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

Poly(macromonomers), Homo- and Copolymerization 133
WMo initial weight of monomer
x fraction of disproportionation in termination
z excluded-volume parameter
˜z
scaled excluded-volume parameter
1
Introduction
A macromonomer is any polymer or an oligomer with a polymerizable functionality
as an end group. Formally, the macromonomer homopolymerizes to
afford a star- or comb-shaped polymer and copolymerizes with a conventional
monomer to give a graft copolymer. Thus the macromonomer serves as a convenient
building block to constitute arms or branches of known structure in the
resulting polymer. A large number of macromonomers, differing in the type of
the repeating monomer and the end-group, have so far been prepared, thereby
offering the possibility of construction of an enormous number of branched
polymers in a variety of architectures, combinations, and compositions. Polymerization
and copolymerization of macromonomers have also been studied in
great detail in order to understand their unique behavior in comparison with
that of conventional monomers. Their useful application in design of polymeric
microspheres has also been appreciated recently. Some interesting properties of
poly(macromonomers) have also been explored very recently as a simple model
of brush polymers which are of increasing interest. Comparatively, however, the
characterization and properties of graft copolymers with randomly distributed
branches have not been investigated to the same extent in spite of their theoretical
and practical importance.
The present article is intended to discuss the state-of-the-art of the design
and characterization of the branched polymers obtained by the macromonomer
technique, with particular stress on the characterization and the properties
of the brush polymers obtained by the homopolymerization of macromonomer.
The synthetic aspects of the macromonomer technique, including preparation
of various kinds of macromonomers, have been recently reviewed by
one of the authors [1]. Therefore, we intend here to outline briefly the macromonomer
technique and describe only the very recent important developments
in syntheses. Preparation and characterization of the polymeric microspheres
by use of macromonomers as reactive (copolymerizable) emulsifiers or dispersants
will be described in some detail to represent one of their unique applications.
Some comprehensive reviews covering earlier references include those by
Kawakami [2], Meijs and Rizzard [3], Velichkova and Christova [4], and those in
books edited by Yamashita [5] and by Mishra [6] among others.