Synthesis, characterization, and stability of poly(ethylene-co-acrylic acid) films surface functionalized with fluorescent moieties

Abstract

Light emission has been introduced onto poly(ethylene-co-acrylic acid) (PEAA) surfaces by covalently grafting two different fluorescent moieties. The facile surface modification method presented allows commercial polymers to be used for light emitting and sensor applications. Two fluorescent compounds, 4′-(octyloxy)-4-biphenyl carboxylic acid (OBC) and 2,7-bis (bromomethyl)-9,9-dihexyl-9H-fluorene (BMDF), were covalently grafted to the surface of PEAA films. Conversion of the carboxylic acid functional group present in PEAA to acid chloride was followed by reaction with ethylenediamine to provide primary amine groups on the film surface. The resultant amine groups then served as the grafting site for OBC and BMDF on the PEAA film (OBC-PEAA and BMDF-PEAA). For each reaction step, the chemical modifications were confirmed using FTIR spectroscopy and static water contact angles. OCB-PEAA and BMDF-PEAA films were evaluated using UV–Vis spectrophotometry to determine UV absorption wavelength ranges. The modified films were then irradiated at their respective maximum absorption wavelengths in a fluorescence spectrophotometer and emissions were identified in both the violet-blue and red regions of visible light. When irradiated at 254 nm, both PEAA-OBC and PEAA-BMDF fluoresce blue. Films were reanalyzed after 6 months and again after 5 years to assess long-term stability of this light emitting behavior. OBC and BMDF grafted to the PEAA films remained chemically stable and functioned effectively as light emitting polymer films for up to 5 years.