Unconventional, amphiphilic polymers based on chiral poly(ethylene oxide) derivatives. I. Synthesis and characterization

The first representatives of a new class of synthetic, amphiphilic polymers-polyethylene oxide-based (PEG-based) polymers 1-3, (see Figure 2)-are introduced. These polymers are constituted in a similar way as coiled-coil-forming peptides: the polymers possess a regular repeat of apolar (A) residues in a polar (P) sequence of residues. Polymers 1-3 can thus be characterized by the formula [PAPPAPP'](n) or [PAPP'](n), in which P stands for an ethylene oxide unit, P' stands for a glycate unit, and A stands for a hydrophobically modified ethylene oxide unit. The preparation of 1-3 comprises the synthesis and SnOct(2)-catalyzed ring-opening polymerization of 2-oxo-crown ether monomers (SS)-4, (S)-5, and (S)-6. Alternatively, polymers 1-3 have been obtained by the polycondensation of their omega-hydroxycarboxylic acid precursors. H-1 NMR and C-13 NMR analysis as well as electrospray mass spectrometry (ES-MS) verified the integrity of the followed synthetic route and, therefore, confirmed the regular repeat of polar and apolar segments in 1-3. The critical aggregation concentrations (cac's) of 1-3 in H2O at 20 degrees C were determined by a fluorescence study, using pyrene as an apolar fluorescent probe. The cac's (i) were strongly influenced by the size of the hydrophobic segments in the polymer and by the frequency at which these segments were repeated in the polymer and (ii) varied over a wide concentration range (i.e. polymer 1 displayed a cac of ca. 0.002 mg/mL, whereas polymer 3 showed a cac of ca. 0.15 mg/mL). Thus, tailoring of the cac is possible in these new synthetic, amphiphilic polymers.