Abstract
Polyurethane networks based on poly(oxypropylene) glycol (PPG, Mn=988) were prepared by incorporating hard segment oligomers. The hard segment oligomers were prepared by step synthesis. Trimers (BD-TDI-BD) were prepared by end-capping 2, 4-tolylene diisocyanate (TDI) with the large excess of 1, 4-butanediol (BD) and were purified by fractional precipitation. Heptamers (BD-(TDI-BD)3) were prepared from the trimer and TDI. The polydispersity indices (Mw/Mn) of trimer and heptamer were 1.1 and 1.4, respectively. Polyurethane networks based on PPG-TDI-BD were isotropic rubbery materials when prepared by usual prepolymer method. The incorporation of the trimer also resulted in isotropic rubbery ones. However, the heptamer resulted in partially micro-phase separated structure. Morphology of these networks were studied by measuring DSC, WAXS, SEM, etc. Properties of the polyurethane networks changed by incorporating hard segment oligimers in the following ways. The effects were enhanced with increasing hard segment length; Chemical crosslinking density and polymer density increased. The glass transition temperature of soft domain lowered. The high temperature transition of hard domain rose. Modulus increased but tensile strength and elongation at break decreased.
