Incorporation of photoluminescent 7-hydroxycoumarin units onto a polyethylene matrix by means of gamma radiation

Abstract

A 60Co source generating gamma radiations was used to graft polyethylene (PE) films with acryloyl chloride (AC). Different doses of radiations (2, 4, 6 and 8 kGy) were employed in order to obtain polymers with different amount of grafted ramifications. Furthermore, the desired photoluminescent polymers (PE-g-AC-CumTEG) were obtained after esterification reaction of the precursor grafted PE films (PE-g-AC) with a 7-hydroxycoumarin derivative functionalized with tetraethylene glycol as a flexible side chain (CumTEG). The incorporated amounts of CumTEG in the resulting films were 1.2%, 6.3%, 10.2% and 15.8% for the polymers irradiated with doses of 2, 4, 6 and 8 kGy, respectively. TGA as well as DSC analysis were conducted in order to evaluate the thermal stability of the obtained grafted PE films. Moreover absorption as well as fluorescence emission spectra were recorded to study the optical properties of the incorporated coumarin chromophore. The UV-vis spectra of PE-g-AC-CumTEG polymers, obtained with doses of 4 and 8 kGy, exhibit two shoulders at 290 and 340 nm, which can be explained through the presence of H and J-type aggregates, respectively. Finally, AFM experiments revealed remarkable differences in morphology for these photoluminescent polymers.