Synthesis and characterization of perfluoro-3-methylene- 2,4-dioxabicyclo[3,3,0] octane: Homo- and copolymerization with fluorovinyl monomers

The synthesis of perfluoro-3-methylene-2,4-dioxabicyclo[3,3,0] octane (D), its radical homopolymerization, and copolymerization with fluoroolefins are presented. Fluorodioxolane (D) was synthesized through direct fluorination of the corresponding hydrocarbon precursor in a fluorinated solvent by F ₂/N₂ gas. It was polymerized in bulk using perfluorodibenzoyl peroxide as the initiator. The resulting homopolymer had a limited solubility in fluorinated solvents, and its glass transition temperature (T_g) was in the range of 180-190°C. The polymeric films prepared by casting from hot hexafluorobenzene (HFB) solution were transparent with low refractive index (1.329 at 633 nm). These films were thermally stable (T _d > 350°C), and were hard and brittle. The copolymers of monomer (D) were prepared with fluorovinyl monomers such as chlorotrifluoroethylene (CTFE), perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, and vinylidene fluoride. The kinetics of radical copolymerization of monomer (D) with CTFE led to the assessment of the reactivity ratios of both comonomers: r_D = 3.635 and r_CTFE = 0.737 at 74°C, respectively. The copolymers obtained were soluble in HFB and perfluoro-2-butyltetrahydrofuran, with T_g in the range of 84-145°C depending on the copolymer composition. The films of the copolymers were flexible and clear with a low refractive index (1.3350-1.3770 at 532 nm).