Comparative examination of sensitizers in photografting on polymer films

Photografting (λ > 300 nm) of methacrylic acid on low-density polyethylene film (thickness 30 μm) was carried out at 60°C for 60 min in water medium, and the activity of sensitizers towards the grafting was examined. Various sensitizers, involving hydrogen atom abstraction (aromatic ketones and quinones), radical generation, and energy transfer (aromatic hydrocarbons), were coated on the film sample beforehand. High percentages of grafting ( > 800%) were recorded for aromatic ketones (xanthone, thioxanthone and benzophenone), for quinones (2-chloroanthraquinone, 2-methylanthraquinone and 9,10-phenanthraquinone) and for radical generators (benzoin ethyl ether and phenyl disulfide). However, energy-transfer types (anthracene, phenanthrene and naphthalene) exhibited little effect on the grafting. Carbazoles, as well as the above sensitizers, were found to be considerably effective. Characteristics of each type of sensitizer are discussed in terms of the amount coated and the kinds of film (polypropylene and nylon 6) and monomer (acrylic acid and methyl methacrylate).