Ultraviolet (UV)-curable maleic anhydride liquid polybutadiene films were prepared by using pentaerythritol tetra(3-mercaptopropionate) (PETMP) as the crosslinker in 10 s. Fourier transform infrared (FTIR) spectra showed that maleic anhydride ring opened rapidly and reacted with sulfhydryl group to form thioester; meanwhile, SH group reacted with a double bond by thiol-ene reaction, and both reactions resulted in the rapid increase in gel contents. Due to the unique flexible nature of maleic anhydride polybutadiene (MLPB) and the moderate cross-linking degree provided by PETMP, the addition of PETMP in the range of 20%–25% significantly enhances their overall mechanical properties. The tensile strength of free-standing MLPB-PETMP films increased by three times, while its elongation reduced by less than 20%; their adhesion to carbon steel increased by more than three times to 5.0 MPa. Additionally, these films could be folded 180° on aluminum foil without damage and maintained a much lower wear level even after 3000 cycles of abrasion. However, the excessive addition of PETMP caused uneven distribution and aggregation, resulting in internal defects and thus the reduction in mechanical performances. Moreover, their thermal stability in air was also found improved, attributing to the increase in cross-linking degree and the formation of higher strength SC bond.