Different from common hydrophobic associative polymers, a new hydrophobic associative polyacrylamide (HAPAM) with ultra-long side chains was synthesized and aimed to be used as drag reducer in this work. Firstly, a water-soluble hydrophobic monomer (named AT114) was obtained by alcoholysis reaction with acryloyl chloride and triton 114, then the drag reducer was obtained by radical copolymerization of AM, AMPS and AT114. The structures of AT114 and drag reducer were characterized by IR and NMR. Slick water was obtained by dissolving a small amount drag reducer in water. Although the viscosity of slick water varied greatly in fresh water and brine, the drag reduction rate always remained at a high level when flowing in pipelines. When the concentration of the drag reducer was 0.03% in fresh water, drag reduction rate can be up to 76.7%, while in high concentration brine, still as high as 76.2%. It shows that salt has no obvious negative impact on the drag reduction rate. That is also to say, in the case of low viscosity, the viscosity change has no obvious impact on drag reduction rate. From the Cryo-TEM observation, it can be concluded that the drag reducer forms sparse network structures in water, which is the direct reason for drag reducing effect. This finding provides knowledge regarding the development of new drag reducers.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13065-023-00968-5.