•A dianhydride containing crosslinkable phenylethynyl pendant group was synthesized.•A flexible microporous polyimide network was prepared via a new two-step pathway.•The flexible polyimide network displayed BET surface area of 322 m2 g−1.A dianhydride monomer 2, 5-bis(3, 4-dicarboxyphenoxy)-4′-phenylethynyl biphenyl (PEPHQDA) containing a chain extendable phenylethynyl pendant group has been successfully synthesized via successive nucleophilic substitution, Sonogashira cross-coupling, hydrolysis and dehydration reactions. A flexible microporous polyimide network has been prepared based on the use of triamine (TAPOB), affording hyperbranched polyimide, followed by the curing of phenylethynyl groups to give network structure. Specifically microporous features such as a well-defined surface morphology, microporous structure and nanometer-sized pore channels have been introduced to the flexible polyimide networks through this two-step pathway. This network exhibit a BET surface area (322 m2 g−1) as well as a comparable CO2 uptake (1.25 mmol g−1 at 273 K and 1 bar) and enthalpy of adsorption (30.3 kJ mol−1) to that of other microporous polyimides derived from rigid tridimensional monomers.Download high-res image (346KB)Download full-size image

•An electroactive hyperbranched polyimide terminated by ferrocene (HBPI-Fc) was synthesized.•A memory device employing HBPI-Fc as the active layer exhibited bipolar WORM behavior.•The switching performances of HBPI-Fc rely on the charge trapping effect of ferrocen terminals.•Modification of the terminals of hyperbranched polymer for preparing polymer-based memory materials.In this work, a novel tetra-amine, bis (4-(3, 5-bis (4-amino-2-(trifluoromethyl) phenoxy) phenoxy) phenyl) methanone, was synthesized and then utilized to produce hyperbranched polyamic acids via polycondensation with 4, 4’-(hexafluoroisopropylidene) diphthalic anhydride (6FDA). The resulting hyperbranched polyamic acids underwent termination by (4-amino) phenyl ferrocene and imidization, leading to ferrocene-terminated hyperbranched polyimide (HBPI-Fc). The resulting HBPI-Fc displayed superior solubility in conventional organic solvents and excellent thermal stability. A memory device with a configuration of indium tin oxide (ITO)/HBPI-Fc/Al was fabricated, in which the HBPI-Fc acted as the active layer. The device exhibited bistable electrical conductivity switching and nonvolatile bipolar write-once-read-many-times memory character with two threshold voltages of 2.2 V and −2.6 V, respectively, during positive and negative voltage sweep. The device exhibited an ON/OFF current ratio of 104 under a constant bias of −1.0 V and good stability in both ON- and OFF-state during the test period of 104 s. The revealed electrical bistability of the HBPI-Fc was found mainly due to the effective charge trapping effect of the electroactive terminal ferrocene groups.A novel ferrocene-terminated hyperbranched polyimide (HBPI-Fc) was synthesized from a tetra-amine and followed by termination with (4-amino) phenyl ferrocene, and the HBPI-Fc based memory device exhibited a bipolar WORM behavior.Download high-res image (269KB)Download full-size image

•Aromatics endcapped hyperbranched polyimides (HBPI) are first explored as polymer memory materials.•Tunable memory characteristics from volatile to nonvolatile were obtained by adjusting the endcapping groups.•Improved memory performances were achieved in HBPIs with large conjugated endcapping groups.Three aromatics endcapped hyperbranched polyimides (HBPIs), with triphenylamine derivative (A3) as core, 4,4-(hexafluoroisopropylidene)diphthalic anhydride as B2 monomer, phthalic anhydride (PA), 1,8-Naphthalic anhydride (NA) and 3,4-perylenedicarboxylic anhydride (PDA) as endcapping reagents are explored as polymer memory materials. All these HBPIs showed excellent solubility in various organic solutions. Tunable memory characteristics from volatile to nonvolatile were obtained by adjusting the endcapping groups. Compared to PA endcapped HBPI, NA and PDA endcapped HBPIs exhibited enhanced nonvolatile memory behaviors with switch voltages low to 0.8 V and 1.0 V, and outstanding thermal stability with 5% weight loss temperatures reaching up to 533 °C and 554 °C, respectively. Such superior performance can be attributed to the introduced polycyclic arenes end-groups, which leads to stronger conjugation intensity, better hole transport ability and higher charge separation stability.

Based on a dianhydride monomer 2,5-bis(3,4-dicarboxyphenoxy)-4′-phenylethynyl biphenyl (PEPHQDA) containing a crosslinkable phenylethynyl pendant group, microporous polyimide networks (HBPI-CRs) were prepared through a two-step pathway combining polymerization and crosslinking reactions. Specifically microporous features such as surface morphology, microporous structure and uniform nanometer-sized pore channels were introduced to the polyimide networks through this two-step pathway. The HBPI-CR networks exhibited a BET surface area (385–497 m2 g−1) as well as a comparable CO2 uptake (1.65–2.04 mmol g−1 at 273 K and 1 bar) and enthalpy of adsorption (28.6–30.0 kJ mol−1) to that of other microporous polyimides derived from rigid tri-dimensional monomers.

A novel diamine monomer bearing double hydrophobic cross-linkable tetrafluorostyrol side-groups has been successfully synthesized. Based on this monomer along with 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), a series of cross-linked highly sulfonated co-polyimide (CSPIy-6FATFVPx) membranes with IEC values ranging from 2.07 to 2.41 meq g−1 were prepared via a high temperature poly-condensation, followed by a thermal cross-linking reaction. The SPI were synthesized by high temperature polymerization. The CSPI membranes were obtained from the SPI membrane by thermal crosslinking reation. The polymerization and crosslinking reation were not performed in one pot. The CSPIy-6FATFVPx membranes showed significantly excellent performance, especially the high proton conductivity (0.153–0.210 S cm−1 at 80 °C), low water uptake (54.1%–87.1% at 80 °C) and swelling ratio (15.5%–23.0% at 80 °C). Furthermore, the CSPIy-6FATFVPx membranes also exhibited outstanding thermal stability (5% weight loss when the temperature exceed 320 °C), excellent hydrolytic stability and mechanical properties. The results indicate that CSPIy-6FATFVPx are promising candidates as proton exchange membranes in fuel cell technology.

•A new diamine monomer bearing hydrophobic cross-linkable side-groups was synthesized.•A series of new cross-linked highly sulfonated co-polyimide membranes were prepared.•These membranes exhibit superior proton conductivity and low swelling ratio.•These membranes show good chemical, thermal and mechanical properties.A novel diamine monomer 3,3′-Bis(2,3,5,6-tetrafluoro-4-vinylphenoxy)biphenyl-4,4′-diamine (TFVBPA) bearing double hydrophobic cross-linkable tetrafluorostyrol side-groups has been successfully synthesized via a nucleophilic substitution reaction. A series of cross-linked highly sulfonated co-polyimide (CSPIy-TFVBPAx) membranes with ion-exchange capacity (IEC) values ranging from 2.27 to 2.44 meq. g−1 have been prepared from this monomer. The CSPIy-TFVBPAx membranes show excellent comprehensive properties, especially the high proton conductivity (0.135–0.190 S cm−1 at 80 °C), low water uptake (60.9–76.7% at 80 °C) and swelling ratio (14.2–19.6% at 80 °C). Moreover, the CSPIy-TFVBPAx membranes also exhibit outstanding thermal stability (5% weight loss temperature exceed 320 °C) and excellent hydrolytic stability. The results indicate that the CSPIy-TFVBPAx membranes are promising candidates for proton exchange membranes in fuel cell applications.

To investigate the properties of hyperbranched polyimides (HBPIs) for potential optical applications, novel fluorinated tetra-amine monomers with ether and sulfonyl groups, 4,4′-di[3,5-di(2-trifluoromethyl-4-aminophenoxy)phenoxy]sulfone, and five kinds of long-chain dianhydrides, have been designed and synthesized. A series of anhydride-terminated hyperbranched polyimides have been prepared via a two-step method with chemical imidization. The HBPIs possess outstanding solubility and show excellent thermal and optical properties. The glass transition temperatures (Tg) of the HBPIs range from 230–242 °C determined by differential scanning calorimetry (DSC), and 232–263 °C by thermomechanical analysis (TMA), depending on the dianhydride used. The 5% weight loss temperatures are in the range of 480–533 °C, showing high intrinsic thermal-resistant characteristics of the HBPIs. The HBPI films show good optical transparency, higher than 80% at 800 nm. The cast polyimide films have favorable mechanical properties with tensile strengths of 91–112 MPa, elongation at break of 5.99–7.99%, and initial modulus of 2.14–2.57 GPa. The polyimides exhibit average refractive indices of 1.5780–1.6271, and birefringence of 0.0065–0.0079 because of the hyperbranched structure. The PI derived from 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane possesses the lowest refractive indices due to the high fluorine content in the polymer chain.

Carbon nanotube (CNT)/polymer composites with high dielectric constants are highly desired by the electronic and electric industries. However, high conductivity CNTs exhibit bad dispersion properties in polymers, leading to high dielectric losses in the composites. One effective strategy to overcome these problems involves the fabrication of core–shell structured fillers with CNT cores and non-conductive or semi-conductive shells. In this study, tetra-amido-phthalocyanine copper (4NH2-CuPc) coated, acidified multi-walled carbon nanotube (a-MWCNT) composites were fabricated through π–π stacking interactions. The coating thickness was controlled by adjusting the concentration of 4NH2-CuPc in the mixture and was subsequently confirmed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses. The a-MWCNTs/4NH2-CuPc were added to poly(vinylidene fluoride) (PVDF) to produce a-MWCNTs/4NH2-CuPc/PVDF composites. The dielectric properties of these composites reached the optimum values when the rate of 4NH2-CuPc adsorption on the a-MWCNTs was the highest. A composite with 9 wt% a-MWCNTs and 13.5 wt% 4NH2-CuPc (mass ratio a-MWCNTs:4NH2-CuPc = 1:1.5) exhibited the largest dielectric constant (3200) and a dielectric loss tangent (2.1 at 1 kHz).

A series of high molecular weight soluble fluorinated cross-linkable co-polyimides (Co-PIs) were synthesized from 1,3-bis(2-trifluoromethyl-4-aminophenoxy)-5-(2,3,4,5-tetrafluorophenoxy)benzene (6FTFPB), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB), 1,4-bis(4-amino-2-trifluoromethyl-phenoxy)-2-(3′-trifluoro-methylphenyl)benzene (m-3F-6FAPB) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). The weight-average molecular weights (Mws) and polydispersities of the co-polyimides were in the range 5.53–7.24 and 1.71–2.04, respectively. By adjusting the feed ratio of diamines, the refractive indices of Co-PIs films were exactly tuned in the range of 1.5203–1.5574 at 633 nm. The co-polyimides showed outstanding solubility in organic solvents and high thermal stability (5% thermal weight-loss temperature beyond 525 °C). Meanwhile, the films had excellent mechanical properties with high tensile strength of 100–108 MPa, Young’s modulus of 3.3–4.2 GPa and elongations at break of 8–15%. Polymers in the form of cast and spun films could be cross-linked by thermal curing at 260 °C. After curing, the Co-PIs films showed excellent chemical resistance, high glass transition temperatures above 270 °C, higher mechanical properties and thermal stability (5% thermal weight-loss temperature beyond 540 °C) and low dielectric constant in the range of 2.37–2.70.