Construction Of Dynamic Polymer Network With Phosphazene Crosslinking Agent

Self-healing polymers have great application in coating,biomedical materials and sealing materials due to their special properties.Cyclophosphazenes,easily modified with different functional groups,provides a premise for dynamic networks in polymers as crosslinking agensts.At the same time,cyclophosphazenes have good flame retardant properties,which can improve the flame resistance of materials and prepare self-healing materials with good mechanical properties and flame retardant properties.In this paper,a series of phosphazene polyurethane and polyurea were prepared and studied.Cyclophosphazenes with furan and aldehyde groups were designed and synthesized,respectively,which were used to crosslink linear polyurethane and polyurea with dynamic network,respectively.The main research work and results of the paper are as follows:(1)Structure characterization and the TGA、DSC and DMA tests were carried out on the prepared products.The initial decomposition temperatures of the prepared polyurethane crosslinked with phosphazene were all higher than 260 ℃.The maximum initial decomposition temperature of polyurea crosslinked with phosphazene is 297 ℃,and the minimum glass transition temperature is-54.3 ℃.(2)The tensile properties of the prepared products were tested.The results show that the prepared products have good tensile properties.The maximum elongation at break of polyurethane crosslinked with phosphazene is 1002%,and the maximum tensile strength is 29.42 MPa.The maximum self-healing efficiency can reach 97.26% at 120 ℃ for 4 h.The maximum tensile strength of polyurea crosslinked with phosphazene is 12.33 MPa and the maximum self-healing efficiency is 92.73% at60 ℃ for 24 h.The prepared polyurethane and polyurea crosslinked with phosphazene have good repeatability,after fourth repeated processing,their tensile strength can be retained 64.78% and 64.64%,respectively.(3)The Limiting Oxygen Index(LOI)and UL-94 grade of the synthesized product were tested.The results showed that when compared to polyurethane crosslinked with the traditional crosslinking agent trimethylolpropane,the UL-94 grade of polyurethane crosslinked with the phosphazene improves from HB to V-1.The limit oxygen index of polyurea crosslinked with phosphazene can reach 26.2%,and the UL-94 grade can reach V-0.