Chemisorption of linear and cyclic polymethylsiloxanes on alumina studied by Fourier-transform infrared spectroscopy

Cyclic and linear versions of polymethylsiloxane (PMS) have been adsorbed on alumina from solution in tetrachloromethane. The Si—H moieties undergo a condensation reaction with hydroxyl groups associated with the alumina surface, with the elimination of molecular hydrogen, and become chemically bound to the surface. The extent of this chemisorption depends on the initial solution concentration and the polymer type; the process of chemisorption is, however, preceded by physisorption. The rate and extent of these polymer–surface interactions have been monitored by Fourier-transform infrared (FTIR) spectroscopy. The results show marked differences in the behaviour of cyclic and linear molecules and are in qualitative agreement with calculations based on the equilibrium mean-field theory of Scheutjens and Fleer. Sequential adsorption studies however, carried out after chemisorption has occurred, indicate irreversible adsorption. Some adsorption results are also presented for AB block copolymers of PMS and polydimethylsiloxane (PDMS).

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