homogeneity of the reaction mixture except when 4,4'-oxydianiline (4,4'-ODA) was used as a diamine component. A good linear relationship was obtained between the amount of cyclodehydration reagent added and the extent of imidization (%) in the partially imidized PAAs (pi-PAAs) obtained. The pi-PAA cast films (10 μm thick) displayed a considerably high light transmittance at 365 nm (> 85%) in addition to its adequately controlled alkali-solubility. The photosensitive films consisting of the pi-PAAs and diazonaphthoquinone (DNQ) as a photosensitizer provided good positive-tone patterns through uv-irradiation and subsequent development using a 2.38 wt% tetramethylammonium hydroxide (TMAH) aqueous solution. The fully imidized films showed very high glass transition temperatures exceeding 300oC in some cases, sufficient film-forming ability (flexibility), and excellent transparency. The use of a thermally crosslinkable mono-functional end-capper, nadic anhydride (NA), was very effective to inhibit gelation during the chemical imidization process even in the H"-PMDA/4,4'-ODA system owing to its adequately controlled molecular weight. In addition, thermal curing of the NA-terminated system significantly improved the film toughness.

Ultralow-Dielectric-Constant Films Prepared from Hollow Polyimide Nanoparticles Possessing Controllable Core Sizes

Polyimide (PI) is a candidate material that is showing promise for use in a wide range of applications in several advanced technologies. In this study, we employed the reprecipitation method and subsequent imidization to prepare unique hollow PI nanoparticles (NPs) by blending a suitable polymer porogen with the PI precursor in the form of individual NPs. The hollow structures were induced through phase separation between the PI and the porogen, a process that was influenced by the compatibility between the two polymers. We then assembled multilayered films by depositing the hollow PI NPs electrophoretically onto a substrate. After spin-coating a solution of the PI precursor and then subjecting the system to thermal treatment, the individual PI NPs were bound to their adjacent neighbors, thereby improving the film strength to some extent. We obtained dense, uniformly packed films having controlled thicknesses in the range from 500 nm to 10 μm. This strategy provided films in which air voids existed between and within the composite PI NPs; as a result, the dielectric constant reached as low as 1.9.

Microstructures and Linear/Nonlinear Optical Properties of Monolayered Silver Nanoparticles

We investigated the microstuctural properties, as well as the linear and the nonlinear optical properties of silver nanoparticles embedded within a polymer matrix. The monolayered silver nanoparticles were fabricated by using a thermal treatment of thin silver films sandwiched between two polyimide (PI) precursor films. From the transmission electron microscopy images of the PImatrix-embedded silver nanoparticles, we found that silver nanoparticles arranged in a monolayer were formed within the polymer matrix. The average diameter (D) and the volume fraction (f) of silver nanoparticles depended on the silver film thickness (t) before undergoing thermal treatment: D = 5.0 nm (f = 14 %) and D = 11.8 nm (32 %) for sample A (t = 2.5 nm) and sample B (t = 10 nm), respectively. The monolayered silver nanoparticles exhibited a surface plasmon eect with tunable resonance wavelengths: SPR = 464 nm (D = 5.0 nm, f = 14 %) and SPR = 523 nm (D = 11.8 nm, f = 32 %). The variation in the surface plasmon resonance wavelengths ( SPR) for the two dierent silver nanoparticles could be described by applying the Maxwell-Garnett eectivemedium approximation to the composite material. From the Z-scan experiment, we obtained the two-photon-absorption coecients

Polyimides with main-chain photosensitive groups: Synthesis, characterization and their properties as liquid crystal alignment layers

In this work, a series of polyimides containing main-chain chalcone groups and side-chain cinnamate or acetate groups were synthesized. In the synthetic route, three dianhydride monomers were prepared by the reactions of 1,3-dihydro-1,3-dioxoisobenzofuran-5-carbonyl chloride with 1,3-bis(4-hydroxylphenyl)prop-2-en-1-one, 1,3-bis(4-(2-hydroxyethyl)phenyl)prop-2-en-1-one, and 1,3-bis(4-hydroxyphenyl)-pent-1-en-3-one-4-en, respectively. The precursor polyimides were obtained by the polycondensation of the dianhydride monomers with 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and the in situ imidization. After the polymerization, the final products were obtained by introducing the side groups through the reactions of the polyimide precursors with cinnamoyl chloride or acetic anhydride. The chemical structures and properties of the polyimides were characterized by elemental analysis, 1H NMR, 13C NMR, FTIR, GPC, and thermal analysis. The polyimides show high thermal stability and good solubility in aprotic polar organic solvents. The polyimides can undergo sensitive [2+2] photocycloaddition reaction upon the UV light irradiation. After irradiation with linearly polarized UV light, the polyimide thin films can induce 5CB liquid crystal molecules to homogeneously align in the liquid crystal cells. Both the alignment ability and pretilt angles of the molecular orientation depend on the chemical structures of the polyimides.

Influence of Surface Modified MWCNTs on the Mechanical, Electrical and Thermal Properties of Polyimide Nanocomposites

Polyamic acid, the precursor of polyimide, was used for the preparation of polyimide/multiwalled carbon nanotubes (MWCNTs) nanocomposite films by solvent casting technique. In order to enhance the chemical compatibility between polyimide matrix and MWCNTs, the latter was surface modified by incorporating acidic and amide groups by chemical treatment with nitric acid and octadecylamine (C18H39N), respectively. While the amide-MWCNT/polyimide composite shows higher mechanical properties at low loadings (<3 wt%), the acid-MWCNT/polyimide composites perform better at higher loadings (5 wt%). The tensile strength (TS) and the Young’s modulus (YM) values of the acid-MWCNT/polyimide composites at 5 wt% MWCNT loadings was 151 and 3360 MPa, respectively, an improvement of 54% in TS and 35% in YM over the neat polyimide film (TS = 98 MPa; YM = 2492 MPa). These MWCNT-reinforced composites show remarkable improvement in terms of thermal stability as compared to that for pure polyimide film. The electrical conductivity of 5 wt% acid modified MWCNTs/polyimide nanocomposites improved to 0.94 S cm−1(6.67 × 10−18 S cm−1for pure polyimide) the maximum achieved so far for MWCNT-polyimide composites.

Superhydrophobic Polyimide Films with a Hierarchical Topography: Combined Replica Molding and Layer-by-Layer Assembly

Artificial superhydrophobic surfaces with a hierarchical topography were fabricated by using layer-by-layer assembly of polyelectrolytes and silica nanoparticles on microsphere-patterned polyimide precursor substrates followed with thermal and fluoroalkylsilane treatment. In this special hierarchical topography, micrometer-scale structures were provided by replica molding of polyamic acid using two-dimensional arrays of polystyrene latex spheres as templates, and nanosized silica particles were then assembled on these microspheres to construct finer structures at the nanoscale. Heat treatment was conducted to induce chemical cross-linking between polyelectrolytes and simultaneously convert polyamic acid to polyimide. After surface modification with fluoroalkylsilane, the as-prepared highly hydrophilic surface was endowed with superhydrophobicity due to the bioinspired combination of low surface energy materials and hierarchical surface structures. A superhydrophobic surface with a static water contact angle of 160 degrees and sliding angle of less than 10 degrees was obtained. Notably, the polyimide microspheres were integrated with the substrate and were mechanically stable. In addition, the chemical and mechanical stability of the polyelectrolyte/silica nanoparticle multilayers could be increased by heat-induced cross-linking between polyelectrolytes to form nylon-like films, as well as the formation of interfacial chemical bonds.

Carbonization of aromatic polyimides and pore development in carbon films

Imidization and carbonization behaviors of various aromatic polyimide films synthesized from an anhydride with different diamines were investigated by FTIR and TG/DTG methods. Imidization of poly (amic acid) s with pendant -CH3 and-CF3 groups directly bonded to phenyl ring required long times for curing at 300°C. Pyrolysis and carbonization of polyimides having pendant groups occurred over a little wider temperature range than those having no pendant groups. The carbonize films were of ultramicroporous character with pore width of ca. 0.5 nm. Pore development in carbon films was found to depend strongly on whether the precursor polyimide contains fluorine or not ; fluorine containing polyimide gave a high microporous surface area of 1400 m2/g and micropore volume of 0.39 mL/g.

A hierarchical structure through imprinting of a polyimide precursor without residual layers

A patterned polyimide without a residual layer is obtained by imprinting with the assistance of a residual solvent. The effects of the wetting behaviors of the poly-amic acid (PAA) solution coated on various surfaces are examined and the formation of hierarchical patterns without residual layers is demonstrated. polydimethylsiloxane (PDMS) and PEI/PDMS are used as imprinting molds with Si and 300 nm SiO2/Si as substrates. The results indicate that the various ambits of patterns without a residual layer are formed due to the dewetting phenomena caused by surface tension (Suh 2006 Small 2 832). During imprinting, PDMS with a low surface energy makes the PAA solution flow away from its surface exposing the contact area due to dewetting. Self-organized hierarchical structures are also obtained from this process due to effective dewetting. The present study provides a new approach for fabricating patterns without residual layers and the consequent preparation of hierarchical structures, which is considered to be impossible using the lithographic technique.

Molecular design of POSS core star polyimides as a route to low-κ dielectric materials

Abstract Star polyimides incorporating the polyhedralsilsesquioxane (POSS-NH2) unit were prepared by in situ curing of polyamic acid macromolecules with amino POSS, octa (aminopropylsilsesquioxane), for the molecular-level design of low dielectric constant (low-κ) materials that can be used to manufacture integrated circuits. Octameric POSS-NH2 having restricted rotation by multiple point attachment to the polyimide backbone is shown to introduce free volume into the films, thereby lowering their dielectric constants. A process for synthesizing POSS-polyimide star nanocomposites is reported, comprising a step forming porous-type POSS and subsequent step with polyimide precursor. The POSS-NH2 containing polyimides exhibit a number of desirable properties including low-water absorption and high thermal stability. Systematic studies demonstrate that proper insertion of POSS into a polyimide backbone can give rise to a reduction in the material's dielectric constant while also improving its mechanical and thermal properties.

A simple approach toward low‐dielectric polyimide nanocomposites: Blending the polyimide precursor with a fluorinated polyhedral oligomeric silsesquioxane

AbstractThis article describes a new and simple method for preparing polyimide nanocomposites that have very low dielectric constants and good thermal properties: simply through blending the polyimide precursor with a fluorinated polyhedral oligomeric silsesquioxane derivative, octakis(dimethylsiloxyhexafluoropropyl) silsesquioxane (OF). The low polarizability of OF is compatible with polyimide matrices, such that it can improve the dispersion and free volume of the resulting composites. Together, the higher free volume and lower polarizability of OF are responsible for the lower dielectric constants of the PI‐OF nanocomposites. This simple method for enhancing the properties of polyimides might have potential applicability in the electronics industry. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6296–6304, 2008

Structural change and proton conductivity of phosphosilicate gel–polyimide composite membrane for a fuel cell operated at 180 °C

Proton-conductive composite membranes were prepared from phosphosilicate gel powders and a commercially available polyimide precursor. The conductivity of a composite membrane containing 75 wt.% of gel powder was about 2.5 × 10 −3 S cm −1 at 180 °C under more than 0.4%RH. However, under dry N 2 atmosphere at 180 °C, the conductivity decreased with time because of the formation of Si 5O(PO 4) 6 crystals. The open circuit voltage (OCV) of a fuel cell in which the phosphosilicate gel–polyimide composite sheet was used as electrolyte and Pt-loaded carbon paper sheets were used as electrodes in the membrane electrode assembly, was about 0.85 V at 80 °C with a flow of hydrogen and air, and the OCV decreased to about 0.70 V at temperatures higher than 100 °C. At 180 °C under 2%RH, the cell OCV was 0.67 V; power density of about 14 mW cm −2 was obtained with current density of 40 mA cm −2. Consequently, the fuel cell using the composite sheet as an electrolyte was verified to operate at temperatures from room temperature to 180 °C.

Molecular design of nanometric zinc borate-containing polyimide as a route to flame retardant materials

Zinc borate (Zn 2B 6O 11·3H 2O) nanoparticles were successfully prepared by using an emulsion liquid membrane (W/O/W emulsion) to control the size of particles with Na 2B 4O 7·10H 2O, boric acid and ZnSO 4·7H 2O as raw materials. All materials were dispersed with the polyimide (PI) precursor, poly (amic acid). Using a combination of dissolving the poly (amic acid) and mixing fatty acid surfactant-coated zinc borate nanoparticles; we have demonstrated the formation of nanocomposites with uniform nanoparticles dispersion. We report the first deposition of nanocomposite polyimides from solution using spin-coating. The microstructures and morphology of the as-obtained samples were studied by X-ray diffraction (XRD), infrared spectra (IR), scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA).

Synthesis and Copolymerization Study of New Polyimide Precursors with Potential Application in Optical and Photonic Field

New polyimide precursors were synthesized by simple one step procedure. (Z)-3-(4-Nitro-phenylcarbamoyl)-acrylic acid (A2), (Z)-3-(4-Ciano-phenylcarbamoyl)-acrylic acid (A3), (Z)-3-(4-Diethyl-phenylcarbamoyl)-acrylic acid (A4) and (Z)-3-[N′-(2,4-Dinitro-phenyl)-hydrazinocarbonyl]-acrylic acid (A6) were characterized by FT-IR, FT-NMR and UV-VIS spectroscopy. Test copolymerization successfully yielded copolymers that were characterized by FT-IR and FT-NMR spectroscopy. Improved solubility of these copolymers make them candidates for potential NLO applications.

Controlled Formation of Optically Reflective and Electrically Conductive Silvered Surfaces on Polyimide Film via a Direct Ion-Exchange Self-Metallization Technique Using Silver Ammonia Complex Cation as the Precursor

Double-surface-silvered polyimide films have been successfully fabricated using silver ammonia complex cation ([Ag(NH3)2]+) as the silver precursor and 3,3',4,4'-benzophenonetetracarboxylic dianhydride/4,4'-oxidianile- (BTDA/ODA-) based poly(amic acid) (PAA) as the polyimide precursor via a direct ion-exchange self-metallization technique. The process has been clarified to involve the loading of silver(I) into PAA via ion exchange, the thermally induced reduction of silver(I) to silver(0) and the concomitant imidization of PAA to polyimide upon thermal treatment, the subsequent silver-catalyzed and oxygen-assisted decomposition of the polyimide overlayer, and the self-accelerated aggregation of silver clusters on the film surface to produce well-defined surface silver layers. By employing [Ag(NH3)2]+ solution with a concentration of only 0.01 M and an ion-exchange time of no more than 10 min, the controlled formation of highly reflective and conductive silver surfaces upon thermal treatment at 300 degrees C for less than 4.5 h indicates that the present work provides an efficient route and an effacious silver species for polyimide surface metallization. Although the alkaline characteristics of [Ag(NH3)2]+ have a strong hydrolysis effect on the polyimide precursor chains, the final metallized films retain the key mechanical and thermal properties of the pure polyimide. Films were characterized by ATR-FTIR, XPS, ICP-AES, SEM, TEM, DSC, TGA, reflectivity, conductivity, and mechanical measurements.