SYNTHESIS AND CHARACTERIZATION OF SURFACE-GRAFTED, HYPERBRANCHED POLYMER-FILMS CONTAINING FLUORESCENT, HYDROPHOBIC, ION-BINDING, BIOCOMPATIBLE, AND ELECTROACTIVE GROUPS

We report the derivatization of hyperbranched poly(acrylic acid) (PAA) films with a wide range of amino-or alcohol-terminated molecules. The se molecules can include moieties such as pyrene, ferrocene, poly(ethy lene glycol), 15-crown-5, and a dye. To derivatize PAA films, we activ ate their carboxylic acid groups with isobutyl chloroformate and allow them to react with amine- or alcohol-containing molecules. Infrared s pectroscopy demonstrates the formation of amide and ester bonds upon c oupling as well as the presence of the derivative functional groups. E xcimer fluorescence from pyrene-containing films implies a high densit y of pyrene groups. However, we can control the amount of pyrene in th e film (and obtain monomer fluorescence) by varying the concentration of Py(CH2)(3)CONH(CH2)(2)NH2 in the derivatization solution. Cyclic vo ltammetry of ferrocene-containing films shows an electrochemically add ressable ferrocenyl surface coverage of (6 +/- 3) x 10(-9) mol/cm(2) i n three-layer PAA films. PAA films and their derivatives are stable un der sonication, Soxhlet extraction, and acidic and basic conditions. P AA films also respond to external stimuli. The ellipsometric thickness of PAA films increases by approximate to 45% upon deprotonation of th e film's carboxylic acid groups and returns to its original thickness after acidification. Using surface acoustic wave mass sensors, we obse rved that pure PAA films adsorb or absorb volatile organic compounds ( VOCs), although the amount is in the monolayer range. Fluorination of PAA films increases the amount of polar VOCs absorbed by an order of m agnitude.