Highlighting the Role of the Random Associating Block in the Self-Assembly of Amphiphilic Block-Random Copolymers

pH-sensitive random P(nBA(1-x)-stat-AA(x))(100) (MHx) and block random P(nBA(1-x)stat-AA)(100)-b-PAA(100) (DHx) amphiphilic copolymers have been synthesized, where x stands for the molar ratios of pH-sensitive hydrophilic acrylic acid (AA) units statistically distributed with hydrophobic n-butyl acrylate (nBA) ones within the random block. Static and dynamic light scattering revealed that self-assembly of the random associating block (MHx) and block random (DHx) copolymers is strongly affected by the pH and ionic strength of the solution and also by the amount of AA units within the MHx blocks. Below a characteristic pH, MHx self-assembles into finite size spherical particles that grow in size with decreasing pH until they eventually become insoluble. DHx self-assembles into similar spherical particles, but the hydrophilic PAA(100) corona surrounding the MI-Ix core prevents insolubility at low pH. Self-assembly of DHx at higher pH is fully correlated to that of the neat MHx blocks, indicating that it is possible to control precisely the extent of self-assembly of diblock copolymers by tuning the hydrophobic character of their associating block. Here this was done by controlling the fraction of charged units within the random associating block.