The radiation copolymerization of tetrafluoroethylene and hexafluoropropylene was investigated at -78℃ with a 20，000-curie Co60 r-source． Values of the copolymeriza-tion rate constant were found to decrease with the increase of the amount of hexafluoro-propylene in the monomcr mixtures．This indicates that hexafluoropropylene has a lower copobrmerization reactivity． Values of n in the rate equation R=KIn are 0.60

0.78，and 0.85

as the mole fractions of hexafluoropropylene in the monomer mixtures are 0.1，0.5，and 0.7，respectively．This signifies that an increase in hexafluoropropylene concentration lowers the propability of biradical termination．A post-effect of the copolymerization was noticed． It was found that values of kp/kt in post-polymerization increase with the irradiation dosage．This fact is explained as due to the decrease in kt resulting from the enrichment of trapped polymeric radicals as a consequence of increased “in source”conversion on lfigher irradiation dosages．The effect of some common organic solvents and inhibitors on the copolymerization rate was also studied．Most of the results support a free．radical mechanism for this low-temperature liquid—phase radiation copolymerization；possibilities of simultaneous radical- cationic polymerization or of cationic polymerization，however，can not bc ruled out．