Xingzhong Fang

Novel polyimides derived from 2,3,3 ',4 '-benzophenonetetracarboxylic dianhydride

Abstract A series of polyimides (PIs) based on 2,3,3′,4′-benzophenonetetracarboxylic dianhydride (2,3,3′,4′-BTDA) and 3,3′,4,4′-BTDA were prepared by the conventional two-step process. The properties of the 2,3,3′,4′-BTDA based polyimides were compared with those of polyimides prepared from 3,3′,4,4′-BTDA. It was found that PIs from 2,3,3′,4′-BTDA have higher glass transition temperature and better solubility without sacrificing their thermal properties. Furthermore the rheological properties of PMR-15 type polyimide resins based on 2,3,3′,4′-BTDA showed lower melt viscosity and wider melt flow region (flow window) compared with those from 3,3′,4,4′-BTDA. The structure–property relations resulted from isomerism were discussed.

Highly flexible and transparent film heaters based on polyimide films embedded with silver nanowires

Highly flexible and transparent film heaters (TFHs) with superior mechanical and thermal stability were fabricated by embedding silver nanowires (AgNWs) into transparent polyimide (PI) films using a solution coating method. The fabricated AgNW/PI hybrid TFHs exhibited higher heating temperatures (∼96 °C) with lower input voltage (∼6 V), shorter response time (T < 40 s), and lower power consumption (160.6 °C cm2 W−1) than ITO/FTO heaters, as well as stability after repeated use. The AgNW/PI hybrid TFHs also showed excellent resistance to bending. After undergoing outer bending for a 1000 times, the change of sheet resistance was less than 18%. The effective embedment of the AgNW network in the surface of the transparent PI film not only decreased the surface roughness (Rrms < 1 nm) but also enhanced the resistance against oxidation and moisture. Potential applications of the AgNW/PI TFHs in window defogging and thermochromics are demonstrated.

Highly Thermostable, Flexible, Transparent, and Conductive Films on Polyimide Substrate with an AZO/AgNW/AZO Structure

Flexible transparent conductive films (TCFs) are used in a variety of optoelectronic devices. However, their use is limited due to poor thermostability. We report hybrid TCFs incorporation in both aluminum-doped zinc oxide (AZO) and silver nanowires (AgNWs). The layered AZO/AgNWs/AZO structure was deposited onto a transparent polyimide (PI) substrate and displayed excellent thermostability. When heated to 250 °C for 1 h, the change in resistivity (Rc) was less than 10% (Rc of pure AgNW film > 500) while retaining good photoelectric properties (Rsh = 8.6 Ohm/sq and T = 74.4%). Layering the AgNW network between AZO films decreased the surface roughness (Rrms < 8 nm) and enhances the mechanical flexibility of the hybrid films. The combination of these characteristics makes the hybrid film an excellent candidate for substrates of novel flexible optoelectronic devices which require high-temperature processing.

Enhanced hydrolytic stability of sulfonated polyimide ionomers using bis(naphthalic anhydrides) with low electron affinity.

In the pursuit of hydrolytically stable sulfonated polyimide (SPI) membranes as promising candidates for proton exchange membranes, usable at elevated temperature, a series of novel SPI ionomers based on the low electron affinity bis(naphthalic anhydrides), 4,4′-sulfide-bis(naphthalic anhydride) (SBNA) and benzophenone-4,4′-bis(4-thio-1,8-naphthalic anhydride) (BPBTNA), were prepared. Tough, flexible, and transparent membranes were obtained from these polymers, although their inherent viscosities ranged from 0.41 to 0.59 dL g−1. The SPI membranes were thermally stable with the decomposition of sulfonic acid groups over 300 °C, and exhibited good mechanical properties with 65 MPa of tensile strength at 25 °C and 50% RH. The proton conductivities of the SPI membranes increases with increasing temperature and ion exchange capability (IEC), and the S–O(80) with 2.23 mequiv. g−1 of IEC showed a higher proton conductivity than Nafion® 212 at 100% RH. For the high IEC membranes, microscopic analyses revealed the hydrophilic clusters were well-dispersed and connected to each other. The accelerated water stability tests demonstrated that the SPI ionomers based on SBNA and BPBTNA maintained a high mechanical strength after being aged in water for 24 h at 140 °C, which was much more stable than the SPI membranes based on 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA). The improved hydrolytic stability of polymers could be well correlated with the results of the electron affinity (Ea) of the dianhydride calculated by the theoretical calculation. This investigation illustrated that this strategy will benefit the further development of hydrolytically stable SPIs applied to high temperature PEFCs.

synthesis and properties of novel melt processable isomeric polythioetherimides

A series of 3,3’,4,4’-diphenylthioethertetracarboxylic dianhydride (s-TDPA), 2,3,3’,4’ -diphenylthioethertetracarboxylic dianhydride (a-TDPA), and 2,2’,3,3’-diphenylthioethertetracarboxylic dianhydride (i-TDPA) isomer mixtures were synthesized from 3- and 4-chlorophthalic anhydrides. Copolythioetherimides derived from TDPAs with different ratios of the isomers and 4,4’-oxydianiline (ODA) were prepared by a two-step polycondensation procedure. Solubility, thermal properties, mechanical properties and melt processability of copolythioetherimides were investigated and compared with corresponding homopolyimides. The dependence of these properties on the composition of TDPA isomers and the effects of molecular structures were discussed in this work in order to obtain an indication for the molecular design of high performance melt-processable polyimides.

Screen-printing fabrication of electrowetting displays based on poly(imide siloxane) and polyimide

Abstract We report a screen-printing fabrication process for large area electrowetting display (EWD) devices using polyimide-based materials. The poly(imide siloxane) was selected as hydrophobic insulator layer, and relatively hydrophilic polyimide as grids material. EWD devices that use poly(imide siloxane) as hydrophobic insulator fabricated with conventional methods showed good and reversible electrowetting performance on both single droplet level and device level, which showed its potential application in EWDs. The compatibility of polyimide-based materials (hydrophobic poly(imide siloxane) and hydrophilic polyimide) guarantee the good adhesion between two layers and the capability of printable fabrication. To this end, the hydrophilic grids have been successfully built on hydrophobic layer by screen-printing directly. The resulting EWD devices showed good switch performance and relatively high yield. Compared to conventional method, the polyimide-based materials and method offer the advantages of simple, cheap and fast fabrication, and are especially suitable for large area display fabrication.

Preparation and characterization of poly(imide siloxane) block copolymers based on diphenylthioether dianhydride isomer mixtures

A series of poly(imide siloxane) block copolymers were prepared based on diphenylthioether dianhydride isomer mixtures (m-TDPA), 4,4′-oxydianiline (ODA) and bis(γ-aminopropyl)polydimethylsiloxane (APPS). The ODA and m-TDPA composed the hard segment, while the APPS and m-TDPA composed the soft segment. The hard segment length was kept constant, while the soft segment lengths were varied with varying the APPS contents. The copolymers had inherent viscosities range from 0.37 to 0.51 dL g−1, and their weight-average molecular weights and number-average molecular weights were in the range of 45 000–52 600 and 21 300–27 000, respectively. All copolymers were readily soluble in many organic solvents, and could afford flexible films via solution casting. The cast films exhibited mechanical properties with tensile strengths at break of 26.7–86.2 MPa, elongations at break of 9.9–112.2%, and tensile moduli of 0.12–2.15 GPa, depending on the soft segment length. The films also exhibited low water uptakes in the range of 0.18–0.68 wt.%. Furthermore, the copolymers showed high glass transition temperatures derived from the hard segments in the range of 196–225 °C, and good thermal stability with almost no weight loss up to 350 °C under nitrogen atmosphere and 335 °C under air atmosphere.

Synthesis and characterization of transparent polyimides derived from ester-containing dianhydrides with different electron affinities

Two series of poly(ester imide)s derived from bis(trimellitic acid anhydride) phenyl ester (TAHQ) and bis[(3,4-dicarboxylic anhydride) phenyl] terephthalate (PAHP), as well as poly(ether imide)s based on hydroquinone diphthalic anhydride (HQDPA), were synthesized with aromatic diamines via solution polycondensation. These polyimide films were transparent with an ultraviolet-visible absorption cut-off wavelength below 375 nm, and with tensile strengths of 42.0–83.8 MPa, tensile moduli of 2.5–4.7 GPa and elongations at break of 2.1–5.4%. Compared with the poly(ether imide)s, the poly(ester imide)s showed higher glass transition temperatures (Tg), lower water absorption (WA) and lower temperature of 5% weight loss (Td5%). Moreover, the poly(ester imide)s derived from PAHP with a low electron affinity of 2.04 eV by theoretical calculation achieved better transparency, lower WA and slightly lower Tg than the corresponding TAHQ-based poly(ester imide)s.

Study on Thermal Properties and Crystallization Behavior of Blends of Poly(phenylene sulfide)/Poly(ether imide)

The thermal behavior of poly(phenylene sulfide) (PPS) blends with poly(ether imide) (PEI) was studied by differential scanning calorimeter (DSC). The crystallization temperature of PPS in blends shifted from 216.8°C to 226.4°C upon addition of 20–70% PEI contents. The heat of crystallization remained unchanged with less than 50% PEI in blends, whereas the heat of fusion decreased with increasing PEI content. The isothermal crystallization indicated that incorporating PEI would accelerate the crystallization rate of PPS. The activation energy of crystallization increased with addition of PEI. The equilibrium melting point of PPS/PEI blends was not changed with compositions.

Synthesis and crosslinking study of isomeric poly(thioether ether imide)s containing pendant nitrile and terminal phthalonitrile groups

Two novel series of highly organosoluble and curable polyimides containing pendant nitrile groups PI (a–d) and phthalonitrile-terminated polyimides PN-PI (a–d) were prepared by solution polycondensation of isomeric bis(chlorophthalimides)s and 2,6-dichlorobenzonitrile with 4,4′-thiobisbenzenethiol. The inherent viscosities of these copolymers were in the range of 0.37–0.59 dL g−1 in N-methyl-2-pyrrolidone (NMP) at 30 °C. The phthalonitrile and pendant nitrile groups in isomeric poly(thioether-ether-imide)s were thermally crosslinked without a catalyst through thermal curing up to 280–360 °C, which led to the transformation from thermoplastic polymers to thermosetting polymers. All PIs before and after crosslinking were characterised by gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy. PN-PI (a–d) and PI (a–d) were found to be highly soluble in some solvents, such as chloroform, dimethylacetamide, m-cresol, dimethlyformamide and N-methyl-2-pyrrolidone, while the crosslinked polymers were insoluble in all tested solvents. The crosslinking results of pendant nitrile and terminal phthalonitrile groups are also compared. Both series of PIs showed high thermal stability based on 5% weight loss temperature (T5%) in the range of 471–509 °C and increased up to 35 °C after thermal curing. Polyimides showed high glass transition temperatures (Tgs) ranging from 191–213 °C as determined by DSC, but no detectable Tg was observed after thermal heating, indicating the crosslinked structure of PIs. The mechanical properties also enhanced after the crosslinking of the copolymers. The tensile modulus and strength of the cured PI films were in the range of 3.3–4.7 GPa and 68–122 MPa, respectively, which were up to 62% and 35% higher than the uncured films.