Grade Selection
As mentioned above, the efficiency of grafting CELLOSIZE™ to a polymer during emulsion polymerization varies based on the reactivity of the monomer toward radical intermediates. Knowing how the monomers in a system will effect HEC allows for the selection of a grade with the optimal chemical structure. When an optimal grade is used it lowers the amount of stabilizer ingredients (both surfactants and protective colloids) providing a reduction in raw material cost and lower water adsorption of the latex.
Vinylic Systems
Vinylic monomers like vinyl acetate and vinyl versatate have a relatively low reactivity toward radical intermediates. This means that HEC radicals generated in systems containing only vinylic monomers will prefer the degradation route. In vinylic systems it is preferable to use CELLOSIZE™ EP 09 as the protective colloid. This grade has a different hydroxyethyl substitution pattern that reduces the tendency for cleavage and promotes the grafting reaction.
Acrylic Systems
Acrylic monomers like methyl methacyrlate, butyl acrylate, and 2-ethylhexyl acrylate are extremely reactive toward radical intermediates. These systems favor the grafting route for HEC radicals. This high degree of grafting can result to latex particle bridging if the reaction conditions are not properly controlled. This ultimately lends to latex agglomeration. In these systems it is recommended to use a lower molecular weight grade like CELLOSIZE™ EP 09, QP 300, or QP 4400. It is also recommended to use much less CELLOSIZE™ than vinylic systems (0.2% maximum) and to add the HEC to the system near the end or after the addition of the monomers.
