Fluoroelastomers, amorphous

However, when the two pendant groups are of dissimilar structure, amorphous fluoroelastomers are realized (4). 

The PFAP(I) selected for this study is an amorphous fluoroelastomer that consists of pendant trifluoroethoxy and octafluoropentoxy groups (II). A small quantity of cross-link site was incorporated also to facilitate vulcanization via conventional methods, i.e., organic peroxides, sulfur-accelerator, and radiation (high-energy electrons). 

The first commercial fluoroelastomer, Kel-F, was developed by the M. W. Kellog Company in the early to mid-1950s and is a copolymer of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE). Another fluorocarbon elastomer, Viton A, is a copolymer of VDF and hexafluoropropylene (HFP) developed by du Pont was made available commercially in 1955. The products developed thereafter can be divided into two classes VDF-based fluoroelastomers and tetrafluoroethylene (TFE)-based fluoroelastomers (perfluoroelastomers).72 The current products are mostly based on copolymers of VDF and HFP, VDF and MVE, or terpolymers of VDF with HFP and TFE. In the combination of VDF and HFP, the proportion of HFP has to be 19 to 20 mol% or higher to obtain amorphous elastomeric product.73 The ratio of VDF/HFP/TFE has also to be within a certain region to yield elastomers as shown in a triangular diagram (Figure 2.2).74... 

Copolymers of VDF and HFP, completely amorphous polymers, are obtained when the amount of HFP is higher than 19 to 20% on the molar base.6 The elastomeric region of terpolymers based on VDF/HFP/TFE is defined by the monomer ratios. Commercially, VDF-based fluorocarbon elastomers have been, and still are, the most successful among fluoroelastomers.7 The chemistry involved in the preparation of fluorocarbon elastomers is discussed in some detail in Chapter 2. 

Applications of fluoropolymers are still growing, even decades after the discovery of the first plastic (polytetrafluoroethylene) in this family. The increasing use of fluoropolymers in such dynamic industries as wire and cable insulation, automotive, aerospace, oil and gas recovery, and semiconductor manufacture has led to significant material developments and trends in the last few years. New fluoropolymers have been introduced to the market (amorphous fluoroplastics, modified PTFE, low-temperature fluoroelastomers, and amine-resistant fluo-... 

With mixtures of alkoxy substituents having longer alkyl chains, crystallization can be avoided to produce an amorphous rubber. The product is referred to as phosphonitrilic fluoroelastomer, a semiorganic rubber. The rubber can be cross-linked with free-radical initiators or by radiation. A... 

Fig. 4.8. Failure envelopes from rubber vulcanizates. (a) Schematic representation of the dependence of tensile stress-strain curves for an amorphous rubber on strain rate and temperature (b) failure points for a resin-cured butyl rubber gum vulcanizate tested at various rates and temperatures, = stress at break, b = elongation at break (c) comparison of vulcanizates (Viton B is a fluoroelastomer). Ab = relative extension at break, Ec = equilibrium modulus. (From Smith, 1962.)...

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