Modification of perfluorinated polymers by high-energy irradiation

Abstract

This review surveys about the possibilities for the modification of perfluorinated polymers using high-energy irradiation: degradation, functionalization, branching, and cross-linking. The reaction mechanisms for the different reaction conditions are discussed. Electron irradiation of polytetrafluoroethylene (PTFE) with a very high dose leads to a complete degradation of the macromolecules to low-molecular products. In the presence of oxygen perfluorocarboxylic acids and in an inert atmosphere, mixtures of perfluorinated olefins and paraffins can be obtained. Virgin PTFE is disintegrated by high-energy irradiation in air with a lower dose into a micropowder modified with COOH groups. This powder can be homogeneously incorporated in other polymers. So, the special properties of PTFE can be made effective in these polymers. Micropowders functionalized with COOH groups and polyamides (PA) form by reactive extrusion PTFE-PA blockcopolymers which can be used as slide bearing materials. The copolymers poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) and poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) irradiated in air show a significantly higher degree of COOH functionalization compared with PTFE. Irradiation of molten PTFE in an inert atmosphere leads to formation of different kinds of double bonds, CF 3 side groups, long-chain branches as well as cross-links. Irradiation of PFA in vacuum results in the generation of COF and COOH groups; in molten state also branches and cross-links are formed. The focus of the present paper is on the work that has been carried out at the Institute of Polymer Research Dresden.