Decrease of methyl methacrylate miniemulsion polymerization rate with incorporation of plant oils

Abstract

Miniemulsion polymerization reactions of methyl methacrylate were conducted in the presence of plant oils, in order to investigate the effect of different types (linseed oil and andiroba oil) and amounts of oils on the polymerization reaction rates and on the molecular weight of the produced polymers. A decrease in the reaction rate, that was proportional to the number of double bonds present in the triglycerides, was observed. Polymers with lower molecular weights were obtained when triglycerides with higher number of double bonds were used. The experimental data were analyzed with a mathematical model developed to represent the kinetics of these reactions, including the kinetic mechanisms associated to free radical miniemulsion polymerization with an oil‐soluble initiator, and the model was able to predict the variation in the polymerization reaction rate depending on the type and amount of the plant oil.Practical applications: Plant oils can be incorporated to polymer latex by free radical miniemulsion polymerization partially substituting petroleum derived monomers. As most plant oils are highly hydrophobic, they act as co‐stabilizers preventing diffusional degradation increasing the stability of the colloidal dispersion. The growing polymer chain can react with the double bonds of the triglyceride molecules resulting in grafting. The grafting increases the compatibility between the polymer and the plant oil. However, the polymer molecular weight and the reaction rate decrease when the amount of unsaturated oil increases. A mathematical model was developed taking into account both addition and chain transfer mechanisms to describe the grafting reactions with the plant oils. The model can predict the variation in the polymerization reaction rate depending on the type and concentration of the plant oil in the reaction medium which helps to understand the mechanisms involved and to optimize formulations and operational conditions of polymerizations in the presence of plant oils.Polymerization rate decreases when plants oils are incorporated in PMMA nanoparticles.