Fluorinated poly acrylates

Synthesis and Structure-Property Relationships of Lo w-Dielectric-C onstant Fluorinated Poly acrylates ... 

Similarly to perfluoropolyethers, the widely accepted explanation for the high solubility of fluorinated poly(acrylates) in SC-CO2 is provided by their low cohesive energy densities and weak self-interactions. Johnston and coworkers reported surface tension values of 10-15 mN/m, which is actually lower than the values for perfluo-ropolyether and poly(vinyl acetate), the other aforementioned C02-philic references. 

Amphiphilic block copolymers that are soluble in CO2 comprise a C02-philic block and a CO2-phobic one and are thus prone to form complex structures in solution such as micelle-like aggregates and polymersomes. As a result of their high solubility, fluorinated poly(acrylates) and polysiloxanes mainly constitute the C02-philic building blocks of choice to design C02-soluble amphiphilic copolymers. 

Similarly to double hydrophilic block polymers, double C02-philic copolymers are made of two chemically different blocks soluble in CO2. At high pressures, they behave as fully soluble block copolymers. Their amphiphilic behavior can be induced by a change in pressure or temperature which renders COj a selechve solvent for one of the blocks. The resulting amphiphUic copolymers with a C02-philic outer sheh and a CO2-phobic core can be expected to self-assemble into aggregates or polymer-somes. To date, the only example of double C02-phihc copolymers concerns block copolymers comprising fluorinated poly(acrylate) andpoly(vinyl acetate) blocks (see Figure 13.21). 

The addition of boron trifluoride as a catalyst has been found to be essential in the fluorination of carboxylic groups of poly(acrylic acid) and poly(methacrylic acid) with sulfur tetrafluoride.12 Boron trifluoride as a Lewis acid is necessary in catalytic amounts to polarize the C = 0 bond before fluorination with molybdenum(VI) hexafluoride takes place.1314... 

Poly(acrylates) and (alkyl acrylates) - Fluorinated acrylics are inherently photostable while the vacuum UV photolysis of PMMA results in de-esterification and double bond formation ". The stereostructure of PMMA also has an important influence on the product distribution. X-Ray and UV exposure of PMMA was fingerprinted via FT NMR analysis. ... 

It has been demonstrated that hydrophobic, fluorinated, hyperbranched poly(acrylic acid) films can passivate and block electrochemical reactions on metal surfaces thus preventing surface corrosion [57]. Hyperbranched films can be synthesized on self-assembling monolayers on the metal surface via sequential grafting reactions to obtain thick and homogeneous films. 

Poly(acrylates) and (alkyl acrylates). - Structured nanopore films of poly(styrene-block-methyl methacrylate) copolymers have been made with controlled spectral sensitivity, such that each block is sensitive to a specific degradation wavelength. In copolymers of 2,2,2-trifluoroethyl methacrylate with vinyl ethers, the photosensitivity is controlled by the vinyl ether units. Photodegradation occurs at the tertiary positions of the ether units followed by lactone formation and chain scission processes. Furthermore, the fluorinated side chains have been found to inhibit cyclization reactions. 

For applications in CO2, silicones are generally considered less effective than their fluorinated counterparts. Poly(dimethyl siloxane) (PDMS) solubility in CO2 was first reported in 1996 at a level of 4 %wt, PDMS n 13k) is soluble in CO2 at 35 °C and 277 bar (55). Block copolymer surfactants consisting of C02-philic PDMS and C02-phobic ionizable poly(methaciylic acid) (PMA) or poly(acrylic acid) (PAA) were used to form w/c and c/w emulsions (17). These PDMS-based block copolymers exhibited remarkable ambidextrous behavior to stabilize PPMA particles both in CO2 on the one hand, and in water on the other hand (56, 57). Steric stabilization is imparted in CO2 by PDMS, which is significantly more soluble in a CO2/MMA mixture than in pure CO2 (58). 

As fluorinated poly(alkylacrylates) have proved to be highly soluble in compressed CO2, they present themselves as possible components in the stabilization of heterogeneous reaction systems in CO2. Indeed, there has been considerable effort in the development and synthesis of polymeric emulsifiers for lipophilic materials and stabilizers for hydrocarbon polymer dispersions in CO2. DeSimone and coworkers demonstrated the feasibility of using fluorinated alkyl acrylate homopolymers, such as PFOA, as efficient amphiphiles, owing to the lipophilic acrylate backbone and the C02-philic fluorinated pendant chains [35, 36]. As was described earlier, these fluorinated alkyl acrylates are readily synthesized homogeneously in CO2. The solution properties and phase behavior of PFOA in compressed CO2 have been thoroughly examined and reported elsewhere [37-39]. 

W.C. Wang, R.H. Vora, E.T. Kang, K.G. Neoh, C.K. Ong, L.F. Chen, Nanoporous ultra-low-K films prepared from fluorinated polyimide with grafted poly(acrylic acid) side chains, Adv. Mater. 16 (1) (2004) 54-57. 

PS-fc-PI diblock copolymers [65], poly(fumarate)s or poly(acrylate)s [131], lamellar structures are found in nearly all cases if the number of m is not too small. The backbone and its flexibility seem to have only marginal influence. In simple terms, the strong phase separation into areas with fluorinated segments and areas with the nonfluorinated rest seems to be the first principle in structure formation. Whereas in sf alkanes besides lamellar structures also hexagonally packed cylinder structures are possible [128], the attachment of the. segments as side chain onto the polymer backbone prevents structure modifications with other symmetries. 

Thanks to their true C02-philicity, macromolecular engineering using fluorinated poly((meth)acrylates) as C02-philic building blocks has been largely investigated by CO2 researchers as it will be developed later in the chapter [34,40 2]. 

Miscellaneous Polymers With Grafted Peifluorinated Side Chains Following the high solubility of fluorinated poly((meth)acrylates), the grafting of long perfluorinated chains has been applied to a variety of C02-phobic polymers including poly(styrene), poly(para-phenylenes), polysiloxanes, and polyphosphazenes to enhance their solubility in SC-CO2. 

While the stabilization of W/C microemulsions with Krytox-type polymers or molecular surfactants has been largely reported [66, 67], examples implying amphiphilic copolymers are scarce in literature. These examples—described below— are exclusively based on fluorinated poly((meth)acrylates) as a consequence of their lower surface tension compared to hydrocarbons and poly(siloxanes). 

Fluorinated poly(methacrylates) or poly(acrylates), rich in trifluoromethyl groups, exhibit superior performance of chemical inertness, excellent weatherability, low refractive index, lower dielectric constant, and special surface properties [14,61]. Poly(2,2,2-trifluoroethyl methacrylate), poly(MATRIF), is an important class of such materials. It has been extensively used in high performance coatings [17], photoelectric communications, and microelectronics [62]. Poly(MATRIF) is easily produced by free radical polymerization using bulk, solution, and emulsion polymerization methods [63]. Structural characterization of NMR of poly(MATRIF) prepared by radical and anionic polymerization has been studied. Syndiotactic structure was obtained by radical initiator in contrast to an isotactic structure achieved by anionic polymerization [64]. 

Wang W-C, Vora R H, Kang E-T, Neoh K-G, Ong C-K, Chen L-F (2004) Nanoporous Ultra-low-K Films Prepared from Fluorinated Polyimide with Grafted Poly(acrylic acid) Side Chains. Adv. Mater. 16 54-57. 

Early formulation of ionomer liquids - simple solutions of poly(acrylic acid) - only yielded workable cement pastes which set sharply when mixed with glasses of high fluorine content. This restricted the number of glass formulations which could be used in the system. Later it was found that other chelating and complex forming compounds had a similar effect (6), tartaric acid proved particularly effective and is now incorporated in all glass-ionomer cement formulations (6,8). 

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