Benzoxazine-bismaleimide blends: Curing and thermal properties

A blend of bisphenol A based benzoxazine (Bz-A) and a bismaleimide (2,2-bis[4(4-maleimidophenoxy) phenyl] propane (BMI), was thermally polymerised in varying proportions and their cure and thermal characteristics were investigated. The differential scanning calorimetric analysis, supplemented by rheology confirmed a lowering of the cure temperature of BMI in the blend implying catalysis of the maleimide polymerisation by benzoxazine. FTIR studies provided evidences for the H-bonding between carbonyl group of BMI and -OH group of polybenzoxazine in the cured matrix. The cured matrix manifested a dual phase behaviour in SEM and DMTA with the minor phase constituted by polybenzoxazine dispersed in an interpenetrating polymer network (IPN) of polybenzoxazine and cured BMI. The IPN possessed improved thermal stability over the constituent polybenzoxazine. A benzoxazine monomer possessing allyl functional groups, 2,2′-bis(8-allyl-3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl) propane (Bz-allyl) was reactively blended with the same bismaleimide in varying stoichiometric ratios (Bz-allyl/BMI), where the curing involved mainly Alder-ene reaction between allyl- and maleimides groups and ring-opening polymerisation of benzoxazine. The rheological analysis showed the absence of catalytic polymerisation of BMI in this case. The overall processing temperature was lowered in the blend owing to the co-reaction of the two systems to form a single-phase matrix. The cured resins of both Bz-A/BMI and Bz-allyl/BMI blends exhibited better thermal stability than the respective polybenzoxazines. The T_g of the IPN was significantly improved over that of polybenzoxazine (Bz-A). However, the co-reaction resulted in a marginal decrease in the T_g of the system in comparison to the polybenzoxazine (Bz-allyl).     

偶联剂对钛酸钾晶须/双马来酰亚胺树脂摩擦磨损性能的影响

研究了不同偶联剂及钛酸钾晶须添加量对钛酸钾晶须 /双马来酰亚胺树脂复合材料的摩擦磨损性能的影响 .结果发现 ,钛酸钾晶须能明显提高复合材料的耐磨性 ,晶须的加入使材料的磨损率得到显著降低 ;钛酸钾晶须对材料具有一定的润滑性 ,添加晶须后材料的摩擦系数与树脂基体基本相当 ;偶联剂对复合材料的摩擦系数影响不大 ,但是合适的偶联剂对材料耐磨性的提高则具有明显的作用 .晶须添加量较低时 ,复合材料的磨损机理主要为较严重的粘着磨损 ,晶须添加量较高时 ,疲劳磨损占主导地位 .     

Morphology controls of the melt blending in a novel highly crosslinked bismaleimide system

A novel bismaleimide of 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BMIP) with a broad working-temperature-range for the melt blending was successfully synthesized. BMIP possesses a considerably broad working-temperature-range from 75 °C to 250 °C, prior to undergoing cure reactions to form a highly crosslinked network. The morphology types of cured BMIP/clay hybrids can be controlled by varying the shearing temperatures and the contents of the clay. The conditions necessary for achieving an exfoliated or an intercalated BMIP/clay hybrid were thoroughly investigated via X-ray diffractometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). All the uncured samples prepared at different shearing temperatures and with an adequate amount of MMT-C (above 3 phr) exhibited an intercalated form of morphology. However, the crosslinking reactions for specified samples prepared at relatively elevated shearing temperatures (above 120 °C) and with a relatively low content of clay (below 15 phr) resulted in morphology changes from the intercalated form to the exfoliated form of morphology. There exists an isotropically mechanical property for the cured matrix of the exfoliated hybrids whereas there exists an anisotropically mechanical property for the cured matrix of the intercalated hybrids.     

Cure behavior and thermal stability of an epoxy: new bismaleimide blends for composite matrices

A new bismaleimide (BMI) resin was synthesized to formulate epoxy(tetraglycidyl diaminodiphenyl methane; TGDDM) – bismaleimide thermoset blends for composite matrix applications. 4,4′-diaminodiphenyl methane (DDM) was used as an amine curing agent for the TGDDM. A Fourier transform infrared (FTIR) spectroscopy was employed to characterize the new BMI resin. Cure behavior of the epoxy–BMI blends was studied using a differential scanning calorimeter (DSC). DSC thermograms of the thermoset blends indicated two exothermic peaks. The glass transition temperature of the thermoset blends decreased with BMI content. Thermogravimetric analysis (TGA) was carried out to investigate thermal degradation behavior of the cured epoxy–BMI thermoset blends. The new BMI resin reacted partially with the DDM and weak intercrosslinking polymer networks were formed during cure of the thermoset blends.     

Novel bismaleimide containing cyclic phosphine oxide and an epoxy unit: Synthesis, characterization, thermal and flame properties

A new type of bismaleimide resin (EPBMI), containing epoxy unit and phosphorus in the main chain, was synthesized. The structure of the new resin was confirmed by infrared spectroscopy (IR), ¹H NMR and ¹³C NMR spectroscopies. In addition, the compositions of the new synthesized bismaleimide with two reactants, 4,4′-diaminodiphenylsulfone (DDS) and 4,4′-diaminodiphenylether (DDE), was used to compare its reactivity and thermal properties with conventional bismaleimide (EBMI). Reactivity was measured by differential scanning calorimetry. Thermogravimetric analysis revealed that the polymers, obtained through the reactions between bismaleimides and diamine agents, also demonstrated excellent thermal properties and high char yield.     

Thermal behavior of bismaleimide resin

The cure of a bismaleimide (BMI) neat resin modified with an aromatic diamine and a siloxane elastomer, has been studied by ¹³C solid state nuclear magnetic resonance. Two chemical reactions occur during the cure cycle; at a low temperature, Michael's reaction predominates, while at a high temperature the polymerization of the double bond maleimide creates the network. The degradation of this BMI material was characterized with isothermal and dynamic thermogravimetric analyses in air and in nitrogen. The BMI thermal stability is lower in nitrogen than in air. This behavior is an indication of oxygen participating in reactions at high temperatures. The activation energy (E_a) of thermal degradation was determined from isothermal data using an Arrhenius equation (In V vs. 1/T). The global E_a for the weight loss in air was found to be 91 kJ/mol. The nature and the evolution of the thermal degradation products were the combined analyzed by techniques of pyrolysis, gas chromatography and mass spectrometry. The major thermal decomposition products obtained in the temperature range of 300–700°C are identified as benzene, methyl formamide, aniline, toluene and isocyanate-derived products.     

Glass fiber reinforced bismaleimide/epoxy BaTiO3 nano composites for high voltage applications

BaTiO₃/bismaleimide/epoxy/glass fiber reinforced composites were prepared using E-glass fiber (E-GF) and silane coated E-glass fiber (SC-EGF) separately as reinforcement. BaTiO₃ nanoparticles were prepared by hydrothermal method. Results show that the addition of BaTiO₃ nanoparticles has significant effects on the mechanical and dielectric properties of the composite. Both E-GF and SC-EGF reinforced BaTiO₃/bismaleimide/epoxy composites with 2 wt percentages of BaTiO₃ nanoparticles showed improved tensile strength, flexural strength and dielectric constant and those with 3% showed high dielectric strength indicating this composition is more adaptable for high voltage insulating applications. Dielectric constants and dielectric loss of the fabricated nanocomposites have been obtained at higher frequencies (in GHz) by using Vector Network Analyser at room temperature and was found to be highest for the BMI-Epoxy nanocomposite with 1% weight nanofiller.     

Thermal decomposition characteristics of Alder-ene adduct of diallyl bisphenol A novolac with bismaleimide: effect of stoichiometry, novolac molar mass and bismaleimide structure

The addition-cured blends of diallyl bisphenol A formaldehyde resin (ABPF) with various bismaleimides (BMIs) were evaluated for thermal stability and degradation behavior by thermogravimetric analysis (TGA). TGA of the blend of ABPF and 2,2-bis 4-[(4-maleimido phenoxy) phenyl] propane (BMIP) with varying maleimide to allylphenol stoichiometry indicated that the thermal stability of the system was only marginally improved by the increase in BMI stoichiometry in the blend. The effect of BMI structure on thermal stability was studied using four different BMIs, viz. bis (4-maleimido phenyl) methane (BMIM), bis (4-maleimido phenyl) ether (BMIE), bis (4-maleimido phenyl) sulfone (BMIS) and BMIP. TGA showed a two stage decomposition pattern for BMIS system and a single stage for all the other three. The thermograms of BMIM and BMIE were identical and superior to that of BMIS; the latter showing a relatively poor performance at lower temperatures. Compared to the BMI-adduct of monomeric diallyl bisphenol A (DABA), the polymeric analog viz. ABPF system exhibited better thermal stability. Non-isothermal kinetic analyses of the different systems showed the decomposition occurring in at least two kinetic steps. The computed activation energy exhibited a direct correlation to the relative thermal stability of the systems.     

Effect of chemical structure on the crosslinking behavior of bismaleimides: Rheological study

The effect of molecular structure on the cure characteristics of bismaleimides (BMIs) was investigated by rheological measurements. BMI resins of different chemical structures were used, prepared from diglycidyl ether of bisphenol A and N-(3-carboxy phenyl) maleimide or N-(4-carboxy phenyl) maleimide. Temperature dependence of the rheological data was correlated to the Arrhenius equation, from which the activation energy of crosslinking was calculated.Upon heating in dynamic curing, viscosity passed through a minimum then sharply increased due to increasing amount of the crosslinking reaction. The temperature at minimum viscosity increased as the chain length became longer. After passing the minimum point, viscosity increased much faster for meta BMIs (3BE1, 3BE2) than para BMIs, however, the difference in the chain length did not show any appreciable difference in the viscosity increase rate (dη^∗/dT). Nonetheless, the final viscosity was lower for longer chains, because their crosslinking density would be lower.In isothermal curing, the final crosslinking density was expected to increase with temperature, which was shown via the increase in the final viscosity. The gelation time decreased with temperature, and the activation energy of the crosslinking reaction was obtained. Using the reaction kinetics parameters obtained from dynamic scanning calorimeter and Arrhenius type equation, the viscosity change during the isothermal curing was simulated and compared with the measurements.     

UV photo curing of N,N-bismaleimido-4, 4-diphenylmethane

The photo curing of a formulation consisting of N,N^′-bismaleimido-4, 4^′-diphenylmethane (BMI), which is most widely used in commercial thermal curing formulations, was performed. Parameters, such as initiator, co-initiator and temperature, which affect the curing rate and enthalpy, were studied using differential photocalorimeter. BMI undergoes copolymerization with 4-hydroxybutylvinylether (HBVE), when exposed to UV radiation, in presence of the photo initiator, Triphenylphosphine oxide (TPO). Diallylbisphenol A has been observed to be an efficient co-initiator, which improves the reaction rate coefficient and enthalpy of the photo curing process for the system BMI/HBVE/TPO.