Fluorescence studies of polymer micelles: Intracoil direct energy transfer

Doubly tagged polystyrene (PS) or polystyrene-poly(methacrylic acid) (PS-PMA) polymers have been prepared by anionic polymerization. These polymers may be represented by the structure N-PSn-A or N-PSn-A-PMA where N and A represent a naphthalene or anthracene chromophore and n is the degree of polymerization (n = 40 or 283). Direct energy transfer (DET) om the N to the A group has been studied in micelles composed entirely of the tagged micelle or mixed micelles which contain ca. 1 wt% of tagged polymer. While DET clearly demonstrated the different end-to-end distances of the two PS segments, very strong environment effects on the fluorescence properties of both chromophores frustrated efforts to elucidate any modification in the end-to-end distribution in going from homogeneous solution to PS films to micelle structures. On the other hand, these complexities demonstrated that there is considerable heterogeneity present in an amphiphilic polymer micelle in mixed organic and aqueous solvents in which it equilibrates. These complexities are also a function of the details of the micelle preparation. Thus the use of fluorescently tagged polymers has permitted a much more molecular view of the process of polymer micelle formation.