Amphiphilic\nBlock–Random Copolymers: Mapping\nthe Boundaries of Aqueous Self-Assembly

The structure–property relationships of polystyrene-<i>b</i>-poly(styrene-<i>r</i>-(acrylic acid)) block–random\ncopolymers in aqueous media have been investigated. A library of copolymers\nwith varied degree of polymerization of the hydrophobic polystyrene\nblock, varied mol % acrylic acid (AA) in the hydrophilic block, and\nvaried volumetric block ratios was designed. Rather counterintuitively,\nit was discovered that PS-<i>b</i>-(PS-<i>r</i>-PAA) block–random copolymers containing relatively low amounts\nof AA in the hydrophilic block disperse much more readily than those\ncontaining higher amounts of AA, despite the decrease in the hydrophilic\nmonomer content. Dispersible copolymers were examined in terms of\ntheir critical aggregation concentration, aggregation number, and\nparticle size of aggregates in relation to their structure. A change\nin interblock interaction parameters is proposed for the differences\nin dispersion behavior between copolymers containing relatively low\nand high amounts of AA in the stabilizing block. The findings of this\nstudy will not only inform their use as stabilizers in emulsion polymerization\nbut shed light on using highly hydrophobic block copolymers to make\nsmall aggregates of a tunable size.