Colorless Polyimides Research Articles

Mechanisms of Atomic Oxygen Erosion in Fluorinated Polyimides Investigated by Molecular Dynamics Simulations.

Traditional polyimides have highly conjugated structures, causing significant coloration under visible light. Fluorinated colorless polyimides, known for their light weight and excellent optical properties, are considered ideal for future aerospace optical lenses. However, their lifespan in low Earth orbit is severely limited by high-density atomic oxygen (AO) erosion, and the degradation behavior of fluorinated polyimides under AO exposure is not well understood. This study uses reactive molecular dynamics simulations to model two fluorinated polyimides, PMDA-TFMB and 6FDA-TFMB, with different fluorine contents, to explore their degradation mechanisms under varying AO concentrations. The results indicate that 6FDA-TFMB has slightly better resistance to erosion than PMDA-TFMB, mainly due to the enhanced chemical stability from its -CF3 groups. As AO concentration increases, widespread degradation of the polyimides occurs, with AO-induced cleavage and temperature-driven pyrolysis happening simultaneously, producing CO and OH as the main degradation products. This study uncovers the molecular-level degradation mechanisms of fluorinated polyimides, offering new insights for the design of AO erosion protection systems.

Synthesis of High-Performance Colorless Polyimides with Asymmetric Diamine: Application in Flexible Electronic Devices.

Colorless polyimides (CPIs) are widely used as high-performance materials in flexible electronic devices. From a molecular design standpoint, the industry continues to encounter challenges in developing CPIs with desired attributes, including exceptional optical transparency, excellent thermal stability, and enhanced mechanical strength. This study presents and validates a method for controlling 2-substituents, with a specific emphasis on examining how these substituents affect the thermal, mechanical, optical, and dielectric characteristics of CPIs. The presence of two CF3 groups on the same side of the diamine structure ensured the transmittance of the film. The charge transfer effect and the molecular distance are dynamically regulated by changing the 2-substituent (-OCH3/-CH3/H/F). The polyimide exhibited a well-maintained equilibrium between transparency and thermal stability, with a T500nm value ranging from 86.2 to 89.6% in the visible region, and a glass transition temperature (Tg) ranging from 358.6 to 376.0 °C. Additionally, the 6FDA-2-MTFMB compound, when combined with methyl, excels as a protective layer and base material, exhibiting excellent performance in various aspects. It has been verified as an appropriate option for flexible photodetectors and wearable piezoresistive sensors. In summary, this systematic investigation will provide a comprehensive and demonstrative methodology for developing CPIs that are capable of adapting to flexible electronic devices.

Systematic exploration of structure-property relationships in colorless polyimides derived from stereoisomeric dianhydrides and various diamines

This study explores the structure-property relationships in colorless polyimides (CPIs) synthesized from stereoisomeric (exo- and endo-form) alicyclic dianhydrides, combined with various diamines. The structural configurations of 5,5’-(1,4-phenylene)bis[hexahydro-(3aR,4R,5R,7S,7aS)-rel-4,7-Methanoisobenzofuran-1,3-dione] (BzDA-exo) and 5,5-(1,4-phenylene)bis(hexahydro-4,7-methanoisobenzofuran-1,3-dione) (BzDA-endo) were confirmed as exo- and endo-forms, respectively, through 1H NMR and 2D NOESY NMR analyses. Wide-angle X-ray scattering (WAXS) data revealed that stereoisomeric structures influence polymer chain packing in synthesized CPIs. The investigation extended to the chemical and physical structure-dependent properties such as physical, thermal and optical properties of the PIs. Notably, structure-dependent physical and thermal properties were evident, with a particularly strong structure-property relationship manifesting in the coloration and yellow index (Y.I.) of PIs. These systematic characterizations offer profound insights into the design and optimization of chemical and physical structures in CPIs, highlighting the versatility of stereoisomeric monomers for various applications.

Synthesis and properties of novel colorless polyimide containing indene and amide groups

AbstractTwo novel diamines 1‐(4‐aminophenyl)‐1,3,3‐trimethyl‐2,3‐dihydro‐1H‐indene‐5‐amine and 4‐amino‐N‐(4‐(5‐(4‐aminobenzamide)‐1,3,3‐trimethyl‐2,3‐dihydro‐1H‐inden‐1‐yl) phenyl) benzamide containing indene and amide groups were successfully designed and synthesized, and a series of colorless polyimides (CPIs) derived from the two diamines with 1,2,4,5‐cyclohexanetetracarboxylic dianhydride in various ratios were copolymerized. The introduction of aliphatic ring structures was conducive to the improvement of optical properties, while the incorporation of amide groups improved thermal and mechanical properties. These CPI films exhibited excellent optical properties (T400 > 80%), high heat resistance (Tg > 300 °C) and mechanical properties with the synergistic action of the two groups. Furthermore, the effect of the content of amide groups on the intermolecular interaction of CPIs was systematically analyzed. This study provides a fancy method for the development of heat‐resistant colorless materials for optical applications.

Synthesis and characterization of high Tg and colorless polyamide-imide films derived from amide-containing diamines with different trifluoromethyl substitution

Four new diamines (3TFDABA, 2TFDABA, 22TFDABA and TFAPTA) were successfully synthesized to investigate the effect of different trifluoromethyl (CF3) substitution position on poly(amide-imide)s (PAIs) properties. High-performance PAIs were prepared from high-temperature polycondensation of these diamines with 6FDA dianhydride. All the PAI films exhibited good heat resistance with glass-transition temperatures (Tgs) of 311–392 °C, good 5% weight loss temperatures (Td5%s) of 480–510 °C in nitrogen, and excellent optical transparency with T450 ranging from 52% to 84%. According to the monomer structural design, a high heat resistant and colorless poly(amide-imide) film (PAI-2-6FDA), with excellent optical properties (T450 of 82%), outstanding thermal properties (Td5% of 499 °C and Tg of 392 °C), and good mechanical properties (tensile strength of 123 MPa, tensile modulus of 4.4 GPa) was achieved. A comprehensive structure-to-property relationship study revealed that the CF3 in ortho-position of the amino group effectively inhibited the rotation between imide ring and benzene, thus improved the heat resistance of the film. Moreover, it could also weaken the generation of charge transfer complexes through strong electron-withdrawing ability, which is beneficial for the synthesis of colorless polyimides.

Development of Fluorinated Colorless Polyimides of Restricted Dihedral Rotation toward Flexible Substrates with Thermal Robustness

Development of Fluorinated Colorless Polyimides of Restricted Dihedral Rotation toward Flexible Substrates with Thermal Robustness

Synthesis of colorless polyimides derived from benzimidazole diamines with bis‐amide structures

AbstractTo make the colorless polyimides (CPIs) suitable for the application of flexible display technology, the polyimide (PI) films need to have both good optical properties and thermal properties. To get the wanted properties, 2‐(2‐methyl‐4‐(2‐methyl‐4‐aminobenzamido)phenyl)‐5‐(2‐methyl‐4‐aminobenzamido)‐N‐phenylbenzimidazol (5a) and 2‐(2‐methyl‐4‐(2‐trifluoromethyl‐4‐aminobenzamido)phenyl)‐5‐(2‐trifluoromethyl‐4‐aminobenzamido)‐N‐phenylbenzimidazol (5b) were synthesized, which both contained benzimidazole and bis‐amide structures. Two kinds of PI films were polymerized with cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride (CBDA). With the contribution of side groups (CH3 or CF3), the resulting PI films presented relatively superior optical properties (transmittance at 400 nm was 59% and 68% respectively) and low coefficient of thermal expansion (CTE = 22 and 25 ppm K−1). These good properties suggest that these PI films have the potential for flexible display usage.

Adhesive properties of deposited Cu films on colorless polyimide using high power impulse magnetron sputtering system

This study explores the deposition of copper (Cu) films onto colorless polyimides (PIs) using the High Power Impulse Magnetron Sputtering (HiPIMS) technique. The impact of varying operating duty cycles and frequencies on sheet resistance, the deposition rate of Cu films, and the adhesion strength between Cu and PI is examined. Adjusting the HiPIMS parameters aims to achieve superior film quality with reduced sheet resistance. Furthermore, post-thermal treatment significantly improves the adhesion of the Cu layer to the PI substrate due to the mechanical interlocking mechanism created by the surface roughness of the PI and the chemical bonding between the two components.

Synthesis of novel colorless polyimides from benzimidazole diamines with various linearity

AbstractTo synthesize colorless superheat‐resistant polyimide films, one of the valid approaches is the incorporation of the asymmetric and warped structures in the main chain. Applying this approach on 5(6)‐amino‐2‐(4‐aminobenzene)benzimidazole (PABZ) and changing its linearity, 6, 5′‐diamine‐2′‐methyl‐1‐methyl‐2‐phenylbenzimidazole (5a) and 6, 3′‐diamine‐2′‐methyl‐1‐methyl‐2‐phenylbenzimidazole (5b) were devised and synthesized successfully, then polymerized with 1,2,4,5‐cyclohexanetetracarboxylic dianhydride (HPMDA). The prepared poly(benzimidazole imide)s (PBIIs) with the rigid main chain and loose packing had the excellent heat‐resistant level (Tg > 400°C) and optical properties (T400 > 80%). Besides, the alterations resulting from various linearities were discussed comprehensively. This research is beneficial to the application of optical field, providing a promising candidate of heat‐resistant colorless materials.

Synthesis of UV-resistant and colorless polyimide films for optoelectrical applications

Due to their excellent mechanical properties and intrinsic flexibility, polyimides (PIs) are promising candidates for optoelectrical applications under harsh conditions such as flexible organic solar cells as well as flexible smart windows, etc. Much progress has been made on their optical transmittance; however, there remain significant concerns about their environmental stability, particularly their UV resistance. Herein, 4 types of colorless polyimides (CPIs) with different molecular structures containing trifluoromethyl, ethers, or fluorenes are carefully designed, and the dependence of their UV resistance on structures is explored systematically. It is found that the introduction of isopropylidene, ethers and fluorenes effectively enhances the UV resistance of CPI and its initial performance (optical transparency, thermal stability, and toughness) simultaneously as a result of the subtle manipulation of the conjugation structures. Specifically, the optimized polyimide film shows decent optical properties (T550 nm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{550{\\rm{nm}}}$$\\end{document} ~ 88%, yellowness index ~3.26), and thermal stability (T5%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{5 \\% }$$\\end{document} ~ 503 °C in N2 atmosphere, Tg\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{{\\rm{g}}}$$\\end{document} ~ 312 °C). Moreover, after high-intensity UV irradiation, CPI not only maintains over 90% of mechanical properties but also retains excellent optical properties (T550 nm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{550{\\rm{nm}}}$$\\end{document} ~ 88%) and thermal stability (T5%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{5 \\% }$$\\end{document} ~ 506 °C). The design strategy paves the way for enhancing the durability of PIs for energy conversion and electronic applications resisting harsh conditions.

Synthesis of novel biphenyl‐fused alicyclic tetracarboxylic dianhydride and its performance in thermostable and transparent colorless polyimides

AbstractBiphenyl fused alicyclic tetracarboxylic dianhydride, 6,6′,7,7′‐tetracarboxylic dianhydride‐5,5′,6,6′,7,7′,8,8′‐octahydro‐2,2′‐binaphthalene (OHBNDA) was successfully synthesized from biphenyltetracarboxylic dianhydride (BPDA) through hydrolysis, reduction, bromination, and Diels–Alder reaction. Three OHBNDA‐based polyimides (PIs) were synthesized by one‐step polycondensation at high temperature with 9,9‐bis(4‐aminophenyl)fluorene (BAFL), 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (TFMB), and 4,4′‐diamino‐2,2′‐dimethyl‐1,1′‐biphenyl (m‐TolDA) diamines, respectively. These PIs have moderate molecular weights and good solubility in polar organic solvents, such as N,N‐dimethylformamide, dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO). OHBNDA‐TFMB, OHBNDA‐m‐TolDA, and OHBNDA‐BAFL display glass transition temperatures (Tgs) of 309, 329, and 377°C from differential scanning calorimetry (DSC) curves, and the decomposition temperatures at 5% weight loss (Td5) of as high as 522, 507, and 548°C under nitrogen, respectively. Meanwhile, these PI films also show good optical transparency with the cut‐off wavelength <315 nm and the transmittance >75% at 400 nm. These results confirm that aryl‐fused alicyclic tetracarboxylic dianhydrides can afford transparent/colorless PIs with high thermal stability, especially the higher decomposition temperatures than the wholly alicyclic dianhydrides.

Novel rigid semi-alicyclic dianhydride with large side groups for high performance colorless polyimides (CPIs)

A new dianhydride 9,10-diphenyl-9,10-bis(trifluoromethyl)-9,10-dihydroanthracene-2,3,6,7-tetraacid dianhydride (6FDPDA) with rigid semi-alicyclic structure was reported. CPI materials were prepared by copolymerizing 6FDPDA with 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) or 4,4’-(hexafluoroisopropene) diphthalic anhydride (6FDA) respectively, with 2,2′-bistrifluoromethyl benzidine (TFDB) as the diamine building blocks. Due to the ladder semi-alicyclic structure as well as –CF3 and phenyl large side groups, this new dianhydride exhibits two important advantages, the cut-off conjugated in the polymer backbone and suppressed intermolecular stacking. When 6FDA as the dianhydride comonomer, the obtained CPIs exhibits distinguished performance with transmission of 90 % at 550 nm, YI of 2.45, CTE of 16.5 ppm/K and Tg over 450 °C. These results demonstrated that 6FDPDA is an excellent building block to prepare the high performance CPIs in optoelectronic devices, for an example the substrates for flexible AMOLED display.

Synthesis and characterization of low retardation colorless polyimides containing m-phenylenediamine with different pendant groups

In this study, 4-biphenyl-3,5-diaminobenzoate (E- m-PDA) was synthesized by three steps using 3,5-dinitrobenzoic acid as a starting material. Two series of colorless polyimides (CPIs) PI-(1a-1d) and PI-(2a-2d) were prepared by traditional two-step polycondensation of m-phenylenediamine ( m-PDA) based diamines with different pendant groups (-H, CF3, COOH and biphenyl ester) with aromatic dianhydrides BPADA and 6FDA, respectively. All of the prepared CPIs exhibited high thermal stability with 5% weight loss at temperatures ranging from 428 to 539°C in nitrogen, and glass transition temperatures ( Tgs) ranging from 228 to 332°C. These PI films displayed a UV-vis absorption cut-off wavelength at 338–376 nm and transparency of 76%–89% at a wavelength of 450 nm. Both series of colorless PI films also showed low birefringence values of 0.0021–0.0100. In addition, the optical retardations of these CPIs were extremely low (48–220 nm), indicating low optical anisotropy of these CPI films. Colorless PI film PI-2d prepared based on E- m-PDA and 6FDA had good comprehensive properties of low birefringence ([Formula: see text] n of 0.0064), high Tg (319°C) and excellent transparency ( T450 of 88%).

Colorless Polyimides Derived from 5,5'-bis(2,3-norbornanedicarboxylic anhydride): Strategies to Reduce the Linear Coefficients of Thermal Expansion and Improve the Film Toughness.

In this paper, novel colorless polyimides (PIs) derived from 5,5'-bis(2,3-norbornanedicarboxylic anhydride) (BNBDA) were presented. The results of single-crystal X-ray structural analysis using a BNBDA-based model compound suggested that it had a unique steric structure with high structural linearity. Therefore, BNBDA is expected to afford new colorless PI films with an extremely high glass transition temperature (Tg) and a low linear coefficient of thermal expansion (CTE) when combined with aromatic diamines with rigid and linear structures (typically, 2,2'-bis(trifluoromethyl)benzidine (TFMB)). However, the polyaddition of BNBDA and TFMB did not form a PI precursor with a sufficiently high molecular weight; consequently, the formation of a flexible, free-standing PI film via the two-step process was inhibited because of its brittleness. One-pot polycondensation was also unsuccessful in this system because of precipitation during the reaction, probably owing to the poor solubility of the initially yielded BNBDA/TFMB imide oligomers. The combinations of (1) the structural modification of the BNBDA/TFMB system, (2) the application of a modified one-pot process, in which the conditions of the temperature-rising profile, solvents, azeotropic agent, catalysts, and reactor were refined, and (3) the optimization of the film preparation conditions overcame the trade-off between low CTE and high film toughness and afforded unprecedented PI films with well-balanced properties, simultaneously achieving excellent optical transparency, extremely high Tg, sufficiently high thermal stability, low CTE, high toughness, relatively low water uptake, and excellent solution processability.

Ultralow Coefficient of Thermal Expansion and a High Colorless Transparent Polyimide Film Realized Through a Reinforced Hydrogen-Bond Network by In Situ Polymerization of Aromatic Polyamide in Colorless Polyimide.

Colorless polyimides (CPIs) are a key substrate material for flexible organic light-emitting diode (OLED) displays and have attracted worldwide attention. Here, in this paper, the dispersion and interfacial interaction of aromatic polyamide (PA) in CPI (synthesized from 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFMB)) were significantly improved by in situ polymerization, and colorless transparent macromolecular polyimide composites (CPI-PAx) were successfully prepared by PA and CPI. By adjusting the ratio of PA to CPI, a high-performance engineering plastic with excellent film-forming properties was obtained. Molecular simulations confirmed the uniform distribution of PA in CPI and its interaction in polymers. In CPI-PAx, the CPI was locked by the PA chain, and numerous molecular chains were mutually entangled to form a hydrogen-bond network structure. Due to the strong interaction between the chains imparted by the hydrogen bonds of the PA, they do not slide under external forces and heating. In addition, the additive PA has excellent dimensional stability, thermal, and mechanical properties, and CPI has outstanding optical properties, so the synthesized CPI-PAx combines the comprehensive properties of PA and CPI. The CPI-PAx has excellent thermal and mechanical properties, with a thermal decomposition temperature of 499 °C, a glass transition temperature of 385 °C, a coefficient of thermal expansion of 0.8 ppm K-1, a tensile strength of 50.9 MPa, and an elastic modulus of 3.9 GPa. Particularly, CPI-PAx has a 90% transmittance in the visible region. These data prove that the strategy of combining PA and CPI by in situ polymerization is an effective method to circumvent the bottleneck of CPI in the current flexible window application, and this design strategy is universal.

Semi aromatic colorless polyimide coatings for dual electrochromic and electrofluorochromic displays and its potential for information encryption

Based on the concept of minimizing the charge transfer complex effect, the diamine monomer which contains amide bond bridged adamantane group and triarylamine unit was synthesized. Subsequently, two colorless polyimides with excellent electrochemical stability and high fluorescence quantum yield were prepared by polycondensation of the aforementioned diamine monomer with 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride and 4,4'-hexafluoroisopropylidene)-diphthalic anhydride, respectively. CPIs coatings ranging from colorless to oxidized blue exhibit excellent electrochromic behaviors and optical transmittance of 80 %, which is 60 % after 15,000 s electrochemical cycles. Interlayer electrochromic displays constructed through a simple strategy can display tailored patterns during electrochemical process. The color contrast between neutral state and oxidized state is strong, which can be used for encrypted transmission of information. Furthermore, the CPI synthesized from HPMDA (PI-HPMDA) demonstrated remarkable electrofluorescence performance, with the fluorescence of the film being controlled by applying voltage. The solution of PI-HPMDA exhibited a fluorescence quantum efficiency of 32.5 %, and the fluorescence intensity of PI-HPMDA could be reduced in the presence of Fe3+. he responsiveness of PI-HPMDA to Fe3+ is expected for specific ion probes.

Fluorinated Colorless Polyimides with High Heat-resistance and Low Birefringence

Fluorinated Colorless Polyimides with High Heat-resistance and Low Birefringence

Atomic oxygen degradation of a fluorine-containing colorless polyimide

Colorless polyimides (PIs) are regarded as the most feasible lens materials deployed in aerospace optical systems due to their light weight, flexibility, transparency, and excellent mechanical properties. However, durability towards atomic oxygen (AO) exposure is a chief concern for externally deployed colorless PI films in low Earth orbit (LEO) environments. In this work, we investigated the degradation behavior of a fluorine-containing colorless PI film with a combination of ground-based AO exposure experiments and reactive molecular dynamics (ReaxFF-MD) simulations. The fluorine-containing colorless PI showed linear erosion dynamics and a constant erosion yield (Ey) of ∼1.4 × 10−24 cm3 atom−1. Microscopic investigations demonstrated an increased surface roughness and shag-like appearance after continuous AO exposure. In addition, spectroscopic transformations resulted from elimination and oxidation processes occurring at specific reaction active sites (C=O, CN, CH, and CF, and CC) and the release of volatile substances. Moreover, the exposed fluorine-containing colorless PI films exhibited gradually deteriorating visible light transmission with increased AO fluence. Furthermore, the ReaxFF-MD simulations demonstrated physical sputtering and bombardment-enhanced chemical reaction models. Considering the limited-scale slab and the system thermal dissipation, the experimental and ReaxFF-MD computational results were largely consistent.

Colorless Polyimides Derived from Octahydro-2,3,6,7-anthracenetetracarboxylic Dianhydride

A cycloaliphatic tetracarboxylic dianhydride, octahydro-2,3,6,7-anthracenetetracarboxylic dianhydride (OHADA) was synthesized to obtain novel colorless polyimides (PIs). Herein, approaches for decolorizing an OHADA prototype and simplifying the entire process are described, and a plausible steric structure for OHADA is proposed. The polyaddition of OHADA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) was unsuccessful; specifically, the reaction mixture remained inhomogeneous even after prolonged stirring. However, the modified one-pot process was applicable to the OHADA/TFMB system. The isolated PI powder form, as well as those for the other OHADA-based PIs, was highly soluble in numerous solvents and afforded a homogeneous and stable solution with a high solid content (20–30 wt%). Solution casting produced a colorless and ductile PI film with a very high glass transition temperature (Tg~300 °C). Furthermore, the OHADA/TFMB system exhibited remarkable thermal stability compared with those of the other related TFMB-derived semi-cycloaliphatic PIs. However, contrary to our expectations, this PI film did not exhibit a low linear coefficient of thermal expansion (CTE). This PI film also possessed excellent thermoplasticity, probably reflecting its peculiar steric structure. The use of an amide-containing diamine significantly enhanced the Tg (355 °C) and somewhat reduced the CTE (41.5 ppm K−1) while maintaining high optical transparency and excellent solubility.

Thermally stable transparent polymer films for flexible electronics: Properties and applications

This article describes the properties of the thermostable transparent polymer films (TSTPFs), their potential use in display and electronic applications, as well as the potential market size. The property targets for different types of applications including free standing and supported films then are discussed. The development focus in TSTPFs, especially colorless polyimides (CPIs) for organic light emitting diodes (OLEDs), is emphasized. Some thermally stable transparent polymers that have been developed by our company are discussed.