Selective and Controlled Grafting from PVDF-Based Materials by Oxygen-Tolerant Green-Light-Mediated ATRP

Poly(vinylidene fluoride) (PVDF) shows excellent chemical and thermal resistance and displays high dielectric strength and unique piezoelectricity, which are enabling for applications in membranes, electric insulators, sensors, or power generators. However, its low polarity and lack of functional groups limit wider applications. While inert, PVDF has been modified by grafting polymer chains by atom transfer radical polymerization (ATRP), albeit via an unclear mechanism, given the strong C–F bonds. Herein, we applied eosin Y and green-light-mediated ATRP to modify PVDF-based materials. The method gave nearly quantitative (meth)acrylate monomer conversions within 2 h without deoxygenation and without the formation of unattached homopolymers, as confirmed by control experiments and DOSY NMR measurements. The gamma distribution model that accounts for broadly dispersed polymers in DOSY experiments was essential and serves as a powerful tool for the analysis of PVDF. The NMR analysis of poly(methyl acrylate) graft chain-ends on PVDF-CTFE (statistical copolymer with chlorotrifluoroethylene) was carried out successfully for the first time and showed up to 23 grafts per PVDF-CTFE chain. The grafting density was tunable depending on the solvent composition and light intensity during the grafting. The initiation proceeded either from the C–Cl sites of PVDF-CTFE or via unsaturations in the PVDF backbones. The dehydrofluorinated PVDF was 20 times more active than saturated PVDF during the grafting. The method was successfully applied to modify PVDF, PVDF-HFP, and Viton A401C. The obtained PVDF-CTFE-g-PnBMA materials were investigated in more detail. They featured slightly lower crystallinity than PVDF-CTFE (12–18 vs 24.3%) and had greatly improved mechanical performance: Young’s moduli of up to 488 MPa, ductility of 316%, and toughness of 46 × 106 J/m3.

In each case 200 ppm Cu and 20 ppm eosin Y relative to the total concentration of monomers were used; in procedures "LA" 400 ppm and 40 ppm eosin Y were used; conversion % was determined using H-NMR spectroscopy using DMSO-d6 solvent.Dispersity for the reactions PEG-a, PEG-b and PEG-c were determined by using GPC with DMF as eluent, while the reaction "LA" was determined by GPC with THF as eluent.
Table S3.An overview of experimental procedures for copolymerization of different monomers from PVDF-co-CTFE together with the grafting outcomes.In each case 200 ppm Cu and 20 ppm eosin Y relative to the total concentration of monomers were used; conversion % was determined using H-NMR spectroscopy using DMSO-d6 solvent.

Figure S1 .
Figure S1.(A) Photochemical reactor set-up with two middle front positions equally exposed to

Figure S3. 1 H
Figure S3.1 H NMR of pristine PVDF.Measured in DMSO-d6 over 256 scans.Signals were assigned according to the literature.2

Figure S4 .
Figure S4. 19F NMR of pristine PVDF.Measured in DMSO-d6 over 128 scans.Signals were assigned according to the literature.2

Figure S6 .
Figure S6.19 F NMR of pristine PVDF.Measured in DMSO-d6 over 128 scans.Signals were assigned according to the literature.3

Figure S13 .
Figure S13.Comparison of the gamma model with the monoexponential model for PVDF sample.

Figure S23 .
Figure S23.GPC traces of aliquots from polymerization solutions at different time points;

Table S2 .
An overview of experimental procedures for polymerization of different monomers from PVDF-co-CTFE together with the grafting outcomes.