Three different types of physical gels originate from a common triblock copolymer precursor: the case of an ionomer gel

Abstract

We report the self-assembly of a triblock ionomer consisting of a long poly(2-vinyl pyridine) end-capped by fully neutralized poly(acrylic acid) (PANa-b-P2VP-b-PANa) in methanol which is a selective solvent of P2VP. This polymer arises from a PtBA-b-P2VP-b-PtBA triblock precursor by acid hydrolysis and subsequent neutralization by MeONa. The PANa-b-P2VP-b-PANa self-assembles through dipole interactions forming flower-like micelles, comprising a great number of ion pairs and P2VP looping chains. As the concentration increased, loop to bridge transitions led to the formation of a transient network. The so-formed physical gel exhibited a percolation concentration at 1.6 wt% and relaxation times of the order of several hundreds of seconds. The present work shows that all the types of ionogenic physical gels, i.e. polyelectrolyte, polyampholyte, ionomer, can be afforded from a common triblock copolymer precursor. The resulting physical gels arise from different types of interactions, i.e. hydrophobic, electrostatic, dipoles, which determine the structural features of the formed transient network and in turn its rheological properties.