mN/m), PCL quickly collapses and crystallizes as indicated by the sharp initial area decrease.

The MMA levels off around 1000 A+2, a value that correlates well with the MMA value obtained

at the end of the plateau in the isotherm.






 S0.8-
 .) *9mNim
 -e11mNim
 eJ0 o 13mN/m
 S.6 -i o




 0.4
 0 10000 20000 30000
 Time (s)


Figure 4-15. Isobaric relaxation plots of Star#6 at 9, 11, and 13 mN/m.

 PCL crystallization in the pseudoplateau region was finally investigated by hysteresis

experiments. The compression-expansion curves for Star#6 with a target pressure of 15 mN/m

are shown in Figure 4-16. As the barriers expand, an expansion pseudoplateau appears that

corresponds to the readsorption (melting) of the PCL chains previously crystallized.

Interestingly, the second and third compression curves overlap each other but do not overlap the

initial compression, with a slight shift toward the low MMA region and a decrease in the

compression pseudoplateau pressure. Similarly as it was observed for PCL homopolymers, this

confirms that crystallization takes place for Star#6 in the pseudoplateau region during

compression. Star#5, Star#4, and Star#3 have a similar behavior with the expansion

pseudoplateau vanishing as the PCL amount is decreased. Because of even lower PCL content in

Star#2 and Star#1, no expansion pseudoplateau was observed, and the subsequent compression-