I have been following the paper https://doi.org/10.1039/C7NR06732A to synthesize them, but I could not synthesize microgels with a Polydispersity Index of less than 0.01. My microgels have a Polydispersity Index of 0.05 and an average hydrodynamic diameter of 750 nm, and zeta potential is also less, -2 mV. I first dissolved 0.25 g NIPAM and 0.009 g BIS in 20 ml of DI water under continuous stirring at 150 rpm in a nitrogen gas atmosphere at 70-degree temperature. After 30 minutes, I added 0.02 g KPS dissolved in 1 ml of DI water to the solution and let the reaction continue for 6 hours. Then it was cooled to room temperature and continuously stirred for 12 hours. Finally, I found that some portions of the polymer precipitated and some amounts dispersed in DI water.
Practice and luck.
The authors may have made ten different batches with only one having a PDI less than 0.01.
Years ago, the PhD group I was in had many projects concerned with making microgels. Most people struggled to get good PDI values at first. It came with practice.
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