Thermo-reversible healing in a crosslinked polymer network containing covalent and thermo-reversible bonds

The self-healing behavior of a modified ureido-amide based thermoplastic hybrid elastomer was investigated by increasing the concentration of non-reversible (covalent) bonds compared to reversible (hydrogen) bonds. A crosslinked polymer network was synthesized using varying amounts of diglycidylether of bisphenol A and reacting with the ureido-amide thermoplastic. Increasing epoxy content produced a more rigid and thermally stable hybrid network, which in turn decreased overall thermo-reversible or healing behavior. Fracture toughness recoveries varied from 25% for the system containing the greatest number of covalent bonds to well over 200% for systems containing higher thermoplastic content. Substantial levels of healing, about 62% recovery, were still achieved despite the crosslinked network having a Tg above room temperature, 31 degrees C as measured by differential scanning calorimetry (DSC). Dynamic mechanical thermal analysis was used to monitor thermo-reversible behavior of the elastic moduli and thus probe molecular mobility within the glassy state. The extent and rate of recovery of the elastic modulus was dominated by the extent of thermal activation above the glass transition temperature. Fourier transform infrared spectroscopic and DSC studies confirmed that reacting the thermoplastic with an epoxy resin produced a covalently bonded crosslinked network and the epoxide groups were completely consumed. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013