Fluorinated polymers density

Surface fluorination changes the polymer surface drastically, the most commercially significant use of polymer surface direct fluorination is the creation of barriers against hydrocarbon permeation. The effectiveness of such barriers is enormous, with reductions in permeation rates of two orders of magnitude. Applications that exploit the enhanced barrier properties of surface-fluorinated polymers include (1) Polymer containers, e.g., gas tanks in cars and trucks, which are produced mostly from high-density polyethylene, where surface fluorination is used to decrease the permeation of fuel to the atmosphere and perfume bottles. (2) Polymeric membranes, to improve selectivity commercial production of surface-fluorinated membranes has already started.13... 

Feijen J (2001) Microbial adhesion onto superhydrophobic fluorinated low density poly(ethylene) films. In Olde Riekerink MB (ed) Thesis Structural and Chemical Modification of Polymer Surfaces by Gas Plasma Etching. Printpartners Ipskamp, Enschede,... 

Arkema s Kynar Flex PPA 5300 is another fluorinated polymer processing aid, available in granular form. This product is targeted at linear low-density and high-density polyethylene and metallocene PE grades. It eliminates orange peel surfaces and improves the transparency and mechanical properties of the extruded product. It also increases extrusion speed, eliminating knots and drool in the extrusion dies. 

Sound Speed. A number of studies have been made on the effect of variations in molecular structure on sound speed. Replacing the hydrogen atoms in polyethylene with fluorine atoms lowers the sound speed, in line with the expectation that there will be a reduction in intermolecular attraction due to the larger size of the fluorine atoms (53). In this case, the sound speed also decreases because the polymer density increases. Similarly, in a series of poly(alkyl methacrylates), the sound speed decreases as the alkyl side-chain length increases (84). Again, there is a volume increase that reduces the intermolecular attraction. 

The sensitivity of the SFM to changes in crosslink density has been exenqjlified with a plasma deposited hexafluoropropylene (HFP) films (25, 28). This fluorinated polymer plays an inqjortant role in biomedical applications, especially the coating of vascular grafts. Plasma deposited fluoropolymer films promote tight protein adsorption, and are relatively non-reactive to blood platelets (29). As mentioned... 

Fluorinated polymers have many feamres different from common hydrocarbon polymers. Since they have high free volume and low cohesive energy density (CED), these fluoropolymers can be dissolved in selected fluorinated solvents. They show extraordinarily high gas and vapor permeabihty (Pinnau and Toy, 1996b Merkel et al., 1999 Polyakov et al., 2003, 2004). Generally, fluoropolymers have lower CED than any other hydrocarbon polymers, resulting in both enhanced gas solubihty and reduced activation energy of diffusion for small molecules. 

Fujitsu has developed a MEA based on an aromatic hydrocarbon solid electrolyte material, coated with a high density of highly active platinum-based nano-particle catalyst, having less than one-tenth of the methanol crossover rate encountered with typical fluorinated polymers. Fig. 10 shows Fujitsu s 15 W micro fuel cell based on a new hydrocarbon solid electrolyte material that enables use of 30% methanol powering a note book PC. The basic specification of a 3.78 W prototype micro fuel cell is given in Table 2. 

Unlike other synthetic polymers, PVDF has a wealth of polymorphs at least four chain conformations are known and a fifth has been suggested (119). The four known distinct forms or phases are alpha (II), beta (I), gamma (III), and delta (IV). The most common a-phase is the trans-gauche (tgtg ) chain conformation placing hydrogen and fluorine atoms alternately on each side of the chain (120,121). It forms during polymerization and crystallizes from the melt at all temperatures (122,123). The other forms have also been well characterized (124—128). The density of the a polymorph crystals is 1.92 g/cm and that of the P polymorph crystals 1.97 g/cm (129) the density of amorphous PVDF is 1.68 g/cm (130). 

Titanium Tetrafluoride. Titanium tetrafluoride [7783-63-3] is a white hygroscopic soHd, density 2798 kg/m, that sublimes at 284°C. The properties suggest that it is a fluorine-bridged polymer in which the titanium is six-coordinate. The preferred method of preparation is by direct fluorination of titanium sponge at 200°C in a flow system. At this temperature, the product is sufficiently volatile that it does not protect the unreacted sponge and the reaction proceeds to completion. The reaction of titanium tetrachloride with cooled, anhydrous, Hquid hydrogen fluoride may be used if pure hydrogen fluoride is available. 

Fluorosilicones consist of PDMS backbones with some degree of fluoro-aliphatic side chains. The fluorinated group can be trifluoropropyl, nonafluorohexylmethyl, or fluorinated ether side group [78,28,79]. These polymers differ not only in substituent group, but also in the amount of fluoro-substitution relative to PDMS, the overall molecular weight and crosslink density, and the amount of branching. In most commercially available cases, these polymers are addition cure systems and the reactions are those discussed previously for silicone networks. 

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