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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 (Tg) and the reaction temperature (Tr) were then studied. Additionally, the evolution of particle diameter, molecular weight, conversion, and Tg 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 (γ0 = 18 mN m−1) and BA (γ0 = 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 Tg and Tr. It was observed that penetration of polymer radical chains was severely limited when the dry Tg was ≥10°C above the reaction temperature, resulting in irregular and undifferentiated particles. However, penetration did occur when the copolymeric shell dry Tg 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