Perfluoroalkylvinyl ether

Core-shell polymers consist of particles with composite structure. The inner portion of particle (core) has a different composition than the outer portion (shell). Typically, they are prepared by introducing a comonomer (e.g., perfluoroalkylvinyl ether [PAVE]) during the polymerization under specific conditions [28]. An example is a composition with the core constituting 65% to 75% of the total weight of the particle. 

HFP is thermally stable up to 400°C to SOOT (752°F to 932°F). At about 600°C (1112°F) under vacuum, HFP decomposes and produces octafluoro-2-butene (CF3=CFCp3) and octafluoroisobutylene [44]. Under basic conditions, hydrogen peroxide reacts with HFP to form hexafluoropropylene epoxide, which is an intermediate in the preparation of perfluoroalkylvinyl ethers [45,46]. Hexafluoropropylene readily... 

Perfluoroalkylvinyl ethers form an important class of monomers in that they are used as comonomers for the modihcation of the properties of homofluoropolymers in addition to their broad nse in copolymers with TFE and other monomers. They are capable of snppressing the crystallization of PTFE efficiently, which imparts usefnl mechanical properties to lower molecular weight of polytetrafluoroethylene polymers. Copolymers of PAVEs and tetrafluoroethylene are thermally stable as PTEE homopolymers. Commercially significant monomers are perfluoropropylvinyl ether and perflnoromethylvinyl ether (PMVE), used for the production of a variety of perflnoroalkoxy resins. 

PFA is a copolymer of TFE and a perfluoroalkyl vinyl ether, such as perfluoropropyl vinyl ether PPVE. Copolymerization of perfluoroalkylvinyl ethers with tetrafluoroethylene can be done in a halogenated sol-... 

Perfluroalkoxy polymer or PFA is one of the most important meltprocessible fluoroplastics due to its relative ease of processing and high service temperature equivalent to polytetrafluoroethylene (260°C). It also has the same excellent chemical resistance and low friction properties as PTFE. Perfluroalkoxy polymers are prepared by copolymerization of a perfluoroalkylvinyl ethers (Rf—O—CF=CF2, where Rj is a perfluorinated alkyl group) with tetrafluoroethylene. Examples of commercially utilized ethers include perfluoromethyl-vinyl ether (CFg—O—CF=CF2), perfluoroethylvinyl ether (C2F5—O—CF=CF2) and perfluoropropylvinyl ether (C3F7—O—CF=CF2). Several percent of ether is incorporated in a copolymer. 

The polymerization of TFE and perfluoroalkylvinyl ethers (PAVE) is described by discussing technology disclosed in selected patents. Copolymerization of perfluoroalkylvinyl ethers with tetrafluoroethylene can be accomplished in a halogenated solvent, in an aqueous phasel l sometimes containing some halogenated solvent, usually in the absence of a surfactant. 

One of the earliest reports of copolymerization of PAVE s and tetrafluoroethylene in nonaqueous perfluorinated phase is by Harris and McCaneJ They reported on copolymerization of TFE and PAVE s in a perfluorinated solvent perfluorodi-methylcyclobutane. The successful perfluoroalkylvinyl ether (Rf—O—CF=CF2) in this study usually contained 1 to 5 carbons in its alkyl (Rf) group. Peroxides and azo compounds were the preferred initiator of the polymerization. 

In the next two sections, polymerization of tet-rafiuoroethylene and perfluoroalkylvinyl ether in aqueous medium are discussed. 

Gresham and Vogelpohll" copolymerized tet-rafluoroethylene and perfluoroalkylvinyl ether in a medium consisting of water and only a minor amount of fluorocarbon solvent. Polymer properties were found to be poorer when polymerization took place in purely aqueous medium. The solvent was shown to also increase the polymerization rate. Their method narrowed the range of the molecular weight distribution... 

Table 5.7. Aqueous Polymerization of Tetrafluoroethylene and Perfluoroalkylvinyl Ethers ... 

Hartwimmer and Kuhls l reported synthesis of non-elastomeric terpolymers of tetrafluoroethylene (TFE) in aqueous medium. These polymers were comprised of perfluoroalkylvinyl ethers (PAVE) and hexafluoropropylene (HFP) in addition to TFE. The authors reported increased PAVE, such as perfluoro-propylvinyl ether (PPVE), incorporation due to the presence of HFP. Additional PAVE suppresses the melting point of the copolymer without a loss of mechanical properties. 

Copolymers of tetrafluoroethylene with perfluoro-alkylvinyl ethers were the ultimate elastomers for fluid, chemical, thermal and oxidative resistance. Cure chemistry mainly determined tensile properties, compression set resistance and upper use-temp. The chemistry was described for a perfluoroelastomer using a nitrile-substituted perfluoroalkylvinyl ether as cure-site monomer. It cured by trimerisation of the nitriles to triazine functionality and was devoid of any C-H bonds. Physical properties and thermal resistance in air over 300C were excellent. Peroxide-curable perfluoroelastomers, using hydrocarbon crosslinkers, were limited in performance. 3 refs. 

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