Solid State NMR Study of the Interfacial Region in Surface Modired Silica-poly(Methyl methacrylate) Composites

Abstract

Polymer composites are high strength materials made by mixing inorganic fillers nto a polymer matrix. The physical and mechanical properties of composite materials are governed by the adhesion between the two phases. A variety of chemical and physical interactions occurring at the interface is responsible for the inherent properties of these materials. Hence, there is a need to understand the interface of the composite materials. Uniform mixing between the components is necessary to achieve the optimum properties. Research in our lab focuses on the preparation of optically transparent composites by incorporating nanometer size particles of colloidal silica into poly(methyl methacrylate) (PMMA, a commodity plastic). The adhesion between the components can be increased by anchoring on the filler a reactive group, which is also compatible with the polymer. In silicate systems the compounds used to bond the silica to the polymer are called silane coupling agents. We used the silane coupling agent 3(trimethoxysilyl)propyl methacrylate (TPM) to improve the adhesion between the components-a molecular glue that bonds silica to PMMA. NMR spectroscopy is the only technique available to determine molecular structure of an amorphous solid such as the composite. The material is exposed to a strong magnetic field to probe nuclei situated in different environments within the sample. NMR can be used to determine both the molecular structure and molecular mobility within the composite. We found that the composite components were intimately mixed at the molecular level, and the presence of TPM silica does not increase rigidity of PMMA in the composite. This lays the ground work for further studies on these composites to elucidate the chemical interactions that occur at the interface of these materials.