Silicone stabilized poly(methyl methacrylate) nonaqueous latex 2. Flocculation by degradation of the steric layer

The steric stabilization layers on silicone stabilized poly(methyl methacrylate) latexes, dispersed in heptane, were slowly degraded resulting in latex flocculation. These experiments were conducted to obtain measurements of the minimum amount of steric stabilizer chains required for colloid stability in good solvent conditions for the steric stabilizer. The silicone was degraded by equilibration chemistry with acidified montmorillonite as the catalyst. The total amount of silicone on the latex at the flocculation point was determined by NMR. The average critical (i.e., minimum) chain length for stable latex in heptane at 70°C, expressed as the number of (CH3)2SiO units, was ⩽164 for a latex with 1.9 × 1017 silicone-PMMA attachments per square meter, and was ⩽191 for a latex with 1.7 × 1017 attachments. Results of simple theoretical models imply the critical chain lengths should have been in the range 20 to 30. The uncertainty in the interpretation of the experimental results was due to the possible presence of silicone in the centers of the latex particles.