Bismaleimides structure

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 ... 

Polymers underwent thermal decyclization at 420 to 485°C regardless of bismaleimide structure and DTA thermograms of polyimides prepared photochemically closely resembled those... 

Table 6.8 The effect of bismaleimide structure on the mechanical properties of a 60% w/w magnesium hydroxide-filled polypropylene block copolymer [31].

PVF-P adhesives have been used at de Havilland in Hatfield, England since 1936 for the manufacture of air screws [199]. Aero Research Ltd. of Duxford, England, which became CIBA (A.R.L.), originally developed them ([200], pp. 76-83). Currently, the Redux business and trademark belongs to the Hexcel Composites Ltd. and is applied to the original polyvinyl-phenolic alloys as well as epoxies and bismaleimide adhesives that give structural performance at even higher temperatures [201]. 

Because of this continued emphasis on adhesive bonding technology development over the years, the airframes of modem front-line aircraft such as the B-2 bomber and the F-117 and F-22 fighters are largely structurally bonded advanced composites. They tend to be comprised of materials that are more advanced (expensive) than commercial aircraft such as carbon and boron fiber reinforcements with cyanate esters, bismaleimides, polyimides or other high-temperature resin matrices and adhesives. 

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 other BCB resin system to be discussed is a blend of a BCB terminated resin synthesized in this laboratory and a bismaleimide (BMI) resin commercially available from Aldrich Chemical Co. The two components were blended in a 1 1 molar mixture and the structure of each is shown below. 

BMI polymers have glass transition temperatures in excess of 260°C and continuous-use temperatures of 200-230°C. BMI polymers lend themselves to processing by the same techniques used for epoxy polymers. They are finding applications in high-performance structural composites and adhesives (e.g., for aircraft, aerospace, and defense applications) used at tem-peratrues beyond the 150-180°C range for the epoxies. Bisnadimide (BNI) polymers are similar materials based on bisnadimides instead of bismaleimides. 

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... 

The most important application for bismaleimide resin is multilayer boards. The development in this area requires resins with low dielectric constants. It is well documented in the literature that fluorine containing linear polyimides show lower dielectric constants vis a vis their non-fluorinated counterparts. Recently, Hitachi Research Laboratory, Japan, reported the thermal and dielectric behaviour of fluorine-containing bismaleimides (29). The chemical structures of the fluorinated BMIs investigated are provided in Fig. 6. The non-fluorinated four aromatic rings containing BMI, 4,4 -bis(p-maleimidophenoxyphenyl) propane, was tested in comparison. 

The most popular route to bismaleimides is the reaction of a diamine with maleic anhydride followed by cyclodehydration. The chemical structure of the... 

Fig. 9. Chemical structure of bismaleimides containing oxyalkylene groups...

Another approach to processable bismaleimide resins via Michael addition chain extension, is the reaction of bismaleimide, or a low melting mixture of bismaleimides, with aminobenzoic hydrazide to provide a resin which is soluble in various solvents, such as acetone, methylene chloride and DMF (49). The idealized chemical structure for a 2 1 BMI-aminobenzoic hydrazide resin is... 

A new family of bis(dienes), the bis(vinylbenzyl) ethers, has been synthesized and was used to modify bismaleimide (82). The chemical structure of divinylben-zyl-bisphenol A is provided in Fig. 27. 

Polyimides have been synthesized by Diels-Alder cydoaddition of bismaleimides and substituted biscydopentadienones (81,82). The intermediate tricyclic ketone structure spontaneously expdl carbon monoxide to form dihydrophthalimide rings, which are readily oxidized to imides in the presence of nitrobenzene. 

BISMALEIMIDE POLYMERS. These relatively new polymeric materials were developed to serve the increasing requirements for materials of high strength in high-temperature applications. Currently, a high percentage of the bismaleimides produced are used for printed circuit boards (PCBs). The materials usually are cured with aromatic amines and then compression molded into the PCBs. Future uses include aircraft structural components where bismaleimides may prove superior for high-temperature skin surface applications as compared with present epoxy composites. 

Structural modifications were envisioned early to overcome these limitations. A first improvement was outlined by preparing copolymers, which were soluble in the state of full imidation, mainly poly(ester-imide)s and poly(amide-imide)s [2,4, 5]. As an alternative to these conventional copolymers, addition polyimides were developed in the 1970s as a new class of thermosetting materials. Thus, bismaleimides, bisnadimides, and end-capped thermocurable polyimides were successfully developed and marketed [6,7]. These resins were the precursors of the modern PMR (polymeric monomer reactants) formulations [8]. 

Pyrones behave as dienes and react with bismaleimides giving biscycload-ducts [62-65]. By heating, carbon dioxide extrusion takes place with formation of bisdienes. This reaction was used to prepare a polyimide with a bicyclooctene structure [51] (Fig. 15). 

Keywords. Cyanate ester, Polycyanurates, Phenolic-triazine, Polymer matrix composite, Cure kinetics, Polymer blends, Cyanate-epoxy blend, Bismaleimide-triazine resins, Aerospace structure... 

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