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

Asymmetric Star Polymers Synthesis and Properties 75
1
Introduction
Asymmetric star polymers are megamolecules [1] emanating from a central
core. In contrast to the symmetric stars very little was known, until recently,
about the properties of the asymmetric stars. This was due to the difficulties associated
with the synthesis of well-defined architectures of this class of polymeric
materials. The synthesis, solution and bulk properties, experimental and theoretical,
of the following categories of asymmetric stars will be considered in
this review:
(a) Stars with molecular weight asymmetry
The arms are chemically identical but differ in molecular weight.
(b) Stars with chemical asymmetry
The arms differ in chemical nature. The term miktoarm stars (coming from
the Greek word µ iktóV
meaning mixed) is used for these polymers. The term
heteroarm star polymers (hetero from the Greek word éteroV
meaning other),
used by others for this class of polymers, is not appropriate since it does
not convey the concept of a group of dissimilar objects. Stars having similar
chemical nature but different end-groups also belong to this category.
(c) Stars with topological asymmetry
The arms are block copolymers which may or not have the same composition
and molecular weight but differ with respect to the polymeric block
which is attached to the central point.
Schematically the above structures are depicted in Fig. 1.
Fig. 1a–c. Asymmetric stars with: a molecular weight asymmetry; b chemical asymmetry;
c topological asymmetry