the invention relates to a process for crosslinking aromatic polymers containing radiation - sensitive methylene groups by exposing the polymers to ionizing radiation thereby causing crosslinking of the polymers through the methylene groups . crosslinked polymers are resistant to most organic solvents such as acetone , alcohols , hydrocarbons , methylene , chloride , chloroform , and other halogenated hydrocarbon , to common fuels and to hydraulic fluids in contrast to readily soluble uncrosslinked polymers . in addition , the degree of crosslinking of the polymers depends upon the percentage of the connecting groups which are methylene which ranges from 5 to 50 % and preferably from 25 to 50 % of the connecting groups and is also controlled by the level of irradiation which ranges from 25 to 1000 mrads and preferably from 25 to 250 mrads . the temperature of the reaction conditions ranges from 25 ° to 200 ° c . and preferably at or slightly above the glass transition temperature of the polymer . the crosslinked polymers are generally more resistant to degradation at elevated temperatures such as greater than 150 ° c ., have a reduced tendency to creep under load and show no significant embrittlement of parts fabricated from the polymers .