Chemical and physical processes in the retention of functional groups in plasma polymers studied by plasma phase mass spectroscopy

Abstract

Surface engineering of functionalised polymer films is a rapidly expanding field of research with cross disciplinary implications and numerous applications. One method of generating functionalised polymer films is radio frequency induced plasma polymerisation which provides a substrate independent coating. However, there is currently limited understanding surrounding chemical interactions in the plasma phase and physical interactions at the plasma-surface interface, and their effect on functional group retention in the thin film. Here we investigate functionalised plasma polymer films generated from four precursors containing primary amines. Using XPS and fluorine tagging with 4-(trifluoromethyl)benzaldehyde, the primary amine content of plasma polymer films was measured as a function of applied power at constant precursor pressure. The results were then correlated with analysis of the plasma phase by mass spectrometry which showed loss of amine functionality for both neutral and ionic species. Surface interactions are also shown to decrease primary amine retention due to abstraction of hydrogen by high energy ion impacts. The stability of the plasma polymers in aqueous solution was also assessed and is shown to be precursor dependent. Increased understanding of the chemical and physical processes in the plasma phase and at the surface are therefore critical in designing improved plasma polymerisation processes.

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

“…In an even more recent paper by Lerouge et al on “amine (NH 2 )‐rich” plasma polymers, published in this journal, the traditional custom was also continued, without any comment on the selectivity issue, and Ryssy et al reported that “the primary amine content of plasma polymer films was measured as a function of applied power” using TFBA, putatively justifying this practice by citing Ruiz et al…”

“…Even more references were cited in a 2012 paper by Casimiro et al on the “Introduction of Primary Amino Groups on Poly(ethylene terephthalate) Surfaces … ” to warrant their use of TFBA: “ To prove the presence of primary amines, labeling with trifluoromethylbenzaldehyde (TFBA) was carried out .” However, in only two of the cited 22 papers aldehyde derivatization was reported at all – aside from the article by Favia et al a paper by Olander et al in which, on the other hand, no further reference related to amine selectivity of aldehydes was given.…”

Análisis reológico y estructural de líquidos iónicos de alto peso molecular

“…Las películas pp-VIm muestran una concentración similar de aminas primarias en ambos métodos con la derivatizacion con TFBA, mientas que la concentración de aminas secundarias con TFAA muestran una pérdida de grupos en ambos métodos. En algunos casos la repetición de unidades es lineal [17][18][19]. En otros casos las cadenas son ramificadas o interconectadas para formar estructuras tridimensionales.…”

“…Ryssy et. al [19] agregaron grupos funcionales a películas por plasma con cuatro precursores diferentes (alilamina, 1,2-etilendiamina, heptilamina y 1,3diaminopropano) que contienen aminas primarias. El contenido de aminas y la estabilidad de los polímeros por plasma dependen de la elección del precursor, independientemente de las condiciones energéticas.…”

“…Los homopolímeros son aquellos que se forman por la repetición de unidades monómericas idénticas. De estos se distinguen cinco familias principales: las poliolefinas, los poliestienicos, los insaturados, los polivinilos y los poliacrilicos[17,19]. En la Figura se muestra la configuración de un homopolímeroA-A-A-A-A-ALos copolímeros están constituidos por dos o más unidades monómericas distintas.…”