Aqueous solution self-assembly of polystyrene-b-poly(l-lysine) diblock oligomers

This paper reports on the dilute, aqueous solution self-assembly of two asymmetric polystyrene-b-poly(l-lysine) (PS_nPK_m) diblock oligomers with PS and PK number-average degrees of polymerization of eight, respectively, 40 and 60. The self-assembly of these diblock oligomers was investigated using static and dynamic light scattering in combination with analytical ultracentrifugation. Direct dissolution of the diblock oligomers in water generates a mixture of solution assemblies, part of which is cylindrical or rod-like in nature according to the light scattering experiments. This is surprising given the highly asymmetric nature of the diblock oligomers. Additional experiments in which the sample preparation conditions were varied and sample solutions subjected to a thermal treatment or prepared via dialysis from an organic/aqueous solution, however, suggest that direct dissolution results in kinetically trapped assemblies, which are (partially) converted into thermodynamically more favored assemblies upon varying the sample preparation conditions.