| A series of model polyurethane (PU) networks based on poly(oxypropylene glycol), trimethylol propane, and diphenyl methane 4.4;Also, energy-absorbing simultaneous interpenetrating networks (SINs) based on polyether-type PU and poly(methyl methacrylate) (PMMA) networks were prepared by both a one-shot procedure and a prepolymer procedure. While the products have single and broad glass transitions, the SINs prepared by the prepolymer procedure show slightly greater transitions than those by the one-shot procedure. The % energy absorption determined from dynamic properties and pendulum impact tests of the prepolymer procedure varies directly with (PU). However, the values from the prepolymer procedure are always larger than those obtained from the one-shot procedure. These larger values from the prepolymer procedure, combined with a greater phase separation, results in better fatigue resistances than for the one-shot procedure. The fatigue fracture surfaces of these SINs show that the dominant factor for the energy dissipating deformations is presumably shear yielding rather than crazing. |
