Complex Self-Assembled Morphologies of Thin Films
of an Asymmetric A<sub>3</sub>B<sub>3</sub>C<sub>3</sub> Star Polymer
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Abstract
An asymmetric nine-arm star polymer,
(polystyrene)<sub>3</sub>-(poly(4-methoxystyrene))<sub>3</sub>-(polyisoprene)<sub>3</sub> (PS<sub>3</sub>-PMOS<sub>3</sub>-PI<sub>3</sub>) was synthesized,
and the details of the structures
of its thin films were successfully investigated for the first time
by using in situ grazing incidence X-ray scattering (GIXS) with a
synchrotron radiation source. Our quantitative GIXS analysis showed
that thin films of the star polymer molecules have very complex but
highly ordered and preferentially in-plane oriented hexagonal (HEX)
structures consisting of truncated PS cylinders and PMOS triangular
prisms in a PI matrix. This HEX structure undergoes a partial rotational
transformation process at temperatures above 190 °C that produces
a 30°-rotated HEX structure; this structural isomer forms with
a volume fraction of 23% during heating up to 220 °C and persists
during subsequent cooling. These interesting and complex self-assembled
nanostructures are discussed in terms of phase separation, arm number,
volume ratio, and confinement effects
