Copolymerization of styrene and butadiene monomers via miniemulsion

Miniemulsions of styrene and butadiene comonomer mixtures were prepared using a two-step method: first, the miniemulsion of styrene monomer was obtained using sodium lauryl sulfate (SLS) as surfactant and hexadecane as cosurfactant; then, the butadiene monomer was charged into the sealed calorimeter reactor (RC1) with the styrene miniemulsion. The butadiene monomer was let to diffuse into the styrene monomer droplets to make a homogenous comonomer system.; The kinetics of the miniemulsion and conventional emulsion copolymerization of styrene and butadiene monomer mixtures were compared. The miniemulsion copolymerization showed a slower polymerization rate with larger average particle sizes compared with the corresponding conventional emulsion polymerization system. The rate of copolymerization and the number of final latex particles were found to have different dependences on the initiator and surfactant concentrations for each copolymerization process.; The kinetics of the copolymerization showed differences between the miniemulsion and conventional emulsion polymerization in terms of nucleation mechanisms: In the miniemulsion polymerization the particles nucleated mainly in the monomer droplets, while in the conventional emulsion polymerization the nucleation took place primarily in the monomer-swollen micelles. The different monomer concentration profile at the nucleation sites resulted in the differences in initial heat of reaction.; The evolution of the copolymer composition was also found to be different between these two methods. The miniemulsion copolymerization system has more butadiene monomeric units in the copolymer backbone than the corresponding conventional emulsion copolymerization. The glass transition temperatures of the copolymers were consistent with this.; The gel fraction results showed that the miniemulsion copolymerization has a lower gel fraction value than the conventional emulsion copolymerization at the same conversion level, indicating that the miniemulsion copolymerization can delay the gel formation to a higher conversion levels.; The pressure of the system was recorded automatically during the reaction process. The data were analyzed based on thermodynamics. These data can be used for calculation of the fractional conversion and the monomer composition in the monomer phase and in the copolymer. The results showed that the calculated values were close to the experimental results.