The effect of alkyl core structure on micellar properties of poly(ethylene oxide)-block-poly(L-aspartamide) derivatives

Block copolymers based on fatty acid esters of poly(ethylene oxide)-block-poly(hydroxy alkyl L-aspartamide) were prepared and characterized by H-1-NMR. The structure of the core-forming block was changed through application of different lengths of the poly(L-aspartamide) (PLAA) block, spacer group or fatty acid and varying the substitution level of the side chain on the polymeric backbone. Transmission electron microscopy and fluorescent probe studies provided evidence for the formation of supramolecular core/shell architectures with nanoscopic dimensions. The same techniques were used to study the effect of hydrophobic block structure on micellar size, critical micelle concentration (CMC), core polarity and viscosity of the polymeric micelles. Among the structural factors studied, it was revealed that the length of the PLAA block and the level of fatty acid attached to the polymeric backbone are the major factors affecting micellar properties. An increase in micellar size and reduction in CMC were observed when the level of fatty acid attachment to the polymeric backbone was raised. The elongation of the PLAA block, on the other hand, resulted in an increase in micellar size and core viscosity. Micellar size was the only characteristic being affected by the length of the attached fatty acid. However, a decrease in microviscosity was revealed when behenic acid (22 carbons) was attached to the core-forming block in a high level of substitution. The length of spacer group was also found to be a useful means by which the level or side chain attachment could be controlled. Chemical tailoring of the core structure in polymeric micelles may be used as an efficient means to change micellar properties. As a result, nanoscopic, spherical and stable micelles with improved core properties may be achieved to insure efficient loading and controlled release of an individual drug from the delivery system. (C) 2001 Elsevier Science B.V. All rights reserved.