The associative behavior of a triblock copolymer olystyrene-b-poly(eth
ylene/butylene)-b-polystyrene dissolved in solvent mixtures of n-octan
e sind 4-methyl-2-pentanone has been studied. When the solvent composi
tion was varied, the solvent mixture shifted from a selective solvent
of the end copolymer blocks (polystyrene) to a selective solvent of th
e middle block (poly(ethylene/butylene)). For solvent mixtures with a
high 4-methyl-2-pentanone content (selective solvent of polystyrene),
only one kind of particles has been detected in solution. These partic
les have a high molar mass and compactness and a small size (R-h appro
ximate to 32 nm). However, for solvent, mixtures with a high n-octane
content (selective solvent of poly(ethylene/butylene)), two types of p
articles of different size were detected. The smaller ones (R-h approx
imate to 22 nm) were considered as free copolymer chains and they were
the more numerous in the solution. The larger ones (R-h approximate t
o 210 nm) were assigned to aggregates with a loose structure different
to ordinary micelles. The n-octane/4-methyl-2-pentanone mixture with
a 50% of ketone behaved as a nonselective solvent, and no aggregates w
ere detected at 25 degrees C and at concentrations so high as 10 x 10(
-3) g.mL(-1).