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

Poly(macromonomers), Homo- and Copolymerization 151
Gnanou and coworkers [15, 22, 23] prepared several types of regular star- and
comb-shaped polymers by living, ROMP of w-norbornenyl macromonomers, 8,
15 and 16. Some of them were characterized by means of the universal calibration
in SEC to discuss the chain density, radius of gyration, and shrinking factor
[63].
Hatada and coworkers [64] have prepared a series of uniform oligo(PMMA
macromonomer)s prepared by a radical or anionic polymerization of uniform
PMMA macromonomer, 14, followed by fractionation by SEC. The MW dependence
of the limiting viscosity, [h], was investigated with monomer to tetramer of
the PMMA macromonomer using SEC-DV.
Ito et al. [65] investigated the MW dependence of the limiting viscosity for a
series of regular polymacromonomers from PEO macromonomers, 26 (m=1)
and demonstrated that the universal SEC calibration holds for these polymers.
The exponent, a, in the Mark-Houwink-Sakurada equation defined by
(10)
decreased with increase of the chain length of the branch. It was found at least
in the MW range investigated that the value of a steeply approaches zero when n
is above 44. Very low values of a clearly suggest that polymacromonomers behave
hydrodynamically as a non-draining rigid sphere and/or constant segment
density particles. The similar results were reported by Tsukahara et al. [66] in
which they studied [h] of PSt polymacromonomers from 24. They also observed
that in high M w region, [h] goes up and increases with M w. This rising of [h] with
M w was suggestive of the change in the molecular conformation of polymacromonomers
from starlike to bottlebrush.
Schmidt et al. [67, 68] have first demonstrated that polymacromonomers
from a series of PSt macromonomers, 24, behave as semi-flexible polymer
chains in dilute toluene solution by the measurements of SEC-MALLS, SEC-DV,
and dynamic light scattering (DLS). The Kuhn statistical segment length was reported
to increase monotonously up to ca. 300 nm with branch chain length.
They termed them, therefore, as “molecular bottlebrushes” (see Fig. 1e). Subsequently,
the diffusion and sedimentation experiments studied by Nemoto et al.
[69] clearly showed that their MW dependence is quantitatively described by the
prolate ellipsoid model with the values of the main and the minor axes calculated
from a planar zigzag PMMA backbone and Gaussian PS branched chains, respectively.
Small-angle X-ray scattering (SAXS) experiments also supported that
the side chains assume a random coil conformation [68].
Figure 4 shows a double logarithmic plot of radius of gyration, z , (open
circles) of a polymacromonomer from PEO macromonomer, 26 (m=4, n=50)
(C 1 -PEO-C 4 -S-50) in 0.05 N NaCl solution against M w [70]. The z data for
M w lower than 1´10 5 (filled circles) were calculated using Eq. (6) and the equation,
z =4.08´10 –4 M w 1.16 for a PEO chain in water at 25 ˚C [71]. Both data are
seen to superimpose in the region of M w ~1´10 5 . It can be expected from Fig. 4
that the plot of log z vs logM w of the polymacromonomers assumes a re-