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

Poly(macromonomers), Homo- and Copolymerization 135
ized structure or morphology in concentrated solutions or in solids. In fact, a
number of possible conformations or morphologies that can be expected from
self-organization of the branched polymers has been a matter of increasing
study for the macromonomer technique.
The variety of branched architectures that can be constructed by the macromonomer
technique is even larger. Copolymerization involving different
kinds of macromonomers may afford a branched copolymer with multiple kinds
of branches. Macromonomer main chain itself can be a block or a random copolymer.
Furthermore, a macromonomer with an already branched or dendritic
structure may polymerize or copolymerize to a hyper-branched structure. A
block copolymer with a polymerizable function just on the block junction may
homopolymerize to a double comb or double-haired star polymer.
If we extend the definition of the macromonomer to include all polymers or
oligomers with a multiple number of (co)polymerizable functional groups at
any positions, then we can design an even larger number of branched polymers
by their polymerization and copolymerization. For example, a “telechelic
macromonomer” with two (co)polymerizable functional groups, each on
one end, may be useful to design a network structure in copolymerization
with control over the inter-crosslink length and/or crosslink density. A “multifunctional
macromonomer” with a multiple number of (co)polymerizable
functional groups along their chain may include already well-known resins
such as unsaturated polyesters used in thermosetting. Although these “macromonomers”
are no doubt practically important in applications, the scope
becomes too broad and complicated and the authors prefer to adhere to the
original, simpler definition of the macromonomer as that with a single
(co)polymerizable end group that affords star- and comb-shaped polymers
and/or graft copolymers with their branches (side chains) of known structure
as in Fig. 1.
So far, a great number of well-defined macromonomers as branch candidates
have been prepared as will be described in Sect. 3. Then a problem is how to control
their polymerization and copolymerization, that is how to design the backbone
length, the backbone/branch composition, and their distribution. This will
be discussed in Sect. 4. In brief, radical homopolymerization and copolymerization
of macromonomers to poly(macromonomers) and statistical graft copolymers,
respectively, have been fairly well understood in comparison with those of
conventional monomers. However, a more precise control over the backbone
length and distribution by, e.g., a living (co)polymerization is still an unsolved
challenge.
Needless to say, the best established architecture which can be designed by
the macromonomer technique has been that of graft copolymers. With this technique
we now have easy access to a variety of multiphased or microphase-separated
copolymer systems. This expanded their applications into a wide area including
polymer alloys, surface modification, membranes, coatings, etc. [5].
One of the most unique and promising applications of the technique may be
found in the design of polymeric microspheres. In this technique macromono-