Free-radical emulsion copolymerization of styrene/1-hexene in an autoclave: Synthesis and property evaluation

A copolymer based on styrene and 1-hexene was synthesized using free-radical emulsion polymerization. Reaction pressure has a significant influence on copolymer formation. There was a phase separation when styrene was copolymerized with 1-hexene at lower pressure (1 bar) and a stable emulsion was observed under a pressurized reaction (4.5 bar). Additionally, a phase separation was also observed at a lower reaction pH (7.2) and was evidenced by the reduced pH value at the end of the copolymerization. H¹ nuclear magnetic resonance (NMR) spectroscopy analysis showed the disappearance of methylene proton peak intensities in both styrene and 1-hexene after the copolymerization reaction indicating the increased conversion of monomers in emulsion. Synthesized copolymer was also studied using the C¹³ NMR analysis. It was further analyzed by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The emulsion was destabilized by the synergistic action of acid and temperature to recover solid polymer. The applicability of the copolymer as a polymer modifier was studied by blending with commercial PS. Copolymer thermal properties were analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Other properties such as emulsion particle size, droplet morphology, and the effect of pH were also investigated in this study.