AB Benzocyclobutene Monomers and Polymers

In general, the predominant methods used to prepare polymers derived from benzocyclobutene monomers have focused upon the reaction of a bisbenzocyc- 

There are many examples of AB monomers in the polymer literature [104]. In particular there are examples of the Diels-Alder reaction being used in successful AB type approaches to polymer syntheses. There are however several practical problems associated with this type of approach. If the diene or dienophile is highly reactive, the synthesis and purification of the monomer can be very difficult. Furthermore, these reactive monomers can be difficult to store without some partial advancement of the molecular weight. If on the other hand the diene or dienophile is not very reactive under moderate conditions, then low molecular weight polymers are obtained. If more stringent conditions for polymerization are employed, the retro Diels-Alder reaction and other side reactions can become more important and therefore lead to the formation of a low molecular weight polymer. 

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. 

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A second class of AB benzocyclobutene monomers and polymers which have been reported in the literature are those in which a benzocyclobutene and a stilbene double bond are contained within the same molecule (Fig. 36) [4, 5]. 

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