Synthesis and Interfacial Behavior of Amphiphilic Hyperbranched Polymers: Poly(ethylene oxide)-Polystyrene Hyperbranches

We report the synthesis of novel hyperbranched amphiphilic poly(ethylene oxide)-polystyrene (PEO-PS)n copolymers obtained by controlled radical polymerizations: nitroxide mediated polymerization (NMP) and reversible addition-fragmentation chain transfer (RAFT). The macroinimers used to synthesize copolymers have the general structure AB*, where A stands for PEO with a terminal double bond and B* stands for a PS block with a terminal initiating group (TEMPO or RAFT CTA). Bulk NMP yielded copolymers with higher molecular weight and higher polydispersity. RAFT polymerization in solution gave hyperbranched copolymers with higher molecular weight but lower polydispersity. Langmuir monolayers displayed reversible amphiphilic behavior at the air-water interface. The random, mixed character of short hydrophilic and hydrophobic fragments results in peculiar surface behavior: unlike regular linear and star block copolymers, the amphiphilic hyperbranched macromolecules with higher PEO content are spread at the air-water interface and short PEO fragments are not submerged into the water subphase even at high compression.