Synthesis and Characterization of Trifluoroethoxy Polyphosphazenes Containing Polyhedral Oligomeric Silsesquioxane (POSS) Side Groups

We report the macromolecular substitution synthesis of a series of soluble polyphosphazenes with different molar percentages of cosubstituted trifluoroethoxy and aminopropylisobutyl polyhedral oligomeric silsesquioxane R7Si8O12(CH2)3NH (R = isobutyl) (POSS-NH) cage side groups. The structure–property relationships of the novel polymers were examined using 1H, 31P NMR, GPC, FTIR, DSC, and TGA techniques, and properties such as contact angles, solubility, materials character, glass transitions, thermal stability, and molecular weight were measured. The average polymer chain length declined steadily from ∼3860 repeating units when only trifluoroethoxy side groups were present to 1354 repeat units when 25 mol % of the side groups were POSS, 603 units when 55 mol % were present, and only 36 units when 82 mol % of the side groups were POSS. At the same time the glass transition temperatures rose from −62 to +30.5 °C as the POSS content was increased. Unlike other bulky cosubstituents reported recently, the introduction of the amino-POSS side groups yields soft, film-forming polymers (up to ∼25% POSS) or nonflexible materials with higher loadings but does not generate elastomeric properties. These properties reflect the steric hindrance limitations imposed by the bulky POSS units. When 25 mol % of the polymer side groups are POSS units, contact angles to n-hexadecane around 67° are generated. These values are higher than all the previously reported phosphazene fluoropolymers or Teflon.