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

Poly(macromonomers), Homo- and Copolymerization 147
en with increasing MW and decreasing frequency of the macromonomer
branches, as well as with increasing conversion, as expected.
Narrow distribution in the backbone length as well as in the chemical composition
or the branch frequency may be expected from a living-type copolymerization
between a macromonomer and a comonomer provided the reactivity ratios
are close to unity. This appears to have been accomplished to some extent
with anionic copolymerizations with MMA of methacrylate-ended PMMA, 29,
and poly(dimethylsiloxane) macromonomers, 30, which were prepared by living
GTP and anionic polymerization, respectively [50, 51]. Recent application [8] of
nitroxide (TEMPO)-mediated living free radical process to copolymerizations
of styrene with some macromonomers such as PE-acrylate, 1a, PEO-methacrylate,
27b, polylactide-methacrylate, 28, and poly(e-caprolactone)-methacrylate,
31, may be a promising approach to this end.
(29)
(30)
(31)
In an apparently homogeneous solution, macromonomers, possibly together
with the resulting graft copolymers, may lead to some structure formation such
as micelle or looser association, which may in turn change the apparent reactivities
due to some specific solvation or partition of the monomers around the active
sites. Such a “bootstrap” effect [52] may be responsible for some complicated
dependency of the apparent reactivities on the monomer concentration and
composition in radical copolymerization of 29 with n-butyl acrylate [53].
Use of macromonomers as reactive (copolymerizable) surfactants in heterogeneous
systems such as emulsion and dispersion constitutes an increasingly
important application in the design of polymeric microspheres, as will be discussed
later in Sect. 6. Here the macromonomers copolymerize in situ with
some of the substrate comonomers to afford the graft copolymers, the grafts
(branches) of which serve as effective steric stabilizers by anchoring their backbone
onto the surfaces of the particles. In general, however, the copolymerization
reactivities of macromonomers in such systems are not well understood
yet.
Copolymerization involving two or more kinds of macromonomers appears
interesting in providing comb polymers with multiple kinds of branches, but
also in reflecting some explicit polymer effects involved in the polymer-polymer