Effect of X-ray beam on the molecular–topological structure of the surface of kynar® polyvinylidene fluoride resin

• Published in: Journal of fluorine chemistry 2019-10, Vol.226 (C), p.109338, Article 109338
• Main Authors: Olkhov, Yurii A., Allyarov, Sadulla R., Vasiliu, Monica, Dixon, David A., Frolov, Ivan A., Demidov, Sergei V.
• Format: Article
• Language: English
• Subjects: Amorphous structure; Crystal structure; Crystallinity; Electron paramagnetic resonance; Electronic structure; Electronic structure calculations; Fluorides; Glass transition temperature; Irradiation; Macromolecules; Molecular chains; Molecular structure; Poly(vinylidene fluoride); Polymers; Polyvinylidene fluorides; Radicals; Radiolysis; Raman spectra; Raman spectroscopy; Thermal expansion; Thermomechanical analysis; Topology; Transition temperatures; Vinylidene fluoride; X ray irradiation; X-rays
• ISSN: 0022-1139; 1873-3328
• DOI: 10.1016/j.jfluchem.2019.06.004

[Display omitted] •Irradiation of PVDF with X-rays leads to the formation of alkyl -CF2–CH–CF2− and polyenyl −CH2-CH-(CH = CH)n−CH2− radicals.•At high doses of radiation, the EPR spectra of irradiated PVDF is dominated by the spectra of polyenyl radicals.•The bands in the Raman spectra of PVDF correspond to different phases of PVDF with the α-phase dominant.•Electronic structure calculations were performed to provide insights into the experimental observed spectral results.•The calculated IR and Raman spectra show distinctive signals for the α and the β phases of PVDF. Thermomechanical analysis of poly(vinylidene fluoride) (PVDF) film shows that, unlike the completely amorphous structure of the native polymer, after irradiation with X-rays, the weight fraction of the crystalline modification in the polymer is 0.5. The initial PVDF film had a linear thermal expansion coefficient of α1 = 11.33х105  K−1 and a glass transition temperature of Tg =256 K. An efficient conversion of the amorphous structures of the polymer pseudo-network into crystalline networks occurs under X-ray irradiation. The irradiated polymer exhibits amorphous (Tg =239 K) and crystalline topological blocks (Tm =385 K). The presence of polyenyl and alkyl radicals is found in the electron paramagnetic resonance (EPR) spectra of the irradiated polymer. Lines with a splitting of 3.3 m T can be observed at the edges of the EPR spectra, consistent with radical centers like -CF2-C•H-CF2-. At high doses of radiolysis, polyenyl radicals are the main observed radicals. The macromolecular chains contain all three (α, β, γ) morphologies of the polymer. The Raman spectra show that X-ray irradiation can lead to carbonization and the formation of unsaturated bonds. Electronic structure calculations were used to aid in the analysis of the observed spectra.