Perfluoro-2-methylene-l,3-dioxolane

These perfluoropolymers have excellent properties in many aspects. However, the preparative methods are complex and expensive and of Cytop is relatively low. Several substituted perfluoro-2-methylene-l,3-dioxolanes (Figure 16.5) have been studied to obtain other perfluorinated polymers. The first example in the class is perfluoro-2-methylene-4-methyl-l,3-dioxolane (Figure 16.5B), which was prepared by DuPont in 1967 through perfluoropyruvyl fluoride prepared from hexafluoro-propylene oxide [7]. Using a similar method, perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolane (Figure 16.5D) was synthesized by Asahi Glass in 1993 [12]. 

TABLE 16.6 The Physical Properties of Perfluoro-2-Methylene-l,3-Dioxolane Monomers and Their Homopolymers... 

At the same time, considerable etfort has been devoted to develop new perfluoropolymers as a substitute for CYTOP. CYTOP has excellent properties in many aspects, whereas the preparative methods are complex and expensive, as shown in Scheme 4.1, and the is relatively low ( 108°C). In particular, several substituted perfluoro-2-methylene-l,3-dioxolanes, shown in Figure 4.9, have been extensively studied. 

The decomposition of perfluorodibenzoyl peroxide occurs at 60—80 C by a homolytic mechanism, resulting in the formation of a pentafluoroben-zyl structural unit at the polymer terminus (Scheme 4.4) [31, 32]. Thus, poly(perfluoro-2-methylene-l,3-dioxolanes) are generally thermally stable, and their decomposition temperature (Tj) in air is >300 C. 

Perfluoro-2-methylene-l,3-dioxolane monomers can be copolymerized with each other to modify the physical properties of the polymers. The refractive index and Tg depend on the copolymer composition. The copolymers are readily prepared in solution and in bulk. For example, the copolymerization reactivity ratios of monomers A and C (Figure 4.10) are = 0.97 and - 0.85 [35]. The data show that this copolymerization yields nearly ideal random copolymers. Figure 4.11 shows the change in Tg as a function of the copolymer composition. The copolymers have only one T, which increases from 110 to 165 C as the mole fraction of monomer A increases. The copolymer films prepared by casting are flexible and tough and have a high optical transparency. 

Perfluoro-2-methylene-l,3-dioxolane monomers can be also copolymerized with various commercially available fluorovinyl monomers. Perfluoro-3-methylene-2,4-dioxabicyclo [3.3.0] octane (Figure 4.9 F) was copolymerized with chlorotri-fluoroethylene (CTFE), perfluoropropyl vinyl ether, perfluoromethyl vinyl ether. 

Y, and Okamoto, Y. (2011) Characterization and properties of semicrystalline and amorphous perfluoropolymer poly(perfluoro-2-methylene-l,3-dioxolane). Polym. Adv. Technol, 22 (8), 1272-1277. 

TABLE 16.5 Effect of the Concentration of the Chain Transfer Agent on the Properties of the Poly(perfluoro-2-Methylene-4-Methyl-l,3-Dioxolane)... 

The molecular weight of the polymers can be controlled by the concentrations of the free-radical initiator and/or chain-transfer agents such as carbon tetrabromide. Typical results of the preparation of poly(perfluoro-2-methylene-4-methyl-l,3-dioxolane) using different concentrations of the initiator and chain-transfer agent are reported in [27]. 

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