Shape memory polymers can offer a large shape change as the environment changes. For thermally induced shape memory polymers, an SMP can be pre-deformed from an initial shape to a deformed shape by applying an external mechanical load at temperature T_d. A subsequently lowering down the temperature to T_s will freeze this deformed shape after the external mechanical load is removed. The shape memory effect is then activated by increasing the temperature to T_r, where the initial shape is recovered. In general, T_d and T_r are in the vicinity of the glassy transition temperature T_g, whilst T_d is above T_g and T_s is below T_g. In such a shape-frozen and shape-recovery cycle, the sample needs to go through its T_g twice. For polymers, as the temperature traverses the T_g, the mechanical behaviors of the polymer will change from a rubbery behavior to a glassy behavior which is a direct result of the transition in the polymer relaxation properties, a process that is strongly dependent on time. In this paper, the effects of thermal rate to the thermal-mechanical recovery of shape memory polymers are first experimentally investigated. Thermal rates essentially have two effects: the first one is concerned with the thermal conductivity of the polymer; the second one is concerned with the glassy transition. Based on experimental observations, a theoretical model is developed to capture the observed thermo-mechanical behaviors of SMP.
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