Macromolecules, Vol. 38, No. 15, 2005
Layered Morphology of Poly(phenylene)s 6409
Figure 9. (a, left) AFM height picture of the film in Figure 8a after annealing further at 150 °C. (b, right) AFM phase picture
of the film in (a).
melting temperature of PCL and the glass transition
temperature of POx. Figure 8b shows the AFM height
picture and Figure 8c the phase picture after annealing
for 18 h. A ∼2 nm thick layer was seen to spread from
the aggregates onto the top surface. These regions have
darker phase contrast, indicating relative softness with
respect to the other parts of the top surface. The
reproducibility of the AFM pictures was confirmed by
taking several pictures in the same area. Spreading of
PCL was favored on top of POx because of lower surface
energy of PCL compared to POx which minimized the
overall interfacial energy of the film. When the film was
further annealed at 150 °C, a smooth film having
smaller and rounded aggregates were observed as seen
in AFM height and phase pictures of parts a and b of
Figure 9, respectively. From the chemical structure of
the molecule (Scheme 4), the 2 nm thick top PCL layer
must have PCL loops sticking out. The expected thick-
ness of such loops for about 3000 g/mol PCL blocks is
consistent with the measured value of 2 nm. Because
PCL crystallization is hindered in such loops, the top
layer is an amorphous PCL layer and has darker phase
contrast. Only the larger PCL aggregates show bright
phase contrast, an indication of crystallinity in ag-
gregates. As expected, for molecules terminated with
amorphous polymers of PSt (polymer 8) or POx (polymer
rings of the backbone. This observation is important
because electronic structure of conjugated polymers is
closely related to the backbone conformation, and the
planarity of chains has been reported to increase
conductivity. Such layering was not observed when
amorphous polymers (PSt or POx) were grafted to the
rigid poly(phenylene) backbone. When PCL crystalliza-
tion was hindered by attaching PS or POx to the end of
PCL, the layered morphology was also not formed.
These observations clearly show that crystallization of
the side groups in well-defined layers induces planarity
of the phenyl rings in the backbone and a layered
morphology in thin films.
Acknowledgment. S.Y. and I.C. thank the Tubitak
BDP programme and Istanbul Technical Universitys
Research Fund for financial support. A.L.D. acknowl-
edges the financial support of the Turkish Academy of
Sciences in the framework of the Young Scientist Award
program (Grant No. EA/T U¨ BA-GEBIP/2001-1-1).
References and Notes
(
(
1) Bredas, J. L. J. Chem. Phys. 1985, 83, 1323.
2) Rughooputh, S. D. J. Polym. Sci., Polym. Phys. 1987, 25,
1071. Inganas, O. J. Synth. Met. 1988, 22, 395.
(3) Witteler, H.; Lieser, G.; Wegner, G.; Schulze, M. Makromol.
Chem., Rapid Commun. 1993, 14, 471.
9), PCL crystallization was hindered and the formation
(
4) Grem, G.; Leising, G. Synth. Met. 1993, 55-57, 4105.
5) Ivory, D. M.; Miller, G. G.; Sowa, J. M.; Shacklette, L. W.;
Chance, R. R.; Baughman, R. H. J. Chem. Phys. 1979, 71,
1506.
of layered structures was prevented.
(
Conclusions
(
6) Schluter, A. D. J. Polym. Sci., Polym. Chem. Ed. 2001, 39,
Poly(p-phenylenes) having grafted PCL side groups
show well-defined layered morphologies in thin films.
Such layered morphology is formed because of the
tendency of semicrystalline PCL in thin films to crystal-
lize such that alternating amorphous/crystal layers
orient parallel to the solid substrate. To obtain such
morphology, we took advantage of not only the effect of
confinement (film thickness) on orientation (flat-on
lamellae) but also the strong interaction of -OH groups
at the end of PCL blocks with the hydroxylated SiO2
substrate. These strong interactions also ensure the
stability of the resulting morphology. Alternating layers
of flat-on PCL lamellae and rigid poly(p-phenylene)
backbones have been identified for polymer 5 (Scheme
1533.
(7) Gin, D. L.; Conticello, V. P. Trends Polym. Sci. 1996, 4, 217.
(8) Schluter, A. D.; Wegner, G. Acta Polym. 1993, 44, 59.
(
9) Park, K. C.; Dodd, L. R.; Levon, K.; Kwei, T. K. Macromol-
ecules 1996, 29, 7149. Remmers, M.; M u¨ ller, B.; Martin, K.;
Rader, H. J. Macromolecules 1999, 32, 1073. F u¨ tterer, T.;
Hellweg, T.; Findenegg, H. Langmuir 2003, 19, 6537. Shi,
H.; Zhao, Y.; Zhang, X.; Zhou, Y.; Xu, Y.; Zhou, S.; Wang, D.;
Han, C. C.; Xu, D. Polymer 2004, 45, 6299.
(
(
10) Berlin, A.; Zotti, G. Macromol. Rapid Commun. 2000, 21, 301.
11) Berresheim, A. J.; M u¨ ller, M.; M u¨ llen, K. Chem. Rev. 1999,
99, 1747.
(
(
12) Lauter, U.; Meyer, W. H.; Wegner, G. Macromolecules 1997,
30, 2092.
13) Francois, B.; Widawski, G.; Rawiso, M.; Cesar, B. Synth. Met.
1995, 69, 463.
(14) Yamamoto, T. Prog. Polym. Sci. 1992, 17, 1153.
(15) Eastmond, G. C. Adv. Polym. Sci. 2000, 149, 59.
(16) Svoboda, P.; Kressler, J.; Ougizawa, T.; Inoue, T.; Ozutsumi,
K. Macromolecules 1997, 30, 1973.
2
) by differences in the microstructures of the layers.
The smoothness of the layers containing poly(p-phe-
nylene) backbones indicates the planarity of the phenyl