Preparation, Characterization And Mechanical Model Of Shape Memory Polyurethanes Chain-extended By Aromatic Diamine

Shape memory polymers (SMP) are those that can revert from the current shape to a previously held shape, usually due to the action of heat. Segmented polyurethanes (PU) possess a micro-phase separated structure, i.e., a frozen hard segment phase and a reversible soft segment phase, which can meet the requirement of SMP structure. Through molecule design, the shape memory temperatures of shape memory PU (SPU) can be tailored in a wide range.For the wide applications of SMP, their mechanical properties are of greater importance than the others. In this research, two series of SPU chain-extended by two aromatic diamines, i.e. m-phenylene diamine (m-PDA) and4,4’-diaminodiphenyle ether (ODA) were prepared. Their structures and properties were characterized by DSC, DMA, tensile test, stress relaxation test, shape recovery test, water vapor transmission (WVT) test and flow properties test. A polarity microscope with a hot stage and an atomic force microscopic were used to observe the pahse separation of SPU.The standard linear viscoelastic (SLV) model was used to describe the stress relaxation behaviors of SPU samples and their relaxation times were calculated. Furthermore, we focus on the modification of classic phenomenological viscoelatic theory which was based on the generalized Maxwell model and time-temperature superposition principle. Through the modified phenomenological theory, relaxation activation energy of SPU samples was calculated. The comparison with the experimental data shows that the proposed mechanical model could reproduce both the dynamic modulus and stress-relaxation modulus of SPU. The results show that the modified phenomenological theory is more convenient than the classical one.