F MAS NMR of irradiated polymers

The field of F NMR of intractable polymers has received an enormous boost in the past few years following the introduction of commercial high-spinning-speed MAS probes.This has led to a number of studies of the effects of radiation on fluoropolymers. - The most important commercial 

In other studies the mechanism of cross-linking in irradiated copolymers of tetrafluoroethylene and perfluoromethylvinylether has been studied by Forsythe e/o/. This material is rubbery at room temperature, and hence sufficient molecular mobility is available to permit radical-radical recombination reactions. Thus the material undergoes both chain scission and cross-linking. The authors were able to quantify the yields of new products using F MAS NMR at moderate spinning speeds, since the chemical shift anisotropy and homonuclcar dipole-dipole couplings of the fluorine nuclei are partially averaged by rapid molecular motion in the rubbery state. 

More recently, this group has also reported the identification of new structures formed by radiolysis of fluorinated ethylene-propylene copolymers The changes to the spectra are similar to those reported for irradiated PTFE by Fuchs and Scheler, and thus the radiation chemistry of these two polymers is similar. Irradiation at low temperatures resulted in the formation of new -CF3 chain ends, while irradiation in the melt (523 K) resulted in the formation of long-chain branches. However, it was clear that chain-scission reactions were still dominant at these higher temperatures. 

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