Do fluorocarbon, hydrocarbon, and polycyclic aromatic groups intermingle? Solution properties of pyrene-labeled bis(fluorocarbon/hydrocarbon)-modified poly(N-isopropylacrylamide)

Fluorescence spectroscopy, microcalorimetry, and isothermal titration calor imetry (ITC) have been used to study the solution properties in water of fl uorocarbon, hydrocarbon, and bis(fluorocarbon/ hydrocarbon) pyrene-labeled poly(IV-isopropylacrylamides). The polymers were prepared by free-radical c opolymerization in homogeneous solution of IV-isopropylacrylamide, N-[4-(1- pyrenyl)butyl]-N-n-octadecylacrylamide, and/or N-(H-1,H-1-perfluoro-n-octyl acrylamide). They were characterized by H-1 NMR and F-19 NMR spectroscopy, FTIR spectroscopy, and viscometry. Dynamic light scattering, ITC, and fluor escence spectroscopy provide strong evidence that the polymers associate in water below the solution cloud point (similar to 30 degreesC). The polymer s aggregate in multichain micellar structures consisting of a loose corona of hydrated poly (N-isopropylacrylamide) chains and a hydrophobic core comp osed of hydrocarbon, aromatic, and fluorocarbon groups. The fact that groun d-state pyrene excimers are detected in aqueous solutions of bis(fluorocarb on/hydrocarbon)-modified polymers, but not in aqueous solutions of hydrocar bon/modified polymers, is taken as evidence for the segregation of fluoroca rbon and hydrocarbon groups into distinct microdomains coexisting within th e hydrophobic core of polymeric micelles.