Maleimide addition

LV) [65]. These maleimide additives appear to be relatively unreactive during the initial anaerobie eure. As the adhesive is exposed to high temperatures the methacrylate backbone degrades and the methacrylates can then copolymerize with the maleimides, forming a more heat-resistant matrix [66],... 

Malofsky and Baccei, from the Loctite Corporation, report on the significant mechanical property improvements obtained with maleimide and nadic capped monomers and prepolymers as additives in anaerobic methacrylate/ acrylate adhesive systems. Significant improvement in thermal resistance was noted in a PEGMA (polyethyleneglycol diroethacrylate) system in which a polymerizable maleimide addition was incorporated. A "neat" polymerized urethane methacrylate failed catastrophically within 1000 hrs. at... 

Examination of pins and collars bonded with EBIPMA/maleimide formulations again show dramatically improved thermal resistance. Here, as shown by Fig. 9, one can clearly see the sequential improvement in going from neat monomer, or monomer with non-reactive PI, to a mono-maleimide additive, to a cross-linkable bismaleimide, to... 

SCHEME 13.1 Preparation of cross-linked polybenzoxazine resin through possible reactions of the retro-DA reaction, the benzoxazine ring-opening reaction, and the maleimide addition reaction. (Adapted from Chou Chou L, and Liu Ying-Ling. J. Polym. Sci. Part A. 46 no. 19 (2008) 6509-6517.)... 

Breslow studied the dimerisation of cyclopentadiene and the reaction between substituted maleimides and 9-(hydroxymethyl)anthracene in alcohol-water mixtures. He successfully correlated the rate constant with the solubility of the starting materials for each Diels-Alder reaction. From these relations he estimated the change in solvent accessible surface between initial state and activated complex " . Again, Breslow completely neglects hydrogen bonding interactions, but since he only studied alcohol-water mixtures, the enforced hydrophobic interactions will dominate the behaviour. Recently, also Diels-Alder reactions in dilute salt solutions in aqueous ethanol have been studied and minor rate increases have been observed Lubineau has demonstrated that addition of sugars can induce an extra acceleration of the aqueous Diels-Alder reaction . Also the effect of surfactants on Diels-Alder reactions has been studied. This topic will be extensively reviewed in Chapter 4. 

The Michael addition of nucleophiles to the carbon—carbon double bond of maleimide has been exploited ia the synthesis of a variety of linear polymers through reaction of bismaleimide with bisthiols (39). This method has been used to synthesize ethynyl-terminated imidothioether from the reaction of 4,4 -dimercaptodiphenyl ether [17527-79-6] and A/-(3-ethynylphenyl)maleimide (40). The chemical stmcture of this Michael addition imide thermoset is as follows ... 

The Michael addition reaction of amines and thiols with bismaleimides or functionalized monomaleimides is a versatile tool ia the synthesis of chain-extended maleimide-terroinated prepolymers. These prepolymers generally are soluble ia organic solvents from which they can be processed to prepreg and molded to high quaUty, void-free laminates. 

In the narrow sense, bis-maleimide resin means the thermosetting resin eom-posed of the bis-maleimide of methylene dianiline (BMI, bis(4-maleimidophenyl)-methane) and methylene dianiline (MDA, bis(4-aminophenyl)methane) (Fig. 1). Beeause of the addition meehanism, the resin is eured without elimination, whieh is a eharacteristic of this resin. Bis-maleimide resin is used as a thermally stable matrix up to 204°C (400 F) whieh typical epoxy resins may not normally be used. However, in spite of having an imide structure, bis-maleimides are classified as being moderately thermally stable resins. The aliphatic structure of the resin is not stable for long periods above 232°C (450°F.) If a highly aromatic thermally stable thermosetting resin is necessary, acetylene end-capped aromatic imide-based oligomers should be used. 

Maleimides have three principal reaction pathways. These are radical addition to vinyl compounds the Michael addition with compounds having active hydrogens and the Diels-Alder reaction with dienes (Fig. 3). Any of the three can be tools for forming thermosetting adhesives. 

A typical maleimide resin is synthesized by the Michael addition of MDA and BMI (Fig. 4). If the stoichiometrically equal amounts of MDA and BMI are added into the reaction solvent under controlled temperature, linear, high molecular weight polyaminoimide (PAI) results. To obtain crosslinkable oligomer (pre-polymer) with maleimide end groups, a calculated 1.1-1.8 times an excess... 

Fig. 5. Curing mechanism of a maleimide resin via Michael addition.

As already mentioned, aromatie polymers are thermally stable but aliphatic portions of them are not as thermally stable. Typical maleimide resins have aliphatic units. This is inevitable because the Michael addition was used to prepare the maleimide-based oligomers. On the other hand, if an adhesive consists of a linear thermoplastic polymer, it is not usable at temperatures above its softening temperature. Introdueing chemical crosslinking is one way to prevent thermal weakening of a material. 

Pyridinium p-toluenesulfonylmethylide 91 has been used as a formyl anion equivalent for conjugate addition to N-substituted maleimides to give the enol ethers 92, which were readily deprotected to give the aldehydes 93 (80TL705). 

The antineoplastic agent mitindomide (160) in fact represents the well-known product from irradiation of maleimide in benzene [30]. The activity of this old compound was uncovered by one of the large antitumor screens maintained by the National Cancer Institute, The structure is sufficiently complex and the starting materials sufficiently available to lead one to suspect that the product is still produced photochemically. The product can be rationalized by assuming successive 1,4 and 1,2 additions to benzene. Intermediate 159a involves the 1,4 followed by 1,2 addition intermediate 159b presupposes the steps occur in the reverse order. 

In 1988 a paper by Zard and coworkers4(, reported that xanlhates were a convenient source of alkyl radicals by reversible addition-fragmentation and used the chemistry for the synthesis of a monoadduct to monomer (a maleimide). Many applications of the chemistry in organic synthesis have now been described in papers and reviews by the Zard group.406 407... 

Turner, S.R., Walker, T.O. and Thaler, W.A. "Sodium Styrene Sulfonate Co-Sodium N-(4-Sulfo Phenyl) Maleimide An Improved Viscosity Control Additive," US Patent 4,478,727(1984). 

Add at least a 10-fold molar excess of NEM over the amount of sulfhydryls present in the reaction. Alternatively, add an equal mass of NEM to the amount of macromolecule present. To facilitate the addition of a small quantity of reagent, a more concentrated stock solution may be prepared in buffer and an aliquot added to the reaction medium. Make the stock solution up fresh, and use it immediately to prevent loss of activity due to maleimide group breakdown. 

Reactive double bonds are capable of undergoing addition reactions with sulfhydryl groups. A popular example of this type of functional group is the maleimide group (Section 2.2, this... 

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