Comparing polyelectrolyte complexes formed from linear polycations and linear, star, and bottlebrush polyanions

Polyelectrolyte complexes form by the interactions between linear polyanions and polycations systems have been the subject of much research. Some limitations of linear commercial homo-polyelectrolyte are related to charge density and ion pairing density. Using synthetic bottlebrush (BB-) and star (s-) homo-polyelectrolytes, the ion charge density will be significantly increased and the architecture of the polymer will strongly influence the spatial distribution of charges locally and globally. In addition, the anchoring of multiple charged chains to a single backbone or a single junction point may also affect the accessibility of charges along the “bristles” or the arms due to the proximity of other charged chains. We use ring opening metathesis polymerization (ROMP) to synthesize star and bottlebrush polyanionic polyacrylic acid, s-PAA, and BB-PAA, respectively. Titration of the s-PAA and BB-PAA allowed us to assess the pKa of these polymers, providing insight into the accessibility of the charges. By mixing L-PAA, s-PAA, or BB-PAA into the aqueous solution of polyethylene glycol (PEG) and dextran (DEX), and linear polyallylamine hydrochloride (L-PAH) into an aqueous solution of PEG and DEX, where the PEG and DEX solution concentrations were set to binodal concentrations at the termini of the tie line of the phase diagram. This allowed the L-PAA, s-PAA, or BB-PAA and the L-PAH to diffuse across the interface of this aqueous two-phase system absent phase separation of the solutions comprising the solutes. Using DLS/SLS, optical and fluorescence microscopy, and turbidity the characteristics of the L-PAH/L-PAA, L-PAH/s-PAA, and L-PAH/BB-PAA complexes were compared.