Grafting well-defined polymers onto unsaturated PVDF using thiol-ene reactions

Abstract

Poly(vinylidene fluoride) (PVDF) is commonly used in membranes, lithium-ion battery binders, and coatings due to its thermal and chemical robustness. Nevertheless, PVDF-based copolymers can broaden the application scope and performance capabilities of pristine PVDF. PVDF has been modified via grafting-from reactions. However, grafting density and graft length, two important properties of graft copolymers, cannot be accurately determined. Herein, we used grafting-onto thiol-ene reactions as a method to modify PVDF. The molar mass of pre-synthesized, thiol-terminated polymers were accurately determined, and grafting densities were calculated. Unsaturated sites were generated through dehydrofluorination and dehydrochlorination in PVDF and P(VDF-co-chlorotrifluoroethylene) (PVDF-CTFE). Various conditions were studied, including the molar mass and chemical structure of grafts, the degree of thiol substitution, and thiol-ene reaction mechanisms. Base-catalyzed Michael addition with secondary thiols performed best, with the highest grafting density calculated to be about 4 chains per PVDF chain. Despite the low grafting density, changes in material properties between the product and starting materials were observed, validating this controlled method for PVDF modification.