Imide benzocyclobutene

The diene undergoes Diels-Alder cycloaddition with dienophiles. Polyimides have been synthesized from various imide-containing benzocyclobutenes and dienophiles (83—85). 

The structure formed through a linear addition of the molecules is Shown at the top of the illustration. The benzocyclobutene groups on either end of the BCB terminated resin molecules react with two other BCB groups as shown to form a poly(o-xylyene) strands. With BCB reactive groups present at both ends of the resin molecules, a double strand of poly(o-xylyene) is formed which is bridged by the aromatic imide chains. 

While there was a substantial amount of data reported on the syntheses of these acetylenic benzocyclobutene imide monomers, there was surprisingly little characterization done on the resulting homopolymers [91, 94, 95]. Table 17 details what information is available. 

A novel and very attractive approach to cure imide oligomers via benzocyclobutene endgroups was first published in 1985 (17). Benzocyclobutene endgroups are particularly attractive because they are neat hydrocarbons (provide low dielectrics), cure thermally around 200-250 °C with no volatile evolution and copolymerize with other functional groups, for instance, male-imide. 

Very interesting Diels Alder comonomers for BMI are the bis(benzocyclobutenes). Under appropriate thermal conditions, the strained four-membered ring of benzocyclobutene undergoes electrocylic ring opening to generate, in situ, o-quinodimethane, which, in the presence of BMI, reacts via a Diels-Alder reaction (83). The chemical structure of a bis(benzocyclobutene-imide) is provided in Fig. 28. The synthesis and properties of BCB and BMI/BCB blend systems is described in detail in chapter I of this book. 

A novel cure chemistry employed for addition poly(imides) has recently been published. The successful preparation of 4-aminobenzocyclobutene allowed the synthesis of benzocyclobutene-terminated imide oligomers and bisfbenzocylobutenes) (17). The benzocyclobutene group is a latent diene which isomerizes to o-guinodimethane at temperatures of about 200 °C and may homo- and/or co-polymerize for example with bismaleimide (83). Details on the benzocyclobutene chemistry are described in chapter I of this book. 

---