Processing of poly(2,6-dimethyl-1,4-phenylene ether) with epoxy resin. 2. Gelation mechanism

Poly(2,6-dimethyl-1,4-phenylene ether) (PPE), having a low dielectric constant and high T-g, is traditionally difficult to process without the use of solvents. To enable processing, PPE is dissolved into epoxy resin, and the gelation mechanism is studied chemorheologically. The gelation was followed by rheometry using multifrequency methods. The gel point of neat epoxy was at a conversion of epoxy similar or equal to 0.60, which agreed with the prediction of Flory-Stockmayer gelation theory. However, the gel point of the PPE/epoxy mixture depended on the curing temperature and occurred at a lower extent of reaction than that of the neat epoxy. The gelation of PPE/epoxy blends is the vitrification of a PPE-rich matrix following phase separation and not chemical gelation. Prediction of the phase diagram during reaction can be achieved using Flory-Huggins theory for phase separation and recursive theory for gelation.