Triblock copolymers were synthesized by ATRP with a poly(acrylic acid) (PAA) central block and random copolymer end blocks containing both AA and n-butyl acrylate (nBA) units. Self-assembly in aqueous solution was investigated over a wide range of concentrations. The degree of ionization of the AA units (α) was varied between 0.1 and 0.9 by varying the pH. The dynamic mechanical properties of the systems were investigated using oscillatory shear measurements. With increasing pH a transition from frozen hydrogels to dynamic networks was observed at pH = 5.2 (α = 0.30). The dynamic polymer networks behaved as viscoelastic liquids with a terminal relaxation time that decreased over 7 decades with increasing pH. This remarkable feature enables fine-tuning and control of the rheology.

We have studied the self-assembly of aqueous dispersions of amphiphilic di- and triblock copolyelectrolytes using static and dynamic light scattering. The hydrophobic blocks contained both ionisable and hydrophobic units rendering the association dynamic and thus ensuring that thermodynamic equilibrium was reached. The incorporation of ionisable units into the hydrophobic blocks caused the self-assembly to be strongly influenced by the pH and the ionic strength. As in the case of neutral block copolymers, diblock copolyelectrolytes self-assembled into star-like micelles and triblock copolyelectrolytes formed flower-like micelles. The latter was not predicted to occur for block copolyelectrolytes. At higher concentrations a system spanning network was formed. The structure of the systems could be quantitatively described by a model of purely repulsive spheres for the diblocks and attractive spheres for the triblocks. The polyelectrolyte effect expressed itself by a sensitivity of the structure to the pH and the ionic strength. The attraction increased with decreasing pH and increasing ionic strength leading at high ionic strength to phase separation.

The ionization behavior of an amphiphilic diblock copolymer poly(n-butyl acrylate(50%)-stat-acrylic acid(50%))(100)-block-poly(acrylic acid)(100) (P(nBA(50%)-stat-AA(50%))(100)-b-PAA(100), DH50) and of its equivalent triblock copolymer P(nBA(50%)-stat-AA(50%))(100)-b-PAA(200)-b-P(nBA(50%)-stat-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(nBA(50%)-stat-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(nBA(50%)-stat-AA(50%))(100) was stronger at higher ionic strength. Remarkably, the covalent bonds between the PAA and P(nBA(50%)-stat-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.