Chemistry Reference
In-Depth Information
13
ASYMMETRIC POLYMERIZATION
SHINGO ITO AND KYOKO NOZAKI
Department of Chemistry and Biotechnology, Graduate School of Engineering,
The University of Tokyo, 7 - 3 - 1 Hongo, Tokyo 113 - 8656, Japan
13.1. INTRODUCTION
The asymmetric synthesis and application of optically active polymers have received
much attention from a wide range of scientists. The reasons are that most biological
polymers such as polypeptides, polysaccharides, and nucleic acids are optically active
and that their chiral nature appears essential to exhibit various well-defi ned functions
such as molecular recognition ability and catalytic ability. In this regard, optically active
polymers are important not only because of their chiral structures and properties but
also because of their possibilities to provide totally new functional polymeric materials
[1-13]. These considerations arouse great interest in potential applications of optically
active polymers: (chiral) molecular recognition, asymmetric catalysis, molecular scaf-
folding to control the alignment of functional groups or chromophores, materials for
optical and optoelectronic devices, etc. However, although a variety of optically active
polymers have already been reported, few of them were successfully applied to the
practical use. One of the most challenging subjects in synthetic chemistry, therefore, is
the construction of novel optically active polymers exhibiting groundbreaking functions
that are comparable to or better than those of natural optically active polymers.
Asymmetric polymerization is one of the methods to synthesize optically active poly-
mers, which can be obtained either by polymerization of achiral monomers by using
optically active catalysts or initiators that introduce chirality in the polymer main chain,
or by polymerization of monomers having an optically active chiral auxiliary. The former
type of polymerization is mainly reviewed in this chapter, which is divided into three
major categories: asymmetric synthesis polymerization, helix-sense-selective polymer-
ization, and enantiomer-selective polymerization. Although the last type of polymeriza-
tion may be outside the scope of this topic, some of them are included because of their
