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

Poly(macromonomers), Homo- and Copolymerization 149
heterogeneities in MW and composition make the relevant characterization
techniques, such as SEC and light scattering, greatly inefficient in a strict sense.
In spite of the fact that characterization of graft copolymers prepared by the
macromonomer method is of essential importance, their characterization is still
not fully realized. Only a very few literature references are available in which a
precise characterization of the MW and compositional distributions of the graft
copolymers is described.
Two papers to be noted here have been reported by Ward's group [51] and
more recently, by Müller's group [53] for the synthesis and characterization of
model PMMA-g-PMMA. The former group synthesized model PMMA-g-PMMA
with narrow MW and compositional distributions by anionic copolymerization
of MMA and a methacrylate-terminated PMMA macromonomer, 29. The graft
polymers were characterized by several methods including membrane osmometry,
static light scattering, and hyphenated techniques such as SEC-LALLS and
SEC-differential viscosity (DV). The combination of these techniques demonstrated
that the PMMA-g-PMMA containing up to 40 mass % of long-chain
branching obeyed the universal calibration in SEC. The small characteristic ratio
values were also determined for the graft copolymers by applying Stockmayer-Fixman
(S-F) plot, though the application of S-F plot to the branched polymer
system is questionable. The shrinking factor, g= b/ l (see below),
determined by SEC-DV, was found to increase with increasing MW; that is, the
apparent branching density decreased with M w.
Müller et al. [53] prepared similar PMMA-g-PMMA by radical copolymerization
of MMA with methacrylate-terminated PMMA macromonomer, 29, and
characterized the samples by SEC-multiangle laser light scattering (MALLS).
The power law exponent, a, in the equation, 1/2 µM a , was found to be 0.36.
In remarkable contrast to the result of Ward et al. [51], the shrinking factor decreased
with increase of MW. This may imply that the difference in graft copolymerization
method, anionic or radical, results in the graft copolymers with
very different branch distribution.
The characterization and solution properties of graft copolymers in which
the backbone polymers are chemically different from the branches require many
difficulties to be overcome, from the viewpoints of the determination of MW, the
branching rate, and their distributions.
In the next section, therefore, we review recent studies of simpler cases, i.e.,
homopoly(macromonomers), star- and comb-shaped polymers, followed by
some interesting properties of the graft copolymers to be used as polymeric surfactants,
surface modifiers, and compatibilizers for blends.
5.1
Characterization and Solution Properties of Poly(macromonomers)
Polymacromonomers can be geometrically classified into two types of regular
branched forms, i.e., stars and combs, depending on the degree of polymerization
of the backbone and side chains. The poly(macromonomers) are probably