SURFACE-INITIATED ATOM TRANSFER RADICAL POLYMERIZATION OF MAGNETO-OPTICALLY ACTIVE NANOCOMPOSITES: ROLE OF RANDOM COPOLYMERS FOR HIGH VERDET CONSTANT MATERIALS

Abstract

Magneto-optically active materials play a crucial role in detection of weak magnetic fields produced by biological systems and are a key component in optical communications systems. Michael Faraday discovered that applications of magnetic field to a lead-doped piece of glass induced rotation of linear polarized light propagating through the glass in 1845. This is now known as the Faraday effect and the strength of this effect is described by the Verdet constant; a wavelength and compositionally dependent quantity. Currently, inorganic crystals containing paramagnetic ions are used to rotate light in traditional systems; however, processing limitations and low Verdet constants require new materials to be explored. In previous work, a new approach in fabrication of high-Verdet material was done by utilizing a matrix of polymer coated cobalt ferrite nanoparticles (CoFe2O4) and high molecular weight polystyrene to fabricate magneto-optically active films.1 In this work, we have a similar end goal however the matrix is made up using surface-initiated atom transfer radical polymerization (SI-ATRP) with cobalt nanoparticles (CoNPs) and a varying amount of two monomers to effectively attempt to improve physical properties. This was done by comparing SI-ATRP with pure methyl methacrylate (MMA) to copolymers that contain small amounts of n-butyl-acrylate (nBA) to introduce rubbery components to a glassy matrix. Three SI-ATRP reactions were performed, one with pure MMA and two copolymerizations with MMA and nBA that had a target composition of 90:10 and 70:30 (MMA: nBA). From this research, we found that as the polymer had a higher molar ratio of nBA, the melt pressed thin films became more brittle and less transparent. This effected our measurement of Verdet, specifically in the 70:30 sample, which could not be measured. However, we found that the 90:10 (MMA-r-nBA) sample had a Verdet constant of 119,800 °/Tm comparative to the control sample of pure MMA, which had a Verdet constant of 84,360 °/Tm. Further polymer and composite characterization was analyzed using size exclusion chromatography (SEC), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC).