Tuning the associative properties and micelles geometry by stepwise quaternization of PDMAEMA

Abstract

We report on the synthesis and characterization of amphiphile copolymers derived from poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) generated by the stepwise quaternization of PDMAEMA, first with 1-hexadecyl bromide (HDB) and then with benzyl chloride (BC). Amphiphile copolymers consisting of hydrophile blocks separated by hydrophobe units were thus prepared in a predictable manner. The chemical structure of the hydrophobically modified polycations was confirmed by FTIR and 1H NMR spectroscopy, and by elemental analysis. The behavior in salt-free aqueous solutions was investigated by viscometry at 25 °C, rheological investigations at different temperatures, and by SAXS measurements. The steady shear measurements revealed an aggregation during the flow at moderate shear rates, the amplitude of this phenomenon depending on the hydrophobic/hydrophilic balance. The clusters are formed due to the intermolecular interactions and they grow as the shear rate is approaching 1 s−1. For the temperatures between 45 °C and 65 °C, the shear forces determine an expansion of the macromolecules that tend to orient in the flow direction and favor either a better interaction of the hydrophilic groups with the water molecules, or the manifestation of hydophobic interactions. The associative properties and the micelles geometry were tuned by the content and distribution of the hexadecyl groups.