Dynamics of Acrylic Coupling Agents at Interfaces of Composites

Hyoryoon Jo
Frank D. Blum, Missouri University of Science and Technology

This document has been relocated to http://scholarsmine.mst.edu/chem_facwork/2400

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Most applications of polymers involve composites, wherein a polymer is used in conjunction with another material, typically a solid fiber or filler. A coupling agent can enhance the adhesion between a polymer matrix and an inorganic filler. Organofunctional silanes, RSiX are often used as coupling agents. The methoxy or ethoxy group, X, can typically be hydrolyzed with water and an acid or a base catalyst in a protic solvent. The silanol groups of a hydrolyzed coupling agent can condense with other silanol groups from a glass surface, while the alkyl group, R, blends physically or bonds chemically to the polymer matrix, thereby enhancing adhesion. In addition to their use as coupling agents in mineral-filled organic composites, organofunctional silanes that contain acrylic or methacrylic groups have been applied to the surfaces of organic-inorganic hybrid materials (OIC). Acrylic silanes may also be useful for ultraviolet (UV) coatings because their structures contain acrylic functional groups. Magnetic resonance (ESR and NMR) studies have been especially useful in determining both the structures and the dynamics of interfacial and surface specimens. Since sold state NMR studies are not adversely affected by the presence of solid fillers or the optical clarity of a sample, they are well suited for studies of filled systems. Both NMR and EST have been used to investigate the dynamics of samples at interfaces and on the surface. The line shapes of deuterium solid-echo spectra are governed by molecular dynamics. Blum et al. have studied the mobility of coupling agents such as aminopropyltrimethoxysilane and aminobutyltrimethoxysilane at the air-solid interface using the deuterium line-shape method. In this study the interfacial properties of deuterated 3-acryloxypropyltrimethoxysilane (APMS-d) were investigated using the deuterium wide-line NMR line-shape method. The motion of the deuteron placed on an acrylic polymer backbone was investigated. A sample having monolayer coverage of APMS-d on a silica surface was polymerized with methyl acrylate (MA), and an organic-inorganic hybrid material was prepared with MA, APMS-d, and tetramethoxysilane. Spectra of these polymerized samples showed relatively slower motion of the polymer backbone.