str10 to the above turbid solution ethyl acetate having a concentration of at least 99 5 was added dropwise while stirring addition of ethyl acetate was stopped at the time when the turbidity white precipitate disappeared since the resulting mixture had already separated into an organic layer and an aqueous layer the organic layer was taken out followed by washing with pure water after washing the organic layer with water two or three times the solvent ethyl acetate was removed to obtain a solidified carboxylic acid to the solidified carboxylic acid a solution mixture 50 50 of ethyl acetate having a concentration of at least 99 5 and methanol having a concentration of at least 99 8 was added dropwise then crystals of the carboxylic acid were obtained by recrystallization 2 the crystals so obtained were added to glycidyl methacrylate followed by stirring for 5 hours under alkaline conditions while maintaining the temperature at 80 to 90 u00b0 c after completion of the reaction ethyl acetate was added to the reaction mixture the resulting mixture was filtered and subjected to desolvation whereby a product represented by the following formula vii str11 the ultraviolet absorbing monomer obtained in example 2 was added in an amount of 1 wt to 2 hydroxyethyl methacrylate hema the resulting mixture was charged in a test tube or the like followed by thermal polymerization at 50 u00b0 c 24 hrs 60 u00b0 c 24 hrs and 70 u00b0 c 24 hrs in a temperature controlled bath and at 100 u00b0 c 24 hrs in an air oven the test tube so treated was then placed in an autoclave at 121 u00b0 c for about 30 minutes whereby thermal polymerization was completed after completion of the thermal polymerization the.