FLUORESCENCE PROBE STUDY OF MICELLE FORMATION OF POLY(ETHYLENE OXIDE)MACROMONOMERS IN WATER

Micelle formation in aqueous solutions of a series of poly(ethylene ox ide) (PEG) macromonomers has been investigated by steady-state and tim e-resolved fluorescence techniques using pyrene as a probe. These mole cules have the structure C-1-PEO-C-m-S-n, where m is the length of the alkyl chain attached to the para position of styrene and n is the deg ree of polymerization of PEG. The partition coefficients (K-v) of pyre ne between the aqueous and micellar phases, the critical micellar conc entration (cmc), and the micellar aggregation number (N-agg) are deter mined and compared to those of other more conventional surfactants. Th e PEO macromonomers were found to form micelles with a very weak hydro phobic core, K-v = 0.27 X 10(4) for C-1-PEO-C-4-S-53 and 0.52 x 10(4) for C-1-PEO-C-7-S-53. The measurements of partitioning, excimer emissi on, and vibrational fine structure of pyrene fluorescence (I-1/I-3) af ford cmc values of 0.90-0.85 wt % for C-1-PEO-C-1-S-53, 0.76-0.71 wt % for C-1-PEO-C-4-S-53, and 0.29-0.25 wt % for C-1-PEO-C-7-S-53 solutio ns. N-agg is determined as 27 for C-1-PEO-C-4-S-53 and 38 for C-1-PEO- C-7-S-53 micelles. A micelle formation mechanism is proposed for nonio nic polymeric surfactants with weakly hydrophobic groups.