Surface encapsulating UV filters based on self-assembly of an amphiphilic random copolymer by miniemulsion polymerization

A nanoparticles encapsulating UV filters were prepared by miniemulsion polymerization, in which methyl methacrylate (MMA) as the monomer, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. Scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS) confirmed that the amphiphilic random copolymers poly (styrene-co-methacrylic acid) P(St-co-MAA) not only acted as the stabilizer but also self-assembled on the surface of the P(MMA-EGDMA) polymers. During the miniemulsion polymerization, most UV filters were encapsulated in the P(St-co-MAA) self-assembly aggregates on the surface of nanoparticles, giving the nanoparticles a raspberry-like structure. As the mass ratio of P(St-co-MAA) to MMA and EGDMA at 1.0, the encapsulation efficiency of UV filters was 69.85%, whereas 70.7% of UV filters were located in the P(St-co-MAA) self-assembly layer. The leakage of UV filters from the raspberry-like nanoparticles was negligible after continuous stirring in isopropyl myristate (IPM) for 24 h. The sun protection factor (SPF) and UVA Protection Factor (UVAPF) value of sunscreen formulation incorporated with the raspberry-like nanoparticles could reach 58.8 and 6.82, respectively. It enhanced UV protection more efficiently than the nanoparticles with a smooth surface.