pH Induced Desaggregation Of Highly Hydrophilic Amphiphilic Diblock Copolymers

P(nBA(20%)-stat-AA(80%))(100)-b-PAA(95), an amphiphilic diblock copolymer consisting of a pure hydrophilic poly(acrylic acid) (PAA) block and a weakly hydrophobic statistical copolymer of n-butyl acrylate (nBA) and acrylic acid (AA) was prepared by ATRP. Kinetic studies revealed that the polymerization was well controlled, leading to a perfectly defined diblock copolymer both in terms of chemical composition and block lengths. This polymer was characterized in aqueous solution by means of light and neutron scattering experiments. In spite of its weak hydrophobic nature, P(nBA(20%)-stat-AA(80%))(100)-b-PAA(95) self-assembles in aqueous solution provided the ionization degree of the AA units is kept as low as alpha = 0-10%. Moreover, the relatively large aggregates (N-agg = 100, R-h = 18nm) formed at alpha = 0% molecularly dissolve at alpha > 20%. This pH sensitivity is in strong contrast with the behavior of the more hydrophobic PnBA(90)-b-PAA(100) which forms frozen aggregates insensitive to external stimuli in aqueous solution.