Preparation and characterization of poly(styrene-alt-maleic acid)-b-polystyrene block copolymer self-assembled nanoparticles

Block copolymers poly(styrene-alt-maleic anhydride)-b-polystyrene (P(St-alt-MAn)-b-PSt) were synthesized via radical addition fragmentation chain transfer copolymerization. The maleic anhydride-containing segments of the block copolymer were hydrolyzed to form amphiphilic poly(styrene-alt-maleic acid)-b-polystyrene (P(St-alt-MA)-b-PSt). In aqueous solution, P(St-alt-MA)73-b-PSt81 and P(St-alt-MA)58-b-PSt130 formed stable dispersed spherical aggregates of approximately 25 and 40 nm, respectively. Particle size was stable under alkaline conditions and was little affected by the polymer concentration in the range of 0.025–1.0 mg mL−1. The critical aggregation concentrations of the block copolymer self-aggregates were 1 × 10−3 and 3 × 10−3 mg mL−1 for hydrophobic PSt block lengths of 130 and 81 monomer units, respectively. The nanoparticles had a negative surface charge at pH > 2. Scanning electron microscopy images revealed that particle–particle coalescence did not occur upon drying of the film and the nanoparticles remained discrete. Controlled aspirin release from the nanoparticles was dependent on the structure of the block polymers and release medium.