Rheological study of crosslinking and gelation in bismaleimide/cyanate ester interpenetrating polymer network

In searching for high performance polymer resins that have a combination of low dielectric constant and loss, high temperature resistance, ease of bei ng processed, and other desirable properties, an interpenetrating polymer n etwork (IPN) based on cyanate eater (CE) and 2,2'-diallylbisphenol A (DBA) modified bismaleimide resin (BMI) was prepared via prepolymerization follow ed by thermal curing. This work discusses the use of multiple waveform theo logical technique to investigate the crosslinking and gelation behavior of this resin system at various temperatures. The gel point can be accurately determined from a single experiment using this technique. At the point of g elation, both the storage modulus (G') and loss modulus (G') of the IPN fol low a similar power law equation with oscillation frequency used in the the ological measurement. Both the relaxation exponent n, a viscoelastic parame ter related to the cluster size of the gel, and gel strength S, related to the mobility of the crosslinked chain segments, were determined via a curve fitting method. Both n and S were found to be temperature dependent in thi s BMI/ DBA-CE IPN system. The apparent activation energy of gelation or cur ing reaction was found to be approximately 47.6 kJ/mol. (C) 2001 John Wiley & Sons, inc.