Curing kinetics, thermal and erosive wear characteristics of bismaleimide blends modified by polyaryletherketone

The work aimed to study the effect of thermoplastic polyaryletherketone (PAEK) on the curing kinetics, thermal stability and erosive wear performances of bismaleimide (BMI) resin blends. Toughened bismaleimide blends were fabricated using the allyl compound modified bismaleimide resin prepolymer as matrix and PAEK as a toughening agent by blending method. The modified PAEK/BMI blends were characterized and analyzed using the fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), the swirling water jet erosive wear apparatus, scanning electron microscope (SEM) and three-dimensional surface profilometer. No obvious glass transition was observed for PAEK modified BMI blends in the temperature range of 50–350°C. In addition, the char yields ( Yc) and the heat-resistance index ( THRI) of the PAEK/BMI blends were affected by PAEK addition. The kinetic parameters, such as the activation energy and the pre-exponential factor of the PAEK/BMI blends were also higher than that of unmodified BMI blends, indicating that the incorporation of PAEK could promote the curing reaction of the epoxy resin without changing the curing mechanism. The erosive wear rate increased with the addition of PAEK especially when the mass fraction of PAEK was 10 parts per hundred of resins ( phr.). These results suggested that the thermal stability of the PAEK/BMI blends was significantly enhanced while the erosive wear resistance decreased by introducing the PAEK.

Synthesis and thermal stability of a novel acetylene end-capped silicon-containing polyimide coupling agent with a silane pendant group

In this study, a novel heat-resistant polyimide macromolecular coupling agent (PSI-C) was designed and synthesized. Silicon-containing diamine was one of the monomers used to increase the solubility of the polyimide, and m-aminophenylacetylene was the end-capping reagent that copolymerized with the resin matrix. A silane coupling group was introduced into the side chain to match the reinforced fiber. Thermogravimetric analysis revealed that the 5% thermal decomposition temperature ( T d5) of the cured PSI-C could reach 454°C and the residual rate at 800°C was 53%. Thermal pyrolysis of the vaporized resin showed that the heat-resistant functional group was still detectable at 550°C. The thermal stability of the alkynyl-terminated silicon-containing polyimide silane coupling agent was higher than those of conventional silane coupling agents. The curing process of the composite system was not affected when adding the coupling agent PSI-C to the quartz fiber/alkynyl resin composite. The interlaminar shear strength and bending strength of the composite were increased by 55% and 61%, respectively, at room temperature. The high-temperature retention rate at 500°C reached 58% and 63%.

Vinyl-terminated butadiene acrylonitrile improves the toughness, processing window, and thermal stability of bismaleimide resin

Structural materials with excellent toughness, a wide processing window, outstanding mechanical performance, and high thermal stability are highly desired in engineering. This work reports a novel bismaleimide (BMI) resin system fabricated using bis[4-(4-maleimidephen-oxy)phenyl)]propane (BMPP), 1-(2-methyl-5-(2,5-dioxo-2H-pyrrol-1(5 H)-yl) phenyl)-1H-pyrrole-2,5-dione (BTM), and diallyl bisphenol A (DABPA) by a melt method. The behaviors of the BTM/BMPP/DABPA resin were modified by adding vinyl-terminated butadiene acrylonitrile (VTBN) in various amounts. The cured BTM/BMPP/DABPA/VTBN resin system exhibited all of the abovementioned desirable properties. Excellent performance was achieved by the post-cured BMI resin containing 6 phr of VTBN (VTBN-6). The glass transition temperature ( Tg) and the 5% weight loss temperature of VTBN-6 were 278°C and 408°C, respectively. Relative to VTBN-0 (BMI resin without VTBN), the impact strength of cured VTBN-6 (12.32 KJ/m2) improved by 45.6%, and the fracture toughness values, KIC and GIC, increased by 48.7% and 26%, respectively. Moreover, the prepolymer of VTBN-6 exhibited low viscosity over a wide temperature range (70–200°C) under dynamic conditions and for an extended time (70 min; 75% improvement over VTBN-0) in an isothermal test. These results confirm the wide processing window of VTBN-6. The high toughness of the VTBN-containing BMI resin was compatible with other excellent performances of the modified resin.

Copolymers of vinyl-containing benzoxazine with vinyl monomers as precursors for high performance thermosets

A benzoxazine containing a vinyl group (P-4va) was prepared by the reaction of phenol, 4-vinylaniline, and paraformaldehyde. A differential scanning calorimetry (DSC) study revealed that ring-opening polymerization of the benzoxazine and chain polymerization of the vinyl group occurred in the same temperature range. When 2,2'-azobisisobutyronitrile was added as a radical initiator to P-4va, however, only the vinyl groups were polymerized at lower temperature, giving oligo(P-4va) that contains pendent benzoxazine units. Radical copolymerization of P-4va with various vinyl monomers such as styrene, methyl methacrylate (MMA), and n-butyl acrylate (BuA) was examined. The chemical structure of the copolymers was confirmed by FT-IR and ¹H-NMR to be one of polyolefins bearing benzoxazine units as the pendant groups. The weight-average molecular weights of the copolymers determined by size exclusion chromatography were to be in the range of 1900–51,500 depending on the comonomers. DSC of the copolymers showed that the maxima of the exothermic peaks corresponding to the ring-opening polymerization of the pendent benzoxazine units were observed in the temperature range of 229–250 °C. Thermal cure up to 240 °C of the copolymer films afforded homogenous transparent films with improved thermal properties. Tough cured film was obtained by the copolymerization with MMA, while a tough and flexible film was obtained by the copolymerization with BuA.

Studies on structurally different benzoxazines

Bisbenzoxazines were prepared by the condensation of the respective bisphenols bisphenol A (BA), indane bisphenol (IBP), and spirobiindane bisphenol (SBI) with paraformaldehyde and aniline. The apparent activation energies for the polymerization curing process ( Ea-C) and the degradation process ( Ea-D) were calculated using Flynn–Wall–Ozawa, Vyazovkin, and Friedman methods. The variation in Ea-C noted for the thermal curing of different bisbenzoxazines is attributed to the operation of different mechanisms for the curing process. The variation of the Ea-D for the degradation of spirobiindane benzoxazine polymerized at high temperature was different from the other materials investigated and is attributed to its complex structure. The volatile products obtained during the thermal degradation of the polymers were analyzed using thermogravimetric–Fourier transform infrared analyses. Aniline was found to be the major product and was released during the primary degradation. At higher temperatures, breakage of the isopropylidine, indane, and biindane structural entities were favored.