Sulfonation of Polyvinylidene fluoride: Investigation of the Microstructure by {1H, 13C, 19F} NMR Spectroscopy and Mechanisms AITranslate

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DOI：https://doi.org/10.1021/acsapm.2c01787

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The cycle between the preparation of sulfonated polyvinylidene fluoride (PVDF) membranes and the study of their properties allows several groups to make critical observations that lead to a hypothesis-driven process for sulfonation optimization. To facilitate this previously poorly understood process, we studied an example of PVDF sulfonation by chlorosulfonic acid (ClSO3H). We prepared sulfonated polyvinylidene fluoride (S-PVDF_X) samples with different sulfonation reaction times (X = 3, 5, and 16 h) and confirmed the sulfonation by means of Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and NMR spectroscopy. The microstructure of the sulfonated sample S-PVDF_5 h was determined using a multinuclear {1H, 13C, 19F} NMR study. The results obtained allowed, for the first time, highlighting the dehydrofluorination of the PVDF chain in a super acidic medium and the formation of a sequence due to the esterification reaction between the alcoholic and acidic chain ends. In addition, we identified the two primary grafting sites of the sulfonic acid groups in the S-PVDF chain and demonstrated the importance of the head-to-head and tail-to-tail defects in the dehydrofluorination and sulfonation mechanisms.