1 5 based on 100 parts of polyurethane as a slid and the resulting mixture was stirred and subjected to dry spinning according to a conventional method to give elastic fiber of 40 denier 5 filaments the product was irradiated in a fade o meter at 0 u00b0 c for 40 hours and retention of breaking strength of the elastic fiber was defined which is shown in table 1 for comparison the data of elastic fiber obtained by adding the resin type polycondensation product from divinylbenzene and p cresol a compound of reference example 1 part to polyurethane 100 parts or elastic fiber without any additives reference example 2 are also shown in table 1 table 1______________________________________ breaking strength of elastic fiber antioxidant retention ______________________________________the compound of ex present 1 90invention 2 90 3 85 4 90 5 95reference resin type poly 55example 1 condensation product from divinylbenzene and p cresolreference 5example 2______________________________________ as is obvious from table 1 showing the case of polyurethane fiber the antioxidant of the present invention has more excellent resistance against light and dry cleaning compared with those of reference examples the polymeric antioxidant of the present invention prevents decrease of antioxidant effect due to scattering of the agent during the processing process and removing of the antioxidant upon processing or usage which has been regarded as defects of the prior art further the polymeric antioxidant of the present invention is white or nearly white and hardly colored therefore coloring of the product upon processing and using can be prevented moreover according to the process of the present invention purification of the starting material is readily carried out therefore the desired antioxidant can be easily produced the polymeric antioxidant of the present invention is generally effective for polymeric compound such.