The effect of the dry glass transition temperature on the synthesis of paraffin microcapsules obtained by suspension‐like polymerization

PRS® paraffin wax was encapsulated by means of suspension‐like copolymerization of methyl methacrylate (MMA) with butyl acrylate (BA). The effects of the polymeric shell dry glass transition temperature ( T g ) and the reaction temperature ( T r ) were then studied. Additionally, the evolution of particle diameter, molecular weight, conversion, and T g during polymerization was also researched. The chemical properties of the shell material (acrylic polymer), together with those found in the core material (PRS® paraffin wax), for instance: polarity and interfacial tensions, largely determine whether the morphology of the microcapsules will be thermodynamically favored or not. The high polarity of MMA (γ 0 = 18 mN m −1 ) and BA (γ 0 = 24 mN m −1 ) should provide a thermodynamic driving force to cover the paraffin wax droplet which would result in a core/shell thermodynamically favored structure. However, most systems are defined by kinetics rather than thermodynamics such as the monomers dry T g and T r . It was observed that penetration of polymer radical chains was severely limited when the dry T g was ≥10°C above the reaction temperature, resulting in irregular and undifferentiated particles. However, penetration did occur when the copolymeric shell dry T g was ∼10°C below the reaction temperature which led to uniform and spherical particles being synthesized. POLYM. ENG. SCI., 54:208–214, 2014. © 2013 Society of Plastics Engineers