Waterborne latex is often called a product-of-process. Here, the effect of semi-batch monomer feed rate on the kinetics and gel formation in seeded emulsion polymerization was investigated for the copolymerization of n-butyl methacrylate (n-BMA) and ethylene glycol dimethacrylate (EGDMA). The gel fraction was strongly influenced by monomer feed rate, even though most of experiments were run under so called starved-fed conditions. More flooded conditions from faster monomer feed rates, including seeded batch reactions, counterintuitively resulted in significantly higher gel fraction. Kinetic Monte-Carlo simulations indicated that the dominant influence on this phenomenon was the sensitivity of primary intramolecular cyclization to the instantaneous unreacted monomer concentration, which is directly impacted by monomer feed rate. This concept has been explored previously for bulk and solution polymerizations, but not for emulsified reaction environments and especially for very low mole fraction divinyl monomer. In addition, while gel fraction could be dramatically manipulated by variations in linear monomer feed rates, it could be markedly enhanced by leveraging non-linear feed profiles built from combination sequences of flooded and starved conditions.

Mechanistic Study on crosslinking in seeded emulsion polymerization: Effect of monomer feed rate on gel formation

ACS Spring Meeting 2021

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