## 2 The Development of the Fluoropolymer Industry from 1930s \(\sim\) 1990s
### 1960s  
Considering the shortcoming of PTFE, researchers looked for new ideas to solve the existing problems. The copolymerization of TFE with other monomers offered many opportunities. The first TFE copolymer was FEP (fluorinated ethylene propylene), which was prepared by the random copolymerization of TFE and hexafluoropropylene (HFP). FEP was commercially introduced to the market in 1960 by DuPont. The structure of FEP is similar to PTFE except that a trifluoromethyl group was introduced along the side of the polymer main chain (Figure 3). FEP is generally prepared by the copolymerization of TFE and HFP in an aqueous medium with a free radical initiator and a dispersing agent. The comonomer ratio and the polymerization conditions are carefully controlled to achieve the desired copolymer composition and molecular weight, which are closely related to the melt viscosity, the processability and the mechanical properties of the final products [15,16]. Generally, FEP contains about 5 mol% of HFP. The introduction of HFP units in the polymer main chain disrupted the crystallization ability of FEP copolymer compared with the homopolymer of TFE. The crystallinity of FEP is about 70%, and its melting temperature is in the range of 260-280 \({}^{\circ}\)C depending on the HFP content. It can be used continuously up to 200 \({}^{\circ}\)C. The molecular weight of FEP is much lower than that of PTFE and resulted in a much lower melt viscosity and better processability. Figure 3: The preparation of FEP. FEP can be processed by the conventional polymer processing techniques such as injection molding, extrusion and film casting. FEP has better impact strength, better wear resistance, and less permeability for organic solvents compared with PTFE. The disadvantage of FEP is the poorer resistance to thermal stress cracking. FEP exhibits similar chemical resistance, weather resistance, flame resistance, radiation resistance, and the electrical properties to PTFE, FEP is easier to surface modify to increase wettability and adhesive bonding. FEP dispersions are generally used for coatings followed by the fuse treatment above the melting temperature of the polymer. The major applications of FEP are wire insulation, thermocouple wire insulation, chemical resistance liners for pipes and fittings, lined tanks for chemical storage, anti-stick applications, and sheet and film products for solar panels and solar collectors. About 65% of overall worldwide consumption for FEP is for plenum cable insulation. The increasing use of local area network (LAN) cable led to a huge increase in the market of FEP. Some typical commercial FEP products are Teflon FEP from DuPont, Neoflon FEP from Daikin, and Dyneon FEP from Dyneon. In 1961, DuPont introduced another fluoropolymer, polyvinylfluoride (PVF) (Figure 4) with the trademark Tedlar. Although only one hydrogen atom was replaced by a fluorine atom compared to the polyethylene, PVF showed more interesting properties than most fluoropolymers. PVF is prepared by the polymerization of vinyl fluoride (VF) in an aqueous medium using a free radical initiator. A higher pressure is necessary due to the lower polymerization activity of VF compared to TFE. The presence of the fluorine atom in PVF put it in between PE and PTFE in terms of crystallization. With a crystallinity of 40%, PVF has a melting temperature around 200 \({}^{\circ}\)C, and can be continuously used in the temperature range from -70 \({}^{\circ}\)C to 110 \({}^{\circ}\)C. The lower crystallinity of PVF compared to PTFE resulted in higher impact strength and better tensile strength. The relatively poor thermal stability of PVF makes PVF difficult to process traditionally. PVF film is manufactured using a plasticized melt extrusion method with plasticizers and stabilizers. The main uses of PVF are in films and coatings applications, such as the premier surface finish for aluminum and steel home siding. The excellent resistances to weather and radiation have led to the wide application of PVF as glazing materials for solar energy collectors.