3.2 Results and Discussion

3.2.1 PS-b-PtBA Dendrimer-Like Copolymer (Dendl)

 The isotherm of Dend1 is presented in Figure 3-2, and the inset shows the static elastic

modulus plot (e,, Equation 3-1) versus surface pressure.101

 d (7)


The surface pressure in the isotherm increases in the high MMA region with a behavior

characteristic of liquid expanded and liquid condensed phases until a plateau suggesting a

biphasic state is observed at 24 mN/m. Upon further compression in the low MMA region, the

pressure sharply increases up to values as high as 70 mN/m. PS and PtBA are two hydrophobic

polymers, but contrary to PS, the presence of slightly polar ester groups in PtBA allows the

adsorption of PtBA homopolymers and PtBA-based block copolymers at the A/W interface. The

isotherm of Dend1 is very similar in shape to the isotherms of PtBA homopolymers, with only

one phase transition observed at 24 mN/m.102 Moreover, the extrapolation of the linear portion of

the isotherm below the plateau to zero pressure (Apancake 103 yields a value of 29 A+2 per PtBA

repeat unit, which is in good agreement with the previously reported literature.104 These two

observations indicate that Dend1 behaves similarly in terms of surface activity to PtBA

homopolymers, with the PS blocks desorbed in the air on top of the adsorbed PtBA blocks.

Nevertheless, these results are significantly different from those obtained by Lennox and co-

workers for linear PS-b-PtBA diblock copolymers with relatively low PtBA wt %.24,97 They

showed that the presence of the PS block induced two additional phase transitions of the PtBA

block below 20 mN/m and suggested that these transitions might originate from the peculiar

surface aggregation into circular micelles. As shown in the inset of Figure 3-2, only one local

minimum characteristic of a phase transition is observed at 24 mN/m for the static elastic