Miniemulsion polymerization involves the use of an effective surfactant and co-stabilizer system to produce very small (100-500 nm) monomer droplets. The co-stabilizer must be hydrophobic enough to retard monomer diffusion from the smaller droplets to the larger. The objective for this study is to investigate the kinetic behaviors for both monomer styrene (ST) and co-stabilizers and also to study the monomer size degradation upon aging with respect to different reactive co-stabilizers.
The high levels of co-stabilizers concentration for both stearyl methacrylate (SMA) and lauryl methacrylate (LMA) were used as variables where the mass ratio of ST/SMA was 1:1, 2:1 and 4:1 whereas 1:1, 2:1, 4:1, 8:1, 16:1 and 50.4:1 for ST/LMA. The surfactant (SLS) was kept constant at 5 mM which is slightly below its critical micelle concentration (CMC) to avoid the formation of micelles. Dynamic Light Scattering (DLS) technique was used to determine average particle size. UV and FTIR spectrometer were used to determine individual conversion of styrene and SMA/LMA.
The Ostwald ripening rate showed the insignificant value when SMA was used as co-stabilizer. The Ostwald ripening rate decreased significantly with increasing of ST/LMA ratio from 50.4:1 up to 4:1, but it slightly increased at ST/LMA ratio 2:1 and 1:1. The polymerization rate for both SMA and LMA were faster than ST. The increasing of co-stabilizer concentrations retarded the polymerization rate of ST. Only Interval I and III was shown during polymerization for all systems. For miniemulsion polymerization of ST/SMA, the particle size decreased to minimum value at early stage and then level off. But it increased when LMA was used as co-stabilizer for all system except 20 mM of LMA. The average reactivity ratio of SMA and ST was 16.66 and 0.7958, respectively where it was calculated using Finemann-Ross, Inverted Finemann-Ross and Kelen-Tudos method. The average reactivity ratio for ST/LMA system was also investigated using the same methods where reactivity ratio of LMA and ST was 9.3411 and 0.082, respectively.

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