Influence of 2‐Hydroxyethyl Acrylate on Network Architecture in Castor Oil‐Based Grafted Hybrid Latexes

ABSTRACT Waterborne polyurethane dispersions (PUDs) derived from castor oil were synthesized and converted into grafted hybrid latexes through emulsion polymerization of styrene and butyl acrylate. 2‐Hydroxyethyl acrylate (HEA) was incorporated during polyurethane synthesis to introduce pendant vinyl functionality for graft‐mediated hybrid formation. Because castor oil has a relatively low average hydroxyl functionality (≈2.7 per triglyceride), variation of HEA content alters the balance between polyurethane network growth and graft‐site incorporation. Thermomechanical and mechanical behavior were evaluated using tensile testing, Mooney–Rivlin analysis, dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy. Moderate incorporation of HEA enhances hybrid integration and improves thermomechanical performance relative to the vinyl‐containing polyurethane. However, at higher HEA concentrations, a compositional threshold is reached at which effective polyurethane strand length is reduced, resulting in measurable changes in particle morphology, cross‐link density, and mechanical behavior. These results demonstrate that competition between castor oil‐derived hydroxyl functionality and HEA‐mediated graft‐site formation governs hybrid network architecture and provides tunable control over grafted hybrid latex performance.