Maleimide terminated oligomers

Maleimide terminated oligomers and other maleimide-like resins... 

Other backbone structures that have generated interest are the polyether ketones. An attempt was made to synthesize amino-terminated arylene ether ketones, which were subsequently converted into the corresponding maleimide-terminated oligomers (37). The aim of this approach was to obtain tough, solvent resistant, high temperature BMI thermosets. 

All BMI building blocks and maleimide-terminated oligomers discussed previously are synthesized from the corresponding polyamine precursor and maleic anhydride simply because of economic reasons. However, there are other synthetic methods available, for instance, the reaction of a functionalized monomaleimide with a polyfunctional monomer or oligomer. Such a functionalized monomaleimide is maleimido benzoic acid or its acid halide. These were used to synthesize maleimide-terminated polyamides (39, 40) or polyesters (41), respectively. 

Besides low molecular weight bismaleimides building blocks, long chain maleimide terminated oligomers have been synthesized. The method involves the preparation of an amine terminated oligomer, which is used to prepare the bismaleimides. In that way, maleimide terminated poly(ether-sulfones) [312], phenoxy resins [313], polyamides [314] and polyesters [315-317] have been prepared. 

The common synthetic route to bismaleimides or maleimide functionalized oligomers is the condensation of diamines or amino-terminated oligomers with maleic anhydride. Another possibiUty is the use of an AB-type monomer of the following general formula to build the polymaleimide, where X represents a functional group that can be employed in condensation reactions. 

Recently a convenient method for the synthesis of maleimide-terminated imide oligomers has been described (38). Aromatic diamine, biphenyl tetracar-boxylic dianhydride and maleic anhydride are reacted in DMAc/Xylene at 50 °C to form the amic acid oligomer which was subsequently cyclodehydrated by refluxing in the presence of pyridine as a catalyst. Water is removed azeo-tropically over a period of three hours. The maleimide terminated imide oligomer is isolated by precipitation in water or a non-solvent. The molar ratio of the monomers can be varied widely to tailor the molecular weight and... 

Fig. 11. Structure of maleimide terminated sulfone-ether oligomer...

Fig. 12. Chemical structure of maleimide-terminated imide oligomer...

An interesting approach to maleimide-terminated phenoxy resin has recently has described (42). para-Maleimidobenzoic acid was reacted with diglyci-dylbisphenol-A epoxy resin in the presence of catalyst to provide the bismale-imide of Fig. 13. Instead of diglycidyl bisphenol-A, linear epoxy resin pre-polymers can be used in this reaction to form a maleimide terminated phenoxy resin. Another suitable functionalized monomaleimide is m- or p- N-(hydroxyphenyl) maleimide which is synthesized from maleic anhydride and m-aminophenol in DMF as a solvent at 70 °C. The purified hydroxyphenyl maleimide was reacted with epoxy resin to form novel BMIs as outlined in Fig. 14. The new BMI and phenoxy oligomers polymerize at temperatures of 200-220 °C, but the cure temperatures can be significantly lowered when catalysts such as imidazoles or triphenylphosphine are added. The cured homopolymers show Tg of 140 and 230 °C for the n = 2 and the n = 1 polymer, respectively(43). 

This concept was introduced during the 1960s and 1970s and the first studied families were the maleimide and nadimide terminated oligomers due to an interesting compromise between processability, thermomechanical properties and cost. Right now both of these materials are used in industry for aerospace and electronic applications. Several reviews or book chapters have been devoted to these types of oligomers [1-5]. 

The double bond of maleimides in very reactive towards electron-rich dienes, to give a normal Diels-Alder cycloaddition. Thus BMIs were used to obtain linear polyimides by reaction with several kind of dienes [46-51]. However the dienes are often difficult to prepare [51] and functionalized dienes have been used. Furan terminated oligomers react with BMIs at 70 °C leading to an oxygen-containing cycloadduct [52-57] which can react with acetic anhydride to give an aromatic imide (Fig. 13) [58-59]. 

A highly porous polymeric foam can be prepared through emulsion templating by polymerizing the continuous phase of high internal phase emulsions [150], A maleimide-terminated aryl ether sulfone oligomer was copolymerized with divinylbenzene in the continuous phase, using a mixed surfactants system, cetyltrimethylammonium bromide, dodecylbenzene-sulfonic acid sodium salt, and a peroxide initiator. The polymers show a CO2 adsorption and improved mechanical properties. The materials exhibit an open cell and a secondary pore structure with surface areas of a 400 m g ... 

The Michael addition reaction of dimercaptodiphenylether with N-(3-ethynyl phenyl) maleimide allowed the synthesis of ethynyl-terminated imido-thioether as shown in Fig. 50 (139). This acetylene terminated imidothioether was blended with acetylene terminated polyarylene ether oligomers of different molecular weights and tested as composite resins (140). Blends of functionalized thermoplastics such as the acetylene terminated polyarylene ethers with brittle high-Tg imide resins are finding increased attention for tough high-Tg composites. 

Bis(maleimides) (BMI) are an important class of polyimides that are characterized by excellent thermal, electrical and mechanical properties Bis(maleimides) are low molecular weight oligomers, generally containing terminal reactive groups. A general structure of a bis(maleimide) is shown in Scheme 28. 

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