Characterization of the relaxation transitions in toluene diisocyanate-based polyurethanes with poly(propylene glycol) as the soft segment by thermally stimulated current depolarization with relaxation mapping analysis

Abstract

Thermal relaxation transitions of toluene diisocyanate (TDI)-based polyurethanes (PU) were characterized by the thermally stimulated current (TSC) technique with verification data from the relaxation mapping analysis (RMA) measurement. TDI-based PU elastomers with poly(propylene glycols) (PPG) as the soft segment and methylene-bis-orthochloroaniline (MOCA) as the hardener, showed three relaxation transitions, (1) a subglass transition (T g ) of the terminal groups occurred near Ϫ135°C; (2) the T g ; and (3) a global transition occurred above the T g (assigned as T global transition). The temperature of T g of PU as expected was varied by the chain length and attributed by the motion of an urethanic chain dominated by the soft segment and may also associate in the cooperative movement with the hard segment. The T global transition appearing above the T g was identified and attributed to the global transition in the macromolecule scale and was supported by the tangent plot of the dynamic mechanical analyzer (DMA) measurement. The TSC measurement on thermal characteristic transitions of TDI-based PU provided a whole range of thermal transitions including a sub-T g , the T g (observed by DSC) to a global transition (may be observed by DMA) with the ease of sample preparation in one single measurement.