Effects of Preparation Methods on Mechanical Properties of Polyurethane Networks

Mechanical properties of polyurethane networks prepared by three different methods were studied. The polyurethanes were prepared from poly (oxypropylene) glycol, 2, 4 - tolylene diisocyanate, and I, 4 - butane diol. The used preparation methods were prepolymer method (P-series), one-shot method (O-series), and semi-polymer method (S-series). The networks obtained were characterized through measurements of allophanate concentration, density, swelling behavior in benzene, thermal properties by means of DSC, wide angle X-ray diffraction scattering, electron microscopy, stress-strain behaviors, and dynamic mechanical properties. Concentration of allophanate linkages in O-series polyurethanes was higher than that of S-, and T-series polyurethanes. Glass transition temperature of O-series polyurethanes was slightly higher than that of other series polyurethanes. X-ray diffraction patterns showed a diffuse amorphous halo for all series polyurethanes. Microgloblues were observed for P-, and S series polyurethanes with high hard segment contents. Young's moduli of P-, and S-series polyurethanes were higher than those of O-series polyurethanes