SIMULTANEOUS INTERPENETRATING NETWORKS OF A POLYURETHANE AND POLY([METHYL METHACRYLATE]-STAT-[N,N-DIMETHYLACRYLAMIDE])

In a previous study, tetrahedron metastable phase diagrams were presen ted for a model simultaneous interpenetrating network (SIN) system of cross-polyurethane-inter-cross-poly(methyl methacrylate) (PU-PMMA). On e triangular face of the overall tetrahedron diagram represented the t ernary system MMA-PMMA-''U,'' wherein ''U'' denotes the monomer/prepol ymer mixture for the PU. In this article, a comonomer, N,N-dimethylacr ylamide (DMA), is incorporated into the PMMA network. Thus, the above- mentioned ternary system is altered to ''A''-PA-''U,'' where ''A'' den otes the acrylic monomer mixture [MMA + DMA] and PA denotes the result ing copolymer. Glass transitions of fully cured samples were determine d by dynamic mechanical spectroscopy (DMS). Phase separation was deter mined by the onset of turbidity, and gelation of the first gelling pol ymer was determined by the sudden resistance of the system to flow. Th e critical point, representing simultaneous phase separation and PA ge lation, divides the overall composition for the reaction mixture (and the final SIN) into two parts. For one, gelation of the acrylic networ k precedes phase separation, and vice versa for the other part. In the absence of DMA in the PA network, the gelation-first region is very n arrow, but with increasing amounts of copolymerized DMA, the critical point moves along the triangular face to increase the working area of the gelation-first region. (C) 1996 John Wiley & Sons, Inc.