Physically cross-linked polyethylene via reactive extrusion

Ureidopyrimidinone (UPy) is introduced into various polyethylenes (PEs) bearing hydroxyl groups by solution grafting, affording physically cross-linked PE via multiple H-bonding. Utilizing low melting UPy where the methyl group is substituted with isopropyl (isopropyl UPy, IPR-UPy), a reactive extrusion process is developed that allows significant shortening of the reaction time and elimination of the use of solvents and catalysts. Chemical grafting is confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and proton Nuclear Magnetic Resonance (1H NMR). Differential Scanning Calorimetry (DSC), rheology and Dynamical Mechanical Thermal Analysis (DMTA) are employed to investigate the thermal stability of the obtained polymers and reveal that UPy functionalized PE can be safely processed via reactive extrusion below 150 °C. Introduction of UPy significantly improves the mechanical properties and alters the rheology, showing that quadruple hydrogen bonding interactions are present both in the solid state and in the PE melt.