Association of a hydrophobically modified polyelectrolyte and a block copolymer followed by fluorescence techniques

By using absorption and fluorescence (steady-state and time-resolved) techniques the
interaction between a poly(acrylic acid) PAA, randomly grafted with pyrene (Py) units
(PAAMePy55) and a triblock copolymer of poly(ethylene oxide) and poly(propylene
oxide) (EO20PO68EO20, P123) was investigated. From the fluorescence data it is shown
that upon addition of P123 a decrease of the (pyrene-pyrene, Py-Py) intramolecular
association, i.e., a decrease of dynamic and static excimer formation, is observed. Timeresolved
fluorescence data reveal the existence of two types of monomers (monomers
that are able to form excimer, MAGRE, and isolated monomers) and two excimers.
Addition of P123 causes also an increase of the amount of isolated Py monomers. The
overall fluorescence data suggest that the PAAMePy55 and the P123 block copolymer
associate strongly at low pH, leading to the formation of P123 micelles surrounded by
one PAAMePy55 chain, where the pyrene groups are located at the PPO/PEO interface
of the P123 micelles. Steady-state fluorescence results also showed that an excess of
P123 micelles in solution is required for the association to occur. At high pH (pH 9 and
above), the situation is less clear, the steady-state (particularly in the I1/I3 ratio) and
time-resolved fluorescence results indicate a contact between the pyrene groups and
PEO, which then would imply that there may be an interaction, but much weaker than at
low pH.