Core‐Fed Methacrylic Acid in Soft‐Core/Hard‐Shell Acrylic Latex: Effects on Colloidal Stability and Waterborne Film Properties

ABSTRACT Methacrylic acid (MAA) is commonly incorporated into the surface region of waterborne acrylic latex particles, where it contributes to surface charge and interparticle interactions. In this study, MAA was introduced solely through the core monomer feed to investigate hows its incorporation at this stage affects polymerization and the properties of the latex‐cast films. Arylic latex particles were synthesized by semi‐continous seeded emulsion polymerization using a poly( n ‐butyl acrylate‐ co ‐methacrylic acid) core feed containing 0–16 wt.% MAA and an MAA‐free poly( n ‐butyl acrylate‐ co ‐methyl methacrylate) shell feed. Increasing the core MAA content increased monomer conversion from 75% to 95%, reduced the coagulum formation and the polydispersity index (PDI), and shifted the zeta potential from −30 to −61 mV. All films exhibited two distinct glass‐transition temperatures ( T g ), indicating phase separation between the core and shell polymers. MAA‐containing films exhibited main derivative thermogravimetric (DTG) peaks 23°C–38°C higher than the MAA‐free film. Tensile strength increased almost threefold, from 2.7 to 7.5 MPa, without a systematic reduction in elongation at break. Meanwhile, the water contact angle increased from 41° to 76°, and the 24 h water uptake decreased from 28% to 18%. Incorporating MAA into the core monomers therefore improved latex stability, thermal stability, tensile strength while reducing water uptake and surface wettability, demonstrating its potential as a formulation variable for soft‐core/hard‐shell acrylic binders.