Use of nonradiative energy transfer to explore interpolymer and polymer-solute interactions in aqueous solutions of poly(N-isopropylacrylamide)

Abstract

N-Isopropylacrylamide (NIPAAM) was copolymerized with small quantities of 9-fluorenylmethyl acrylate to yield labeled poly(N-isopropylacrylamide) (PNIPAAM) for use in nonradiative energy transfer (NRET) experiments with various pyrene derivatives in aqueous solution. Microcalorimetry and cloud point measurements of the lower critical solution temperatures (LCST) of these copolymers showed very slight depressions in the LCST as compared to that of the homopolymer. NRET investigations showed no energy transfer from fluorene-labeled PNIPAAM to free pyrene or to PNIPAAM-bound pyrene in mixed aqueous solutions at 24.5 "C in contrast to literature reports of similar work done with (hydroxypropyl)-cellulose. NRET was observed between fluorene-labeled PNIPAAM and amphiphiles with pyrene terminally bound to their hydrocarbon tails. NRET was much more efficient for a quaternary ammonium amphiphile than for a zwitterionic sulfobetaine-based surfactant.

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