Design, synthesis and properties evaluation of emulsified viscosity reducers with temperature tolerance and salt resistance for heavy oil

•A novel high temperature tolerant and high salinity resistant emulsified viscosity reducer for heavy oil was prepared.•Various experiments were conducted to investigate properties of the viscosity reducer.•The synthesized reducer had a strong ability to reduce interfacial tension and emulsify Bohai crude oil.•The structure-performance relationship and viscosity reduction mechanism were discussed.