A new synthetic route for the preparation of well-defined model polyelectrolyte networks based on the photodimerization of monodisperse star polymers, bearing terminal anthryl groups, is presented. Poly(tert-butyl methacrylate) (PtBMA) star precursor polymers were prepared via living anionic polymerization. 1-(2-anthryl)-1-phenylhexyllithium (APH-Li) served as the novel initiator by which photo-dimerizable anthryl groups were introduced. In order to vary the functionality of the stars, two different terminating agents were used: 1,3,5-trisbromomethylbenzene (TBMB) and octa[(3-iodopropyl)]-silsesquioxane (T8-(prop-I)8). The length of the respective star arms was varied accordingly: 14 ⪇ Pn ⪇ 195. Subsequent cleavage of the tert-butyl ester moieties by acidic hydrolysis gave access to photocrosslinkable, monodisperse polyelectrolyte star polymers. Fluorescence experiments indicated on aggregation of low molecular weight poly/methacrylic acid) (PMAA) stars in salt containing solutions. Upon irradiation with UV light (λ = 366 nm) photodimerization of the terminal anthryl groups was induced and thus formation of a well-defined polyelectrolyte network was accomplished. In model experiments we demonstrated by 1H-NMR, UV-VIS spectroscopy as well as GPC analysis, that linear ω-anthryl-functionalized precursor PtBMA polymers dimerize quantitatively, as long as a critical degree of polymerization (Pn ≈ 100) is not exceeded.
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Mengel et al. (2001) studied this question.