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A new hydroxy-silane coupling agent was synthesized from 3-butene-1-alcohol and mercaptopropyl-3-methoxysilane based on a click reaction between double bonds and sulfhydryl groups and was successfully used in the synthesis of silane-modified polyether (STPE). The effect of molecular weight of polypropylene glycol (PPG) on the properties of silane-modified polyether was studied. It was found that with the increase in PPG molecular weight, the initial thermal decomposition temperature and hardness of STPE elastomers decreased, but the molecular structure hardly changed. In addition, with the increase in molecular weight, the elongation at break of the elastomer will gradually increase, but the tensile strength of the elastomer does not change much. When the molecular weight reaches 20 000 g/mol, the resin with a viscosity of 1.6 × 105 mPa s can be obtained, and the elongation at break of the cured elastomer reaches 383.4% and the tensile strength is 0.25 MPa. After the STPE resin was prepared into a silane modified sealant, the tensile strength reached 1.31 MPa and the elongation at break reached 406.2%, which had the best mechanical properties among the prepared sealants. This shows that the sealant prepared from high molecular weight resin has stronger mechanical properties, which provides a new idea for the preparation of sealants.