Temperature Triggered Shape Memory Effect of Transpolyisoprene-based Polymer

Introduction: Pure gutta-percha (trans-1, 4-polyisoprene [TPI]) has been used extensively as a main component of gutta-percha for root canal filling. TPI has the interesting shape memory property by cross-linking, and this polymer was commercialized under the product name of SMP-2 (Kuraray Corp, Kashima, Japan). Therefore, the purpose of this study was to examine the thermal properties and the mechanism of the shape memory function of cross-linked SMP-2. Methods: The crystalline of the TPI was observed by x-ray diffraction. The effects of temperature on shape recovery, recovery stress, and relaxation modulus (Er[5]) were measured in cross-linked cylindrical specimens of SMP-2. Differential scanning calorimetry was used to monitor thermal events. Results: On heating, a pronounced increase in recovery stress, a marked decrease in Er(5), and endothermic DSC peaks were observed over the same temperature range (38 degrees 51 degrees C) with shape recovery. On the other hand, on cooling, a pronounced decrease in recovery stress, a marked increase in Er(5), and an exothermic DSC peak were observed over the same temperature range (27 degrees 33 degrees C). Conclusions: The shape memory property of TPI is derived from its crystallinity and cross-linking ability. Fixing the deformed shape and shape recovery from the deformed shape to the original shape is relatively easy to achieve by changing the temperature of SMP-2. The shape memory function of the cross-linked SMP-2 was expected to be very useful as a root canal filling material by the modification of its some thermal properties.