Colorless Polyimides Research Articles

Colorless polyimides derived from adamantane-containing diamines

Colorless polyimides with high glass transition temperatures (up to 440 °C) were developed from three adamantane-containing diamines, and the structure–property relationship of this series of polyimides was established.

SAMSUNG DISPLAY BETS ON FOLDABLE GLASS

SAMSUNG DISPLAY HAS MADE A substantial investment in the ultra-thin glass substrate firm Dowoo Insys, whose technology will be used by Samsung Electronics for its next generation of Galaxy Fold devices. In late December, Samsung Display acquired 600,000 shares of Dowoo Insys for 13.5 billion won, or $11.6 million, through a collaborative fund with Samsung Venture Investment Corp. The purchase makes Samsung the company's largest shareholder, with a 27.7 percent stake. Samsung Display has invested a total of 48.5 billion won, or $41.5 million, in Dowoo Insys since May 2018. According to Ross Young, CEO of the market research firm Display Supply Chain Consultants, Samsung's move to gain a controlling interest in Dowoo Insys makes sense as it looks to gain a competitive advantage in the nascent foldable market. Ultra-thin glass is expected to produce a more robust display than the colorless polyimides that Samsung used in its first Galaxy Fold product, providing a better feel and eliminating the visible crease in the flexible OLED display. “They think it's a strategic technology to make foldable more successful,” he said. Young notes that the ultra-thin glass Samsung will be using is actually produced by the German firm Schott, and that Dowoo Insys has a proprietary method for processing the glass. Opting for Ultra-Thin Glass Young believes a 1.5 mm radius will be implemented on the next Samsung foldable phone with Schott's ultra-thin glass. It was 3 mm in the first Galaxy Fold. Image: Samsung “Our understanding is that it could potentially be more than a single piece of glass in order to deal with the elongation,” Young said, adding that Dowoo Insys may also be helping to thin the glass and is expected to be laminating a protective film over it from another Korean supplier in case of any unforeseen cracking. Details from Dowoo Insys about its process are scarce, he said. As the foldable market expands, Young sees Schott having an early edge with its ultra-thin glass, which can be chemically strengthened and made thinner than some competing products. “They've talked about going as thin as 10 microns, but what's more likely is around 30 microns,” he said. “As the glass gets thinner, the fold radius gets smaller. We believe that they're going to be implementing a 1.5 millimeter (mm) radius on the next Samsung foldable phone with the ultra-thin glass.” In comparison, the radius of the first Galaxy Fold was 3 mm. The new Galaxy Fold, which is expected to use a clamshell design, will officially be unveiled in February. Although Samsung Display doesn't have an exclusive deal with Schott for its glass, it does have an exclusive deal with Dowoo Insys through its investment, which means that Samsung alone has access to the company's processing and laminating technology. Young says the Dowoo Insys deal is consistent with Samsung's recent emphasis on sourcing key technology from Korean suppliers in the wake of trade tensions with Japan. “They've become a lot more focused on self-sufficiency within Korea,” Young said. —Glen Dickson U.S. carriers may have launched limited 5G services months ahead of their Chinese counterparts, but at the close of 2019, Chinese carriers recorded almost 17 times the number of 5G phone sales, according to data from the market research firm M Science. Chinese carriers, the firm reports, have been selling more than 100,000 5G-phones every week since early November, while U.S. carriers haven't moved more than 15,000 5G phones per week since September. Why? Varied and competing 5G technologies on the U.S. end versus a standardized market in China (led by Huawei) are key. For the week of Dec. 7, the 5G adoption rate in the U.S. was 1.9 percent, having received a sizable bump after T Mobile launched its 5G network on Dec. 2, while in China the penetration rate was 3.42 percent, according to M Science. —Nicole Saunders Image: vchal/Shutterstock Image: vchal/Shutterstock

Recent Trends on Transparent Colorless Polyimides with Balanced Thermal and Optical Properties: Design and Synthesis

AbstractRecently, colorless and transparent plastic substrates with high glass transition temperature and suitable thermo‐mechanical properties are in high demand in optoelectronic device industries, due to their various optical applications. Colorless polyimides (CPIs) exhibit both high thermo‐mechanical stability as well as high transparency that are suitable for optoelectronic applications. The most recent (2010–2018) developments on CPIs, in terms of design and synthesis of new monomers and their effects on the thermo‐optical properties of the obtained CPIs, are reviewed in this article.

A Highly Sensitive Flexible Capacitive Tactile Sensor with Sparse and High‐Aspect‐Ratio Microstructures

AbstractHighly sensitive flexible tactile sensors that can be fabricated in a low cost and efficient way are in great demand for intelligent soft robotics and friendly human–machine interaction. Herein, a highly sensitive flexible tactile sensor is developed by using bionic micropatterned polydimethylsiloxane (m‐PDMS) replicated from lotus leaf. The m‐PDMS substrate consists of high‐aspect‐ratio and low‐density microtowers, and is covered by ultrathin silver nanowires as a bottom electrode. The capacitive sensing device is constructed by sandwiching the bottom electrode, a colorless polyimides dielectric layer, and a top electrode, and exhibits a high sensitivity of ≈1.2 k Pa−1, a ultralow limit of detection <0.8 Pa, and a fast response time of 36 ms. The finite‐elemental analysis indicates that the sparse and high‐aspect‐ratio microtowers are critical to achieve high sensitivity, low limit of detection, and fast response to external stimulus. The flexible tactile sensor also exhibits high robustness: it can be tested for at least 100 000 cycles without showing fatigue. More importantly, the flexible tactile sensors are potentially useful in intelligent soft robots, health monitoring, and motion detection. Besides, the fabrication strategy may offer a guideline to design other microstructures for improving the performance of flexible tactile sensors.

Synthesis of a new diamine and its effect on the residual stress of colorless polyimide

A new diamine was designed and synthesized to improve the flexibility of colorless polyimides by reducing residual stress. Four variations of colorless polyimides with the same dianhydride (4,4′-(hexafluoroisopropylidene)-diphthalic) and four different diamines (bis[4-(3-aminophenoxy)-phenyl] sulfone, bis(3-aminophenyl) sulfone, 2,2′-bis(trifluoromethyl)benzidine, and 2,2-bis(4-aminophenyl)-hexafluoropropane) were used. A series of colorless polyimides were prepared by adding the new diamine. The carbon and ether bonds between the benzene rings of the new diamine affected the flexibility and optical properties of colorless polyimide. The synthesis of the new diamine was confirmed by NMR measurements. Furthermore, the decrease in residual stress at room temperature and the glass transition temperature was confirmed. The effect of the new diamine was most evident for polyimide with a bulky and rigid structure. Though a slight yellow color appears because of the broken charge transfer complex balance, controlling the content of the new diamine will allow application of polyimides in flexible display.

Partially bio‐based aromatic polyimides derived from 2,5‐furandicarboxylic acid with high thermal and mechanical properties

ABSTRACTTwo novel bio‐based diamines are synthesized through introduction of renewable 2,5‐furandicarboxylic acid (2,5‐FDCA), and the corresponding aromatic polyimides (PIs) are then prepared by these diamines with commercially available aromatic dianhydrides via two‐step polycondensation. The partially bio‐based PIs possess high glass transition temperatures (Tgs) in the range from 266 to 364 °C, high thermal stability of 5% weight loss temperatures (T5%s) over 420 °C in nitrogen and outstanding mechanical properties with tensile strengths of 79–138 MPa, tensile moduli of 2.5–5.4 GPa, and elongations at break of 3.0–12.3%. Some colorless PI films (PI‐1‐b and PI‐1‐c) with the transmittances at 450 nm over 85% are prepared. The overall properties of 2,5‐FDCA‐based PIs are comparable with petroleum‐based PI derived from isophthalic acid, displaying the potential for development of innovative bio‐based materials. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1058–1066

Colorless polyimides derived from isomeric dicyclohexyl-tetracarboxylic dianhydrides for optoelectronic applications

Two isomers of conventional cis-dicyclohexyl-3,3′,4,4′-tetracarboxylic dianhydride (4,4′-HBPDA), i.e. dicyclohexyl-2,3′,3,4′-tetracarboxylic dianhydride (3,4′-HBPDA) and dicyclohexyl-2,2′,3,3′-tetracarboxylic dianhydride (3,3′-HBPDA), were prepared through a four-step procedure. The data from single crystal X-ray diffraction revealed that 3,3′-HBPDA possessed higher structural rigidity/linearity than 4,4′-HBPDA. The one-step polycondensation of isomeric HBPDAs with commercial diamines enabled the synthesis of alicyclic polyimides. The isomer effects of the dianhydrides on the properties of resulting polyimides were studied in detail. For certain diamines, 3,3′-HBPDA-derived polyimides possessed higher glass transition temperatures (Tg) and better dimensional stability compared with those from 4,4′-HBPDA and 3,4′-HBPDA. These phenomena could be attributed to the higher structural rigidity/linearity of 3,3′-dicyclohexyl-tetracarboxydiimide, and restricted rotation of 3-substituted cyclohexylimide. Owing to the asymmetric structures and suppressed rotation of 3-substituted cyclohexylimides, 3,4′-HBPDA-based polymers exhibited higher Tg, improved dimensional stability, and enhanced solubility compared with 4,4′-HBPDA-based ones. Furthermore, all the isomeric HBPDA-derived polyimides were essentially colorless with excellent optical transparency in the UV–Visible region. The excellent overall properties of polyimides from 3,3′-HBPDA and 3,4′-HBPDA made them promising candidate materials for optoelectronic applications.

Development of Solution-Processable, Optically Transparent Polyimides with Ultra-Low Linear Coefficients of Thermal Expansion.

This paper reviews the development of new high-temperature polymeric materials applicable to plastic substrates in image display devices with a focus on our previous results. Novel solution-processable colorless polyimides (PIs) with ultra-low linear coefficients of thermal expansion (CTE) are proposed in this paper. First, the principles of the coloration of PI films are briefly discussed, including the influence of the processing conditions on the film coloration, as well as the chemical and physical factors dominating the low CTE characteristics of the resultant PI films to clarify the challenges in simultaneously achieving excellent optical transparency, a very high Tg, a very low CTE, and excellent film toughness. A possible approach of achieving these target properties is to use semi-cycloaliphatic PI systems consisting of linear chain structures. However, semi-cycloaliphatic PIs obtained using cycloaliphatic diamines suffer various problems during precursor polymerization, cyclodehydration (imidization), and film preparation. In particular, when using trans-1,4-cyclohexanediamine (t-CHDA) as the cycloaliphatic diamine, a serious problem emerges: salt formation in the initial stages of the precursor polymerization, which terminates the polymerization in some cases or significantly extends the reaction period. The system derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and t-CHDA can be polymerized by a controlled heating method and leads to a PI film with relatively good properties, i.e., excellent light transmittance at 400 nm (T400 = ~80%), a high Tg (>300 °C), and a very low CTE (10 ppm·K−1). However, this PI film is somewhat brittle (the maximum elongation at break, εb max is about 10%). On the other hand, the combination of cycloaliphatic tetracarboxylic dianhydrides and aromatic diamines does not result in salt formation. The steric structures of cycloaliphatic tetracarboxylic dianhydrides significantly influence the polymerizability with aromatic diamines and the CTE values of the resultant PI films. For three isomers of hydrogenated pyromellitic dianhydride, the steric structure effect on the polymerizability and the properties of the PI films is discussed. 1,2,3,4-Cyclobutanetetracarboxylic dianhydride (CBDA) is a very unusual cycloaliphatic tetracarboxylic dianhydride that is suitable for reducing the CTE. For example, the PI system derived from CBDA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) yields a colorless PI film with a relatively low CTE (21 ppm·K−1). However, this PI is insoluble in common organic solvents, which means that it is neither solution-processable nor compatible with the chemical imidization process; furthermore, the film is somewhat brittle (εb < 10%). In addition, the effect of the film preparation route on the film properties is shown to be significant. Films prepared via chemical imidization always have higher optical transparency and lower CTE values than those prepared via the conventional two-step process (i.e., precursor casting and successive thermal imidization). These results suggest that compatibility with the chemical imidization process is the key for achieving our goal. To dramatically improve the solubility in the CBDA-based PI systems, a novel amide-containing aromatic diamine (AB-TFMB), which possesses the structural features of TFMB and 4,4′-diaminobenzanilide (DABA), is proposed. The CBDA(70);6FDA(30)/AB-TFMB copolymer has an ultra-low CTE (7.3 ppm·K−1), excellent optical transparency (T400 = 80.6%, yellowness index (YI) = 2.5, and haze = 1.5%), a very high Tg (329 °C), sufficient ductility (εb max > 30%), and good solution-processability. Therefore, this copolymer is a promising candidate for use as a novel coating-type plastic substrate material. This paper also discusses how the target properties can be achieved without the help of cycloaliphatic monomers. Thus, elaborate molecular design allows the preparation of highly transparent and low-CTE aromatic poly(amide imide) and poly(ester imide) systems.

Soluble polyimides containing 1,4:3,6‐dianhydro‐d‐glucidol and fluorinated units: Preparation, characterization, optical, and dielectric properties

ABSTRACTAiming to develop soluble and colorless polyimides, two novel diamines, 2,5‐bis(2‐trifluoromethyl‐4‐amino‐phenoxy)‐1,4:3,6‐dianhydrosorbitol (2a) and 2,5‐bis(2‐methyl‐4‐amino‐phenoxy)‐1,4:3,6‐dianhydrosorbitol (2b), were designed and synthesized by the reduction of corresponding dinitro monomer which was obtained via solvent‐free melt heating method. Polyimides (PI–(1–5)) containing 1,4:3,6‐dianhydro‐d‐glucidol fragments were prepared from 2a and five kinds of common dianhydrides and PI–6 was synthesized from 2b and 4,4′‐(hexafluoroisopropylidene)‐diphthalic anhydride (6FDA) via a two‐step thermal imidization. All the polyimides were readily soluble in common polar solvents and could afford flexible, tough, and transparent films with transparency as high as 87% at 450 nm. Meanwhile, PI–(1–6) exhibited unexpectedly low dielectric constants of 2.02–2.52 at 1 MHz. In addition, analogs PI–7 derived from 2,5‐bis(4‐amino‐phenoxy)‐1,4:3,6‐dianhydrosorbitol (2c) and 6FDA and PI–8 derived from 4,4′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl (2d) and 6FDA were also obtained via a two‐step thermal imidization for comparision with PI–(1–6) on aspects of thermal, mechnical, optical, electrical, and morphological properties. The structure–property relationships of PI–(1–8) were discussed in detail. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2017,55, 3253–3265

Colorless polyimides derived from 2R,5R,7S,10S-naphthanetetracarboxylic dianhydride

Colorless polyimides with excellent thermal and mechanical properties were developed from 2R,5R,7S,10S-naphthanetetracarboxylic dianhydride, and their properties were systematically compared with those based on 1S,2R,4S,5R-cyclohexanetetracarboxylic dianhydride.

Synthesis and characterization of colorless polyimides derived from 4-(4-aminophenoxy)-2,6-dimethylaniline

A new aromatic polyimides (PIs) having asymmetric aromatic diamine with methyl groups at the ortho position of amino group has been developed to prepare transparent film in the visible region. The all aromatic PIs presented here are derived from 4-(4-aminophenoxy)-2,6-dimethylaniline (APDMA) and aromatic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4'-biphthalic anhydride (BPDA), and pyromellitic dianhydride (PMDA) via a two-step polycondensation. All PIs show good thermal properties: 5% weight loss at a temperature range of 510-529 °C and their glass transition temperature found above 290 °C. The PIs exhibit good optical transparency, such as cut-off wavelength in the region of 296-358 nm and above 92-99% at 550 nm. In addition, all PIs show low refractive indices in the range of 1.567-1.637 at wavelength of 637 nm and low birefringence.

Solution‐processable colorless polyimides with ultralow coefficients of thermal expansion for optoelectronic applications

AbstractThis work reports colorless polyimides (PIs) that are applicable as plastic substrates in image display devices, which produce an ultralow coefficient of thermal expansion (CTE) by solution casting without thermal imidization and mechanical stretching. An effective monomer molecular design is proposed for this purpose. Chemical imidization (CI) process compatibility is the key factor in attaining the target properties. We focused on a PI system derived from 1,2,3,4‐cyclobutanetetracarboxylic dianhydride (CBDA) and a novel para‐amide‐linked diamine (AB‐TFMB) with CF3 groups as it has great potential as an ultralow CTE material, although it offers no CI process compatibility because of its poor solubility. The CBDA/AB‐TFMB system was modified by copolymerizing with 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride. This approach drastically improved CI process compatibility. The CTE of the PI films linearly decreased with increasing CBDA content. At a CBDA content of 70 mol%, the PI achieved an ultralow CTE of 7.3 ppm K−1, non‐coloration/non‐turbidity, a very high glass transition temperature of 329 °C and sufficient ductility. The ultralow CTE results from the highly oriented main chains along the X–Y direction during the casting process as supported by the very high birefringence exceeding 0.1. Thus, our materials almost achieved the target properties required for novel coating‐type high‐temperature plastic substrate materials. © 2016 Society of Chemical Industry

Synthesis and characterization of highly-fluorinated colorless polyimides derived from 4,4′-((perfluoro-[1,1′-biphenyl]-4,4′-diyl)bis(oxy))bis(2,6-dimethylaniline) and aromatic dianhydrides

The authors report the synthesis and characterization of a polyimide (PI) series derived from 4,4′-((perfluoro-[1,1′-biphenyl]-4,4′-diyl)bis(oxy))bis(2,6-dimethylaniline) (8FBPODMA). The 8FBPODMA monomer containing a perfluorobiphenyl group with two 2,6-dimethylaniline units connected by an ether bond was synthesized and polycondensed with several aromatic dianhydrides, including 4,4′-biphthalic anhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA), pyromellitic dianhydride (PMDA), and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), by the traditional two-step imidization procedure. All PIs shows high optical transparency, higher than 80% at 500 nm for a thickness of ca. 10 μm and good thermal properties. The thermal decomposition temperatures (T10%) of the PIs are in the range of 507–527 °C and the glass transition temperatures (Tg) are in the range of 280–345 °C. In addition, the PIs have low refractive indices because of their high fluorine contents. In particular, 8FBPODMA–6FDA shows a very low refractive index (1.5389) and a low birefringence (0.0054) at 637 nm.

Colorless polyimides derived from 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride, self-orientation behavior during solution casting, and their optoelectronic applications

A novel cycloaliphatic monomer for polyimides (PI), 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride (H′-PMDA) is proposed in this work. H′-PMDA shows high polymerizability with various diamines in contrast to its isomer, i.e., conventional hydrogenated pyromellitic dianhydride (H-PMDA) and leads to highly flexible and colorless PI films with very high Tg's. In particular, the combinations with rigid structures of diamines give rise to PIs with significantly decreased coefficients of thermal expansion (CTE) owing to high extents of in-plane chain orientation induced by thermal imidization, whereas the H-PMDA-based counterparts do not. The decreased CTE reflects structural rigidity/linearity of the H′-PMDA-based diimide units as supported by liquid crystallinity observed in the corresponding model compound. Solution casting of a chemically imidized PI derived from H′-PMDA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) results in a lower CTE than that of the thermally imidized counterpart, suggesting the presence of a self-orientation phenomenon during solvent evaporation. The mechanism is proposed in this work. H′-PMDA/TFMB and its copolymer systems can be useful as plastic substrates in image display devices and/or novel coating-type optical compensation films.

Colorless polyimides with low coefficient of thermal expansion derived from alkyl-substituted cyclobutanetetracarboxylic dianhydrides

Alkyl-substituted cyclobutanetetracarboxylic dianhydrides (CBDAs) were synthesized by photo-dimerization of alkyl-substituted maleic anhydrides to obtain novel colorless polyimides (PIs). Dimethyl-substituted CBDA (DM-CBDA) showed much higher polymerizability with various diamines than conventional cycloaliphatic tetracarboxylic dianhydrides and led to high molecular weights of PI precursors. Polyaddition of non-substituted CBDA and trans-1,4-cyclohexanediamine (t-CHDA) was completely inhibited by salt formation in the initial reaction stage. The use of DM-CBDA allowed the formation of a homogeneous/viscous PI precursor solution by overcoming the salt formation problem. The prominent substituent effect probably reflects how the methyl substituents of DM-CBDA contributed to increasing the salt solubility. Some of the thermally imidized DM-CBDA-based systems simultaneously possessed non-coloration, low coefficient of thermal expansion (CTE), very high Tg exceeding 300 °C and very low dielectric constant. Copolymerization was very effective for improving the solubility of DM-CBDA-based PIs. The copolyimide cast films prepared via chemical imidization displayed a further decreased CTE without sacrificing other target properties, suggesting that the present materials can be useful as plastic substrates in display devices. The mechanism of self-chain orientation behavior during solution casting is also discussed. A potential application of the copolyimide systems as optical compensation film materials in liquid crystal displays is proposed. © 2013 Society of Chemical Industry.

Properties of magnetron-sputtered moisture barrier layer on transparent polyimide/graphene nanocomposite film

Colorless polyimides (PIs) have been considered as potential substrates for flexible displays due to their excellent transparency, thermal stability, mechanical strength and flexibility. However, high water vapor transmission rate (WVTR) of PI films limits the lifetime of electronic devices using PI films as substrates. Two approaches were applied to reduce the WVTR of PI films. Graphene (RG), which is thermally reduced graphene oxide (GO), was blended with a nearly colorless PI solution synthesized from an alicyclic tetracarboxylic dianhydride and aromatic diamine in cosolvent to obtain PI/RG nanocomposites. Subsequently, a barrier thin film was deposited on those PI nanocomposites by radio frequency magnetron sputtering from a Si3N4 target. The deposited barrier layer was amorphous and its composition along the thickness was homogeneous based on the X-ray diffraction patterns and the depth profile by X-ray photoelectron spectroscopy. An optimum deposition thickness of the barrier layer is 30nm to obtain a close-packed, smooth and continuous barrier film on PI. The presence of a 30nm-thick barrier layer on PI/RG-0.1 nanocomposite film capably reduces the WVTR to 0.17g/m2-day compared to 181g/m2-day for pure PI and 13g/m2-day for PI/RG-0.1. The surface of PI/RG is more hydrophobic and the capacity of moisture absorption by PI/RG is lower than PI/GO indicating the water resistance by RG is superior to that by GO. This flexible nanocomposite film remains high optical clarity and simultaneously shows excellent water barrier performance, enhanced dimensional stability and sufficient mechanical strength for advanced electronic applications.

Solution‐processable colorless polyimides derived from hydrogenated pyromellitic dianhydride with controlled steric structure

AbstractThis work presents novel colorless polyimides (PIs) derived from 1R,2S,4S,5R‐cyclohexanetetracarboxylic dianhydride (H″‐PMDA). Isomer effects were also discussed by comparing with PI systems derived from conventional hydrogenated pyromellitic dianhydride, that is, 1S,2R,4S,5R‐cyclohexanetetracarboxylic dianhydride (H‐PMDA). H″‐PMDA was much more reactive with various diamines than H‐PMDA, and the former led to PI precursors with much higher molecular weights. The results can be explained from the quite different steric structures of these isomers. The thermally imidized H″‐PMDA‐based films were colorless regardless of diamines because of inhibited charge‐transfer interaction. In particular, the H″‐PMDA/4,4′‐oxydianiline system simultaneously achieved a very high Tg exceeding 300 °C, high toughness (elongation at break &gt; 70%), and good solution processability. In contrast, the H‐PMDA‐based counterparts were essentially insoluble. The outstanding solubility of the former probably results from disturbed chain stacking by its nonplanar steric structure. An advantage of chemical imidization process is also proposed. In some cases, a copolymerization approach with an aromatic tetracarboxylic dianhydride was effective to improve the thermal expansion property. The results suggest that the H″‐PMDA‐based PI systems can be promising candidates for novel high‐temperature plastic substrate materials in electronic paper displays. A potential application as optical compensation film materials in liquid crystal displays (LCD) is also proposed in this work. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

XPS Surface Characterization of UV Photo-Oxidized Colorless Polyimides

The colorless polyimides LaRC™-CP1 (6FDA–1BDAF) and LaRC™-CP2 (6FDA–APB), which are frequently used in the aerospace industry, were exposed to UV photo-oxidation at atmospheric pressure. XPS data show a significant increase in the oxygen concentration and decrease in the carbon concentration as a result of treatment. There are slight, but significant, increases in the concentrations of nitrogen and fluorine as a result of treatment indicating ablative degradation of low molecular weight carbon-containing compounds. The increase in the concentration of oxygen appears to be primarily due to the O=C–O moiety.

(1R*,2S*,4S*,5R*)-Cyclohexane-1,2:4,5-tetracarboxylic dianhydride

The title compound, C10H8O6, a promising raw material to obtain colorless polyimides which are applied to microelectronic and optoelectronic devices, adopts a folded conformation in which the dihedral angle between the two anhydro rings is 55.15 (8)°. The central six-membered ring assumes a conformation inter­mediate between boat and twist-boat. In the crystal, mol­ecules are linked by weak C—H⋯O inter­actions, forming a layer parallel to the bc plane.

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.