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

Poly(N-isopropylacrylamide) copolymers (PNIPAMs) containing pendent perfluo roalkyl (R-F) or dodecyl groups have been synthesized by copolymerization o f NIPAM with small amounts of R-R-acrylates or -methacrylates containing a sulfonamido moiety between the acrylate and R-F groups or with dodecyl acry late. Evidence for strong intermolecular hydrophobic association of the flu orocarbon groups is provided by large viscosity increases with copolymer co ncentration and upon addition of NaCl and surfactants, These interactions a ppear to be much stronger than that of the corresponding copolymers of poly (N,N-dimethylacrylamide) with similar comonomer contents, Hydrophobic assoc iation 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 solut ions, particularly in the presence of perfluorocarbon surfactants, was unus ually temperature sensitive, decreasing by a factor of at least 1000 upon i ncreasing the temperature from 10 to 20 degrees C. This large decrease is m ost probably related to the collapse of the copolymer coils near the lower critical solution temperature. This is in sharp contrast to the correspondi ng polyacrylamide or poly(N,N-dimethylacrylamide) R-F-acrylate copolymers t hat show viscosity increases with increasing temperature in the 40-60 degre es 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.