Ionization Of Amphiphilic Acidic Block Copolymers

The ionization behavior of an amphiphilic diblock copolymer poly­(<i>n</i>-butyl acrylate_50%-<i>stat</i>-acrylic acid_50%)₁₀₀-<i>block</i>-poly­(acrylic acid)₁₀₀ (P­(<i>n</i>BA_50%-<i>stat</i>-AA_50%)₁₀₀-<i>b</i>-PAA₁₀₀, DH50) and of its equivalent triblock copolymer P­(<i>n</i>BA_50%-<i>stat</i>-AA_50%)₁₀₀-<i>b</i>-PAA₂₀₀-<i>b</i>-P­(<i>n</i>BA_50%-<i>stat</i>-AA_50%)₁₀₀ (TH50) were studied by potentiometric titration either in pure water or in 0.5 M NaCl. These polymers consist of a hydrophilic acidic block (PAA) connected to a hydrophobic block, P­(<i>n</i>BA_50%-<i>stat</i>-AA_50%)₁₀₀, whose hydrophobic character has been mitigated by copolymerization with hydrophilic units. We show that all AA units, even those in the hydrophobic block could be ionized. However, the AA units within the hydrophobic block were less acidic than those in the hydrophilic block, resulting in the preferential ionization of the latter block. The preferential ionization of PAA over that of P­(<i>n</i>BA_50%-<i>stat</i>-AA_50%)₁₀₀ was stronger at higher ionic strength. Remarkably, the covalent bonds between the PAA and P­(<i>n</i>BA_50%-<i>stat</i>-AA_50%)₁₀₀ blocks in the diblock or the triblock did not affect the ionization of each block, although the self-association of the block copolymers into spherical aggregates modified the environment of the PAA blocks compared to when PAA was molecularly dispersed

Amphiphilic Diblock Copolymers with a Moderately Hydrophobic Block: Toward Dynamic Micelles

Amphiphilic Diblock Copolymers with a Moderately Hydrophobic Block: Toward Dynamic Micelle