Fluorescence probe and scanning force microscopic studies of water soluble comb-shaped copolymers consisting of a hydrophobic poly(p-alkylstyrene) main chain and hydrophilic poly(ethylene oxide) grafted chains

Abstract

Solution properties of regular amphiphilic comb-shaped polymers have been studied in water by means of fluorescence technique using pyrene as a probe, dynamic light scattering, 1H NMR, and scanning force microscopy (SFM). They consist of a hydrophobic poly(p-alkylstyrene) as a main chain and hydrophilic poly(ethylene oxide) (PEO) chains as a graft chain. Two types of the comb-shaped polymers have been explored, which were prepared by micellar, organized homopolymerization of amphiphilic PEO macromonomers (1) (C1-EOn-(CH2)m-S, with a p-alkylstyrene ((CH2)m-S) end group, with m = 1 and 7, and a PEO chain with n = 18, 46, 115, and 469) and by copolymerization of C1EO18-(CH2)7-S with styrene in water, respectively. Partitioning, I1/I3, and excimer formation of pyrene were studied for their dilute aqueous solutions, and rationalized with the local concentration and structure of the comb-shaped polymers. Hydrophobic pyrene molecules were principally dissolved into the vicinity of the hydrophobic p-heptylstyrene main chain of the comb-shaped polymers. The nature of the hydrophobic main chain of poly(styrene-co-C1-EO18-(CH2)7-S) was found to be essentially similar to that of a series of poly(C1-EOn-(CH2)m-S). Direct observation of single macromolecule of poly(C1-EO46-(CH2)7-S) by SFM revealed a high molecular weight, cylindrical brush-like conformation with ca. 12.8 nm in thickness. In contrast, small fine particles were observed for poly(styrene-co-C1-EO18-(CH2)7-S), suggesting formation of a unimolecular micelle in water.