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The thermally induced polymerization of monomers containing two benzocyclobutenes and one or two a.d-disubstituted alkenes has been studied. Polymers prepared from monomers of this type are highly cross-linked thermosets with high storage moduli. Spectroscopic analysis of partially polymerized monomers suggests that the dominant mode of polymerization is the Diels-Alder reaction of a reactive intermediate o-quinodimethane with ,/3-disubstituted olefin. The rate of polymerization appears to be controlled by the first-order rearrangement of benzocyclobutene to o-quinodimethane. Rate constants for polymerization of two such monomers were calculated from residual monomer and FT-IR analyses. A relationship between molecular weight growth and functional group conversion based on the approach of Macosko and Miller23 has been applied to the polymerization of monomers containing two benzocyclobutenes and one or two olefins. Molecular weight growth and gel point for a divinyltetramethyldisiloxane-linked bis(benzocyclobutene) was found to be well predicted by this model, and an energy of activation of 37 kcal/mol was calculated for the polymerization of this monomer, trans-1,2-Bis(3-benzocyclobutenyl)ethylene monomer was found to deviate substantially from the proposed mode of polymerization at functional group conversions approaching the gel condition. An earlier than predicted gel point and broadening of the molecular weight distribution during the polymerization of this monomer are thought to occur as a result of o-quinodimethane self-reaction as the olefin concentration decreases.

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