Like sealant, low free TDI prepolymers can meet the requirements of new European regulations, which can greatly improve the working environment for on-site coating workers and ensure their health. Due to the high fluidity of MDI or TDI low free prepolymers, resin greatly improves processability. Moreover, due to the regular molecular structure, compared to conventional prepolymers, the coating obtained from low free prepolymers has better physical properties and medium resistance, which can greatly improve coating properties.