Fluorine‐containing hydrophobically associating polymers have been synthesized by copolymerization of acrylamide with a small amount of an acrylate or methacrylate having a fluorocarbon containing ester group. It was found that hydrophobic associations occurring between these fluorocarbon chains was stronger than the interactions of the corresponding hydrocarbon comonomers and depend on the length of the fluorocarbon chain. The rheological properties of the copolymer solutions were studied. The solutions were found to be highly pseudoplastic but the viscosity loss was completely reversible upon removal of shear. Evidence for hydrophobic association of the fluorocarbon groups was obtained by the dependence of the Brookfield viscosity on temperature, the addition of NaCl, and the addition of organic solvents, urea, and surfactants.

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The synthesis of polyacrylamide copolymers containing fluorine-containing acrylates 1, 2, 4 or 5 or silicone-containing methacrylate 6 was carried out by emulsion polymerization using persulfate as initiators and ionic perfluoro surfactants. The Brookfield viscosities of these copolymers, especially those containing 1 or 2, were much higher than the laurylacrylate (3) containing co polymer. The comonomer content of the 1 or 2 containing copoly mers that were most strongly viscosifying was only .07-.28 mole percent, well below that of the corresponding copolymers contain ing 3. Viscosity increases of the 1 and 2 copolymers, observed upon increases in temperature or NaCl concentration were consis tent with association of these copolymers through intermolecular hydrophobic binding. Reduced viscosity or dynamic light scattering studies are consistent with the existence of polymer assemblies above polymer concentrations of about 100 pm. Addition of surfac tants water miscible organic solvents or increasing shear rate was shown to lead to sharp viscosity decreases consistent with the proposed model.The replacement of hydrocarbon-by perfluoroalkyl groups in hydrophobically associating polymers 1 is of potential interest since the hydrophobic character of perfluoroalkyl groups is more pronounced compared to their hydrocarbon analogs. 2 Thus, the critical micelle concentrations of fluorocarbon surfactants generally are significantly lower than the hydrocarbon analogs of the same chain length and surface tensions of fluorocarbon surfactant solutions are also much lower. 2 -3 Also hydrophobic bonding of fluorocarbon surfactants to β-cyclodextrines is much stronger (about 300 times) compared to similar hydrocarbon containing surfactants. 4 Significantly, the latter process is enthalpy driven (ΔΗ = -9.0 kcal/mole, AS = -12 eu) whereas the bonding of the fluorocarbon

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Poly(N‐isopropylacrylamide) copolymers (PNIPAMs) containing pendent perfluoroalkyl (RF) or dodecyl groups have been synthesized by copolymerization of NIPAM with small amounts of RR‐acrylates or ‐methacrylates containing a sulfonamido moiety between the acrylate and RF groups or with dodecyl acrylate. Evidence for strong intermolecular hydrophobic association of the fluorocarbon groups is provided by large viscosity increases with copolymer concentration and upon addition of NaCl and surfactants. These interactions appear to be much stronger than that of the corresponding copolymers of poly(N,N‐dimethylacrylamide) with similar comonomer contents. Hydrophobic association between the RF groups is found to be much stronger than that of the corresponding dodecyl groups. The viscosity of some of the copolymer solutions, particularly in the presence of perfluorocarbon surfactants, was unusually temperature sensitive, decreasing by a factor of at least 1000 upon increasing the temperature from 10 to 20 °C. This large decrease is most probably related to the collapse of the copolymer coils near the lower critical solution temperature. This is in sharp contrast to the corresponding polyacrylamide or poly(N,N‐dimethylacrylamide) RF‐acrylate copolymers that show viscosity increases with increasing temperature in the 40–60 °C range. The NIPIAM copolymers were also found to be different from the acrylamide or N,N‐dimethylacrylamide perfluorocarbon acrylate copolymers in that they were found to be Newtonian at a low RF content but dilatant at a higher comonomer content. © 2000 Society of Chemical Industry

The esterification reaction of chitin with perflurocarboxylic acid was studied in methanic acid or perfluorocarboxylic acid as solvent. A series of substituted derivatives of trifluoroacyl. perfluorobutyric and perfluorooctanoyl chitin were synthesized. The properties of these chitin derivatives were investigated.

AbstraaA fluomarbon-modified p l y ( N-isopropylacrylamide) has been synthesized by copolymerization of N-isopropyl acrylamide with a small amount of acrylate or methacrylate containing a pertluomalkyl p u p . It was found that the hydmphihcity of macromolecular backbone is an important factor to the solution properties of the copolymers and that hydrophobic association between fluorocarbon group is stronger than that between the correspondmg hydrocarbon analogies. The viscosity of some of the copolymer solutions was very sensitive to temperature. It was blatant at higher fluorocdiun c o m m e r content ( > 0.20-1,O 4 % ) and was Newtonian a t ve~?; low fluorocarbon comnomer content (0.03-0.2 mol% ) . Evidence for hydrophobic association of the fluorocarbon groups was obtained from the effects of adding NaCl and surfactants on the solution viscosity. The LC-,Cr properties of these copolymers were studied by DSC method and this was a h found to be consistent with hydrophobic association between the fluorocarbons. Keywords contairung hydro-phobically associating polymersGreen chemistry, hydrophobic association, p l y ( N-isopropylacrylamide) , EST, fluorocarbon- IntroductionHydrophobic intemctions"*play an important role in surfactant micellation and related phenomena including association of hydrophobically modified water-soluble polymers. l 4 Thus solutions of polymers containing a small fraction of pendent hydrophobic p u p s (1-3 mol% ) can form reversible networks by intermolecular hydrophobic association thereby increasing hydrodynamic volume and hence increasing solution viscosity. 3 s 4 Such polymers have attracted considerable attention5" because of unique heological properties, and potential applications including mobility control agents for enhanced oil recovery, thickener for coatings and cosmetics, caniers for phase-transfer catalysts, flocculates, etc .Fluorochmcontaining hydrophobically associating polyac~ylamide~' lo was recently synthesized by B a n g et ul . Compared to the corresponding hydmcarbon analogies, these copolymers show much stronger hydrophobic association, resulting in greatly enhanced viscosification . Not withstanding considerable efforts the microstructures of these hydrophobically modified copolymers are still not well understood so that Received July 9. 1998; revised October 13, 1998. Poly( N-isopropylacrylamide) ( PNIPAM) is unlike polyacrylamide, in its aqueous solutions the plymer w i l l be precipitated out at a relatively low value of the lower critical solution temperatme (LC-ST), and this gives rise to many interesting properties especially close to the LCST.The LCST behavior of PNIPAM and its hydrophobically modified copolymers has been studied intensively but the investigations on the copolymers were only concerned with the hydmcahon derivatives.However its rheological properties in semi-concentrated solution have not been investigated. In this paper, the synthesis and heological and aqueous solubility properties of perfluorocarbon derivatives of PNIPAM synthesized by c...