Polymerization modified PTFE

Major research efforts resulted in the development of a modified PTFE, which contains a small amount (0.01 to 0.1 mol%) of a comonomer. The most suitable comonomer was found to be perhuoro propylvinyl ether (PPVE).94 The comonomer reduces the degree of crystallinity and the size of lamellae.95 The polymerization process is similar to that for standard PTFE except additives to control the molecular weight are used.96... 

PTFE is called a homopolymer, a polymer made from a single monomer. Recently, many PTFE manufacturers have added minute amounts of other monomers to their PTFE polymerizations to produce alternate grades of PTFE designed for specific applications. Fluoropolymer manufacturers continue to call these grades modified homopolymer at below 1% by weight of comonomer. DuPont grades of this type are called Teflon NXT resins. Dyneon TFM modified PTFE incorporates less than 1% of a comonomer perfluoropropyl vinyl eflier (PPVE). Daikin s modified grade is Polyflon M-111. 

The modified parfait method developed here replaced silica gel with porous polytetrafluoroethylene (PTFE, Teflon). Properly wetted Chromosorb T, an aggregate of aqueous dispersion-polymerized PTFE, is an efficient adsorbent for many hydrophobic substances in water... 

The same polymerization process makes aqueous dispersions of PTFE as fine powder. The dispersion is concentrated and stabilized using a variety of ionic and nonionic surfactants. Several concentration methods have been reported including electrodecantation, evaporation and thermal concentration. Chemical additives to match them with the fabrication process or part property requirements can modify the final PTFE dispersion. 

PTFE can be compounded with polymeric fdlers with adequate thermal stability. Examples of such polymers include polyarylates such as polyether-ketone, polyphenylene sulfone, and polyphenylene sulfide. Surface characteristics such as wear rate, coefficient of friction, and surface tension can be modified with these additives. 

DNA synthesis has utihzed PTFE membranes of 0.2 /xm pore size, surface modified with a terpolymer coating to provide an amino derivatized support [149]. The terpolymer was formed by polymerization of N,N-di-methylacrylamide (1), methylene-bis-acrylamide (2), and aminopropyl-methacrylamide (3) (Fig. 11). 

For areas with special application requirements, specifically modified polyester fabrics, as well as fabrics from aramid fibres, fluorine polymers and arylamides like Kevlar (ref. DuPont), have proved to be satisfactory. The membranes show different characteristics depending on the coatings used. Fluorine polymers such as PVDF (polyvinylidene fluoride) are used on PES fabrics (refs Mehler and Ferrari) a PTFE (polytetrafluoroethylene) coating is very suitable for fibreglass fabrics (ref Verseidag) and there is a newly developed composite membrane with THV (ret Dyneon), a polymeric blend of tetrafluoroethylene, hexafluoropropylene and vinylidenefluorine, used as a coating on PES fabrics, of which VALMEX vivax (ret Mehler) is one example. 

Lately, surface-initiated atom transfer radical polymerization (ATRP) has been used to obtain a surface-grafted membrane (Liu et al. 2010). A porous PTFE membrane was treated by the hydrogen plasma and the C-F groups of the modified surface became effective initiators of ATRP. PEG methacrylate or its copolymer with A-isopropylacrylamide was grafted in such a way and the modified membranes showed temperature-responsive and protein repulsion features (Liu et al. 2010). 

Polymeric microporous hydrophobic membranes, typically polytetra-fiuoroethylene (PTFE), polypropylene (PP) and polyvinylidenefluoride (PVDF), are major membrane materials. Modified hydrophilic membranes such as cellulose acetate and cellulose nitrate modified with plasma polymerisation, have also been successfully tested in MD operations (Lawson and Lloyd, 1997). Furthermore, modified inorganic membranes, such as ceramic membrane modified with CgFi7(CH2)2Si(OC2H5)3 perfluoroalkylsi-lane molecule (Cg) and carbon nanotube based membranes, have also been developed for MD (Susanto, 2011). 

Because of its chemical inertness and high molecular weight, PTFE melt does not flow and cannot be fabricated by conventional techniques. The suspension-polymerized PTFE polymer (referred to as granular PTFE) is usually fabricated by modified powder metallurgy techniques. Emulsion-pol5unerized PTFE behaves... 

Different organic local modificatimi, e.g., diazonium attachment, polymer reduction, and thiol desorption, have been demonstrated and studied [82, 97-106]. Local oxidation or desorption of self-assembled mmiolayers was followed by local deposition or specific attachment onto the modified patterns [ 105,106]. The reduction of polymer, such as PTFE, made it possible to locally metalize or further polymerize the reducing sites [101-104]. More recently, a few approaches have been developed for the formation of either an anisotropic structure using a non-disk-shaped nricroelectrode and imprinting its structure [107] or by constructing... 

In this chapter, synthesis and properties of major monomers for polymerization of melt-processible fluo-roplastics are discussed. Tetrafluoroethylene is the primary monomer. Small amounts of other monomers are incorporated in the TFE polymer structure to modify its properties and processing characteristics. These monomers include hexafluoropropylene (HFP), per-fluoroalkylvinylethers (PAVE), and chlorotrifluoro-ethylene (CTFE). A number of specialty monomers, though less common, are also used to modify the PTFE structure. Examples include perfluoroisopropyl vinyl ether and perfluorobutyl ethylene. Preparation of important monomers including vinyl fluoride and vinylidene fluoride are reviewed. 

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