Fluorocarbon-hydrocarbon diblock

Various gaseous (F-propane, SFe) and liquid (F-octane, F-decalin, F-perhydrophe-nanthren, mixed fluorocarbon-hydrocarbon diblocks, and fluorosilicones) F-com-pounds are being used as intraocular tamponades for use in vitreoretinal surgery [Chapter 9 by Rico-Lattes et a ., this volume]. Polymers with F-alkyl moieties are used in corneal inlays and implants and in intraocular lenses. 

Fluorinated surfactants (or fluorosurfactants, i.e., surfactants with hydrophobic tails comprising a fluorocarbon moiety) provide an alternative means of achieving extremely stable PFC emulsions, as they can provide very low PFC/water interfacial tensions [cr , another factor in Eq. (2)]. d s yet, this option has not been developed, in part because of the added cost involved in the evaluation for approval of a novel active excipient. A further means of effectively increasing the stability of EYP-based PFC emulsion consists of supplementing standard phospholipids with mixed fluorocarbon-hydrocarbon diblock compounds, such as 14 or 15. Such diblocks, which have fluorophilic-lipophilic amphiphilic properties, are expected to improve the adhesion of the phospholipid film onto the PFC droplet. 

Formulations containing small percentages of highly lipophilic fluorocarbon-hydrocarbon diblocks are also being explored. It has been proposed that the diblock compounds are interfacially active at fluorocarbon/water interfaces and orient in such a way so as to extend their fluorinated portion into the FC phase, and... 

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

If pushed to an extreme the perfluorinated bridge concept can be used to obtain liquid crystals with no cyclic moieties in their mesogenic core structure [4-8]. Since the beginning of the 1980s it has been known that semi-fluorinated n-alkanes, so-called diblock compounds, F(CF2) (CH2) H, form smectic phases [49], because of microphase separation as a result of separate, layer-like aggregation of the hydrocarbon and fluorocarbon moieties. Nevertheless, if introduced into a nematic host mixture, even small quantities of these diblocks cause gelation of the mixture. Their solubility is also limited to a few percent by weight. 

Microphase separation does occur at shorter block lengths when the two blocks are highly immiscible, such as with hydrocarbon and fluorocarbon blocks. For example, all of the diblock copolymers of (perfluorooctyl)ethyl vinyl ether and n-[(4 -cyanophenyl-4"-phenoxy)alkyl] vinyl ethers (PRf-PCNVE ) or 2-[(4 -biphe-nyloxy)ethyl]vinyl ether (PRf-PbiPHVE2) listed in Table 16 exhibit the phases characteristic of both of the corresponding homo-... 

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