Plasmabromination – the Selective Way to Monotype Functionalized Polymer Surfaces

Abstract

In contrast to other plasma modification processes of polymer surfaces, the bromination is very selective and shows a high yield in CBr groups. The most convenient bromination process was found using bromoform, which was thus preferred to elemental bromine, allyl bromide, vinyl bromide or tert‐butylbromide. The bromoform process give yields in CBr up to 40 CBr or more, with only 2–3% co‐introduction of O‐functionalities whereas allyl bromide results in yields of about 20 CBr and more, but in more than 10% oxygen‐containing by‐products. CBr groups serve as anchoring points for grafting of molecules, oligomers and pre‐polymers of diole or diamine character.

Haloform plasma modification of polyolefin surfaces

“…The allyl bromide plasma polymer (cf. [1]) showed an extraordinary high introduction of oxygen in the range of 10-18 oxygen per 100 C atoms. Not more than 75% of the Br introduced with the allyl bromide monomer (33 Br/100 C) could be found in the allyl bromide plasma polymer layer, also after applying the wash process with THF (27 Br/100 C).…”

“…Br atoms attach onto the macromolecules of the polymer substrate. Alternatively, Br-containing plasma polymer films (50-150 nm) using allyl bromide or vinyl bromide were deposited [1]. The maximal yield in Br introduction of the bromoform cw-plasma were 100 Br/100 C, after 180 s treatment, applied to polypropylene and 120 Br/100 C, after 180 s treatment, applied to polyethylene, cf.…”

“…The fraction of electrons with the maximal level of electron energy ("high-energy tail" of the electron energy distribution function, ca. N10 eV [4]), exceeds strongly the dissociation energies of C-C and C-H bonds (≈ 3 eV) in polymers [1].…”

“…The alternative formation of Br − (HBr) was not problematic because of the easy volatizing of HBr in the vacuum. The Br3d peak fitting in the X-ray photoelectron spectrum (XPS) did not show indications for Br − [1]. Another important hindrance for selective reactions in the plasma is the excess of energy transferred from the electrically produced plasma to the molecules in the gas phase and to the surface of the polymer substrate [11,12].…”

“…The polyolefin (polyethylene and polypropylene) surface functionalization using the bromoform or bromine plasma is very selective and produces high concentrations of C-Br groups [1,2]. This lowpressure process is the only known way for introduction of monosort functional groups onto polyolefin surfaces and was found 20 years ago [3,4].…”