ESR investigation of radicals formed in γ-irradiated vinylidene fluoride based copolymer: P(VDF-co-HFP)

Samples of copolymer based on vinylidene fluoride and hexafluoropropene P(VDF-co-HFP) were exposed to γ-radiation performed under an inert atmosphere and the total amount of radicals was quantified by electron spin resonance spectroscopy (ESR). An in-depth study of recorded ESR spectra allowed the identification of several types of radical species formed during radiolysis. Starting from an ESR simulation model established for irradiated PVDF, seven radical species have been identified in the case of P(VDF-co-HFP): five of them are related to the VDF units while the two others are derived from the HFP unit. The model used to simulate the complex superimposed ESR signals is presented. The proportions of each species are discussed and correlated to the amount of HFP units contained in the copolymer, and to the stability of each species depending on their local environment. Furthermore, the evolution of radical density with radiation dose and the decay resulting from annealing at a given temperature are presented. Corresponding spectral evolution shows the progressive predominance of most stable species.

► ESR signal of γ-irradiated P(vinylidene fluoride-co-hexafluoropropene) containing 6 wt% of hexafluoropropene is modeled.
► The formation of seven major radical species is proposed for the first time.
► Despite a low comonomer content, 43% of radicals are localized on hexafluoropropene.
► Effect of dose and annealing highlight radical stability.
► Radical stability is found to depend on both chemical environment and chain location.