Reversible hydrogels from amphiphilic polyelectrolyte model multiblock copolymers: the importance of macromolecular topology

Abstract

The association ability of model amphiphilic polyelectrolytes with multi-block architecture, i.e. ABA, BABAB, ABABABA and BABABABAB (A hydrophobic, B polyelectrolyte block) was studied in aqueous media. The gelation efficiency of these multiblock copolymers in semidilute aqueous solutions with variable molecular weights, hydrophobic content, topology and length of the associative stickers has been investigated by rheological measurements, light scattering and transmission electron microscopy (TEM). The behaviour of these associative polyelectrolytes seems to be governed by the interplay of the hydrophobic attractive interactions of the A blocks and the electrostatic repulsive interactions of the B blocks. Rheological results showed that only the copolymers bearing hydrophobic end-blocks are able to form hydrogels at relatively low copolymer concentrations. Therefore the topology of the A blocks and the degree of ionization of the B blocks influence significantly the gelation efficiency of these polymeric materials. Comparing the rheological behavior of multiblocks of the same topology (heptablock) it was observed that small differences in the degree of polymerization of the building blocks result in remarkably different rheological properties.