High Solids Hydroxy‐TEMPO Mediated Radical Semibatch Emulsion Polymerization of Styrene

Stable polystyrene latexes having controlled molecular weight distribution (MWD) with solids contents up to 40 wt% are obtained using potassium persulfate as initiator with the nitroxides 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (hydroxy‐TEMPO) and 4‐amino‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (amino‐TEMPO). Using different concentrations of styrene (St) in the nucleation step, it is possible to create colloidal dispersions with particle size ranging from ≈57 to ≈390 nm, conversions up to ≈96%, nitroxide efficiencies (NEff) up to ≈0.76, and number average molecular weight (Mn) ranging from ≈10 000 to ≈85 000 g mol−1. The effect of the monomer feed rate in the semibatch step is also studied. These polymerizations do not require a separate macroinitiator synthesis, since this is formed in situ during the heating ramp. A mathematical model is used to compare the mechanistic understanding of the system with the experimental results. A process for producing stable polystyrene latexes via a high‐solids (40 wt%) ab initio semicontinuous emulsion polymerization controlled with 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl, suited for industrial scale‐up, is reported. Monomer conversions up to 96% (5–12 h) and average molecular weights of 10 000–85 000 g mol−1 are achievable. A mathematical model of the process is used to analyze the experimental results.