Poly(vinylidene fluoride) (PVDF) is a commercially available fluoropolymer, second in market value only to polytetrafluoroethylene. PVDF displays great thermal and chemical stability, making it a popular material in coatings, membranes, and lithium-ion battery fillers. Pristine PVDF lacks specific functionality, as such, there has been great interest in functionalizing PVDF by synthesizing graft copolymers. These materials have been used in advanced applications such as wearable nanogenerators and solid polymer electrolytes in batteries.

Many authors have reported using PVDF as a backbone for “grafting-from” using atom transfer radical polymerization (ATRP). However, the mechanism of this functionalization is unclear. Homolytic cleavage of the carbon-fluorine bond (BDE ~480 kJ/mol) to generate the initiating radical is difficult, if not impossible. Additionally, PVDF is subject to side reactions with the basic, amine-like ligands commonly used in ATRP in the form of dehydrofluorination. All these factors affect the reactivity of PVDF and result in poorly defined graft copolymers.

Because of the lack of mechanistic insight, we propose an alternative method- grafting onto PVDF. PVDF that has undergone dehydrofluorination will possess unsaturated sites on the backbone that can react with thiol-terminated polymers in a thiol-ene click reaction. Thiol-terminated polymers can be easily synthesized using various controlled radical polymerization techniques like ATRP and reversible addition-fragmentation chain-transfer (RAFT) polymerization. These polymers are uniform and well-defined, and the molecular weight can be determined prior to grafting. This information can then be used to calculate grafting density and efficiency. Herein, we systematically investigate how different starting materials and thiol-ene click reaction mechanisms affect the grafting efficiency of grafting onto PVDF-based materials.

Martin Cvek

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