Approaches to Quantify Amine Groups in the Presence of Hydroxyl Functional Groups in Plasma Polymerized Thin Films

Abstract

The quantification of primary and secondary amines in plasma polymerized allylamine and plasma copolymers of allylamine/octadiene films was carried out using chemical derivatization followed by X‐ray photoelectron spectroscopy. Data was analyzed using a combination of the peak‐fit‐analysis method (PFA) and the quantitative‐elemental‐analysis method (QEA). The latter method overestimates the secondary amine contribution, since it does not account for the additional reaction of TFAA with OH groups that may be present as a result of surface aging effects. In the current work the PFA method has been extended to enable the separation of –OH groups and secondary amines, thus allowing for a more precise determination of the secondary amine groups even after surface aging.

Plasma Parameter Aspects in the Fabrication of Stable Amine Functionalized Plasma Polymer Films

“…Survey spectra were charge corrected by setting the aliphatic carbon peak to 285 eV. The concentration of surface primary amines was determined using the QEA method described elsewhere …”

Challenges in the characterization of plasma polymers using XPS

“…Klages et al [120] and Ruiz et al [121], however, underline that derivatization is not a trivial and easy method, and that in some cases, a distinction between primary, secondary amines or hydroxyl groups is not obvious due to a lack of specificity of the derivatization agents and necessitates calculations. Klages et al even suggest that, due to the presence of imines (randomly generated during plasma polymerization), the derivatization of primary amines on plasma-deposited coatings will always present uncertainties, due to the poor selectivity with respect to imines [120].…”

“…Fluorine (F 1s) [121] TFAA also reacts with C-OH [121], >NH [121,127], and amidogroups [127]** 4-(trifluoromethyl)benzaldehyde (TFBA) Fluorine (F 1s) [121] C-OH (alcohol) 286.5 eV [128] trifluoroacetic anhydride (TFAA) Fluorine (F 1s) [24,121,122,126,[129][130][131][132] Epoxyde 287.2 eV [133] trifluoroacetic acid Fluorine (F 1s) [133] Trifluoroacetic acid also reacts with C-OH [133] [125,126,129,131,132,[137][138][139][140] TFE is used with different catalysts such as dicyclohexylcarbodiimide (DCC) [125] and di-tertbutylcarbodiimide (DBC) [129] * The XPS C-N component may include primary, secondary amines, or other moieties, which results in variability of the average BE. ** However, Holländer et al have shown that it is still possible to differentiate alcohols and primary amines on the C 1s lineshape [141].…”

Critical remarks on chemical derivatization analysis of plasma‐treated polymer surfaces and plasma polymers

“…Another important derivatization reagent which has frequently been used for XPS analysis of oxygenated or nitrogenated polymer surfaces is trifluoroacetic anhydride (TFAA), generally supposed to form trifluoroacetate esters with hydroxy groups and trifluoroacetamides with secondary and primary amino groups . The dominant opinion today is that TFAA reacts exclusively with XH moieties, X = O, N; other reaction possibilities of TFAA were mostly neglected (see below, chapter 2.5, for an exception).…”