Kaichang Kou

The effect of bis allyl benzoxazine on the thermal, mechanical and dielectric properties of bismaleimide–cyanate blend polymers

Thermosetting terpolymers composed of bis allyl benzoxazine (Bz-allyl), cyanate ester (BADCy) and 4,4′-bismaleimidodiphenyl methane (BMI) were prepared via co-curing reactions. The curing kinetics of Bz-allyl/BMI/BADCy were investigated via non-isothermal DSC at different heating rates using the Flynn–Wall–Ozawa method. The dielectric, thermal and mechanical properties of Bz-allyl/BMI/BADCy terpolymers were systemically investigated in detail through mechanical measurement, scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and thermo-gravimetric analysis (TGA). The results show that a suitable addition of Bz-allyl can enhance the impact strength and flexural strength as well as reduce the dielectric constant and the dielectric loss of BMI/BADCy. The dynamic mechanical analysis reveals that the cross-link density of the blend is higher than BMI/BADCy. The higher crosslinking density of the terpolymer led to good thermal stability of the terpolymer. Scanning electron microscopy analysis shows the distinct characteristics of ductile fracture of the blends. All of these changes in properties are closely correlated to the copolymerization between Bz-allyl and BMI/BADCy, which could form an interpenetrating polymer network in the system.

The effect of functionalized benzoxazine with allyl groups on the dielectric, mechanical and thermal properties of BMI/BADCy composites

Functionalized benzoxazine with allyl groups has recently attracted a great deal of attention due to its polymerizable group. In order to improve the properties of 4,4′-bismaleimidodiphenyl methane (BMI)/cyanate ester (BADCy), benzoxazine (Boz) was added into the BMI/BADCy system in this paper. The effect of functionalized Boz with allyl groups on the dielectric, mechanical and thermal properties of BMI/BADCy composites was systematically investigated in detail using mechanical measurements, scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and thermo-gravimetric analysis (TGA). The results showed that the formation of Mannich bridge networks and an interpenetrating polymer network through the polymerization of Bz-allyl and BMI/BADCy increased the cross-linking densities and thermal stability. Allyl-based polymers also exhibited high glass transition temperatures, and higher char yields. The dielectric constant value and the dielectric loss factor of BBz2 reached minimum values of 3.17 and 0.083 at 106 Hz respectively. The mechanical properties (a high flexural modulus of 4.18 GPa and flexural strength of 120 MPa) of BBz2 were superior. Scanning electron microscopy analysis showed a distinct characteristic of ductile fractures for the blends.

Investigation of Tribological Properties of PI/FEP Laminated Composites Under Dry Sliding, Water- and Oil-Lubricated Conditions

Polyimide/fluorinated ethylene propylene (PI/FEP) laminated composites were fabricated by means of hot-press molding. The friction and wear behavior of high performance PI/FEP laminated composites has been comparatively evaluated under dry sliding, water- and oil-lubricated conditions. The worn surface morphologies of samples under different lubrication conditions were examined by scanning electron microscope and the wear mechanisms were comparatively discussed. As the results, PI/FEP laminated composites sliding against stainless steel under water lubrication registered lower friction coefficients, but higher wear rates than those under dry sliding. The friction coefficients and wear rates of samples under liquid paraffin-lubricated condition were lowest in three sliding conditions. The lateral surface of samples exhibited better wear resistance than parallel surface did under dry sliding.

Synthesis and Properties of Semicrystalline Copolyimides Based on 4,4′-Diaminodiphenylether and 1,3-Bis(4-aminophenoxy) Benzene

Copolyimides were prepared from 4,4′-diaminodiphenylether (4,4′-ODA), 1,3-bis(4-aminophenoxy) benzene (TPER), and pyromellitic dianhydride (PMDA) through a three-step imidization process with different monomer compositions. The copolymerization disrupted the molecular regularity and decreased the intermolecular interaction of the polyimide chains. The X-ray diffraction (XRD) results indicated the prepared copolyimides showed the same semicrystalline character, but had various crystallinity and crystal forms. The copolymerization also changed the crystal morphologies of the polyimides. With increasing TPER ratio, the copolyimides started to form spherulites and hedrites, which then tended to grow more perfectly as the TPER ratio was further increased. The solubility of the copolyimides and their dependence on the crystallnity and the chain flexibility was investigated. These copolyimides exhibited excellent thermal and thermo-oxidative stability.

Synthesis and characterization of pyrimidine-containing hyperbranched polyimides

We reported the design, synthesis, and properties of two series of polyimides based on pyrimidine nuclei with adjusted monomers’ molar ratios, using 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) as dianhydride monomer, 2,4,6-triaminopyrimidine (TAP), and 4,4′-diaminodiphenyl ether (ODA) as amine monomers. Nuclear magnetic resonance spectroscopy (1H NMR) was used for chemical structural characterization, and the results indicated the various forms of TAP and branched structure units in the obtained polyimides. The morphology and structures of the polyimides were evaluated by X-ray diffraction patterns. The results suggested that all the polyimides, except co-HBPI-3, were hardly crystallized. Most of the resulting polyimides possessed excellent solubility in polar aprotic solvents. The thermogravimetric analysis results showed that the polyimides obtained by copolymerizing with ODA exhibited better thermal stability; and incorporating moderate amount of ODA was helpful for imidization.

Preparation and properties of Nano-SiO2/TDE-85/BMI/BADCy composites

A new type of the nanometer particles and epoxy/bismaleimide-triazine nanocomposites were prepared using a nanometer silica (nano-SiO2), a 4,5-epoxycyclohexane 1,2-dicarboxylic acid dilycidyl (TDE-85) epoxy resin, a 4,4′-bismaleimidodiphenymethane (BMI) and a bisphenol a dicyanate (BADCy). The properties of nano-SiO2/TDE-85/BMI/BADCy composites, such as mechanical and thermal properties, were systemically investigated in detail by mechanical measurement, scanning electron microscope (SEM), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). The experimental results showed that the addition of the appropriate amount of nano-SiO2 could improve the impact strength and the flexural strength of the nano-SiO2/TDE-85/BMI/BADCy composites. Simultaneously, the thermal stability of the blends was found to be higher than that of the TDE-85/BMI/BADCy copolymers.

Synthesis and Characterization of Novel Sulfone-containing Polyimides Molding Powder Derived from 2, 2-Bis[4-(4-aminophenoxy) phenyl] Sulfone and Aromatic Dianhydrides

A novel sulfone ether diamine was successfully synthesized by aromatic nucleophilic chloro-displacement reaction of 4-chloronitrobenzene with the 4, 4′-dihydroxydiphenylsulfone, followed by a catalytic reduction. Two kinds of aromatic polyimides molding powder containing sulfone and ether linkages was prepared from the resulting diamine with pyromellitic dianhydride (PMDA) and benzophenonetetracarboxylic dianhydride (BTDA) by a new three-step imidization procedure. The monomer and polyimides powder obtained were characterized by various methods. The monomer was synthesized with high purity and yield. The novel polyimides powder exhibited semi-crystalline character, good solubility in organic solvents, as well as high Tg value and excellent thermal stability in N2 and air.

Thermal, mechanical and dielectric properties of BMI modified by the Bis allyl benzoxazine

In this paper, Bis allyl benzoxazine (Bz-allyl) was blended with 4, 4′-Bismaleimidodiphenyl methane (BMI) to improve the properties of BMI. The properties of Bz-allyl/BMI copolymers, such as mechanical properties, thermal properties and dielectric properties were systemically investigated in detail by mechanical measurement, scanning electron microscope (SEM), dynamic mechanical analysis (DMA) and thermo-gravimetric analysis (TGA). The results show that a suitable addition of Bz-allyl can enhance the impact strength and flexural strength as well as reduce the dielectric constant and the dielectric loss of BMI. The dynamic mechanical analysis reveals that the cross-link density of the blend is higher than neat BMI. Scanning electron microscopy analysis shows distinct characteristics of ductile fracture of the blends. In addition, the dielectric constant and the dielectric loss of modified system decreases, compared with the cured BMI. BMI containing suitable Bz-allyl still remains a good thermal resistance. All these changes in properties are closely correlated to the copolymerization between Bz-allyl and BMI, which could form an interpenetrating polymer network in the system.

Synthesis, characterization, and thermal properties of benzoxazine monomers containing allyl groups

The polymerization mechanism of allyl-functional benzoxazine (Bz) monomers is reported in this article. Following the traditional route of Bz synthesis, a series of monofunctional Bz monomers were synthesized via allylamine and amine condensation reaction with 2,2′-diallyl bisphenol-A and paraformaldehyde. Resulting chemical structures of the synthesized monomers were confirmed by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance analyses. The polymerization behavior of the prepared allyl-functional monomers was studied using differential scanning calorimetry and FTIR. Three reactions were observed in the curing process: polymerization reaction of N-allyl groups in the oxazine ring, ring-opening polymerization of Bz, and polymerization reaction of allyl groups in benzene. Compared to a typical polybenzoxazine (PBz), higher cross-linking density in PBz-allyl-2 leads to a higher glass transition temperature and 5% weight loss temperature, which indicates improved thermal stability in PBz-allyl-2 as well as superior thermal conductivity compared to 2,2′-bis(3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl)propane. Data on dielectric properties also show that PBz-allyl-2 outperforms typical PBzs. This work focuses on the manipulation of Bz monomer structures to alter their ring-opening polymerization mechanism, as well as cross-linking, in order to derive a PBz with improved properties.

SYNTHESIS, MECHANICAL AND ELECTRICAL PROPERTIES OF CARBON MICROCOILS AND NANOCOILS

The results on the synthesis, mechanical and electrical properties of carbon microcoils and nanocoils (CMCs, CNCs) synthesized using catalytic CVD and Ni-P and Co-P catalyst alloys, respectively, are reported. SEM analysis reveals that the CMCs and CNCs have unique helical morphologies, and diameters of 5.0-9.0 μm and 450-550 nm, respectively. Moreover, CMCs with flat cross-section can be stretched to 3 times their original coil lengths. Current-voltage characteristics of a single microcoil have also been obtained. It is found that the CMCs have the electrical conductivity between 100 and 160 S/cm, whereas the electrical resistance increases by about 20% during the coil extension. Besides, the microcoils can produce light in vacuum when the test voltage reaches 10 V. The emission intensity increases as the voltage increases. The mechanical and electrical properties of CMCs and CNC make them potentially useful in many applications in micromagnetic sensors, mechanical microsprings and optoelectronics.