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 -( 1 H, 1 H-perfluoro- n -octylacrylamide). They were characterized by 1 H NMR and 19 F 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.