Design and Application of Macro‐<scp>RAFT</scp> Copolymer for <scp>pH</scp>‐Switchable Coagulation and Redispersion Acrylic Emulsions

ABSTRACT A high‐solid‐content emulsion system exhibiting pH‐responsive reversible coagulation and redispersion behavior was successfully developed through reversible addition–fragmentation chain transfer (RAFT) polymerization. The system was constructed using amphiphilic macro‐RAFT copolymers comprising poly(acrylic acid) (PAA) as the hydrophilic block and poly(methyl methacrylate) (PMMA) as the hydrophobic segment. These block copolymers were precisely designed with hydrophilic–lipophilic balance (HLB) values optimized for effective oil‐in‐water (O/W) emulsion stabilization. The influence of the hydrophilic‐to‐hydrophobic ratio in macro‐RAFT copolymers on the stability, rheological properties, and reversible coagulation–redispersion behavior of the resulting emulsions was systematically investigated. Rotational viscometry, gel permeation chromatography (GPC), dynamic light scattering (DLS), and zeta potential measurements revealed that the macro‐RAFT copolymers, when effectively anchored at the oil–water interface, significantly enhanced emulsion stability while maintaining low viscosity and exhibiting excellent reversible solid–liquid transition behavior upon pH modulation. Emulsions stabilized by macro‐RAFT copolymers with extended hydrophilic segments demonstrated remarkably low viscosities (~700 mPa·s) even at a high solid content of 60 wt.%. These emulsions exhibited excellent colloidal stability, as evidenced by zeta potentials consistently maintained below −34.0 mV after five consecutive coagulation–redispersion cycles. Furthermore, the variations in particle size and particle size distribution (PSD) remained within 20% and 10%, respectively, highlighting the system's robust reversibility and structural integrity.