Synthesis, Physical,\nand Mechanical Properties of\nFluorinated Vinyl Copolymers Bearing Phosphonate Groups

Phosphonic acid-functionalized polymers\nare receiving\nmuch attention\nin proton-exchange materials, while phosphonic acid-bearing fluorinated\ncopolymers are difficult to access for high ion-exchange capacity\n(IEC) resins. To overcome the limitation of the lower reactivity ratio\nof perfluorinated vinyl ethers, herein, the emulsion copolymerization\nof perfluorophosphonate vinyl ether and vinyl acetate was screened\nand performed using NaHSO<sub>3</sub>–Na<sub>2</sub>S<sub>2</sub>O<sub>8</sub> redox catalysts at 30 °C to produce fluorinated\nphosphonate copolymers with a high molecular weight of 220 kDa. These\nfluorinated phosphonate copolymers and their alcoholyzed ones with\nphosphonic acids exhibit good thermostability of <i>T</i><sub>d</sub> > 270 °C, relative hydrophobicity with water\ncontact\nangle >90°, and a high Young’s modulus >340 MPa\nwith a\nfracture elongation of >40%. Noteworthy is that the fluorinated\ncopolymer\nwith 34.7 mol % phosphonate had an IEC of 3.19 mmol/g, which was ∼3-\nfold higher than that of commercial Nafion@117. Importantly, this\nwork provides an efficient, safe, and low-pollution method for the\npreparation of phosphonic acid-bearing fluorinated copolymers with\ngood thermal, mechanical, and high IEC properties, holding potential\napplications in solid polymer electrolytes or proton-exchange membranes.