Bioinspired polyimide film with fire retardant and gas barrier properties by gravity-induced deposition of montmorillonite

Flame retardants play a crucial role in improving theflame retardant properties of polymer materials.In recent years,environmental problems caused byflame retar-dants have attracted widespread attention.It is urgent to use green and effective methods to prepareflame retardant polymers.Bioinspired nanocomposites with lay-ered structures seem to provide effective ideas,but in general,their hydrophilic raw materials limit their applications in certainfields.Here,we prepared biomimetic composites with a layered“brick-and-mortar”structure by gravity-induced depo-sition using polyimide as the polymer matrix and montmorillonite(MMT)as thefiller.The well-arranged structures of the composite material could isolate oxygen and prevent combustible gases from escaping.The gas barrier performance has been greatly improved,in which the water vapor transmission rate and the oxygen trans-mission rate decreased by 99.18%and three orders of magnitude,respectively.Theflame retardant performance has also been improved,and its limiting oxygen index can reach 67.9%.The polyimide matrix can be converted to water-insoluble by ther-mal imidization of water-soluble poly(amic acid)salt precursors,which endows the composites with low hygroscopicity.The coating containing MMT can protect against polyurethane(PU)foam fromfire.During the conical calorimetric test,the coated sample self-extinguished,and the peak heat release rate,total heat release,and total smoke production are significantly decreased by 53.39%,40.69%,and 53.03%,respectively.Taking advantage of these properties,this work utilizes a facile method to prepare biomimetic composites with low moisture absorption,excellent gas barrier properties,andflame retardancy,which have great application potential.

Synthesis and Properties of High Performance Functional Polyimides Containing Rigid Nonplanar Conjugated Fluorene Moieties

A diamine(WuFDA) containing vertical rigid non-planar conjugated fluorene moiety and low polarizability group(C―F)was designed and synthesized through three steps of reactions(halogenated reaction, Suzuki coupling reaction, and reduction reaction).Four kinds of high performance functional polyimides(WuFPI-6 F, WuFPI-BP, WuFPI-BT, and WuFPI-PM) were thus prepared by the condensation polymerization of WuFDA with four commercial dianhydride 6 FDA, BPDA, BTDA, and PMDA, respectively. The polyimides exhibited low dielectric constant, excellent thermal stability, outstanding solubility, good film-forming property, and mechanical properties. The dielectric constants of the polyimides were in the range of 2.28-2.88(f = 10~4 Hz). The 5% weight-loss temperatures(Td 5%)in nitrogen were in the range of 555-584 °C, and the glass transition temperatures(T_g) were in the range of 408-448 °C. The weight loss of WuFPI-BP maintaining at 450 and 500 °C for half an hour was only 0.33% and 1.26%, respectively. All the WuFPIs could be dissolved in almost all organic solvents, even chloroform. The tensile strength and tensile modulus of these films were in the ranges of 78.6-85.7 MPa and 3.1-3.2 GPa, respectively. In addition, the polyimides displayed light color with special fluorescent and resistive switching(ON-OFF) characteristics; the maximum fluorescence emission was observed at 422-424 nm in NMP solution and at 470-548 nm in film state. The memory devices with the configuration of indium tin oxide/WuFPIs/aluminum(ITO/WuFPIs/Al) exhibited distinct volatile memory characteristics of static random access memory(SRAM), with an ON/OFF current ratio of 10~5-10~6. These functional polyimides showed attractive potential applications in the field of high performance flexible polymer photoelectronic devices or polymer memory devices.

A Facile Strategy for Non-fluorinated Intrinsic Low-k and Low-loss Dielectric Polymers: Valid Exploitation of Secondary Relaxation Behaviors

High-performance low-k and low-loss circuit materials are urgently needed in the field of microelectronics due to the upcoming FifthGeneration Mobile Communications Technology(5 G Technology).Herein,a facile design strategy for non-fluorinated intrinsic low-k and low-loss polyimides is reported by fully considering the secondary relaxation behaviors of the polymer chains.A new amorphous non-fluorinated polymer(TmBPPA)with a k value of 2.23 and a loss tangent lower than 3.94×10^-3 at 104 Hz has been designed and synthesized,which to the best of our knowledge is the lowest value amongst the non-fluorinated and non-porous polymers reported in literature.Meanwhile,TmBPPA exhibits excellent overall properties,such as excellent thermostability,good mechanical properties,low moisture absorption,and high bonding strength.As high-performance flexible circuit materials,all these characteristics are highly expected to meet the present and future demands for high density,high speed,and high frequency electronic circuit used in 5 G wireless networks.

An AEE-active Polymer Containing Tetraphenylethene and 9,10-Distyrylanthracene Moieties with Remarkable Mechanochromism

A polymer （poly（9,10）anthracenevinylene-alt-4,4＇-（9,9-bis（4-（4＇-（1,2,2＇-triphenyviny）phenoxy）butyl）-9H- fluorene-2,7-diyl） dibenzaldehyde）, P1） was successfully synthesized through the Wittig-Horner reaction by employing fluorene and 9,10-distyrylanthracene moieties as building blocks for backbone and tetraphenylethenes as pendant groups. Photophysical and thermal properties of the resulting polymeric emitter were fully characterized by ultraviolet-visible （UV- Vis） absorption and photoluminescence （PL） spectra, thermogravimetric analysis （TGA） and differential scanning calorimetry （DSC）. While P1 emits an orange-light centered at 567 nm in dilute tetrahydrofuran （THF） solution, the solid powder of the polymer exhibits strong yellow emission peaked at 541 nm. It is also found that the as-synthesized polymer shows unique property of aggregation-enhanced emission （AEE）. In addition, P1 possesses high thermal stability with a decomposition temperature （Td,5%） of 430 ℃ and high morphological stability with a glass transition temperature （Tg） of 171℃. Under the stimulus of mechanical force, the emission of P1 can be changed from yellow to red （△λmax = 61 rim）, showing a remarkable mechanochromism. The results from XRD analysis suggest that such mechanochromic phenomenonof PI is probably caused by the destruction of crystalline structure, which leads to the conformational planarization of the distyrylanthracene moieties forming by the polymerization and the increase of molecular conjugation of the backbone.

Instantaneous deformation characteristics of a single bubble in immiscible fluids

The passage of a rising bubble through immiscible fluids is encountered in bath smelting.In order to investigate characteristics of bubble deformation in immiscible fluids,the bubble shape change at the interface and the relationship between the bubble aspect ratio(E)and dimensionless number of forces were obtained.A three-dimensional model was established,and the free-floating behavior of a single bubble in immiscible fluids was numerically simulated by phase-field method.The simulation results are in good agreement with experimental results.The results indicate that when the bubble passes through the interface,the bubble shape is divided into four types in turn:“pear”,inverted“pear”,“convex”and“droplet”shape.In the lower liquid,the relationship of E to Weber number(We),Tadaki number(Ta),and Reynolds number(Re)is distributed between two intersecting lines.The relationship of E to Eötvös number(Eo),a dimensionless group,and Galilei number(Ga)is distributed near the lines with slopes of−3.325×10^(-5),−0.0855,and−8.73×10^(-4),respectively.In the upper liquid,the relationship of E to We,Ta,and Re is distributed between two parallel lines.Compared with gravity,the inertial force plays a leading role in the bubble shape in the lower and upper liquid.Compared with the viscous force,the surface tension dominates the bubble shape in the lower liquid.