AbstractA number of commercial and experimental fluoropolymers were subjected to ionizing radiation at elevated temperatures and the changes in melt viscosity were measured as an indication of the degree of crosslinking or degradation which occurred. Polytetrafluoroethylene, polychlorotrifluoroethylene, polyhexafluoropropylene, and a copolymer of hexafluoropropylene with perfluoroheptene‐1 decrease in melt viscosity when irradiated at 200–250°C., while copolymers of tetrafluoroethylene with hexafluoropropylene, octafluorobutylene, or perfluoroheptene‐1 increase in melt viscosity, indicating crosslinking. The results suggest that the reaction of species of the type · (where × is F or CF3) with is the important one leading to cros