Benzocyclobutene-Maleimide Polymers

Of all of the AB benzocyclobutene maleimide homopolymers prepared, 114a appeared to have the best combination of thermal and mechanical properties as well as ease of fabrication (Table 21). This monomer/polymer was used as a... 

Reaction of 4-nitro-l-benzoyl chloride with benzocyclobutene 1 provided the benzoylated product 15 [36]. The nitro group of 15 was reduced with hydrogen in the presence of palladium on charcoal to afford he amine product 16 [44]. Reaction of the amine with maleic anhydride provided the amic acid which was converted to the maleimide 17 by cyclodehydration with acetic anhydride and sodium acetate at 95 °C [45-47], This monomer and its homo-polymer will be discussed in greater detail in a later section. 

The use of benzocyclobutene as the source of the diene in a Diels-Alder polymerization offers a unique solution to the problems described above. Benzocyclobutene containing monomers can be stored indefinitely at room temperature without concern for further advancement of the molecular weight. It is only when benzocyclobutene is heated to temperatures of approximately 200 °C that the reactive diene, o-quinodimethane, is formed at a significant rate and enters into reaction with the dienophile. The only requirement of the dienophile is that it must be stable at these temperatures and not undergo reaction with itself. The most common dienophiles that have been successfully used in the formation of polymers from AB type benzocyclobutene monomers have been acetylenes, olefins and maleimides. 

As before, the homopolymer forming reaction involved the generation of an o-quinoidimethane from benzocyclobutene which in turn reacted with the double bond of a maleimide functionality on a second monomer to give chain extended AB material via a Diels-Alder pathway. The polymers prepared to date using this type of approach have been shown to have excellent thermal and mechanical properties and have been considered as potential candidates for use as matrix resins for advanced composites. This area has been investigated by the researchers at both the Air Force Wright Laboratories and the Dow Chemical Co. 

AB maleimide benzocyclobutene monomers and polymers have also been actively studied and developed by researchers at the Dow Chemical Co. The first AB maleimide type benzocyclobutene monomer prepared and polymerized by Kirchhoff was the benzocyclobutenyl maleamic acid 106 [6]. The detailed synthesis of 106 is shown in Fig 44. 

---