FT-IR Studies of Stereo Regular PMMA on Silica: Drying Effects
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A great amount of work has been done on the configuration of surface adsorbed poly(methyl methacrylate) (PMMA), especially on surfaces to which they have a strong attraction. Some studies have been make on the relationships between configuration and tacticity, molecular weight, adsorbed amount, and density of surface hydroxyl groups. The effect of tacticity on the conformation of alumina-adsorbed PMMA in solution and dry spin-coated films were studied by Grohen et al. Their results showed that surface-adsorbed PMMA chains adopted a relatively flat configuration, but iso-PMMA (isotactic) adsorbed on aluminum, with a much larger fraction of the bound carbonyl groups, had a flatter configuration than syn-PMMA (syndiotactic) and a-PMMA (atactic). They attributed this phenomenon to the chain segmental rearrangements6 which may allow iso- PMMA to favor the establishment of interfacial acid-base bonds, while local stiffness of the tt state of the syn-PMMA does not. Compared to interfacial conformation studies of liquid state and dry PMMA films, less work has been done to understand the effect of the drying process that could have a crucial impact on film properties in the dry state. Prest and Luca proposed that the preferential alignments of chains on the planes of the films occured as a result of the competing effects of the rapidly increasing relaxation times of the concentrating solution and the time scale of the contraction process as the films dried. As more solvent is lost, the increased viscosity increases the relaxation times of the molecules and reduces their ability to respond to the constantly decreasing film volume. At some point, the longest relaxation times exceed the effective time scale of the collapsing film so that the molecules are no longer able to relax in their new state. In the present paper, ultra-thin stereoregular PMMA films were adsorbed on silica particles. FT-IR was used to observe the interaction between the surface-bound PMMA and the silica surface following various drying processes.