Synthesis, Characterization and Solution Properties of Cholesterol Substituted Poly(N-isopropylacrylamide)

Abstract

<p> Poly(N-isopropylacrylamides) and copolymers of N-(isopropylacrylamide) and N(tetrahydrofurfurylacrylamide) bearing cholesterol substituents were prepared and their solution properties in water and in methanol were studied by dynamic light scattering, turbidity measurements and by fluorescence spectroscopy. These polymers were obtained in two steps: 1) preparation of a reactive polymer; and 2) coupling of cholesterol to the reactive polymer. In one case the reactive group (N-hydroxysuccinimide) was introduced at one chain end, in the other case, the same group was introduced randomly along the polymer chain. Reaction of an amino-terminated cholesteryl derivative with the reactive polymers led to modified polymers in which cholesterol was attached either to one chain end or to a small number of monomer units along the polymer chain. In the latter case, copolymers bearing pyrene and cholesterol were prepared as well. The copolymers were characterized by 1H NMR, IR and UV spectroscopy and their molecular weights were determined. </p> <p> Studies of the cholesterol-bearing polymers in aqueous solution by dynamic light scattering and fluorescence spectroscopy provided evidence for the formation of polymeric micelles via association of the cholesterol groups. Fluorescence probe and label experiments, using pyrene as a chromophore, gave strong indication that the micelle formation is controlled primarily by the cholesterol groups and only to a lesser extent by the architecture and composition of the polymer. </p>