THERMODYNAMIC ANALYSIS OF THE PHASE-SEPARATION IN POLYETHERIMIDE-MODIFIED EPOXIES

The miscibility of polyetherimides (PEIs) with epoxy monomers based on diglycidylether of bisphenol-A (DGEBA), and with reactive mixtures ba sed on stoichiometric amounts of DGEBA and an aromatic diamine (DA) {e ither 4,4'-diaminodiphenylsulfone (DDS) or 4,4'-methylenebis[3-chloro 2,6-diethylaniline] (MCDEA)}; was experimentally studied. Cloud-point curves (temperature vs. composition) are reported for PEI-DGEBA and PE I-DGEBA-DA initial mixtures. Cloud-point conversions are reported for the reactive mixtures, for various PEI amounts and polycondensation te mperatures. A thermodynamic model based on the Flory-Huggins-Staverman approach, taking polydispersity of both components into account, was used to analyze the experimental information. A single relationship be tween the interaction parameter and temperature, chi(T), could fit exp erimental results of mixtures of two commercial PEIs with DGEBA. The a ddition of DDS led to a decrease in miscibility whereas MCDEA improved the initial miscibility. In both cases, the interaction parameter dec reased with conversion, meaning that PEI was more compatible with olig omeric species than with the mixture of starting monomers. The phase s eparation process in initially miscible rubber- or thermoplastic-modif ied thermosetting polymers is the result of two factors: increase in t he average molar size of the thermosetting oligomer (main driving forc e favoring demixing), and variation of the interaction parameter with conversion, which may act to increase or decrease the cloud-point conv ersion determined by the first factor. (C) 1996 John Wiley & Sons, Inc .