Synthesis and characterization of fluorocarbon-modified poly(N-isopropylacrylamide)

Poly(N-isopropylacrylamide) copolymers (PNIPAMs) containing pendent perfluoroalkyl (R-F) or dodecyl groups have been synthesized by copolymerization of NIPAM with small amounts of R-R-acrylates or -methacrylates containing a sulfonamido moiety between the acrylate and R-F 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 R-F 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 degrees 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) R-F-acrylate copolymers that show viscosity increases with increasing temperature in the 40-60 degrees 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 R-F content but dilatant at a higher comonomer content, (C) 2000 Society of Chemical Industry.