Self-gradient mechanism, morphology and damping analysis of a thickness continuous gradient epoxy-polyurethane interpenetrating polymer networkElectronic supplementary information (ESI) available. See DOI: 10.1039/c6ra13093c

A simple and affordable gradient-distributing interpenetrating polymer network (IPN) composite was created that takes advantage of the relatively poor compatibility and the curing rate discrepancy between epoxy (EP) and polyurethane (PU) resins. Organic element content analysis (CHNS/O) and attenuated total reflection infrared spectroscopy (ATR-FTIR) reveal that the PU content is a gradient that changes along the direction of the thickness. Morphology analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM) proves that it has a continuously changing modulus with no stratified structure. Dynamic thermomechanical analysis (DMA) and fatigue testing demonstrate that the composite has better performances than traditional homogeneous IPNs with the same compositions. A gradient IPN is self-generated without any external help and no restriction in thickness. It has excellent damping and fatigue properties.