Abstract:
Multiple-shape memory polymers (multiple-SMPs) are highly class of smart materials that can memorize more than one temporary shape and can be recovered to their original shape in a single deformation cycle upon external stimuli such as heat. In this research, novel series of multiple-SMPs were prepared from urethane prepolymer (which acts as reversible switching unit) and benzoxazine resin (BA-a) (which also acts as net-point networks). The BA-a mass fraction in BA-a:PU multiple SMPs was in the range of 55% to 80% . The multiple-SMPs properties including shape fixity and shape recovery were investigated by universal testing machine (UTM) in three-points bending mode. The results revealed that BA-a:PU multiple-SMPs showed excellent shape fixity values of 70-96% for first temporary shape and 83-99% for second temporary shape. In terms of shape recovery, the multiple-SMPs also provided outstanding values of 88-96% for first temporary shape and 97-99% for original shape by increasing the amount of BA-a resin from 55% to 80% of BA-a mass content. In addition, the flexural strength and flexural modulus were also characterized by UTM. The results showed the increase of both flexural strength and flexural modulus with increasing of BA-a mass fraction. However, these values were decreased with increasing of temperature from room temperature to Tg - 10oC and Tg + 10oC, respectively. The glass transition temperature was systematically increased with the increase in BA-a content; it was reported to be in the range of 130oC to 180oC. Interestingly, the glass transition temperatures for each composition of BA-a/PU were in a board range (ca. 100oC). Furthermore, all BA-a/PU samples could be greatly recovered to the original shape for 5 cycles.
