THERMAL POLYMERIZATION OF BIS(BENZOCYCLOBUTENE) MONOMERS CONTAINING ALPHA,BETA-DISUBSTITUTED ETHENES

The thermally induced polymerization of monomers containing two benzoc yclobutenes and one or two alpha,beta-disubstituted alkenes has been s tudied. 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 poly merization is the Diels-Alder reaction of a reactive intermediate o-qu inodimethane with alpha,beta-disubstituted olefin. The rate of polymer ization appears to be controlled by the first-order rearrangement of b enzocyclobutene 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 functiona l group conversion based on the approach of Macosko and Miller23 has b een applied to the polymerization of monomers containing two benzocycl obutenes and one or two olefins. Molecular weight growth and gel point for a divinyltetramethyldisiloxane-linked bis(benzocyclobutene) was f ound to be well predicted by this model, and an energy of activation o f 37 kcal/mol was calculated for the polymerization of this monomer. t rans-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 predi cted gel point and broadening of the molecular weight distribution dur ing the polymerization of this monomer are thought to occur as a resul t of o-quinodimethane self-reaction as the olefin concentration decrea ses.