Chemistry of radiation crosslinking of branched fluorocarbon resins

Abstract

synopsisA number of commercial and experimental fluoropolymera 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 decresse in melt Viscosity when irradiated at 2W250°C., while copolymers of tetrafluoroethylene with hexaftuoropropylene, octafluorobutylene, or perfluoroheptene-1 increase in melt viscoSity, indicatr ing crosslinking. The results suggest that the reaction of species of the type w(-CF&CX-(CF2),. (where X is F or CFa) with -CF~-CFZ. is the important one leading to crosslinking.

Influence of Irradiation Temperature on Grafting of Styrene into Poly(tetrafluoroethylene‐co‐hexafluoropropylene) Films

“…However, one process will predominate, depending on the chemical structure of the polymer and the irradiation conditions such as temperature, atmosphere and dose rate 8–10. FEP was disclosed to undergo cross‐linking by ionizing radiation if the polymer is irradiated in nitrogen atmosphere at temperatures above the glass transition temperature 11, 12. This was concluded from changes in melt flow characteristics.…”

Book Review: Molecular Modeling—Basic Principles and Applications, Second Edition. By Hans‐Dieter Höltje, Wolfgang Sippl, Didier Rognan, and Gerd Folkers.

“…Early reports indicated that cross‐linking predominates in FEP irradiated under vacuum at temperatures above the T g 11, 20. However, the results obtained here from 19 F NMR studies show that FEP undergoes only scission at 363 K but branching occurs when it is irradiated under vacuum at 523 and 543 K.…”

Chemical Structures Formed in Electron Beam Irradiated Poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP)

“…This reaction was also suggested by Zhong et al24, who used X‐ray photoelectron spectroscopy (XPS) for the characterization of FEP γ irradiated at elevated temperatures. On the other hand, Lovejoy et al25 have postulated that this recombination reaction is unlikely from steric considerations. In summary, there are hypotheses about the origin of the peaks at −59 and −62 ppm, but an unambiguous assignment is not possible at the moment.…”