COMPLEXATION OF POLY(ACRYLIC ACID) AND POLY(METHACRYLIC ACID) WITH PYRENE-END-LABELED POLY(ETHYLENE GLYCOL) - PH AND FLUORESCENCE MEASUREMENTS

The pH behavior of pyrene-end-labeled polyethylene glycol) (PEG) complexed with either poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMAA) has been examined. The effect of pH on the ratio of pyrene excimer to monomer fluorescence emission, ID/ IM, is reported. Both the intramolecular and intermolecular ID/ IM in PAA-PEG and PMAA-PEG systems are affected by changes in pH. A maximum in the PMAA intermolecular IU/IM as a function of the ratio of PMAA-PEG concentrations is shown to be caused by the collapse of the PMAA coils. It was found that the hydrophobic pyrene fluorescent labels interact with the hydrophobic a-methyl groups of PMAA, causing enhanced complexation. The pyrenes interact in the ground state and participate in preformed excimers. A qualitative model is presented that summarizes the interactions that occur in the PMAA-PEG and PAA-PEG systems. This model explains the observed red-shifted monomer excitation and absorption spectra, blue-shifted excimer excitation spectra, increases in monomer lifetimes, the absence of excimer rise times, a rapid initial decrease in intramolecular ID/ IM, and a rapid initial increase in intermolecular ID/ IM in PMAA-PEG solutions. Since there are no hydrophobic regions in the analogous PAA-PEG systems, none of the non-hydrogen-bonding phenomena are observed. All of these hydrophobically driven phenomena can be eliminated by destroying the consolidated hydrophobic regions in PMAA systems. This has been experimentally accomplished by the addition of methanol and by the ionization of the carboxy groups in PMAA. We also demonstrate the usefulness of Ko/Kco-op, the ratio of the initial complexation equilibrium constant to the equilibrium constant when 50% of the hydrogen bonding sites are complexed. This parameter describes the interaction between specific types of complementary complexing units and is related to the chemical nature of the interacting polymers. It is independent of molecular weight and concentration. © 1990, American Chemical Society. All rights reserved.