Dear Muhammad Mehtab Ali Syed unfortunately, methacrylic anhydride has a rather high boiling point around ca. 200 °C at normal pressure. You could try to remove the last traces under high vacuum and slight warming (ca. 40-50 °C). Better is perhaps trying to recrystallize your urethane dimethacrylate product from a suitable solvent (e.g. toluene, diethyl ether, acetonitrile) or a solvent mixture such as diethyl ether / n-pentane. Then the residual methacrylic anhydride should remain in solution. Good luck!

Thanks a lot for your answer.