Surfactant and pH-mediated control over the molecular structure of poly(phenylsilsesquioxane) resins

Control over the macromolecular structural characteristics of poly(phenylsilsesquioxane) resin materials was obtained by combining the effects of surfactant addition with dynamic pH modification in aqueous condensation media. Average molecular weight, polydispersity, and the degree of condensation in the resulting polymer were adjusted over a wide range by tuning the pH and by the selective use of alkylammonium-based surfactants. The average intermolecular spacing of condensate exhibits a linear dependency on the pH of the polymerization medium during condensation. A 14% increase in spacing occurs as pH is increased from 1.7 through neutrality to 11. The addition of cetyltrimethylammonium surfactant acts to either promote or inhibit the growth of the polymer, depending on the pH range of condensation. Under acid conditions (pH 3-4), 14 wt % alkylammonium surfactant increases the average molecular weight of condensate by over 4 times from 2700 amu. Near neutral conditions (pH 8), the molecular weight of resin product decreases 6-fold from 18900 amu with the same concentration of surfactant. The interruption of siloxane growth is tunable by selecting different alkylammonium components and is stronger using smaller cations. Dynamic mechanical thermal analyses were used to identify preliminary structure-property correlations for selected resin products.