The Fundamentals of Admicellar Polymerization

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Abstract - Grady - 9521985 A process called admicellar polymerization has been developed which can be used to form a very thin layer of polymer on a surface via a surfactant template. In this process a polymer is formed in the hydrophobic region of a surfactant bilayer absorbed on the surface. Through a cooperative research effort between PPG Industries and the Institute of Applied Surfactant Research at the University of Oklahoma, it has been shown that admicellar polymerized styrene-diene copolymers formed on a commercial precipitated silica significantly improve the properties of the silica as a filler for a rubber which serves as a model for automobile tires. Silica-filled tire treads may have advantages over normal carbon black filled tire treads, such as lower heat buildup and improved resistance to chipping/chunking. Silica-filled treads can also have a lower rolling resistance leading to better fuel economy and reduced emissions of greenhouse gases, while also having improved traction on wet pavement. These tires have not been popular because use of a costly organosilane coupling agent and increased mixing times are required. Admicellar polymerization might offer a mechanism for producing a silica-filled tread with these same performance advantages, yet a coupling agent is not required. The objectives of this research are to: (1) develop a kinetic expression for admicellar polymerization, (2) understand the effect of polymer composition on the improvement in filler properties, and (3) determine the relationship between silica pore structures and admicellar polymerization. To address the first objective, model surfaces will be used to isolate the kinetic problem from the pore diffusion problem. Since admicellar polymerization superficially resembles emulsion polymerization, Smith-Ewart kinetics will provide the theoretical starting point. The second objective is motivated by the fact that a silica modified with a styrene-diene copolymer has better filler properties than a silica modified with either homopolymer. The third part of the project will explore pore structure effects using controlled pore-size precipitated silicas in combination with scattering and liquid adsorption measurements to quantify changes in pore size.