Collaborative Research: Optical Gradient Polymeric Materials via Isothermal Frontal Polymerization

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The goal of the project is to learn how isothermal frontal polymerization (IFP) can be efficiently used to produce gradient optical materials. IFP is a method of producing polymers in which a localized reaction zone of free-radical polymerization propagates at the rate of about one cm per day through an unstirred solution of monomer and initiator. A "seed" of polymer is placed at the bottom of a cuvette, and a solution of the polymer's monomer with a free-radical initiator is placed over it. The system is maintained at a constant temperature. Polymerization occurs slowly in the bulk solution but much faster in the region of polymer as the monomer swells it because of the gel effect. The overall effect is the slow propagation of a transition zone between polymer and the monomer/initiator solution. Using Laser Line Deflection, we will measure the gradients created during the polymerization of methyl methacrylate and compare these to analytical and numerical models.A gradient optical material is a material that possesses a spatial gradient of an optical property. Two types can be prepared via IFP. One type is Gradient Refractive Index (GRIN) lenses and fibers. The other type is organic optical limiters. The RI gradient can be produced by adding a dopant, with a refractive index different from that of the polymer, to the monomer/initiator solution. The dopant is redistributed by the propagating front to create a dopant concentration gradient and resulting refractive index gradient. Using a nonlinear optical dye as the dopant allows the creation of a concentration variation of this dye in a polymer matrix.Impact:This project will result in a superior understanding of how isothermal frontal polymerization can be used to prepare special materials with useful applications. Gradient refractive index fibers are used commercially for applications in which large amounts of digital signals must be transferred between devices over a short distance. Plastic fiber is cheaper to produce and so this research can help the production of consumer products and fibers for computer networks. Optical limiters are used for protecting human eyes from intense laser pulses. Preparing such devices with polymers can make their weight and cost lower and thus their utility greater.The research will benefit the education of two graduate students. The collaboration between mathematicians and chemists will provide them an important learning experience in collaborative research. Because of the significant number of African-Americans and women at USM, these groups will benefit from this project.