Polyimide Main Chain Research Articles

Acid-doped Polyimide Electrolyte Membranes with Pendant Benzimidazole Groups for Fuel Cell Applications

A benzimidazole pendant diamine, 5-(1H-benzoimidazol-2-yl)- benzene-1-3-diamine, was synthesized from 2-(3,5-dinitro- phenyl)-1H-benzoimidazole. Here the dinitro compound was prepared from 3,5-dinitrobenzoyl chloride and 1,2-phenylene diamine. The benzimidazole pendant diamine was used to synthesis polyimide with pendant benzimidazole groups. These pendant benzimidazole groups present in polyimide main chain were used to dope phosphoric acid and phosphomolibdic acid thereby proton conducting polyelectrolyte membranes were prepared from them. The effect of changing concentration of phosphoric acid and phosphomolibdic acid on the properties of the membranes was studied. It was found that doping of phosphoric acid increased the conductivity at 30% R.H. and further addition of phosphomolibdic acid further increased the conductivity, which can be a promising applicable candidate for the high temperature operation and low humidity required fuel cell.

A solution processible semiconducting polymer interlayer for blue light-emittingdiodes

Polyimide containing triphenylamine derivative (TPD-PI) was synthesized to prepare apolymer interlayer having insolubility in common nonpolar solvents for light-emittingpolymers. The TPD-PI was prepared from the synthesized diamine monomer and4,4′-(hexafluoropropylidene)-diphthalic anhydride by the standard two-step polymerizationmethod, which involved ring-opening polymerization and subsequent cyclodehydration. Weincorporated this novel semiconducting polymer (TPD-PI) between the hole conductinglayer (PEDOT:PSS) and the blue-emitting layer (PFO, poly(dioctylfluorene)) of alight-emitting diode. The molecular architecture of the TPD-PI interlayer means that itis soluble in most aprotic polar solvents, and completely insoluble in acetone,toluene, and xylene, which are used as solvents for most emitting layers; thesesolubility properties make the direct spin-coating of the interlayer possible. Thesurfaces of interlayer have stability against the general organic solvents for apolymeric layer with a nanometre scale. The efficiency increases from 0.25 to0.351 cd A−1 and the lifetime rises by 50% as a result of the insertion of the interlayer, which also hasadvantages in the following areas: interface structure, solubility characteristics, energeticposition, hole transport of the interlayer, and thermal stability of the polyimide mainchain.

Synthesis and characterization of organosoluble aromatic copolyimids

A series of aromatic copolyimides was successfully synthesized from the commercial pyromellitic dianhydride (PMDA) with a commercial diamine p-phenyldiamine (PDA) and a diamine 4,4′-methylenebis-(2-tert-butylaniline) (MBTBA) specially designed by the authors. The copolyimides were characterized by Infra-red (IR), Nuclear Magnetic Resonance (NMR), Gel Permeation Chromatography (GPC), Ultraviolet Visual (UV-Vis), Thermogravimetic Analysis (TGA) and Dynamic Mechanical Analysis (DMA). The copolyimide was precipitated in m-cresol in the polymerization process when the molar ratio of MBTBA and PDA was lower than 6/4. The number-average molecular weight of the soluble copolyimides measured by GPC was larger than 4.0 × 104, and the polydispersity index was higher than 1.5. Only one glass transition temperature of these copolyimides was detected around 360°C by DMA. The copolyimides did not show appreciable decomposition up to 500°C under N2, and the thermal stability of the copolyimide increased a little with the introduction of PDA into the polyimide main chain.

Synthesis and Properties of Polyimides Containing Multiple Alkyl Side Chains

A series of diamine monomers, i.e., 2,2‘-bis{4-[3,4,5-tris(n-alkan-1-yloxy)benzoate]}-4,4‘-biphenyldiamines containing multiple alkyl side chains, were synthesized in which the length of the alkyl side chains was varied from 5 to 18 carbon atoms. Polyimides were prepared from the diamines and pyromellitic dianhydride (PMDA), 3,3‘4,4‘-biphenyltetracarboxylic dianhydride (BPDA), 2,2‘-dibromo-4,4‘,5,5‘-biphenyltetracarboxylic dianhydride (DBBPDA), and 2,2‘-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), respectively, using a one-step method in 1,2-dichlorobenzene or 1-chloronaphthalene. Most of the polymers had good solubility in chlorinated solvents. Several copolyimides were prepared: BPDA, 2,2‘-bis(trifluoromethyl)benzidine (PFMB), and C14 and C16 diamines. The solubility of copolyimides was dramatically affected by different monomer addition sequences. The high-molecular-weight polyimides could be solution cast into flexible, tough films except for those based on PMDA. The side chains that contained at least 10 carbon atoms crystallized. The melting points of the crystalline regions increased as the length of the side chains increased. Variable-temperature (VT) solid state 13C nuclear magnetic resonance (NMR) showed that the polyimide containing C18 side chains crystallized at room temperature. A wide-angle X-ray diffraction (WAXD) study showed that the spacing between the main chains increased as the number of carbon atoms in the side chains increased. The diameter of aggregated backbones was 2.14 nm, indicating several polyimide main chains stacked each other to form supermolecular, nanoscale structures. Three polyimides and one copolyimide were used to prepare alignment layers. The films generated liquid crystal pretilt angles of 6, 9, 90, and 90°, respectively.

Effect of Reactive Channel Functional Groups and Nanoporosity of Nanoscale Mesoporous Silica on Properties of Polyimide Composite

Novel covalently bonded nanoscale mesoporous silica (NMS)/polyimide (ODPA−BAPP) nanocomposites were synthesized through the bridge 3-aminopropyltrimethoxysilane. Abundant reactive amino functional groups inside the mesopore channels of NMS can interconnect with numerous polyimide main chains, forming multilinked and complex NMS/PI networks. These multilinkages, NMS inherent nanoporosity, and the uniform dispersion of NMS in polyimide significantly improve thermal stability, mechanical properties, elongation, moisture absorption, and dielectric constant of these novel materials over those of neat polyimide. For instance, the storage modulus is increased by 160%, the decomposition temperature by 35.7 °C, and the glass transition temperature by 14.5 °C. The maximum elongation increases by 66%, hardly observed in other polyimide nanocomposites, probably because the covalent bond and NMS nanopore can absorb more energy than pristine poyimide before failure. The nanoporosity of the core of the NH2-NMS material within the nanocomposite film is most likely responsible for the decrease of dielectric constant by 10%.

Synthesis and Characterization of Main Chain Polyimides Containing Chalcone Derivatives for LC Alignment

Two soluble polyimides containing chalcone derivatives in the main chains were successfully prepared using the Mitsunobu reaction at room temperature, reacting diols with diimides. With this reaction procedure the high temperature imidization step normally needed for the synthesis of polyimides is avoided and the polymers can be used for temperature sensitive applications. The main chain polyimides were characterized with FT-IR, NMR and DSC and the extent of the photoreaction was measured with FT-IR and UV-vis spectroscopy. Isobestic points were observed in the absorption spectral changes at the early stage of UV irradiation as a result of a single photochemical process. Further photoirradiation is accompanied by deviation from the isobestic points, implying that another photochemical process has started. With FT-IR investigations it was concluded that photodimerization is the process occurring at low UV exposure doses and that trans-cis isomerization is starting simultaneously at higher doses. The optical anisotropic properties were investigated upon exposure of the polymers as thin films to linearly polarized UV (LPUV) light of different doses. Selected crosslinking in the parallel direction relative to the direction of the LPUV light and subsequent optical anisotropy in the film were achieved.

Photo-Alignment Properties of Photo-Crosslinked Films of Liquid Crystalline Polymers Containing Chalcone Derivatives

ABSTRACT Side-chain polymethacrylates, side-chain polyimides, and main-chain polyimides containing chalcone derivatives were synthesized in order to investigate the photo-alignment behavior of liquid crystalline (LC) molecules in the LC cell fabricated from the polymer film irradiated with linearly polarized UV (LPUV) light under different conditions. The side-chain polyimides and the main-chain polyimides containing the 6FDA (4,4′-(hexafluoro-isopropylidene)-diphthalic anhydride) derivative are soluble in organic solvents and fusible, while the main-chain polyimides with the BPDA (4,4′-biphthalic anhydride) derivative show only fusibility. Only the polymethacrylate and main-chain polyimides with the BPDA derivative demonstrate a smectic A phase. The mixture of 4-cyano-4′-n-pentylbiphenyl (5CB) and dichroic dye was filled in the LC cell. In the LC cell using the polymethacrylate film irradiated in the LC state and the side-chain polyimide film irradiated above glass transition temperature, 5CB was easily aligned parallel to the electric vector of incident LPUV light, while 5CB in the LC cell using the irradiated main-chain polyimide film was aligned perpendicular to the electric vector of incident LPUV light.

The Structural Effects on the Pretilt Angle of Alignment Materials with Alkylcyclohexylbenzene as a Side Chain in Polyimides

ABSTRACT We have investigated the relationship between the surface property of rubbed polyimides and the variation of pretilt angle according to the side chain and main chain structures. We calculated the surface free energy of synthesized polyimide surface by measuring the contact angles of distilled water and methylene iodide on the rubbed polyimide surface. Consequently, we found that pretilt angles on rubbed polyimides changed according to the side chain and main chain structures of the polyimide. Our calculations show that LC pretilt angles of polyimide films with a liquid crystal structure as a side chain were approximately 90° when a linear and rigid polyimide main chain and a side chain of suitable length were employed.

Photo-alignment Properties of Main-Chain Liquid-Crystalline Polyimides Containing Chalcone Derivative

We investigated photo-alignment properties of main-chain polyimides prepared from acid anhydrides [4,4′-(hexafluoro-isopropylidene) diphthalic anhydride (6FDA) or 4,4′-biphthalic anhydride (BPDA)] and diamine derivatives containing a chalcone group. The polyimides in the film state were irradiated with linearly polarized UV (LPUV) light under different conditions. The liquid-crystalline (LC) cell was fabricated from the polyimide film irradiated with LPUV light. A mixture of a low molecular liquid crystal (4-cyano-4′-n-pentylbiphenyl: 5CB) and a dichroic dye was filled in the LC cell. 5CB in the LC cell was easily aligned perpendicular to the electric vector of the incident LPUV light.

Highly Thermal Stable Lambda-Shaped Main-Chain Nonlinear Optical Polyimide

ABSTRACTIn poled electro-optical (E-O) polymer systems, the relaxation of oriented chromophores is maintained by either introducing the guest chromophores into host polymers with high glass transition temperatures, or by confining the chromophores in polymer networks. Various highly stable NLO polymers have been prepared by grafting NLO-active chromophores onto aromatic polyimide backbones. The pendent chromophores of side chain polyimides can be stabilized at low temperature because they have rigid rod-like structures. However, the orientation decays quickly at elevated temperatures because the local free volumes that surround the chromophores increase. Taking advantage of the multifunctional characteristics of carbazole along with rational molecular design, a new NLO-active lambda-shape main-chain polyimide that comprises the two-dimensional carbazole chromophore was synthesized. This polyimide exhibits high thermal and temporal stability. it can endure as high as 240 °C in a transient time and maintain large SH signal at 100 °C for a long time. The high-glass transition polyimide as a matrix and embedding the two-dimensional chromophore into the polymer backbone are the major reasons that effectively restrict randomization of the oriented dipole.

Synthesis and Thermal Properties of Main Chain Polyimides Containing Chalcone Derivative

We synthesized main chain polyimides containing photosensitive chalcone moiety and investigated thermal properties of the polyimides. The polyimides were prepared by acid anhydrides [4,4′-(hexafluoro-isopropylidene) diphthalic anhydride (6FDA) or 4,4′-biphthalic anhydride (BPDA)] and diamine derivatives containing a chalcone group. The polyimides with 6FDA derivative were soluble in organic solvents such as tetrahydrofuran, chloroform and N,N-dimethylformamide. On the other hand, the polyimides with BPDA derivative were insoluble in common organic solvents. The polyimides with 6FDA derivative did not exhibit any mesophases, while the polyimides with BPDA derivative displayed a smectic phase.

40.4: New Photoalignment Polymeric Materials with Excellent Photosensitivity and Stability

AbstractNovel soluble photoalignment materials with high photosensitivity and good thermal stability were synthesized by chloromethylation of 6FDA‐ODA polyimide, and their photoalignment properties were investigated. The photosensitivity of 6FDA‐ODA polyimide was improved greatly by the introduction of chloromethyl side group. The ECB LC cell made with photoaligned films could be stored at 85°C. for at least 14 days without deteriorating LC alignment. The irradiation of polarized UV light on the polymer surface induced thermally stable alignment of LC due to the surface anisotropy caused by photodecomposition of polyimide main chain.

Synthesis and properties of highly sulfonated proton conducting polyimides from bis(3-sulfopropoxy)benzidine diaminesElectronic supplementary information (ESI) available: 1H NMR spectra of BSPB diamines and IR spectra of resulting polyimide membranes. See http://www.rsc.org/suppdata/jm/b3/b313276e/

Two novel sulfonated diamine isomers, 2,2′-bis(3-sulfopropoxy)benzidine (2,2′-BSPB) and 3,3′-bis(3-sulfopropoxy)benzidine (3,3′-BSPB), were successfully synthesized and the highly sulfonated polyimides (SPIs) with sulfonic acid groups in the side chains were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and BSPB monomers. Transmission electron microscopy (TEM) analysis revealed that these side-chain-type SPI membranes have a microphase-separated structure composed of hydrophilic side chain domains and hydrophobic polyimide main chain domains. They showed high proton conductivities similar to or higher than those of Nafion 117 in the high relative humidity range (>70% RH). The proton conducting behavior was analyzed by percolation theory. Despite their high ion exchange capacity (IEC = 2.89 meq. g−1) and high water uptakes, they displayed much better water stability than common sulfonated polyimides with the sulfonic acid groups directly bonded to the polymer backbone. This is probably due to the microphase-separated structure of the membrane and the strong basicity of BSPB diamine moieties resulting from the electron donating effect of the propoxy groups. The sulfopropoxy groups were stable against aging in acidic aqueous solution at 373 K. Both the polyimide membranes showed good mechanical strength under high moisture conditions (about 6 GPa at 90% RH) and displayed anisotropic membrane swelling.

Novel Liquid Crystal Photoalignment System Based on New Soluble Polyimide

Novel liquid crystals(LCs)photoalignment system, which exhibits outstanding photosensitivity and excellent thermal stability, has been developed based on new soluble polyimide. Homogeneous alignment of liquid crystals(LCs)was induced by soluble polyimide(CMPI)having chloromethyl side groups upon irradiation of linearly polarized UV light(LPUVL)with short irradiation time. The photoaligned film was thermally stable without destroying LC alignment when LC cell was stored at 85°C for 14 days. The pretilt angle of LC decreased with irradiation time, which is contributed by the increased polar surface energy of CMPI film after irradiation of LPUVL. FT-IR spectra confirmed that the photosensitivity of polyimide was improved greatly by introducing chloromethyl group and the alignment of LC was contribute by the photo-decomposition of polyimide main chain upon irradiation.

Photosensitive fluorinated polyimides with a low dielectric constant based on reaction development patterning

AbstractThe fluorinated polyimide PI(6FDA/HFBAPP) was prepared by the reaction of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane (HFBAPP) in 1‐methyl‐2‐pyrrolidone/toluene. A multiblock copolyimide with both fluorinated and rigid‐rod segments, PI(6FDA/HFBAPP)(BPDA/2‐DMB), was prepared by the addition of a second dianhydride, 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), and a second diamine, 2,2′‐dimethylbenzidine (2‐DMB), to the polyimide main chain. The potential lithographic performance of photosensitive polyimides composed of nonphotosensitive fluorine‐containing polyimides and photosensitive diazonaphthoquinone (DNQ) was studied on the basis of a new imaging principle recently proposed by our laboratory, that is, reaction development patterning. Neat PI(6FDA/HFBAPP) showed a low dielectric constant (ϵ) of 2.41 and a low dissipation factor (tan δ) of 0.0027 at 20 GHz, and a 10‐μm resolution of the fluorinated polyimide/DNQ system was demonstrated with reactive development with a solution including ethanolamine after ultraviolet exposure. Although slight changes in the dielectric properties were observed in the presence of DNQ residues, these values (ϵ = 2.63 and tan δ = 0.0033 at 20 GHz) were low enough for use in microelectronic applications. However, PI(6FDA/HFBAPP)(BPDA/2‐DMB), having a lower coefficient of thermal expansion (CTE; 33 ppm/°C) than PI(6FDA/HFBAPP) (49 ppm/°C), exhibited good positive photosensitivity, whereas the relatively low‐CTE multiblock copolyimide displayed a much higher ϵ value (3.48 at 1 MHz) than the highly fluorinated polyimide (2.88 at 1 MHz). A film consisting of PI(6FDA/HFBAPP)(BPDA/2‐DMB) and the remaining DNQ derivatives showed a CTE value comparable to that of the neat polyimide film. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 861–871, 2003

Sulfonated Polyimides for Polymer Electrolyte Membrane Fuel Cell

Two types of novel sulfonated diamines bearing sulfonic acid groups directly bonded to polyimide main chains (main-chain type) or in the side alkoxy chains (side-chain type), and the corresponding sulfonated polyimides were successfully synthesized. Water vapor sorption, proton conductivity σ, methanol permeability PM, membrane stability toward hot water, and size change with water uptake of the sulfonated polyimide membranes were investigated. The membranes of sulfonated polyimides prepared on the basis of the proper molecular design showed much better water stability and higher proton conductivity compared with the conventional polyimides based on 2,2'-benzidinedisulfonic acid. They also displayed the higher ratio of σ over PM than Nafion 117 membrane. They might have potential for polymer electrolyte fuel cell and methanol direct fuel cell applications.

Synthesis, photo-reaction and photo-induced liquid crystal alignment of soluble polyimide with pendant cinnamate group

In this paper, the synthesis, photo-reaction and photo-induced liquid crystal alignment of a polyimide with a pendant cinnamate group are reported. The polyimide was synthesized by the thermal imidization of the polyamic acid derived from 4,4'-(hexafluoro-isopropylidene)diphthalic anhydride and hydroxydiaminopropane, followed by the attachment of the cinnamate group to the main chain polyimide. The surface of thin layers of the polyimide was found to be preferentially occupied by the pendant cinnamate groups, and liquid crystal alignment on the polyimide thin film exposed to polarized UV was independent of the cinnamate content. The thermal stability of the photo-induced liquid crystal alignment was enhanced with decrease in the cinnamate content. This could be attributed to the strong interchain interaction of the polyimide chains which prevents thermal randomization of the photo-product of the pendant cinnamates. The dependences of the photo-reaction temperature and the annealing temperature of the alignment layer on the azimuthal anchoring energy of the photo-aligned liquid crystal suggest that the local stress developed during the UV irradiation profoundly influences the thermal stability of the liquid crystal alignment.

Synthesis and characterization of side-chain polyimides for second-order nonlinear optics via a post-azo-coupling reaction

A two-step, generally applicable synthetic approach for nonlinear optical (NLO) side-chain polyimides was developed. This included the preparation of a preimidized, organosoluble polyimide with benzene moiety pendant from main chains, followed by the covalent bonding of the NLO chromophores onto the polyimide backbone via a post-azo-coupling reaction. The degree of functionalization of polyimides was estimated by UV-VIS spectroscopy. The glass transition temperature (Tg) of a polyimide decreased by only 10–20°C after the functionalization, which was much smaller than the decrease in Tg when the chromophores were chemically bonded to the polyimide main chains through an ether linkage using a post-Mitsunobu condensation. The solubility and thermal stability of polyimides were also studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 290–295, 2000

The possibility of intra-molecular nematic order via chain folding in perylene-containing polyimides: a molecular dynamics study

Perylene containing main-chain polyimides are candidate materials for the photogenerator layer of electrophotographic devices. These polymers are semi-crystalline as synthesized. Annealing improves the crystallinity while causing subtle changes in the X-ray diffraction pattern and a red-shift in the UV–vis absorption spectrum. Molecular dynamics simulations of linear chains of …Pe–C12–Pe… led to chain folded collapsed structures. It is known that a minimum chain length of 150 CH2 units is required, in the case of linear alkanes, for stable folding to occur. However, the strong attractive π interaction between the perylene units causes the chain to fold, with as few as 12 CH2 spacer units. This shows that both intra and intermolecular nematic order can occur in these systems, the former caused by chain folding.

Thickness dependence of the anisotropy in thermal expansion of PMDA-ODA and BPDA-PDA thin films

The thickness dependence of the anisotropy in thermal expansion of poly(pyromellitic dianhydride oxydianiline) (PMDA-ODA) with flexible chains and poly(biphenylene tetracarboxylic dianhydride p-phenylene diamine) (BPDA-PDA) ranging from 2.5 to 20 μm has been investigated. The lateral (in-plane) coefficient of thermal expansion (CTE) of PMDA-ODA and BPDA-PDA increases with increasing film thickness; in contrast, the vertical (out-of-plane) CTE of PMDA-ODA and BPDA-PDA decreases with increasing film thickness. The vertical CTE of PMDA-PDA is 4–7 times larger than the lateral CTE. The vertical CTE of BPDA-PDA is 14–20 times larger than the lateral CTE. It is believed that the thickness dependence of the anisotropy in CTE is caused by the in-plane orientation of the polyimide main chain. Since BPDA-PDA has a rigid-rod-like structure, this leads to a better in-plane orientation and a larger anisotropy in CTE than PMDA-ODA.