Design and synthesis of a two compartment micellar system based on the self-association behavior of poly(N-acylethyleneimine) end-capped with a fluorocarbon and a hydrocarbon chain

Abstract

The synthesis, characterization, and association behavior of a new class of amphiphilic polymer surfactants are described. Living cationic polymerization of 2-methyl-2-oxazoline was utilized to create a series of water-soluble polymer surfactants FPxLn, where F denotes a well defined flourinated end group C8F17CH2CH2, Px denotes the degree of polymerization and Ln a hydrocarbon end group of variable length CnH2n+1, n = 6, 8, ..., 18. The molecular weights and polydispersities of the polymers were determined by gel permeation chromatography (GPC) in chloroform. 1H NMR spectroscopy was used to calculate the number average degree of polymerization and the degree of end group modification with the hydrocarbon chain containing termination agent. The molecular weights and degree of polymerization corresponded closely to the values expected from the monomer/initiator ratio. The polydispersities were low, ranging from 1.15 to 1.20. The extent of end group modification was calculated to be a minimum of 85% for all polymers. Fluorescence experiments employing pyrene as a probe showed that these polymers form aggregates in water through self-association in the concentration range from 0.018 to 0.061 wt.-%. In addition, the micropolarity experienced by the peak ratio I1/I3 in the vibronic fluorescence spectrum of pyrene above the cmc up to 1.0 wt.-% changed from hydrocarbon-like for FPL12, FPL14, FPL16 and FPL18 to fluorocarbon-like for FPL6 and FPL8, and intermediate behavior for FPL10. Dynamic light scattering of FP25L16 showed single micelles at a concentration of 0.50 wt.-% and 2.0 wt.-% with a hydrodynamic radius of Rh = 5.5 and 6.7 nm, respectively. 19F NMR experiments were applied for FP25L16 to study the aggregation behavior of the fluorocarbon end group. T2 relaxation experiments indicated that the degree of aggregation increased linearly with polymer concentration. Moreover, the results of the T2 relaxation experiments suggested the presence of pure fluorocarbon phases consistent with those found by fluorescence spectroscopy for FP25L16.