2 , 4 &# 39 ;- dihydroxy - 4 - pentadecyl benzophenone is prepared by mixing in the presence of an acid catalyst equimolar amounts of meta pentadecyl phenol and parahydroxy benzoic acid . thermoplastic resins , normally susceptible to degradation upon prolonged exposure to ultraviolet light , become resistant to such degradation when a small amount of 2 , 4 &# 39 ;- dihydroxy - 4 - pentadecyl benzophenone is blended therein .