I think the amount of KPS is too high. It's probably flocculating the SDS. Maybe try reducing it to 1/5 of the original amount. Or better yet, use ammonium persulfate instead of KPS. Please let me know how it works out.

Common mistakes in styrene emulsion polymerization include insufficient emulsifier concentration, too high reaction temperature, and excessive stirring speed causing bubble entrapment and coagulum formation. Proper control of emulsifier amount, reaction temperature (around 70-75℃), and moderate stirring is essential for stable emulsions without solid aggregates or surface bubbles.

I agree with Xian, it seems that polymerization rate is too high in your system. Try to decrease concentration of KPS and lower reaction temperature.

A common flawed scheme involves charging all ingredients (water, surfactant, initiator, and full monomer charge) at once and heating. This approach is incorrect and leads to failure due to three main issues:

Improper Nucleation: Adding all monomer initially creates large droplets that compete with micelles for radical capture, resulting in unstable, broad particle size distribution and coagulum (lumps).

Incorrect Initiator: Using an oil-soluble initiator (e.g., AIBN) instead of a water-soluble one (e.g., potassium persulfate, KPS) prevents radical generation in the aqueous phase, which is essential for proper particle nucleation via micellar entry.

Thermal Runaway & Instability: The reaction is highly exothermic. A full monomer charge risks a dangerous temperature spike, and the surfactant concentration may be insufficient to stabilize the rapidly growing particles, causing coagulation.

The correct approach is a semi-batch process: Deoxygenated water, surfactant (above the CMC), and buffer are heated first. The monomer and initiator are then gradually fed into the reactor. This ensures monomer polymerizes primarily within established particles, ensuring control over heat generation, particle size, and colloidal stability.

Did you redo the experiment with your initial amount of KPS at lower temperature? I am curious about the outcome. Thanks.