Controlled Grafting Density of Zwitterionic Polymer Brushes for Enhanced Antifouling Properties of Polymer Particles

Polymer particles are widely used in biomedical applications as a latex, in which antifouling properties are essential for minimizing nonspecific biomolecular adsorption. In this study, polymer particles grafted with zwitterionic polymer brushes at controlled densities were prepared to suppress nonspecific adsorption. Particles bearing atom transfer radical polymerization (ATRP) initiators were synthesized via emulsifier-free emulsion polymerization via a mixture of ATRP inimer and dummy inimer. The surface-accessible ATRP initiator density, quantified by fluorescence labeling, was tunable by varying the inimer feed ratio. Poly(2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate) (PMPC) brushes were grown from the particle surfaces and free ATRP initiator in solution via surface-initiated activator generated by electron transfer ATRP (SI-AGET ATRP) in a methanol/water mixture using tris[2-(<i>N</i>,<i>N</i>-dimethylamino)ethyl]amine as a ligand. The free polymer showed a linear increase in the number-average molecular weight with conversion and relatively low dispersity (<i>M</i>_w/<i>M</i>_n = 1.25-1.30), confirming well-controlled polymerization. The grafting density of the resulting brushes on the particles was correlated with the surface-accessible ATRP initiator density. The antifouling performance, evaluated by quantifying bovine serum albumin adsorption, indicated that the particles coated with high-density PMPC brushes (0.11 chains/nm²) exhibited significantly reduced nonspecific adsorption compared with those coated with lower-density brushes. Both controlled SI-AGET ATRP of MPC and high-grafting density were essential for producing polymer particle surfaces with significantly effective antifouling properties. This approach enables the facile fabrication of antifouling polymer particles for highly sensitive diagnostic methods and precise bioseparation.