Free-Radical Emulsion Copolymerization of Ethylene and Butyl Acrylate Monomers: Synthesis, Properties, and Application

This work presents a novel approach for synthesizing ethylene–butyl acrylate (PEBA) copolymers via free-radical emulsion polymerization under high-pressure conditions, using ammonium persulfate (APS) as the initiator. Unlike conventional emulsion systems limited by poor ethylene solubility, we employed a high-pressure autoclave to systematically explore the influence of temperature (60, 70, and 80 °C), ethylene pressure (15, 20, and 25 bar), and butyl acrylate (BA) concentration on ethylene incorporation and resulting copolymer properties. Nuclear magnetic resonance (¹H and ¹³C NMR) analysis confirmed that increasing both temperature and pressure significantly enhances ethylene incorporation into the polymer backbone. The resulting copolymers exhibited a marked reduction in glass transition temperature (T_g) from – 43.9 °C in PBA to as low as – 49.7 °C alongside improved thermal stability, with decomposition temperatures exceeding 400 °C. Morphological studies via SEM and TEM revealed the formation of semi-cylindrical micelle structures with rough surface textures, indicative of structural rearrangement due to copolymerization. Importantly, the synthesized PEBA copolymers were blended with high-density polyethylene (HDPE), leading to a notable increase in storage modulus up to 15 wt% addition, thereby demonstrating potential as mechanical performance modifiers. Water contact angle measurements showed enhanced hydrophobicity (up to 95.5°), suggesting promising applications in water-repellent coatings and polymer blend compatibilization. This work offers a scalable alternative to coordination and controlled radical polymerizations for producing functionalized polyolefins with tunable properties under high-pressure emulsion conditions.