Branching and cross-linking in radiation-modified poly(tetrafluoroethylene): A solid-state NMR investigation

Fluoropolymers exhibit a number of favorable properties such as high-temper ature stability, chemical resistivity, and a low surface energy. However, t he possibility to incorporate fluoropolymers into other materials is limite d because of the low surface energy. Modification procedures such as radiat ion modification can be applied to overcome these difficulties. High-resolu tion fluorine-19 solid-state NMR using high-speed magic-angle sample spinni ng has been applied to investigate the structural changes resulting from ir radiation of poly(tetrafluoroethylene) (PTFE) with high-energy electrons un der vacuum. PTFE irradiated at room temperature mainly shows chain scission . PTFE irradiated at high temperatures, above the melting point, under vacu um, however, contains branches as well as cross-links. Evidence for cross-l inks in this material is derived from structural information. A quantitativ e analysis of the data is used to establish the density of side soups and b ranches. The excess of branches to end groups is interpreted as cross-links .