Synthesis and self-assembly of optically active random copolymers bearing L-alanine and L-glutamic acid moieties in aqueous medium

Abstract

This study reports the synthesis by free radical polymerization and aggregation behavior of two new optically active hydrophilic random copolymers comprising glutamic acid or alanine-derived acrylamides and N-[3-(dimethylamino)propyl] methacrylamide (DMAPMA) taken in a 3:1 molar ratios. Their structures, chemical composition and optical activity are confirmed by spectral analysis (FTIR, 1H/13C NMR), thermal methods (TGA, DSC), molecular weight measurements (GPC) and specific rotation measurements. In addition, surface tension, fluorescence spectroscopy, dynamic light scattering (DLS), atomic force microscopy (AFM) and transmission electron microscopy (TEM) are utilized for the characterization of the self-assemblies in solution and/or thin films. The critical aggregation concentration (CAC) determined by surface tension and fluorescence spectroscopy shows similar values of 6 × 10−2 and 5 × 10−2 g∙L−1, respectively. Steady-state fluorescence measurements using 1-pyrene-methanol as molecular probe suggest the tendency of micro-domain formation as a result of interpolymer hydrophobic interactions, while their hydrodynamic sizes are determined by DLS technique. Moreover, the micrographs from AFM technique evidence a combination of comb and brush-shaped orderly structures for the L-glutamic acid-based copolymer, and a star-type structure with four arms, in which each arm presents in turn a brush structure for the L-alanine-based copolymer.