Adhesion promotion of thick polyphosphate-poly(allylamine) films onto polyolefin substrates by plasma polymers

The adhesion of thick poly(allylamine)-polyphosphate layers (1 μm) deposited by the wet-chemical layer-by-layer (LbL) technique onto polyethylene or polystyrene (each 100 μm) was very low. To promote the adhesion of these LbL deposited layers, the polyolefin substrates were oxidized at the surface by short exposure to the oxygen plasma (2 or 5 s) and subsequently coated with an interlayer of plasma-deposited poly(allylamine) or poly(allyl alcohol) (100 nm). The plasma polymer interlayers have improved strongly the adhesion between polyolefin substrates and polyphosphate coatings. Such phosphate coatings are interesting for life sciences (nucleotide formation) but also for fire retardancy in combination with N-rich compounds such as melamine. The intention was to prefer chemical hydrogen bonds for adhesion promoting because of their high binding energy. Therefore the introduced oxygen-containing groups at the polyolefin surface could interact with the OH or NH₂ groups of the adhesion-promoting plasma polymer interlayer. These groups were also able to interact strongly with the poly(allylamine)-polyphosphate topcoating. The coated polyolefins were investigated using Fourier transform infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR), X-ray photoelectron spectroscopy, thermogravimetric analyses and atomic force spectroscopy, and 90° peel test.