## 2 The Development of the Fluoropolymer Industry from 1930s \(\sim\) 1990s
### 1960s
#### 1970s
PFA powder can be used directly for extrusion or injection molding, and a PFA dispersion can be prepared for spray or dip-coating applications. Like PTFE, PFA can be filled with glass or carbon fibers, graphite or bronze powder to improve wear and creep properties. The main applications of PFA are chemical resistance components for valves, pumps and pipes. PFA is also widely used in the semiconductor manufacturing industries for high purity and chemical resistant moldings. The commercial PFA products are Teflon PFA from DuPont, Aflon PFA from Asahi Glass, Dyneon PFA from Dyneon, Neoflon PFA from Daikin, and Hydlon PFA from Solvay. After ECTFE, the other fluoropolymer containing ethylene units--ETFE was commercialized in 1973 by DuPont. ETFE is comprised of alternating ethylene and TFE units in the polymer main chain (Figure 9). Due to the risk of explosive decomposition reaction, the copolymerization of ethylene and TFE must be conducted in special vessels at low pressure. Suspension polymerization is generally carried out in an inert chlorofluorocarbon solvent using fluorinated peroxides as initiator and methanol as a chain transfer agent [31, 32]. The polymer chains in ETFE adopt an extended zigzag conformation and a close packing. The crystallinity of ETFE ranges from 40% to 60%, and it has a melting temperature of 225-300 \({}^{\circ}\)C depending on the comonomer ratio and the processing method. Figure 9: The preparation of ETFE. ETFE possesses superior processability and improved mechanical properties compared to other TFE copolymers. ETFE can be processed by all thermoplastic processing methods such as injection molding, compression molding, blow molding, rotational molding, extrusion, and wire coating. ETFE has high tensile strength, high flexibility, excellent impact strength, moderate stiffness, good abrasion resistance and high cutting resistance. ETFE modified by glass fiber reinforcement is tougher and stiffer and has higher tensile strength than PTFE, PFA or FEP. ETFE has a broad operating temperature range from as low as \(-100\)\({}^{\circ}\)C to \(150\)\({}^{\circ}\)C.  
As a copolymer of ethylene and TFE, ETFE has medium chemical resistance and flame resistance. Its radiation resistance is high with the advantage of being cross-linked by high-energy radiation. The radiation cross-linked ETFE wire insulation can be continuously used at 200 \({}^{\circ}\)C.  
The main application for ETFE is wire and cable insulation, accounting for 60% of its market. ETFE has good resistance to petroleum and fuel permeation, which resulted in a significant growth of ETFE as fuel tubing. The commercial ETFE products include Tefzel from DuPont, Fluon from Asahi Glass, Halon ETFE from Solvay, Neoflon ETFE from Daikin, and Dyneon ETFE from Dyneon. _1980s_  
Before 1980s, all the industrial fluoropolymers were semicrystalline materials. Crystalline fluoropolymers have certain shortcomings such as low optical clarity, high creep and poor solubility, which limited their processability and the type of applications. In 1985, DuPont developed an amorphous perfluoropolymer--Teflon AF. Teflon AF is a copolymer of TFE and perfluoro-2,2-dimethyl-1,3-dioxole (PDD) (Figure 10). The copolymerization of PDD and TFE is carried out in aqueous media with a fluorinated surfactant and ammonium persulfate as an initiator [33,34]. The composition of the copolymers could be adjusted by the comonomer feeding ratios. Different grades of Teflon AF products were prepared for different applications. At the same time, Asahi Glass also introduced a new amorphous perfluoropolymer--Cytop. Cytop is a homopolymer obtained via the cyclo-polymerization of perfluoro-3-butenyl-vinyl ether (PBVE) (Figure 10) [35,36]. Figure 10: The preparation of Teflon AF and Cytop. As amorphous perfluoropolymers, Teflon AF and Cytop share certain advantageous properties compared to the crystalline perfluoropolymers. Amorphous perfluoropolymers inherited the excellent chemical, thermal and electrical properties from the crystalline perfluoropolymers.