7 - Polyimides

Polyimide (PI) materials with a low coefficient of thermal expansion (CTE) while still retaining high strength and toughness are desirable in various applications. In this study a sol–gel process was used to incorporate silica into homopolyimides and copolyimides with highly rigid structures in an attempt to pursue this aim. A number of highly rigid monomers were used, including pyromellitic dianhydride (PMDA), p-phenylene diamine (PPA), m-phenylene diamine (MPA), benzidine, 2,4-diaminotoluene, and o-toluidine. No homopolyimide flexible films were obtained. However, it was possible to obtain flexible films from the copolyimides. Therefore, a copolyimide based on PPA, MPA, and PMDA (PPA/MPA = 2/1 mol) was then chosen as the matrix to prepare the PI/silica hybrids. Flexible films were obtained when the silica content was below 40 wt %. The hybrid films possessed low in-plane CTEs ranging from 14.9 to 31.1 ppm with the decrease of the silica content. The copolyimide film was strengthened and toughened with the introduction of an appropriate amount of silica. The thermal stability and the Young's modulus of the hybrid films increased with the increase of the silica content. The silica particle size was assessed by scanning electron microscopy and was about 100 nm for the hybrids containing 10 and 20 wt % silica and 200–500 nm for the hybrids containing 30 and 40 wt % silica. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 794–800, 2001

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.

Construction of novel Cu-α-diimide interactions for enhancing thermal resistance and dimensional stability of polyimide films

Ion-conducting membranes are crucial in electrochemical storage and energy conversion technologies such as fuel cells, alkaline ion batteries, and redox-flow batteries. The purpose of the membrane is to prevent direct contact between the electrodes while allowing selective ions to pass through. The characteristics of the ion-conducting membranes include excellent mechanical and thermal stability, chemical resistance, high ionic conductivity, and selectivity. Polymers and polymer-based precursors make up the majority of the materials that have been used as ion-conducting membranes. However, most polymer-based membranes have issues related to poor chemical resistance, recyclability, and thermal and mechanical stability. In addition, as more sustainable materials are being sought to create a sustainable society, new environmentally friendly and economically viable materials are in high demand. The clay-based material could be an alternative for ion-conducting applications due to its porous structure, high surface area, tunable interlayer spacing, excellent thermal and mechanical stability, and high ion conductivity. Clay minerals are primarily used in water treatment, pharmaceutics, ceramics, paints, and coating industries. Furthermore, clay minerals have been used as a filler material in energy storage and conversion system to improve the thermal stability and ion conductivity in electrodes, electrolytes, and separators.Herein, we report a novel approach to making non-polymeric hybrid clay membranes using environmentally benign materials such as clay and zwitterion (i.e., sulfobetaine). These membranes with improved ionic conductivity will find immense potential in applications in energy storage and conversion systems. Such membranes have been synthesized by intercalating sulfobetaine molecules into the interlayer spacing of the bentonite clay matrix. Sulfobetaine is a zwitterion composed of quaternary ammonium cations and sulfonate anions. Leveraging the unique structure-property features that exist in zwitterions helps to alter the interlayer spacings in the clay matrix, thereby enabling ion diffusion through the silicate layers. Furthermore, it helps in the formation of a self-supporting membrane. The functionalized membrane's crystal structure and chemical composition were investigated using XRD, XPS, and ATR-FTIR. XRD was used to identify the layered structure of the silicates in clay and the increased interlayer spacing (1.15 nm to 1.8 nm) of the hybrid clay membrane. Data from XPS and ATR-FTIR confirmed the successful functionalization of clay with sulfobetaine. Furthermore, the ionic conductivity of the hybrid clay membrane was characterized using a non-aqueous lithium electrolyte solution, and found a conductivity of . This is one of the first reports showcasing how zwitterions can impart conductivity in clay silicate motifs. It suggests an easy and novel approach to transport lithium-ion through silicate layers, thereby making it suitable for use as membranes in batteries and supercapacitors. The current study demonstrates an easy and versatile approach to developing cost-effective and eco-friendly membranes from sustainable materials such as clay, which, when functionalized, has the potential to be a highly efficient ion-conducting material with applications in energy storage, devices, and technologies.

The preparation of porous polyamide-imide nanofiber membrane by using electrospinning for MF application

Polyimide (PI) film is widely used in aerospace, microelectronics, and other fields because of its excellent thermal stability and mechanical strength. However, there are very few reports about its application in the direction of optical imaging. To use PI film for imaging, the requirements for the optical homogeneity of the PI film are extremely demanding. The optical homogeneity of the stretch-resistant PI film proposed in this paper with 100 mm diameter and low thermal expansion coefficient meets the Rayleigh criterion, which has the potential for applications in the imaging field. In addition, the tensile strength of this PI is 285 MPa, which is ~2.6 times that of the PMDA-ODA type PI; the coefficient of thermal expansion is about 3.2 ppmK-1, which is comparable to that of the Novastrat®905 type PI and is one order of magnitude lower than that of the commercial PI films. These excellent basic properties reserve more space to further improve the space adaptability of the PI film. The solution of the optical homogeneity of the PI film will lay the foundation for its application in thin film diffractive optical elements.

Herein, we report a series of titania (TiO2)-coated polymeric nanofibers membranes with superb strength, excellent thermal stability, and admirable wettability via in situ coating TiO2 nano-shells on the surface of polyimide (PI) nanofibers. TiO2 nano-shells are able to weld the PI nanofibers and serve as a reinforcement layer, endowing the TiO2-coated PI separator with high tensile strength of 43.94 MPa. Specifically, the in situ coating technique is a simple and controllable method to fabricate high-performance hybrid separator and meet the demand of low-cost industrial production. Moreover, TiO2-coated PI separator displays preferable wettability, thermal stability, and ion conductivity than the Celgard separator. Importantly, the unique thermal dimensional stability of TiO2-nanoshells and PI materials also improves the safety of lithium ion battery (LIB). Notably, TiO2-coated PI separator exhibit superior LIB capability of 140.1 mAh g−1 at 5 C compared to the commercial Celgard separator (95.4 mAh g−1, 5 C). Besides, the present battery with TiO2-coated PI separator can operate stably after being tested at 1 C for 100 cycles. Thus, we believe that this work provides a significant contribution for realizing industrial production preparation of high-performance hybrid separators for LIBs.

ABSTRACTNovel phosphorus‐containing polyhedral oligomeric silsesquioxane (POSS)/polyimides (PI) hybrid materials with low dielectric constant and low linear coefficients of thermal expansion (CTE) were prepared and characterized. The POSS/PI hybrid materials were synthesized with octa(aminopropyl)silsesquioxane (OAPS) and a series of phosphorus‐containing polyamide acids(PAA). The PAAs were synthesized with bis(4‐aminophenoxy) phenyl phosphine oxide (BAPPO), 4,4’‐diaminodiphenyl ether (ODA) and 3,3',4,4'‐biphenyl tetracarboxylic diandhydride (BPDA). The structures and properties of the hybrid materials were characterized. And the effect of the phosphorus‐containing structure on the POSS/PI hybrid materials was discussed. The dielectric constants and CTE of the hybrid materials were remarkably lower than that of the unmodified POSS/PI films. The lowest values of dielectric constant and CTE could achieve as low as 2.64 (1 MHz) and 27.45 ppm/K. Besides, the hybrid materials also had excellent thermal properties. The highest 5% weight loss temperature of the hybrid materials was as high as 580°C under air. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42611.

We report on label free highly sensitive electrochemical immunosensor for monitoring alcohol consumption through the detection and quantification of ethyl glucuronide (EtG) -a metabolite of ethanol-based on two-dimensional (2D) zinc oxide (ZnO) nanoflakes (NFs), which were synthesized on flexible Au-coated polyethylene terephthalate (PET) substrate using simple one step sonochemical approach. Highly sensitive detection of EtG using cyclic voltammetry (CV) is achieved by immobilizing EtG antibody on the as-synthesized sensing electrodes of ZnO NFs. Continuous monitoring of alcohol detection is imperative for the prevention of accidents, point of care monitoring, and personal safety. The cutting-edge technologies are mostly focused to detect alcohol from the breath (e.g. breathalyzer), which is not compatible for the real-time monitoring. The relationship between the blood and breath alcohol concentrations and the improvement of the detection techniques of alcohol biomarkers from the sweat render an opportunity for point of care monitoring. Among different biomarkers, Ethylglucuronide (EtG) has been found as a promising indicator of alcohol due toit’s prolonged existence in sweat (24 hours for one or two “drinks” or 2-4 days for binge drinking), which prevents relapsing. PET has gained popularity as substrate for wearables because of its intrinsic elasticity, thermal stability, hydrophobicity, excellent dielectric properties, low coefficient of thermal expansion, structural resiliency against repeated bending forces and compatibility with roll-to-roll fabrication processes for low cost and scalable manufacturing. ZnO, a semiconducting material with piezoelectricity,high catalytic efficiency, biocompatibility, chemical stability in physiological environments, low toxicity and a high isoelectric point (IEP) of about 9.5, has been proposed for biosensing applications. ZnO nanostructures (NSs) with different morphologies such as nanorods, nanowalls, nanobelts and quantum dots have been used as immobilizing matrix in fabrication of biosensors for the detection of physiologically relevant biomarkers such as cholesterol, galactose, glucose. Considering their promising properties and potential applications, many techniques have been developed to synthesize various ZnO NSs. In comparison to the more conventional approaches such as hydrothermal method, sonochemical synthesis method is not only significantly faster, inexpensive and performed at ambient conditions but also highly stable and reproducible with the advantages of more uniform size distribution, faster reaction time and a higher surface area, which are essential to design sensing platform withimproved performance. Compared to bulk materials, the 2D ZnO NFs provide unique sensing advantages with polarized (0001) plane orientation and high surface charge density, which could enhance EtG antibody loading and thus improve sensing performance. High isoelectric point allows immobilization of most biomolecules without any additional biding layer. This provides a direct, stable pathway for rapid electron transport when an analyte is immobilized on NFs and improves electron transfer rate greater than 1D ZnO nanorods, high isoelectric point,that results in change of the resistance.Taking advantage of these unique properties, we immobilizedEtG antibody on the synthesized ZnO NFs. When an analyte binds the antibody, there is a change in the current due to increase in the charge transfer resistance. The cyclic voltammetry (CV) measurements were taken in the potential range of -0.1V-0.8V at a scan rate of 50mVs-1. For the EtGconcentrationsof1ng/mL-100µg/mLusing PET/Au/ZnO NFs as the working electrode. The minimum detection limit was found to be much lower than 1ng/mL which covers the physiological range. The sensitivity of the sensor was found to be 18.48 mA/ng/mL/cm-2.

Polyimides (PIs) are a class of representative high-performance engineering plastics possessing the cyclic imide and aromatic groups. Aromatic polyimides have been extensively investigated due to their excellent thermal stability, mechanical properties, along with their good chemical resistance and dielectric properties. Carbon nanotubes (CNTs) have been widely used in many fields such as electrodes, nanometer electron device, and composites etc, as CNTs are considered as the ideal reinforcing nanofillers owing to low density, high aspect ratio, high stiffness, and extremely high strength. With the development of the electrospinning technology, PI nanocomposites containing CNTs have received more significant attention. However, only a few studies have described the conductive mechanism and mechanical properties of PI/CNTs nanocomposites by electrospinning. In this paper, in order to improve the interfacial interaction and compatibility between the MWNTs and the matrix, pristine MWNTs were firstly treated with concentrated HNO3 to obtain the acid-functionalized MWNTs, and then the electrospinning solutions are prepared via in-situ polymerization. At last, PI nanofibers and the nanofiber composites with MWNTs were fabricated by electrospinning. The controllable structure such as parallel fiber is formed. The dispersion and alignment morphologies of MWNTs in the electrospun nanofibers, as well as the thermal and mechanical properties of the nanofiber composites, were studied in detail. The relationship between structure and electrical properties of the nanofiber composites are also studied. To sum up, such a homogeneity approach to fabricate high-performance PI/CNTs nanofiber films is a good attempt toward utilizing CNTs in polymer matrices to achieve excellent thermal, electrical, and mechanical properties in practical use.

To 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.

Preparation and characterization of fluorine-containing benzimidazole polyimide films with a micro-branched crosslink structure

In this study, practically useful colorless polyimides (PIs) with low coefficients of thermal expansion (CTEs) and other desirable properties were prepared from hydrogenated pyromellitic dianhydride (1-exo,2-exo,4-exo,5-exo-cyclohexanetetracarboxylic dianhydride, H-PMDA). A modified one-pot polymerization method afforded a high-molecular-weight PI with sufficient film-forming ability from 2,2′-bis(trifluoromethyl)benzidine (TFMB) with a rod-like structure and H-PMDA. However, the PI film cast from its homogeneous solution did not have low CTEs, similar to the analogous system using meta-tolidine. To solve this problem, a series of amide- and amide-imide-containing diamines were designed and synthesized. The modified one-pot polymerization of H-PMDA and the diamines in γ-butyrolactone produced homogeneous, viscous, and stable solutions of high-molecular-weight PIs with high solid contents. The cast films of certain systems examined in this study simultaneously achieved low CTEs, high optical transparency, considerably high glass transition temperatures (Tgs), and sufficient ductility. A possible mechanism for the generation of low CTEs, which is closely related to the spontaneous in-plane orientation behavior during solution casting, was proposed. Certain H-PMDA-based PIs developed in this study are promising colorless heat-resistant plastic substrates for use in image display devices and other optical applications.

Polyimides have inherently high mechanical properties, good chemical resistance, a low dielectric constant and high thermal stability [1]. In recent years, polyimide-based sensor materials have received much attention due to their simple preparation method, chemical inertness, mechanical and thermal stability, and high biocompatibility[2–4]. Thus they have a wide range of diverse and potential applications in several major technologies. Among the polymers, polyimides (PI) possess reliable high-temperature stability, excellent chemical resistance, high hydrolytic stability, adhesive properties, and good mechanical strength [7– 9]. Polysulfones and phosphine oxidecontaining polyimides have excellent adhesive properties without sacrificing thermal stability [10–12].

Fan-Out Wafer Level Packaging (FOWLP) is considered to be one of the most important basic packaging forms for advanced packaging industry. Polyimide (PI), especially aromatic polyimide, stands out among many polymers due to its excellent comprehensive properties and has been used as a typical redistribution layer (RDL) dielectric material. However, the mismatch of coefficient of thermal expansion (CTE) between the polyimide (PI) insulating layer and copper wires in FOWLP always cause reliability issue. In this paper, one-pot method was used to synthesize block copolymerized PI (B-PI) and random copolymerized PI (R-PI) with the same ratio of the rigid segment and flexible segment, the two PIs were prepared by controlling the addition order of diamine and dianhydride. To better understand the relationship between their structures and properties, we also prepared R-PIs and B-PIs with different rigidity-flexibility ratios. These copolymers were characterized by fourier transform infrared (FT-IR), dynamic mechanical thermal analysis, thermomechanical analyzer and polarized light microscope. The test results showed that B-PI exhibits higher elongation at break and lower coefficient of thermal expansion than R-PI. In addition, the crystallinity and mechanical properties of B-PIs and R-PIs also changed regularly with the increase of the rigid segment ratio. The copolyimide films obtained by different feeding sequences exhibited excellent thermal stability, and the carbon residue rate at 800 °C was as high as 50 % or more. These results suggest their promising application as RDL dielectrics of FOWLP.