A study on the micellar polarity of hydrophobic poly(N-isopropylacrylamides)

The parameters of solvent polarity (pi*) and hydrogen bond donor ability (alpha) of a series of different hydrophobically modified poly (N-isopropylacrylamides)(PNIPAM) micelles have been studied using the Kamlet-Taft solvatochromic comparison method, on the basis of the determination of the relationship between two probe's maximum wavenumber in fluorescence spectrum and solvatochronic parameters of different solvents. Results show that, at the same molar feed ratio, the micellar environments of solubilized probe molecules become more nonpolar and have much stronger hydrogen bond donating ability with the increase of the alkyl length of acrylic ester in the copolymers. While for copolymer of N-isopropylacrylamides and octadecyl acrylate (NIPAM-C-18), on increasing the molar feed ratio of ODA, the polarity of the micellar environments have the same rule as the above, however, their alpha have no obvious rule. A preliminary discussion about these phenomena has been given.