Polymeric fluorinated surfactants

Polymeric and oligomeric surfactants [176-178] are used in various technical and biological applications, most importantly as stabilizers or flocculants of disper- 

Silicone-containing polymeric surfactants have been described in Section 1.7 and Chapter 12. Polymeric fluorinated surfactants with a carbon containing backbone are discussed below. 

Polymeric fluorinated surfactants (1) have a fluorinated backbone or (2) contain perfluroalkyl groups, as pendant perfluoroalkyl groups attached directly or indirectly to the polymer backbone, or as one or two fluorinated end groups of the polymer. A perfluoroalkyl tail can be attached to poly(tris(hydroxymethyl)-acrylamidomethane or to a natural product, such as a sugar, polyol, and so forth [180]. A fluorinated group may be attached to a poly(oxyethylene) chain —CH2CH2O—, to an ethylene oxide-propylene oxide block polymer, or to an acrylic comonomer. 

A fluorinated backbone may contain —CF2CF2— or polyether units. The polyether chain may be perfluropoly(oxypropylene) 

Perfluoroalkane ionomers consist of a perfluorinated backbone and pendant chains terminated with an anionic group, for example with sulfonic acid groups (Nafion H) [181-185]  

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Laser desorption FTICR is also a valuable technique for the characterization of industrial materials. Simonsick and Ross analyzed novel dispersants (used in emulsion polymerization), fluorinated surfactants, and natural oils with masses in the range of 500-3000 Da. Specifically, poly(ethylene oxide)... 

Polymeric fluorinated surfactants containing ionic groups may or may not be surface active, depending on their structure [213]. 

Fluorinated surfactants (e.g. ammonium perfluoroocatanaote and sodium perfluo-rooctanoate) are used to emulsify chlorocarbons and fluorocarbons in emulsion polymerization [111-114] (see Polymerization). Fluorinated surfactants are used as emulsifiers in medicine (see Fluorochemical Oxygen Carriers in Section 10.4) and in cosmetics. Fluorinated surfactants improve leveling of acrylic emulsions, floor polishes, and shoe brighteners (see Polishes and Waxes). 

To keep the precipitating polymers in the dispersed state throughout the polymerization, requires steric stabilizers. This problem is classically tackled via copolymerization with fluoroalkylmethacrylates or the addition of fluorinated surfactants, both being only weak steric stabilizers. DeSimone el al. also applied a fluorinated block copolymer,9 proving the superb stabilization efficiency of such systems via a rather small particle size. One goal of the present chapter is therefore an investigation of our fluorinated block copolymers as steric stabilizers in low-cohesion-energy solvents. 

Poly vinylidene fluoride is polymerized under pressure at 25-150°C in an emulsion using a fluorinated surfactant to minimize chain transfer with the emulsifying agent. Ammonium persulfate is used as the initiator. The homopolymer is highly crystalline and melts at 170°C. It can be injection molded to produce articles with a tensile strength of 7000 psi (48 MPal. a modulus of elasticity in tension of 1.2 x 105 psi and a heat deflection of 3003F (149°C). 

Emulsion polymerization requires the use of free radical initiators, fluorinated surfactants, and often chain transfer agents. The polymer isolated from the reaction vessel consists of agglomerated spherical particles ranging in diameter from 0.2 to 0.5 jm.56 It is then dried and supplied as a free-flowing powder or as pellets, depending on the intended use. If very pure PVDF is required, the polymer is rinsed before the final drying to eliminate any impurities such as residual initiator and surfactants.57... 

Polymerization of vinylidene fluoride by emulsion or suspension polymerization in water is conducted at conditions of 10-130 °C and 10-200 bar. In the emulsion polymerization, either water-soluble peroxides or monomer-soluble peroxy or organic peroxides are used as initiators [ 17]. Fluorinated surfactants, such as ammonium perfluorooctanoate, are used as dispersing agents. Chain transfer agents, such as acetone, chloroform, or trichlorofluoromethane, may be... 

Another trend in the polymerization process is to reduce or completely remove surfactants based on perfluorooctanoic acid (PFOA), which is suspected to be carcinogenic [6,7], Another approach is to use bifunctional fluorinated surfactants with molecular weights in the range 600-1000 [8],... 

Surfactants used in the polymerization are water-soluble, halogenated surfactants. They are in particular fluorinated surfactant such as ammonium, substituted ammonium, quarternary ammonium, or alkali metal salts of perfluorinated or partially fluorinated alkyl carboxylates, monoalkyl phosphate esters, alkyl ether or polyether carboxylates, alkyl sulfonates, and alkyl sulfates. 

PREPARATIVE TECHNIQUES Emulsion polymerization (a) 300-800 psig, perfluorinated surfactant initiator, 65-85°C, 2-6 h (b) 2001bin, 50-110°C, fluorinated surfactant,... 

Any future application of inverse emulsion polymeriTation in CO2 will depend entirely upon the design of suitable surfactants, combined with choosing suitable monomer systems. The surfactant and monomer must exhibit phase behavior in CO2 according to Fig. 7.2 to operate in the emulsion polymerization regime. At present, fluorinated surfactants allow for technical success, yet are not sufficiently economical to allow for commercial success as well. 

Fluoropolymers are typically synthesized in aqueous polymerization systems (both emulsion and suspension), non-aqueous systems (Freon-113), or Freon-113/aqueous hybrid systems [8]. Such processes require the use of large quantities of water and CFCs (for non-aqueous polymerizations) or fluorinated surfactants (for emulsion polymerization). Aqueous suspension and dispersion poly-... 

The free-radical addition of TFE to pentafluoroethyl iodide yields a mixture of perfluoroalkyl iodides with even-numbered fluorinated carbon chains. This is the process used to commercially manufacture the initial raw material for the fluorotelomer -based family of fluorinated substances (Fig. 3) [2, 17]. Telomeri-zation may also be used to make terminal iso- or methyl branched and/or odd number fluorinated carbon perfluoroalkyl iodides as well [2]. The process of TFE telomerization can be manipulated by controlling the process variables, reactant ratios, catalysts, etc. to obtain the desired mixture of perfluoroalkyl iodides, which can be further purified by distillation. While perfluoroalkyl iodides can be directly hydrolyzed to perfluoroalkyl carboxylate salts [29, 30], the addition of ethylene gives a more versatile synthesis intermediate, fluorotelomer iodides. These primary alkyl iodides can be transformed to alcohols, sulfonyl chlorides, olefins, thiols, (meth)acrylates, and from these into many types of fluorinated surfactants [3] (Fig. 3). The fluorotelomer-based fluorinated surfactants range includes noiuonics, anionics, cationics, amphoterics, and polymeric amphophiles. 

Fluorinated surfactants have been used for decades as processing aids during aqueous emulsion polymerization synthesis of fluoropolymers such as poly (tetrafluoroethylene). The function of the fluorosurfactant is to solubilize both the fluorinated monomer(s) as well as the growing fluoropolymer. Historically, the... 

FluorinatGd MethacrylatGS. Fluorinated polymers are very important materials because of their water- and oil-repellent properties. The synthesis of fluoropolymers is one case in which special polymerization techniques are required eg, emulsion polymerization with added fluorinated surfactant, and... 

Emulsifiers such as fatty alcohol sulfates, alkane sulfonates, alkali salts of fatty acids, and others are slightly to marginally effective (77). Fluormated surfactants, particularly perfiuorinated carboxylic acids containing seven or eight fluorine atoms, are specially effective in maintaining a high rate of polymerization after about 40% conversion. Fluorinated surfactants are characterized by low values of critical concentration of micelle formation (74). They are thermally and chemically stable, and their incorporation does not impair the PVF properties. 

VDF and suitable comonomers can be polymerized as a microemulsion where fluorinated oil-in-water microemulsion and fluorinated surfactant are present (37-39). The core-shell structure of these self-assembling systems and their distinctive pol5unerization features along with the range of particle size distribution have been reported (40). 

Details of the processes used to produce vinylidene fluoride-hexafluoropropylene copolymers have not been disclosed but the copolymers may be prepared by emulsion polymerization under pressure using a persulphate-bisulphite initiator system. Highly fluorinated surfactants, such as ammonium perfluorooctoate, are most commonly used in order to avoid chain transfer reactions. The preferred vinylidene fluoride content for commercial copolymers is about 70% mole. The structure of such a copolymer might be represented as follows ... 

The commercial elastomers are commonly prepared by aqueous emulsion polymerization at elevated temperatures and pressures using a redox initiating system such as a bisulphite-persulphate mixture. Ammonium perfluorooctoate or some other highly fluorinated surfactant is used as a dispersing agent since it is important that any surfactant used does not become involved in transfer reactions. 

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