BIN-SMPU

BIN-SMPU can significantly affect the mobility of the SMPU molecules (Chen et al., 2009b). As has been suggested by Jaczewska et al. (2007), the water absorption of poly(vinyl pyridine) is several times higher than that of polythiophene. The pyridine ring is also sensitive to moisture. Therefore, the BlN-SMPUs with pyridine may respond to moisture. 

In this chapter, a series of BIN-SMPU supramolecular networks were synthesized from the pyridine derivative and diisocyanate. The structure and morphology of BIN-SMPUs were investigated using a number of techniques, including FT-IR, DSC, WAXD and DMA, and the conclusions drawn can be summarized as follows ... 

Comparison of BINA-based shape memory polyurethane (BIN-SMPU) with other SMPUs... 

Another shape memory polymeric product is the shape memory flower shown in Fig. 7.2. The flower has eight petals and is cut from a flat square film made of BIN-SMPU. To begin with, the shape is that of an opening flower, but as the temperature is increased to over T, i.e. 80°C, the petals of the flower can be coiled by hand to make a closed flower, as shown in Fig. 7.2(a). Cooling to room temperatnre fixes the shape as a closed flower however, when the closed flower is pnt into an oven at 80°C, the flower can be observed to open its petals one by one. Fignre 7.2 shows that the petals are completely opened into a full flower shape within 5 seconds. These two examples therefore show that BIN-SMPUs have typical thermally-induced SMEs. 

Cyclic tensile curves of typical BIN-SMPU (PUPyBD053). 

Thermally-induced properties of polymers 171 Table 7.1 Cycle tensile testing results of BIN-SMPU with various BINA contents... 

Strain stability of BIN-SMPU with various BINA contents and eiongations. 

When BIN-SMPU is cooled to room temperature, both the hydrogen bonds with a lower association temperature and those with a higher association temperature contribute to the strain fixation. Moreover, most of the strains are fixed by the hydrogen bonds with the higher association temperature since these are first associated when BIN-SMPU is cooled. Hence, the recoverable strain is small at temperatures lower than 100°C. Raising the temperature to the dissociation temperature of hydrogen bonds will result in further strain recovery. 

To test the influence of the thickness of the contact surfaces on moisture absorption. Fig. 8.7 presents the moisture absorption per unit over time for BIN-SMPUs containing different amounts of BINA. The initial slope of moisture absorption is observed to increase in close correlation with the increase in BINA content, i.e. the BIN-SMPU sample with higher BINA content has a higher moisture absorption speed. The BINA content reflects the pyridine content in the... 

A large fraction of water molecules may be absorbed into BIN-SMPU in the form of moisture. According to Couchman (1978) and Couchman and Karasz (1978), moisture influences the thermal properties of polymers. As the moisture content increases from 0 to 20 wt.%, the of collagen, elastin and cellulose decreases by approximately 200, 145 and 260°C, respectively (Agarwal et ai, 1997). Recently, Yang et al. (2005) foimd that a decrease in of more than 35°C was obtained when the polymer absorbed about 4 wt.% water. Shape reeoveiy could consequently be achieved through immersion in water instead of heating. 

Table 8.4 Moisture-sensitive SME resuits of BiN-SMPU at various RH...

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