Synthesis, Physical, and Mechanical Properties of Fluorinated Vinyl Copolymers Bearing Phosphonate Groups

Phosphonic acid-functionalized polymers are receiving much attention in proton-exchange materials, while phosphonic acid-bearing fluorinated copolymers are difficult to access for high ion-exchange capacity (IEC) resins. To overcome the limitation of the lower reactivity ratio of perfluorinated vinyl ethers, herein, the emulsion copolymerization of perfluorophosphonate vinyl ether and vinyl acetate was screened and performed using NaHSO3–Na2S2O8 redox catalysts at 30 °C to produce fluorinated phosphonate copolymers with a high molecular weight of 220 kDa. These fluorinated phosphonate copolymers and their alcoholyzed ones with phosphonic acids exhibit good thermostability of Td > 270 °C, relative hydrophobicity with water contact angle >90°, and a high Young's modulus >340 MPa with a fracture elongation of >40%. Noteworthy is that the fluorinated copolymer with 34.7 mol % phosphonate had an IEC of 3.19 mmol/g, which was ∼3- fold higher than that of commercial Nafion@117. Importantly, this work provides an efficient, safe, and low-pollution method for the preparation of phosphonic acid-bearing fluorinated copolymers with good thermal, mechanical, and high IEC properties, holding potential applications in solid polymer electrolytes or proton-exchange membranes.