Do Fluorocarbon, Hydrocarbon, and Polycyclic Aromatic Groups Intermingle? Solution Properties of Pyrene-Labeled Bis(fluorocarbon/hydrocarbon)-Modified Poly(<i>N</i>-isopropylacrylamide)

Abstract

Fluorescence spectroscopy, microcalorimetry, and isothermal titration calorimetry (ITC) have been used to study the solution properties in water of fluorocarbon, hydrocarbon, and bis(fluorocarbon/hydrocarbon) pyrene-labeled poly(N-isopropylacrylamides). The polymers were prepared by free-radical copolymerization in homogeneous solution of N-isopropylacrylamide, N-[4-(1-pyrenyl)butyl]-N-n-octadecylacrylamide, and/or N-(1H,1H-perfluoro-n-octylacrylamide). They were characterized by 1H NMR and 19F NMR spectroscopy, FTIR spectroscopy, and viscometry. Dynamic light scattering, ITC, and fluorescence spectroscopy provide strong evidence that the polymers associate in water below the solution cloud point (∼30 °C). The polymers aggregate in multichain micellar structures consisting of a loose corona of hydrated poly(N-isopropylacrylamide) chains and a hydrophobic core composed of hydrocarbon, aromatic, and fluorocarbon groups. The fact that ground-state pyrene excimers are detected in aqueous solutions of bis(fluorocarbon/hydrocarbon)-modified polymers, but not in aqueous solutions of hydrocarbon-modified polymers, is taken as evidence for the segregation of fluorocarbon and hydrocarbon groups into distinct microdomains coexisting within the hydrophobic core of polymeric micelles.