Structural changes in poly(2-methoxyethyl acrylate) thin films induced by absorption of bisphenol A. An infrared and sum frequency generation (SFG) study

The structural changes in poly(2-methoxyethyl acrylate) (PMEA) thin films induced by the absorption of bisphenol A (BPA), which is suspected to be an endocrine disrupter disturbing the hormone balance in a living body, have been investigated by infrared reflection absorption spectroscopy (IRRAS) and sum frequency generation (SFG) measurements. BPA molecules are absorbed in PMEA thin film. By controlling the thickness of the intermediate polystyrene (PS) film between the PMEA and Au substrate, we are able to probe the molecular structure at the different PMEA interfaces of air/PMEA (free) and PMEA/PS (buried) by the SFG measurements. The ether methyl (OCH₃) group in the side chain of PMEA at both interfaces has the same vector orientation with respect to Au, i.e., pointing into air at the free interface and pointing into PMEA at the PMEA/PS buried interface. The OCH₃ groups at the PMEA interfaces are likely to stand up and that the interfacial ordering on the PMEA is increased by the BPA absorption. The structural changes in the PMEA bulk and its interface induced by BPA absorption and desorption are reversible.