Use of fluorescent probes in supporting functional group analysis resulting from polymer ageing

摘要

Based on the determination of the solvatochromic parameters of a series of polymers with various functional groups containing oxygen atoms, a method was proposed which allowed for discriminating the oxidation products formed by exposure of polymers to photo- and/or thermo-ageing. The polymers used to determine the solvatochromic parameters contained polar groups such as chain-pendant ester (EVA, PMMA, PVAc), chain ester (PLA), alcohol (EVOH, PVA), chain-pendant acid (PAA), ketone (PK), ether (PEO). The solvatochromic parameters π*, α and β were determined following procedures reported in the literature, and it was shown that the most apolar polymer PE, displays the lowest π* value; the presence of acetate groups in PE makes the π* value increase. Polyesters (PLA, PMMA, PVAc) have similar π* values. Then, alcohols and ether groups (EVOH, PVA, PEO) have higher π* values. Finally, the highest π* values are obtained for PAA and PK. Concerning the β value, the highest value was obtained for (PE, EVOH, PEO), which have the highest capacity to accept a proton, and are close to polyethylene in terms of chemical structure. On the contrary, the polymers with the lowest β value are the ones which have acid/ ester/ketone functions (PK, PAA, PLA), reflecting their lowest capacity to accept a proton. This method was successfully applied to discriminate the oxidation products formed in thermo- and photo-oxidation of polyethylene which are known to be slightly different due to the Norrish reactions that do not occur in thermooxidation.