A series of random PEK with cardo group copolymers were synthesized by reaction of mixture of phenolphthalein(PPH) and 3

3' -bis(4-hydroxyphenyl) -isobenzopyrrolidone(HPP) with equivalent molar bis(4-nitrophenyl) ketone(DNBP).The permeabilities of these copolymers to hydrogen

nitrogen and oxygen were observed to vary with HPP molar content in S-form different from other random copolymer systems reported previously. This peculiar phenomenon was explained according to polymer free volume

chain flexibility and strong intermolecular hydrogen-bond interaction.