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TP
PT UAcknowledgments:U
For constant concentration (2wt%) of the IB2BS grafts (MBnB~90000), micelles are formed only above a certain
polystyrene volume fraction fBPSB=0.32 (Figure 3), while the core size as well as the aggregation number increase with
increasing fBPSPB
P(Figure 4). The shape of the micelles seems to change from spherical to rod-like cylindrical, for the
copolymers with the highest PS content, and macro-phase separation takes place. Moreover, the number density decreases
with fBPSB, in accordance with mass balance, whereas there is strong evidence that the polystyrene volume fraction in the core
increases. These results are in good qualitative agreement with the theoretical predictions of the thermodynamic model which
describes the micellization of graft copolymers [6], while the quantitative deviation is attributed to the preparation method.
The results were also compared to those for the respective linear diblock copolymers and different trends are revealed [7].
Intensity (cm -1 )
10 1
10 -2
f PS
= 0.09
SRS
10 -1
10 -5
10 1 f PS
= 0.90
ESRF
10 -5
10 1
f PS
= 0.32
10 -2
10 -5
10 1
f PS
= 0.46
10 -2
10 -5
10 1
f PS
= 0.64
10 -2
10 -5
10 1 f PS
= 0.82
10 -2
10 -2
10 -5
q (nm -1 )
10 0
R c
(nm)
Qm
40
30
20
10
Theoretical
Experimental
Rod-like
micelles
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
f
1800
PS
Theoretical
1600 Experimental
1400
1200
1000
800
600
400
200
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
f PS
Figure 3: The SAXS intensity curves as a function of the
scattering vector q for the 2wt% blends of the various IB2BS
graft copolymers in PI. The curves obtained at ESRF are
presented shifted by an order of magnitude for clarity.
Figure 4: The core radius (RBcB) and the aggregation number
(QBmB) for the IB2BS micelles versus the polystyrene volume
fraction fBPSB. The triangles correspond to the theoretical
values.
Finally, the effect of copolymer concentration and temperature on the formation and characteristics of the micelles
was studied, in order to determine the critical micelle concentration (CMC) and temperature (CMT), respectively, and their
dependence on the macromolecular architecture. Above CMC, the concentration affects mainly the number of the micelles
present and slightly their size. The micelles swell and the percentage of free chains increases as the concentration decreases
until the system reaches the CMC, below which only free chains exist in the mixtures. As far as the temperature effect is
concerned, the micelles appear to be fairly stable up to the crosslinking temperature of PI.
UReferences:
[1] Riess G., Prog. Polym. Sci.. 28 (2003) 1107. Gohy J.-F., Adv. Polym. Sci. 190 (2005) 65
[2] Rigby D., Roe R.-J., Macromolecules 17 (1984) 1778. Roe R.-J., Macromolecules 19 (1986) 728
[3] Kinning D. J., Thomas E. L., Fetters L. J., J. Chem. Phys. 90 (1989) 5806
[4] Pedersen J. S., Advances in Colloid and Interface Science 70 (1997) 171
[5] Pavlopoulou E. et al., in preparation (2007)
[6] Retsos H., Anastasiadis S. H., Pispas S., Mays J. W., Hadjichristidis N., Macromolecules 37 (2004) 524
[7] Pavlopoulou E. et al., in preparation (2007)
*
Part of this research was sponsored by the Greek General Secretariat for Research and Technology
(ΠΕΝΕΔ 2003 programme 03ΕΔ581)
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