Double hydrophilic poly(ethylene glycol)-block-poly(dehydroalanine) four-arm star block copolymers: synthesis and solution behavior

Star-shaped block copolymers are of interest as versatile and highly functional polymeric building blocks and show interesting solution properties or self-assembly. Herein, we report the synthesis of novel, double hydrophilic four-arm star-shaped block copolymers, based on different poly(ethylene glycol) cores (PEG) and short blocks ("stickers") of polydehydroalanine (PDha). As PDha is a polyampholyte we were mainly interested in the pH-dependent solution behavior, which we characterize by dynamic light scattering (DLS), atomic force microscopy (AFM), potentiometric titration, and zeta potential measurements. Our main interest was to elucidate how the presence of a short (6-7 units) or intermediate (up to 41 units) PDha segment influences the solution properties of such double hydrophilic block copolymers depending on the solution pH. As we can show, even short "stickers" show a profound influence and lead to increasing aggregation tendency at low pH values, as demonstrated by DLS and AFM experiments with aggregate sizes beyond 1 mu m.