Noncollapsing polyelectrolyte conetwork gels in physiologically relevant salt solutions

Abstract

In consequence of some unique properties, such as nanophase separation, biocompatibility and mechanical stability, amphiphilic polymer conetworks (APCNs) have received significant attention in recent years. APCNs are composed of hydrophilic and hydrophobic polymer chains connected with covalent bonds. The unique properties of APCNs make them suitable for many specialized applications. Although APCNs were widely investigated and described in the literature, this is the first study on the swelling behavior of these materials in the solutions of physiologically relevant salts. Homopolymer polyelectrolyte hydrogels are known to suffer phase transition like rapid gel collapse at a certain salt concentration in the solutions of bi- or multivalent metal salts. Systematic swelling investigation of poly(methacrylic acid)-l-polyisobutylene (PMAA-l-PIB) conetwork series in CaCl2 salt solutions led to unexpected findings. Our results indicate that these polyelectrolyte APCNs do not behave the same way in salt solutions as the homopolymer hydrogels, i.e. APCNs do not suffer gel collapse, the change of the swelling degree remains continuous with increasing salt concentration. The gel contraction was reversible by changing the solute to NaOH solution, i.e. the gels returned to their original volume by reswelling. This non-collapsing swelling means that the presence of hydrophobic polymer segments as cross-linkers in amphiphilic polyelectrolyte gels radically change the swelling behavior of such materials, which become substantially different from that of homopolymer polyelectrolyte gels.