Admicellar Polymerization of Polystyrene on Natural Rubber Particles

Admicellar polymerization is a reaction for coating a thin-film of polymer on a surface. The process consists of the polymerization of the adsolubilized monomer in the hydrophobic regions of the surfactant bilayers that adsorbed on the substrate surface. In this research, the admicellar polymerization of polystyrene was carried out using micron to submicron size natural rubber particles as substrates. Cetyl trimethyl ammonium bromide (CTAB) was used to form the surfactant template. The adsorption isotherm of CTAB was determined in the absence and presence of salt. Styrene adsolubilization was found to increase with initial styrene concentration and in the presence of salt. The synthesized polystyrene in the molecular bilayer of micelles surrounding the natural rubber particles was characterized by optical microscope, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The observed morphology of the rubber particles after reaction was clearly two phases, a core-shell structure having the natural rubber core covered by the polystyrene shell. These core-shell particles were spheres and aggregated strongly in the emulsion. Effect of initiator type was investigated. The synthesized products showed core-shell morphology, which was still obtained after heating but after cooling phase inversion occurred and showed polystyrene-rich core and natural rubber-rich shell. Thin lamellar of both components was found in both polystyrene-rich core and natural rubber-rich shell making unique morphology and extended single transition of thermal decomposition. FTIR results show characteristic peaks of natural rubber and polystyrene and the absorbance of styrene increases with increasing styrene content. The TGA result showed that the decomposition temperatures of the products were altered by the amount of polystyrene.