SYNTHESIS AND SOLUTION PROPERTIES OF FLUORESCENTLY LABELED AMPHIPHILIC (N-ALKYLACRYLAMIDE) OLIGOMERS

Amphiphilic poly(N-alkylacrylamide)s substituted at one chain end with the hydrophobic moiety N-n-octadecyl-[N-4-(1-pyrenyl)butyl] were prep ared by end-group modification of carboxyl-terminated oligomers of N-i sopropylacrylamide (NIPAM), N-(3-methoxypropyl)acrylamide (MPAM), and N,N-bis(2-methoxyethyl)acrylamide (BMEAM). The oligomers, M-n 2000-100 00, were prepared by free-radical polymerization in the presence of me rcaptopropionic acid acting as a chain-transfer agent. The oligomers w ere characterized by potentiometric titration of the end groups, H-1 N MR spectroscopy, and UV absorption measurements. Quasi-elastic light-s cattering measurements and fluorescence experiments revealed the exist ence of oligomeric micelles, consisting of a hydrophobic core hosting pyrene aggregates captured within the octadecyl chain assembly, and a corona of solvated poly(N-alkylacrylamide) chains. The oligomeric PNIP AM micelles interact readily with hydrophobically modified PNIPAM,as e videnced by the following photophysical observations: (1) disappearanc e of pyrene excimer emission in favor of pyrene monomer emission and ( 2) relief of the pyrene/pyrene self-quenching prevalent within the int act micellar cores.