Unimolecular micelle formation is investigated by means of light
scattering for poly(methyl
methacrylate)-graft-polystyrene copolymers with low grafted
chain densities in dilute solution of mixed
selective solvents. Molecular weights of poly(methyl
methacrylate) (PMMA) backbone and polystyrene
(PS) branch are about 6 × 106 and 9 × 103 g
mol-1, respectively, and the grafted chain
density ranges
from 6 to 17 wt % in terms of PS composition. The mixed solvents
are marginally good solvents for
PMMA and are nonsolvents for PS. From the results of static and
dynamic light scattering measurements
as a function of temperature and solvent composition, it is
demonstrated that, at higher branch densities
and lower temperatures, the rod like unimolecular micelles are formed,
made of a few linearly connected
flowers with small cores of associated PS branches and petals of PMMA
backbone chain. The number of
petals per flower increases with increasing branch density and
decreasing solubility of solvents for PMMA.
On the other hand, at the lowest branch density of 6 wt %,
instead of unimolecular micelle formation,
intermolecular associations take place, even at low copolymer
concentration.
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