Segmental Dynamics of Poly(Vinyl Acetate)- D₃ Absorbed on Silica by Solid State 2HNMR: Effect of Small Molecule Plasticizer

Rakesh R. Nambiar
Frank D. Blum, Missouri University of Science and Technology

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There has been significant progress in understanding the behavior of polymeric thin films on surfaces. The change in the apparent glass transition temperature (Tg) of supported thin polymer films with thickness (Tg -nanoconfinement effect) has been widely studied over the last fifteen years. While many studies focused on the thickness dependence of Tg, there are other aspects which are important to understand in a nanoconfined polymer system. For example, polymeric photoresists contain small-molecule photoactive compounds, plasticizers, and processing aids. These components interact with the polymer chains and affect the segmental mobility, which, in turn, affects the Tg - nanoconfinement effect. Plasticizers or low molecular mass diluents are often blended with polymers to increase flexibility by effectively shifting the Tg to lower temperatures. 1 the mechanism of plasticization is not understood in great detail, but the conventional model envisions a dynamic interaction between the polymer and diluent, resulting in reduced chain-chain interactions, reduced local viscosity and increased chain mobility.2 in this paper we report the effect of plasticizer on the dynamics of poly(vinyl acetate) (PVAc) chains adsorbed on silica surfaces using solid-state deuterium nuclear magnetic resonance (NMR) and modulated differential scanning calorimeter (MDSC). The deuterium NMR technique is an excellent tool to probe interfacial phenomena and study the dynamics of polymer chains on surfaces.3,4 in our lab, we have used deuterium NMR extensively for characterizing different types of polymers like poly(methyl acrylate)5,6,7 and PVAc8 on silica surfaces. The methyl groups of PVAc have been deuterated in order to probe the mobility of their segments. Random orientations of the methyl groups, with respect to the static magnetic field, result in powder patterns in the 2H NMR spectrum for segments with little or no motion. Segmental mobility averages the quadrupole couplings and ultimately leads to the collapse of the powder pattern into a single resonance for rubbery polymers