Dioxole monomers

Other dioxole monomers and polymers have been prepared from halogenated dioxoles with different substituents in the 2,4, and 5 positions of the dioxole ring. 

Table 2.1 lists a number of dioxole monomers and indicates their ability to homopolymerize and/or copolymerize with TFE in CFC-113 solution. The copolymerization of dioxoles with chlorine in the 4 and 5 position of the dioxole ring further demonstrates the very high reactivity of this ring system. Thus an almost infinite number of dioxole polymers can be prepared with one or more comonomers in varying proportions. We have chosen to focus our present work on copolymers of TFE and PDD to preserve the outstanding thermal and chemical properties of perfluorinated polymers. At this point it should be noted that fully fluorinated ethers are nonbasic and effectively possess the same chemical inermess as fluorinated alkanes. Perfluorinated ether groups in polymers are even less reactive as a result of their inaccessibility to chemical reagents. 

Amorphous perfluoroplastics developed by DuPont (Teflon AF) and Asahi Glass (Cytop) contain bulky structures that are responsible for the absence of crystallinity. When Teflon AF was irradiated by low-energy x-rays, it was found that the inclusion of the dioxole monomer not only improves the optical properties but also increases the radiation tolerance of the homopolymer [43]. 

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. 

The other commercial dioxole monomer is 4-trifluoromethoxy-2,2,5-trifluoro-l, 3-dioxole, (TDD, XXI). Copolymers of TDD and tetrafluoroethylene are produced and sold by Solvay-Solexis as Hyflon AD amorphous fluoropolymer (XXII).Monomer XXII (TDD) has been synthesized by two related routes via perfluorohypofluorite intermediates (Eq 13.20). In the first route, trifluoromethylhypofluorite formed from either COF2 or CO and fluorine is added... 

Solubility of Copolymers A usual strategy to enhance the solubility of PVDF- or PTFE-based polymers in SC-CO2 is the copolymerization of VDF (or TFE) with a comonomer such as hexafluoropropylene (HFP) [4], dioxole monomers [4], or vinyl acetate (VAc) [ 19,20]. The microstmcture of the resulting copolymer is affected in order to decrease or suppress the crystalline domains and incorporate strong Lewis base sites to promote interactions with CO2. 

PDD as well as other dioxoles have been copolymerized with monomers such as vinyl fluoride, vinylidene fluoride, tiifluoroediylene, perfluoroalkylethylenes, chlorotrifluoroethylene, hexafluoropropylene, and perfluorovinyl ethers, some of which contain functional groups. 

In addition to the alkenyldioxolanes, 4-methylenedioxolane (87) and dioxoles (88) and (89) can be utilized to produce heterocyclic polymers containing this ring system. In a comparative study on the cationic polymerization of these monomers (79MI11105) it was found that the order of reactivity is (87) > (88) > (89). In these polymerizations, ring-opening reactions were found to the extent of 35% and 9%, respectively, for monomers (89) and (88) in addition to the normal 1,2-addition mode. 

Leismann et al.[182] have recognized this problem in their publication of 1984, in which they describe a thorough and detailed investigation of the kinetics of formation and deactivation of exciplexes of. S) benzene or toluene and 1,3-diox-ole, 2,2-dimethyl-l,3-dioxole, and 2,2,4-trimethyl-l,3-dioxole. The evolution in time of monomer and exciplex fluorescence after excitation using a nanosecond flash lamp was analyzed, and again it was concluded that the formation of exciplexes is diffusion controlled their decay proceeds mainly (>90%) via radiationless routes. The polar solvent acetonitrile enhances radiationless deactivation, possibly by promoting radical ion formation. Because decay of benzene fluorescence is essentially monoexponential, dissociation of the exciplex into Si benzene and dioxole is negligible. 

Spontaneous 1 1 copolymerization has been noted when sulfur dioxide was bubbled through bicycloheptene at —40°C. (88), when isobutylene was bubbled through methyl a-cyanoacrylate (54), when 1,3-dioxole was mixed with maleic anhydride (17), and when vinylidene cyanide was mixed with styrene (20), the latter reactions at room temperature. None of these monomers undergoes homopolymerization under the same experi-... 

Bis(trifluoromethyl)-4,5-difluoro-l,3-dioxole represents the monomer of a new family of amorphous fluoropoiymers (Teflon AF, DuPont) with unusual properties [89JFC(45)100]. Novel fluorinated 2,2-bis(triflu-oromethyl)dioxolanes containing alkyne groups have been synthesized from hexafluoroacetone and propargylic alcohol, bromomethyloxirane, or 1,2-bis(bromomethyl)oxirane [90MI1 91JFC(52)I59] (Scheme 95). 

Dioxole, 4,5-difluoro-2,2-bistrifluoromethyl-, monomer for polymer formation, 60, 47... 

Russo, A. Navarini, W. Perfluoro-4-methyl-l,3-dioxole a new monomer for high-Tg amorphous fluoropolymers. J. Fluorine Chem. 2004,125, 73-7S. 

It should be noted that these dioxoles are extremely reactive in free radical polymerizations. Dioxoles are the hrst fluorinated monomers containing an internal olehnic structure that homopolymerize and possess reactivity similar to tetrafluoroethylene. This high reactivity is believed to a result of the steric accessibility of the double bond. 

Bis(trifluoromethyl)-4,5-difluoro-l,3-dioxole (Fig. 18) was copolymerized with TFE and a PSVE monomer shown in Fig. 5. A homopolymer of this third monomer exhibits a glass transition temperatme of 330 °C [56]. The terpolymer exhibits a high softening temperatme like the above short side chain copolymers [57]. This is one of the another approaches to obtain high temperatme membranes. The temperature dependency of the modulus of the terpolymer is compared with that of a conventional copolymer in Fig. 19 [58]. 

The random co-polymers of tetrafluoroethylene ( IFF) used in this work are amorphous and glassy. They are Teflon AF 1600 and 2400 (second monomer perfluoro-2,2-dimethyl-1,3-dioxole, DuPont) and Hyflon AD 60X (second monomer perfluoro-4-methoxy-... 

Preparation. 2,2-Bistrifluoromethyl difluoro-l,3-dioxole (PDD) monomer is synthesized in four steps (2). In the first step, hexafluoroacetone and ethylene oxide are reacted to form 2,2-bistrifluoromethyl-4,5-dichloro-4,5-difluoro-l,3-dioxolane. This product is then fully chlorinated and subsequently partially fluori-nated to difluoro-l,3-dioxolane. In the last step, the fluorinated product is dechlo-rinated to obtain the final product, PDD. 

Commercial fluoropolymers include homopolymers and copolymers. According to the convention of the American Society for Testing Materials (ASTM), homopolymers contain 99% or more by weight of one monomer and 1% or less by weight of another monomer. Copolymers contain more than 1% by weight of one or more comonomers. The major commercial fluoropolymers are based on three monomers tetrafluoroethylene (TFE), vinylidene fluoride (VDF), and, to a lesser extent, chlorotrifluoroeth-ylene (CTFE). Examples of comonomers include perfluoromethyl vinyl ether (PMVE), perfluoro-ethyl vinyl ether (PEVE), perfluoropropylvinylether (PPVE), hexafluoropropylene (HFP), ClFE, perfluo-robutyl ethylene (PFBE) and exotic monomers such as 2,2-bis(trifluoromethyl)-4,5-difluoro-l,3-dioxole. 

Amorphous copolymers of TFE with exotic monomers such 2,2-bis(trifluoromethyl)-4,5-difluoro-l,3-dioxole are soluble in special halogenated solvents. They can be applied to surfaces as a polymer solution to form thin coatings. The dried coating is resistant to almost as many chemicals as PTFE [5]. 

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