Single-alkyl and multi-alkyl chain-containing amphiphilic oligomers with several sugar side chains: solution properties and nanostructural analysis of aggregates by SANS

Abstract

Single-alkyl chain-containing amphiphilic oligomers with a terminal alkyl chain and several sugar side chains (i.e., C n -mGEMA, where n represents alkyl chain lengths of 12 or 16 and m represents the polymerization degree of glycosyloxyethyl methacrylate (GEMA) units of 3.0–7.1), and multi-alkyl chain-containing amphiphilic oligomers with several sugar side chains (i.e., xC12-mGEMA, where x represents the average number of alkyl chains and x–m is 0.2–6.6, 1.8–4.7, and 3.4–3.7), were synthesized via the radical oligomerization of one or two monomers in the presence of alkanethiol or 2-aminoethanethiol hydrochloride. Surface tension, pyrene fluorescence, and small-angle neutron scattering (SANS) measurements were used to characterize the solution properties of the oligomers and the nanostructures of their aggregates. Both amphiphilic oligomers are highly efficient in reducing the surface tension of water (42–48 mN m−1 for C n -mGEMA and 36–46 mN m−1 for xC12-mGEMA), despite the relatively large structures of the hydrophilic parts in sugar GEMA units. The critical micelle concentration (CMC) of C n -mGEMA and xC12-mGEMA increased with an increase in the degree of polymerization for hydrophilic GEMA units and a decrease in the alkyl chain length. The results of SANS determined that C n -mGEMA formed prolate ellipsoid micelles with a radius of 1.96 nm and an axial ratio of 1.58 for a low degree of polymerization (m = 3.0) in solution. However, the radius decreased to 1.33 nm and the axial ratio increased to 5.04 as the degree of polymerization of the amphiphilic oligomers increased to m = 7.1, indicating structural transformation to an asymmetric ellipsoid. On the other hand, the structure of the aggregates formed by xC12-mGEMA changed from ellipsoidal to an ellipsoidal cylinder shape with increasing number of alkyl chains, i.e., decreasing the number of GEMA units.