Characterization of polyacrylate membrane-coated fibers used in chemical absorption studies with programmed thermal treatment and FT-IR microscopy

A polyacrylate (PA) film was coated onto a fused-silica fiber as a permeation membrane in a membrane-coated fiber (MCF) technique and a solid-phase microextraction technique. The molecular changes of the PA membrane after different temperature treatments were studied with FT-IR microscopy. The absorption bands of the PA aliphatic backbone at 2902, 2795, and 2740 cm(-1) remained unchanged over the elevated thermal treatments, indicating that the polymer backbone was stable over these conditions. The spectra of the PA membrane remained unchanged when the thermal treatment temperature was under 150 degreesC. When the temperature was 250 degreesC, the O-H stretching band in the -COOH groups of the poly(acrylic acid) at 3315 cm(-1) was significantly reduced. When the temperature was higher than 280 degreesC, this O-H band disappeared. These evidences suggested that the PA membrane underwent dehydroxyl reaction to form an anhydride when the thermal treatments were higher than 250 degreesC. Thermal treatments of a deuterated PA MCF confirmed the anhydride formation mechanism. The anhydride formation explained the absorption property of PA MCFs in GC applications where they must be preconditioned at 300 degreesC. The absorption data suggest that a PA fiber does not preferably absorb polar compounds (with permanent dipole moment); instead, it absorbs preferably aromatic compounds.