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 lengths (“stickers“) of poly(dehydroalanine) (PDha). As PDha is a polyampholyte we were mainly interested in the pH-dependent 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 µm.