Fluorinated vesicles allow intrabilayer polymerization of a hydrophobic monomer, yielding polymerized microcapsules

Intrabilayer polymerization of hydrophobic monomers has been attempted as a way to strengthen the structure of vesicles and producing polymer microcapsules. However, no clear evidence has been provided that demonstrates the formation of polymerized vesicles. On the contrary, it has recently been shown that polymerization of hydrophobic monomers within a vesicular bilayer did not yield the expected capsules but led to the formation of hybrid surfactant-polymer particles constituted by a polymer latex lump attached to the vesicle. We now report that use of highly ordered, microcompartmentalized fluorinated vesicles, i.e., made from fluorinated lipids, allows to achieve true intrabilayer polymerization. mie have studied the thermally induced free radical polymerization of isodecyl acrylate (ISODAC) in small unilamellar vesicles (SUVs) made from a perfluoroalkylated phosphatidylcholine (F-PC) and compared it to polymerization of ISODAC in vesicles made from standard egg phospholipids (EggPC). Cryogenic transmission electron microscopy (cryo-TEM) confirmed that extended polymer/bilayer phase separation occurred in the EggPC vesicles. On the other hand, no evidence of phase separation was observed in the case off-PC vesicles. The polymer, poly(isodecyl acrylate) (poly(ISODAC)), was homogeneously distributed within the bilayer. In addition, the rate of polymerization in F-PC vesicles, as monitored by H-1 NMR, was higher than in EggPC vesicles. The molecular weight of poly(ISODAC), as determined by size exclusion chromatography (SEC), was smaller when obtained in F-PC than in EggPC vesicles. The internal fluorinated core present in F-PC vesicles significantly reduces the space available fur polymerization, the monomer being excluded from the central core and confined in the two tight, nonexpandable lipophilic regions of the vesicles. Such conditions of confinement, which likely result both in an increase in local monomer concentration and in probability of polymerization termination steps, may explain the observed higher reaction rate and lower polymer molecular weight.