Fluorinated styrene monomers

In summary, almost 80 distinct ATRP polymerizations of 4-X-styrene monomers and over 215 copolymerization via lactide ROP were conducted. A set of optimized polymerization parameters were successfiilly identified that allowed the highly reproducible synthesis of well-defined diblock copolymers on a gram scale fhat adopt the double-gyroid nanomorphology during microphase separation as will be discussed in the following chapter. To reduce the synthesis cost and make the polymers more environmentally sustainable, the fraction of expensive fluorinated styrene monomer was gradually decreased. 

Grafting of fluorinated styrene monomers such as a, yff-trifluorostyrene before proceeding to sulfonation [138]. However, such fluorinated monomers require careful handing and special set-up as well as safety procedures, which eventually introduce a tremendous additional cost to the economy of these membranes. 

One alternative to the tetrafluoroethylene-based backbones of the previously discussed materials is the use of styrene and particularly its fluorinated derivatives to form PEMs. As extensively reported in the literature, styrenic monomers are widely available and easy to modify, and their polymers are easily synthesized via conventional free radical and other polymerization techniques. 

Among all remaining monomers, those containing (per)fluorinated side chains such as fluorinated acrylates, vinyl ethers or esters, maleimides and styrenic monomers are also very interesting and have been studied in (co)telo-merisation. Most of them have been previously reviewed [15]. However, they are not mentioned in this chapter. 

Furthermore, we have reported on the first examples of free radical homopolymerization and copolymerization of 2,3,4,5,6-pentafluorostyrene (3) with styrene (5) and its derivative 4-((V-adamantylamino)-2,3,5,6-tetrafluorostyrene (4) in aqueous solution via the host-guest complexation with Me-p-CD using water-soluble initiators (Fig. 5) [31]. The fluorinated monomers (3 and 4) and styrene (5) were complexed by Me-p-CD in water. The stoichiometries of the host-guest complexes were determined by NMR spectroscopy according to the Job method [32-34], It was clearly shown that styrene (5) forms a defined 1 1 complex while the fluorinated monomers (3 and 4) are encapsulated by two Me-p-CD molecules. In the case of fluorinated monomer (3) this result was not expected since 3 and 5 have the same molecular scaffold and molecular modelling showed that the fluorinated styrene derivative 3 is only slightly bigger than styrene itself (Fig. 6) [35],... 

The hydrophobic monomers styrene and MMA were copolymerized with the sodium salt of vinylbenzylsulfosuccinic acid as a polymerizable surfactant grafting of the surfactant onto the particles was estimated to be about 50-75% [51]. A polymerizable surfactant was formed by the esterification of hydroxypropylmethacrylate or hydroxyethyhnethacrylate with succinic anhydride [53]. However, in addition to the surfmer, sodium dodecyl sulfate (SDS) was employed to provide a sufficient stability to the latexes. A mono-fluorooctyl maleate surfactant was used to stabilize the polymerization of styrene in miniemulsion [55]. Although the polymerizable moiety was not fixed at the end of the fluorinated chain (the hydrophobe part), the surfactant could be copolymerized with the styrene monomer. Subsequently, on comparison of the infrared (IR) spectra (vibration of -CF2 and -CFj) before and after dialysis, it was estimated that 92% of the surfactant had remained grafted post-dialysis. 

Patents relating to the apphcation of radiation-grafted ion-exchange membranes in fuel cells have been granted to Scherer et al. [89] and to Stone and Stock [90, 91]. These patents mention the functionalization of base polymers with quaternary ammonium groups to yield alkaline polymers. The use of fluorine-substituted styrenic monomers is also claimed to improve membrane chemical stability when utilized in fuel cells (removal of undesired and reactive C-H bonds). 

A variety of ionomers have been described in the research literature, including copolymers of a) styrene with acrylic acid, b) ethyl acrylate with methacrylic acid, and (c) ethylene with methacrylic acid. A relatively recent development has been that of fluorinated sulfonate ionomers known as Nafions, a trade name of the Du Pont company. These ionomers have the general structure illustrated (10.1) and are used commercially as membranes. These ionomers are made by copolymerisation of the hydrocarbon or fluorocarbon monomers with minor amounts of the appropriate acid or ester. Copolymerisation is followed by either neutralisation or hydrolysis with a base, a process that may be carried out either in solution or in the melt. 

A preferable system is poly(p-fluorostyrene) doped into poly(styrene). Since rotations about the 1,4 phenyl axis do not alter the position of the fluorine, the F spin may be regarded as being at the end of a long "bond" to the backbone carbon. In standard RIS theory, this polymer would be treated with dyad statistical weights to automatically take into account conformations of the vinyl monomer unit which are excluded on steric grounds. We have found it more convenient to retain the monad statistical weight structure employed for the poly(methylene) calculations. The calculations reproduce the experimental unperturbed dimensions quite well when a reasonable set of hard sphere exclusion distances is employed. 

An alternative approach to the use of partially fluorinated systems to reduce the cost of fluorinated PEMs has been developed by DeSimone et al. a perfluo-rinated vinyl ether is copolymerized with a hydrocarbon monomer (styrene), sulfonated, and then subsequently fluorinated to replace existing C-H bonds with C-E bonds (Eigure 3.18). Thus yields the perfluorinated, cross-linked sul-fonyl fluoride membrane that can then be hydrolyzed to give the PEM (7). Because the membranes are cross-linked, considerably higher acid contents (up to 1.82 meq/g) are possible for these materials in comparison to Nafion, leading also to higher proton conductivity values. 

As shown in Figure 1.2, the solvent strength of supercritical carbon dioxide approaches that of hydrocarbons or halocarbons. As a solvent, C02 is often compared to fluorinated solvents. In general, most nonpolar molecules are soluble in C02, while most polar compounds and polymers are insoluble (Hyatt, 1984). High vapor pressure fluids (e.g., acetone, methanol, ethers), many vinyl monomers (e.g., acrylates, styrenics, and olefins), free-radical initiators (e.g., azo- and peroxy-based initiators), and fluorocarbons are soluble in liquid and supercritical C02. Water and highly ionic compounds, however, are fairly insoluble in C02 (King et al., 1992 Lowry and Erickson, 1927). Only two classes of polymers, siloxane-based polymers and amorphous fluoropolymers, are soluble in C02 at relatively mild conditions (T < 100 °C and P < 350 bar) (DeSimone et al., 1992, 1994 McHugh and Krukonis, 1994). 

The cleavage of C-I bond can be achieved from various methods [373-375]. However, according to well chosen monomers, two main ways have been developed in order to control telomerisation from alkyl iodides iodine transfer polymerisation (ITP) and degenerative transfer. ITP can be easily applied to fluorinated monomers whereas degenerative transfer concerns the controlled polymerisation of methyl methacrylate, butyl acrylate [376] or styrene [377] and will not be discussed in this chapter. 

Additions occur more easily if a carbanion with resonance or inductive stabilization is formed in the addition. Thus, fulvenes are very reactive, vinylsilanes and highly fluorinated alkenes somewhat less so. Styrene, 1,3-dienes, and enynes are more reactive than isolated alkenes, and Grignard reagents may be used to initiate anionic polymerization of styrenes, dienes, and acryhc monomers. Strained alkenes such as norbomenes and cyclopropenes are also more reactive. Examples of additions facilitated by resonance or substitution are shown in Scheme 8. 

Perfluoroalkyl (meth)acrylates FM-12 and FM-15 have been polymerized homogeneously in SCCO2 with copper catalysts/fluorinated ligand systems, but the MWDs of the products are not reported due to the lack of appropriate analytical methods.95 Other flu-orinated monomers (FM-13 and FM-14) were used for block copolymerization with styrene and acrylates with CuBr/L-1 in the bulk under heterogeneous conditions.315... 

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