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.