METASTABLE PHASE-DIAGRAMS FOR SIMULTANEOUS INTERPENETRATING NETWORKS OF A POLYURETHANE AND POLY(METHYL METHACRYLATE)

Phase separation and gelation in simultaneous interpenetrating network s (SINs) are studied for the model system polyurethane-poly(methyl met hacrylate) (PU-PMMA). A metastable phase diagram is developed as a tet rahedron in three dimensions in which the four vertices represent the four individual components: the two polymers, PMMA and PU, and the two monomer (or prepolymer) mixtures, MMA and 'U'. The time order of thre e events, gelation of polymer I, gelation of polymer II and phase sepa ration of polymer I from II, is explored. The tetrahedron constructed represents these three events as curved or planar surfaces going throu gh its volume. The intersections of any two surfaces produce critical curves or lines representing, for example, simultaneous phase separati on and PMMA gelation, or simultaneous gelation of PMMA and PU. These a re critical conditions capable of playing key roles in the development of an SIN's morphology and hence properties. The metastable phase dia gram allows visualization of the course of the three events during SIN synthesis, and provides direction for controlling them with respect t o these critical conditions.