Amorphous perfluorinated polymers

G. Golemme, J. B. Nagy, A. Fonseca, C. Algieri, Y. Yampolskii, Xe-NMR study of free volume in amorphous perfluorinated polymers comparsion with other methods. Polymer, 44, 5039-5045 (2003). 

To avoid the formation of the crystalline phase, introduction of aliphatic rings into the main chain, which causes it to become twisted, is an effective method. The most well-known amorphous perfluorinated polymers are Teflon AF, Hyflon AD, and CYTOP, developed by DuPont, Solvay Chemicals, and AGC, respectively. The chemical structures of these three polymers are shown in Figure 4.2. They have excellent clarity, solubility in some fluorinated solvents, thermal and chemical durability, low water absorption, and low dielectric properties. In particular, their high transparencies arise from the cyclic structures that exist in the polymer main chains. Teflon AF is a copolymer of 2,2-bis(trifluoromethyl)-4,5-difluoro-... 

Also, new polymer elechet materials have been added to the family of electrets, i.e., parylene HT (referred to as polymer AF-4 ) and the amorphous perfluorinated polymer CYTOP. The development of such high-performance electrets is mainly motivated by the apphcation in micro electret power generators (Suzuki 2011 Yang... 

Table 4.8 Physical properties and gas transport properties of amorphous perfluorinated polymers...

Perfluorinated dioxole monomers have been used to prepare a series of amorphous fluoropolymers such as Teflon AF and Hyflon AD. A third amorphous fluoropo-lymer, Cytop contains perfluorotetrahydrofuran and perfluorotetrahydropyran rings, but is prepared in a cyclopolymerization process from an acyclic monomer. These amorphous fluoropolymers retain the outstanding chemical, thermal, and surface properties associated with perfluorinated polymers while also having unique electrical, optical, and solubility characteristics. 

All three commercial amorphous fluoropolymers. Teflon AF, Hyflon AD, and Cytop posses a unique set of properties. All dissolve in fluorinated solvents and thus may be spin coated to produce thin hlms and coatings. The polymers may also be extruded and molded using traditional polymer processing techniques. Note that the polymers are not soluble in hydrocarbon solvents or water and retain the chemical and thermal stability of perfluorinated polymers such as Teflon . These polymers have lower density than the well-known semicrystalline perfluorinated polymers such as pTFE that results in lower refractive index, lower thermal conductivity, higher gas permeability, and lower dielectric constant. The polymers are transparent and have excellent mechanical properties below their Tg due to their amorphous character. The presence of a heterocyclic ring in the polymer backbone of these materials is key... 

Teflon AF is an amorphous copolymer of tetrafluoroethylene (TFE) and 2,2-bis(trifluoromethyl)-4,5-difluoro-l,3-dioxole (PDD). It combines the properties of amorphous plastics, such as optical transparency and solubihty in organic solvents, with those of perfluorinated polymers, including high thermal stability, excellent chemical stability, and low surface energy. Moreover Teflon AF exhibits the lowest dielectric constant (1.90 for Teflon AF 2400) and the lowest re-... 

A perfluorinated polymer made by DuPont called Teflon AF breaks down the crystallinity completely, hence its designation amorphous fluoropolymer (AF). It is a copolymer made from 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole (PDD) and TFE. The structure of Teflon AF is shown in Figure 9.170. 

Copolymers of tetrafluoroethylene and 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole (PDD) are perfluorinated amorphous polymers and possess unusual combination of properties. They retain the outstanding chemical, thermal, and surface properties of perfluorinated polymers in addition to having excellent electrical and optical properties and have solubility at ambient temperature in a normal fluorosolvent. This family of copolymers is manufactured by DuPont and sold under the trade name of Teflon AF, amorphous fluoropolymers. 

TABLE 16.8 Pure Gas Permeabilities and Selectivities of Selected Amorphous Perfluorinated Glassy Polymers at 35°C... 

Commercial forms of the amorphous glassy perfluorinated polymers AF2400 and AF1600 purchased from DuPont Co in powder form were used as received. Some of the properties of these materials are described in (13), The films were cast from 2 wt.% solutions in perfluorotoluene and dried in the same way as the PTMSP films. 

Fluoropolymers are semicrystalline polymers most do not exhibit glass transition in the conventional sense during which all crystalline structures are converted to the amorphous. The glass transitions of fluoroplastics have been described as molecular relaxation (conformational disorder) that takes place in the amorphous phase of the polymer. These temperatures are also called second order transitions their value depends on the technique and the frequency of energy addition to the polymer sample. Table 3.61 presents these temperatures and melting points of perfluorinated and partially fluorinated fluoroplastics. 

These are described in literature as the new type of principal amorphous heterochain fluorine polymers containing the stable perfluorinated cycloalkane and aromatic fragments in the main chain of macromolecules [92]. The authors reported studies on the characterisation of various random polyfluorocyclobutene (PFCB) copolymers of new type of monomers F2C=CF-0-Ar-0-FC=CF2 (Ar, see Figure 8.16). These monomers were prepared from their corresponding phenolic precursors and have been described previously in paper [93]. 

All tetrafluoroethylene-based homo- and copolymers, described in earlier papers, are semicrystalline with distinct melting points. On the other hand, tetrafluoroethylene-PDD copolymers are totally amorphous and can be tailored for speciflc glass-transition temperatures by altering the polymer composition (1). So these perfluorinated amorphous polymers exhibit properties derived from their amorphous structure and perfluorinated chains. 

---