Effect of cyclodextrin on the γ-radiolysis initiated emulsion polymerization of styrene

In emulsion polymerization (EP) of styrene, methyl-β-cyclodextrin (CD) was used to complex the monomer in order to increase its aqueous phase solubility and investigate its effects on kinetics. Although CD is not necessary for successful EP of styrene, the well studied nature of such systems makes them an ideal candidate for elucidating the effects of CD on EP mechanisms. Initiator-free (‘thermal’) and γ-ray-initiated EP experiments were run with and without CD. The thermal entry rate coefficient, ρ thermal , and the exit rate coefficient, k, were evaluated. Thermal entry was found not to be an aqueous phase process; ρ thermal was almost constant with and without CD. On the contrary, k was found to change in the presence of CD, especially for a cationically stabilized latex, with which k increased at 50 °C from 7.00 × 10−3 s−1 without CD to 1.18 × 10−2 s−1 with 4% CD. This result confirms that exit is an aqueous phase process and it highlights the accuracy of the entry model used for the analysis, which assumes that exit rate is proportional to the aqueous phase solubility of the monomer. Anionically stabilized latex did not show similar behavior in the presence of CD; this may be because of monomer-surfactant competition for CD cavities.