Homogeneous Reversible Addition Fragmentation Chain Transfer Synthesis of Amphiphilic Poly(Styrene-b-Acrylamide) Copolymers and Their Solution Characterization: a Thermogelating and Salinity Resistant Viscosifier from Largely Available Monomers

Even though styrene and acrylamide are among the most abundant monomers, their copolymers are understudied due to the difficulties connected to their synthesis, especially if well-defined structures are desired. This study explores the synthesis and solution properties of poly(styrene-b-acrylamide) block copolymers. We report for the first time the synthesis of such diblock copolymers with RAFT polymerization in homogeneous conditions, utilizing DMSO as a common solvent. Despite their nonpolyelectrolyte nature and a very low content of the hydrophobic comonomer, poly(styrene-b-acrylamide) diblock copolymers have been found to be remarkably good viscosifiers for water. Gelation concentration as low as 1 wt % was observed for copolymers containing as little as 1 mol % of styrene constituting a block less than 10 repeat units long. An irreversible gelation upon heating was observed according to a new mechanism of microgel particle hydration, which is proposed for applications in the fields of biomaterials and 3D printing. The properties are speculated to arise from strong hydrogen bonding within the PAM domains. Amid the current growing focus on polyelectrolytes, this work highlights ubiquitous acrylamide as a building block in nonpolyelectrolyte block copolymers for design of smart soft materials.