Blends with Bismaleimides

Assuming co-reaction, the cure reaction of a mixture of bis(4-maleimido phenyl) methane and BACY was followed by FTIR [221]. The reaction kinetics, studied by DSC, suggested dependency of cure mechanism on blend composition. The apparent activation energy computed by the Prime method increased with BMI content. The rate maximum at a fractional conversion range of 0.32-0.33 indicated an autocatalytic nature of the reaction. The different pattern of activation energy with fractional conversion for two different blend compositions indicated non-identical cure mechanisms for the two compositions. The cyclot-rimerization of BACY occurred during the cure of a 1 2 molar ratio of BMI and BACY. Since activation parameters derived from DSC method are generally not consistent, and since the cyanate cure can be catalyzed by impurities present in BMI, which was not taken into consideration, the authors conclusions on the cure mechanism based on DSC kinetics can be erroneous. 

Blends of BMM with modified allyl cyanate alone could also develop useful properties. Such modified cyanate esters include bis [4-[(3-allyl-4-cyanatophe-nyl) isopropylidene]phenoxy]phenyl sulfone and 22-bis[3-allyl-4-cyanatophe- 

Resin ILSS (MPa) Flexural Strength (GPa) Flexural modulus (GPa) Compr strength (GPa) GIC (Jnr2) 

2-bis (3-allyl-4-cyanatophenyl) propane bis(4-maleimido phenyl) methane 

If network linking can help make miscible the phases in the IPN of B-T resins, the same could be achievable by using the bismaleimide component having a 

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Bismaleimides can also be cured using a Diels-Alder comonomer [187]. When a bisdiene is reacted with excess bismaleimide, a prepolymer-carrying maleimide termination is formed as an intermediate, which can be further crosslinked to form a 3D cured network. Bis-(o-propenylphenoxy) benzophenone (Compimide TM123, Technochemie, Germany) is an example of a commercial Diels-Alder comonomer. CompimideTM123 is a low melting, low viscosity material and can be readily melt-blended with bismaleimide (BMI) and cured at high temperature to get a heat-resistant network. 

Bismaleimide Resins via EI E Reaction. The copolymerization of a BMI with o,o -diallylbisphenol A [1745-89-7] (DABA) is a resia coacept that has beea widely accepted by the iadustry because BMI—DABA bleads are tacky soHds at room temperature and therefore provide all the desired properties ia prepregs, such as drape and tack, similar to epoxies. Crystalline BMI can easily be blended with DABA, which is a high viscosity fluid at room temperature. Upon heating BMI—DABA blends copolymerize via complex ENE and Diels-Alder reactions as outlined ia Eigure 8. 

Modified Bismaleimides. Bismaleknide resins may be further modified and blended with other thermoset resins or reactive diluents to achieve either specific end-use properties or processibiUty. Thermoset resins that can be used for modification are unsaturated polyesters, vinylesters, cyanate esters, and epoxies. 

Rubber blends with cure rate mismatch is a burning issue for elastomer sandwich products. For example, in a conveyor belt composite structure there is always a combination of two to three special purpose rubbers and, depending on the rubber composition, the curatives are different. Hence, those composite rubber formulations need special processing and formulation to avoid a gross dissimilarity in their cure rate. Recent research in this area indicated that the modification of one or more rubbers with the same cure sites would be a possible solution. Thus, chlorosulfonated polyethylene (CSP) rubber was modified in laboratory scale with 10 wt% of 93% active meta-phenylene bismaleimide (BMI) and 0.5 wt% of dimethyl-di-(/ r/-butyl-peroxy) hexane (catalyst). Mixing was carried out in an oil heated Banbury-type mixer at 150-160°C. The addition of a catalyst was very critical. After 2 min high-shear dispersive melt mix-... 

The saiq>les studied were a BCB terminated aromatic imide oligomer and a BCB terminated imide monomer blended with a compatible bismaleimide (BMI) resin. Neat properties studied on both resin systems included the thersial and rheological properties of the uncured specimens subsequently used to determine appropriate cure conditions. Thermal and mechanical properties of the cured materials are also discussed. 

The advantage of using free radical inhibitors to facilitate the copolymerization of a bisbenzocyclobutene with a bismaleimide was first noted in a patent to Bartmann [78]. Subsequent to this, Corley in a series of patents described some detailed experiments on the copolymerization of bisbenzocyclobutenes with bismaleimides both with and without the addition of a free radical inhibitor [33, 34]. The structures of the bisbenzocyclobutenes used in this study are shown in Fig. 33. The bismaleimide component that was used was a mixture of three different bismaleimides in the molar ratio shown in Fig. 34. The individual bisbenzocyclobutenes were blended at elevated temperature with varying amounts of the bismaleimide composition. In some of the experiments, the free radical inhibitor phenothiazine was added at a 0.5 mole % level. The various monomer mixtures were then copolymerized using one of the cure schedules described in Table 14. The copolymers were then physically characterized using a variety of techniques. Table 14 shows the results obtained from copolymers... 

Imide blends are usually cross-linked and inherently stable strucmres. The additivity rule seems to be appropriate for blends with Novolak resins [Kundu et al, 1986] and the addition of a phosphine oxide to bismaleimide lowered the curing temperature without sacrifice of thermal properties [Varma and Mittal, 1989]. 

Blends of bismaleimides with poly(betaamino crotononitrile) are storage stable materials, converted with heat to thermosetting compositions useful as coating and laminating resins. 

Bismaleimides are produced by the condensation reaction of a diamine, such as methylenedianiline, with maleic anhydride. The reaction product tends to be crystalline with a high melting point. Eutectic blends of different bismaleimides reduce the melting point. However, a coreactant generally is required to improve the processing properties of the material. Bismaleimides owe their reactivity to the double bonds on each end of the molecule, which can react with themselves or with other compounds containing functional groups (vinyls, allyls. or amines). A typical bismaleimide structure is shown by ... 

CEs are known to react with groups like epoxy, bismaleimide, etc. These reactions are described in detail in Sect. 8 devoted to blends. Although reaction with triple bonded compounds has been postulated, evidences for this remain to be furnished. 

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