An interpenetrating polymer network, IPN, is defined as a combination of two or more polymers in network form, at least one of which is polymerized and/or crosslinked in the immediate presence of the other(s). The synthesis, morphology and mechanical properties of recent works are reviewed, with special emphasis on dual phase continuity, and the number of physical entanglements that arise in homo‐IPNs. The concepts of phase diagrams are applied, especially to simultaneous interpenetrating network phase separations and gelations. Recent engineering applications are discussed.

Any simultaneous interpenetrating network (SIN) synthesis contains three key events. These are gelation of polymer I, gelation of polymer II, and phase separation of polymer I from polymer II. Metastable phase diagrams of SINs are developed, in which the time occurrence of these three events is represented. A polyurethane/poly(methyl methacrylate) (PU/PMMA) system was chosen as a model. Polymerization kinetics were followed in situ for both PU and PMMA using Fourier Transform Infrared Spectroscopy (FTIR) with the aid of a heated demountable cell. Glass transitions of fully cured samples were determined by dynamic mechanical spectroscopy (DMS) and differential scanning calorimetry (DSC). Phase separation was determined by the onset of turbidity, and gelation of the first gelling polymer was determined by the sudden resistance of the system to flow. As a result, a metastable phase diagram was constructed for the four‐component SIN system (the two monomers and their respective polymers) as a tetrahedron in three dimensions with the two monomers and two polymers at the four apexes. Phase separation and gelations of the two polymers are indicated by various surfaces. These surfaces intersect at lines and curves, representing unique conditions of an SIN synthesis, e.g., simultaneous gelation of both polymers, or simultaneous phase separation and gelation of polymer I, etc. These conditions are critical in terms of the development of the SIN morphology, dividing the reaction space into specific regions. Finally, it is shown how the tetrahedron diagram helps visualize the course of the three key events during SIN synthesis, and provides direction for controlling them. © 1995 John Wiley & Sons, Inc.

SYNOPSISIn a model polyurethane/poly(methyl methacrylate) (PU/PMMA) system, the partitioning of unreacted methyl methacrylate monomer (MMA) is studied in the late stages of its polymerization, simulated by incorporating controlled amounts of MMA in otherwise fully cured simultaneous interpenetrating networks (SIN) samples. Glass transitions temperatures (T,) were determined using dynamic mechanical spectroscopy and differential scanning calorimetry as a function of MMA content of the SINs. The lowering of T, in each phase due to the plasticization effect of MMA is used to calculate a plasticization coefficient for each phase, finally allowing calculation of the partition coefficient of MMA between the two phases. It is found that the MMA monomer distributes itself almost uniformly across the two phases of the current SIN system, leading to speculation as to the locus of late SIN polymerization.

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SYNOPSISSemi-interpenetrating polymer networks based on two elastomers, cis-1,4-polyisoprene (PI) and thermoplastic polyurethane elastomers ( TPUs ) were prepared in varying compositions. The PI component was cross-linked using peroxide initiators. Modulus and mechanical properties were investigated as a function of composition and temperature. Slight synergisms were observed in mechanical properties, particularly for compositions containing 10% PI by weight. Little or no molecular mixing is shown by differential scanning calorimetry (DSC) for these two-phase materials.