Page 169 - Biodegradable Polyesters

6.2 Shape Memory Polymer Systems 147

Quasi semi-IPN structure can be produced by other ways. Such a structure is
given when electrospun PCL nanofiber mat is infiltrated by EP followed by cur-
ing of the latter. This material showed triple shape behavior. The T of PCL and
m
T of EP served to set the two temporary shapes. The T of EP was below the
g
g
T m of PCL [77]. Fej˝ os et al. [78] not only confirmed this concept on the same
material combination but compared the SM behavior with that of a “real” semi-
IPN-structured EP/PCL at the same composition. The latter was generated in a
one-pot synthesis via phase segregation. The storage modulus versus tempera-
ture traces of the PCL nanoweb containing EP and semi-IPN-structured EP/PCL
were similar (Figure 6.7). The dynamic mechanical analysis (DMA) traces clearly
show that both EP systems have a bicontinuous phase structure because their stor-
age moduli do not drop at the T of EP which would happen for dispersed PCL.
g
Instead of that, the moduli run in between those of the PCL and EP. The SM prop-
erties of the EP/PCL with semi-IPN structure were somewhat better than that

10 kV ×500 50 μm 09 46 SEI 15 kV ×500 50 μm 12 40 SEI
(a)

3
10
Storage modulus (MPa) 10 2 EP

PCL
EP/PCL nanoweb
1
10
EP/PCL blend
–40 –20 0 20 40 60
(b) Temperature (°C)
Figure 6.7 Structure of the electrospun structured EP/PCL and the parent PCL and
PCL nanoweb (left) and the semi-IPN (right, EP (b). Note: the PCL content in the EP/PCL
fracture surface) (a) and DMA traces of the combinations was 23 wt%.
electrospun PCL nanoweb containing EP, IPN