PYRENE-LABELED AMPHIPHILIC POLY-(N-ISOPROPYLACRYLAMIDES) PREPARED BY USING A LIPOPHILIC RADICAL INITIATOR - SYNTHESIS, SOLUTION PROPERTIES IN WATER, AND INTERACTIONS WITH LIPOSOMES

Fluorescently labeled amphiphilic poly-(N-isopropylacrylamides) (PNIPA M) substituted with a N-[4-(1-pyrenyl)butyl]-N-n-octadecyl group at th e chain end were prepared by free-radical polymerization in dioxane of N-isopropylacrylamide (NIPAM) using obis{4-cyano-N,N-[4-(1-pyrenyl)bu tyl]-n-octadecyl} pentanamide as the initiator. The solution propertie s of the polymers in water were studied as a function of polymer conce ntration and temperature. Quasi-elastic light-scattering measurements and fluorescence experiments monitoring the pyrene excimer and pyrene monomer emissions revealed the presence of multimolecular polymeric mi celles below the fewer critical solution temperature (LCST) of PNIPAM. These underwent partial, reversible reorganization as they were heate d above the LCST. The interactions of the pyrene-labeled amphiphilic P NIPAM with dimyristoylphosphatidylcholine (DMPC) liposomes have been e xamined in water at 25 degrees C. From fluorescence experiments it was established that the polymeric micelles are disrupted irreversibly up on contact with the liposomes. The anchoring of the polymer chains occ urs by insertion of their hydrophobic tail within the phospholipidic b ilayer, as evidenced from a large decrease of the pyrene excimer emiss ion relative to pyrene monomer emission. The copolymers remained ancho red within the bilayer as the temperature of the copolymer-liposome su spension was raised above the LCST of PNIPAM.