Characterization of Poly(2-Hydroxyethyl Methacrylate) (PHEMA) by XPS

Abstract

The surface composition of anionic polymerized poly(2-hydroxyethyl methacrylate) (PHEMA) films cast onto glass coverslips was examined with x-ray photoelectron spectroscopy (XPS). The elemental composition determined from a survey scan was 68.3 at. % carbon and 31.7 at. % oxygen. This composition is within experimental error of the composition expected based on the structure of PHEMA (66.7 at. % carbon and 33.3 at. % oxygen). The C 1s spectrum was fit using four components corresponding to C—H/C—C, beta-shifted C—H, C—O, and O=C—O species. The O1s spectrum was fit using three components corresponding to C=O, C—OH, and C—O—C species. The assignment, binding energies, and relative areas are all consistent with the structure of PHEMA and previous XPS studies of methacrylates [D. G. Castner and B. D. Ratner, Surf. Interface Anal. 15, 479 (1990) and G. P. Lopez, D. G. Castner, and B. D. Ratner, 17, ibid. 267 (1991)]. The surface composition of PHEMA after reaction of the hydrdoxyl groups with (CH3Si)2NHSi(CH3)3Cl to produce trimethyl silyated PHEMA (PHEMA-TMS) was also examined with XPS. The elemental composition of PHEMA-TMS determined from a survey scan was 69.2 at. % carbon, 21.9 at. % oxygen, and 8.9 at. % silicon. This composition is within experimental error of the composition expected based on the structure of PHEMA-TMS (69.2 at. % carbon, 23.1 at. % oxygen, and 7.7 at. % silicon). The C 1s spectrum was fit using four components corresponding to C—H/C—C, beta-shifted C—H, C—O, and O=C—O species. The O 1s spectrum was fit using two components corresponding to C=O/C—O—Si and C—O—C species. The assignment, binding energies, and relative areas are all consistent with the structure of PHEMA-TMS and previous XPS studies of methacrylates [D. G. Castner and B. D. Ratner, Surf. Interface Anal. 15, 479 (1990) and G. P. Lopez, D. G. Castner, and B. D. Ratner,17, ibid. 267 (1991)].