Synthesis and characterization of polystyrene-b-poly(vinyldipicolinic acid) pH-responsive core-shell nanoparticles

The self-assembly of a new series of amphiphilic polystyrene-b-poly(4-vinyldipicolinic acid) PS-b-PVDPA diblock copolymers in aqueous solution is reported in order to obtain core-shell nanoparticles composed of a PS core and a PVDPA shell. Diblock copolymers were synthesized by Supplemental Activation Reducing Agent-Atom Transfer Radical Polymerization (SARA-ATRP) with a degree of polymerization (DP) of the PS block in the range 112-260 and a DP of PVDPA block of 10, 30 or 50. Anionic latex nanoparticles of PS-b-PVDPA were prepared by solvent displacement methods. All the nanoparticle suspensions had a narrow size distribution (0.014 <= PDI <= 0.144) with zeta potential in the range -27 mV to -38 mV indicating electrostatic repulsions due to carboxylate anions and therefore high colloidal stability. DLS was used to determine nanoparticle size, with SEM and TEM used to determine and confirm both size and spherical shape. All three methods found the size for these nanoparticles to be in the range 75-120 nm. Using fluorimetry and DLS methods, Critical Aggregation Concentration (CAC) for each type of nanoparticle was determined to be within the range of 33-69 mg/L. Micelles were pH-responsive with stability in aqueous conditions for pH > 3.5. Micelles were stable at pH 5.5 for up to 40 days and at temperature up to 60 degrees C.