Formulas and reaction conditions for the radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene were studied at room temperature in the presence of gaseous monomers containing 50 mole % tetrafluoroethylene content. Stable latex was obtained by the use of ammonium perfluorooctanoate emulsifier. The resulting copolymer was a rubberlike material. A percentage of emulsifier greater than 1 wt% to water was suitable in this emulsion copolymerization. The conversion and the molecular weight were independent of the stirring speed above 400 rpm and decreased with a rise in temperature. An induction period was observed in the presence of oxygen. There was no effect of water purity on the emulsion copolymerization. When the stainless-steel reaction vessel was cleaned with a dilute acidic aqueous solution, the conversion was almost the same as that for a Pyrex reaction vessel.