Strain-reporting pyrene-grafted polyethylene

High Density and Very Low Density PolyEthylene-graft-Maleic AnHydride (HDPE-MAH and VLDPE-MAH respectively) functionalized with 1-aminopyrene (AP) are prepared via reactive extrusion. Covalent attachment of AP is confirmed by lack of residual free AP after extraction with dichloromethane. Differential scanning calorimetry, tensile test, dynamical mechanical thermal analysis and rheology are employed to investigate the influence of AP incorporation on thermal, mechanical and rheological properties when grafted on both HD and VLDPE-MAHs. Fluorescent emission spectroscopy reveals pronounced changes in fluorescent behavior under stress due to the breakup of the pyrene excimers. For HDPE-MAH-AP this change is sudden with a clear drop of excimer content (IE/IM) of around 50% due to necking of the material stretched above 50% strain. In contrast,VLDPE-MAH-AP shows no necking and a linear decrease of IE/IM ratio down to 30% when elongated up to 1100% strain, while HDPE-MAH-AP broke after 200% strain.