142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

Asymmetric Star Polymers Synthesis and Properties 117
Fig. 10. Bright field TEM micrograph of I 2 S miktoarm with 53 vol.% PS (reproduced with
permission from [83])
polyisoprene “cylindrical” micelles in a matrix of polystyrene, was shown to be
an equilibrium one by selective solvent casting and annealing experiments. On
careful annealing the authors were able to observe the transition from a kinetically
trapped non-equilibrium folded layer morphology into the equilibrium
randomly oriented wormlike phase through an intermediate “fold-lace” morphology.
Furthermore the experimentally determined phase diagram for the I 3S
stars showed absence of the spherical morphology in the high PS volume fraction
(92%) region. The micrographs of an I 3S sample with 39 vol.% PS had the
structure of PS cylinders instead of spheres, a sample with 86% PS, PI cylinders
instead of lamellae and a sample having 92 vol.% PS consists of disordered PI
cylinders in a PS matrix. It is obvious that as the number of arms in A nB type
samples increases differences between the present theory and experiment become
more apparent. The theory may be brought “in line” with the experimental
findings if the theoretical boundary curves (see Fig. 7) could be “bend back” towards
the low volume fraction side of the phase diagram. Presently the theory
omits the multiple domain effects, i.e., effects of crowding of chains emanating
from different but neighboring interfaces [83].
The microdomain morphology of asymmetric miktoarm stars of the type
AA'B with A, A'=PI of different molecular weight and B deuterated PS, covering
a wide range of compositions, was investigated by Gido and coworkers [52] by