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Polyphosphazenes Elastomers.
Materiales Polímeros

Carlos Muñoz Ortolá 2010/2011

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1.- Introduction……………………………………….3 2.- Synthesis of elastomers……………………………4
2.1. Polyphosphazenes as Thermally Stable Elastomers. 2.2. Fluorinated Polyphosphazenes.

3.- Applications……………………………………….7
3.1. Fire-Retardant Elastomers. 3.2. Aircraft. 3.3. Fluorinated Polyphosphazenes Elastomers (FPEs). 3.4.Ceramics. 3.5. Gas Separation Membrane Elastomers.

4.- Conclusions………………………………………...11 5.- References………………………………………....11

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1.- Introduction.
In 1965, Allcock and Kugel synthesized linear polydichlorophosphazenes (PDCP) from hexachlococyclotriphosphazenes (HCCP) trimer by thermal ring opening polymerization successfully and they further substituted halogens with alkoxy and aryloxygroups. Polyphosphazenes are unique, attracting, most interesting class among polymers and have novel characteristics due to inorganic main chain structure, combination of organic and inorganic parts and applications such as hydrogels, drug delivery, membranes, biomaterials, fiber and film forming, elastomers, ionic conductors, flame retardant, and optical applications. Polyphosphazenes have manynumerous properties and applications and among them elastomeric property was attracting keen interest as being compared to others due to the presence of nitrogen and phosphorus atoms at the backbone (-N=P-). Elastomers are defined as polymeric materials of very high deformation and recovery. For elasticity, bonds in polymers should be highly flexible and mobile. The general structure ofpolyphosphazenes was shown in Figure 1. These polymers have inorganic backbone polymeric structures and their glass transition temperatures lower than room temperature. Generally, polyphosphazenes with different side chains were obtained by the replacement of halogens with alkoxy, aryloxy or amino groups in polyphosphazenes chain. Ring opening polymerization and replacement of halogens by alkyl groups wereshown in Figure 2. The properties of polyphosphazenes depended upon the side groups. The small and flexible organic groups were better as being compared to bulky groups for elastomers. Polymers with 2, or more than 2, different fluoroalkoxy or aryloxy side groups were shown in Figure 3. Polyphosphazenes with 2 different types of side groups such as OCH3, OC2H5, OCH2CH2OCH2 CH2OCH3 attached to samephosphorus in the polyphosphazenes chain were of elastomeric properties because of low glass transition temperature, flexibility and resistant to crystallization, while polymers with same side group such as OCH2CF3 attached to same phosphorus at polyphosphazenes was of microcrystalline nature. Generally, elastomers were divided into 2 types. First, elastomers have same or mixed groups of alkoxy orfluoroalkoxy in phosphazenes. Second, polymers have two or more than two categories of aryloxy side groups (Figure 3). Further, polymers would be converted into cross linking rubbery elastomeric state in the presence of light, heat and peroxide followed by a free-radical reaction. Aryloxy phosphazenes elastomers were also used for making rubber foam elastomer.

Figure 1. Structure ofpolyphosphazenes.

Figure 2. Thermal ring opening and replacement of halogens.

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2.- Synthesis of elastomers.
There were many methods for the synthesis of stable high molecular weight polyphosphazenes elastomers. In the main method halogen atoms connected with phosphorus in polyphosphazenes backbone were replaced with alkoxy, aryloxy or amino groups. Generally, polyphosphazenes properties dependedupon side groups (same or different) attached to their backbone. Polymers with same side groups connected to backbone were of crystalline or elastomeric property while polymers with two different side groups have elastomeric property. Polyphosphazenes elastomers and rubbers have 3 major types. First, single atoms such as Cl, Br or F as side groups were connected to polymer backbone. Flexibility...
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