Synthesis and Properties of Q-Silicon Crosslinked Siloxane Networks: H3PO4 Catalyzed Sol-Gel Dehydration/Crosslinking of a,w-bis(Hydroxy)-oligodimethylsiloxanes with Tetrakis(hydroxydimethylsiloxy)silane

Six silicate-crosslinked oligodimethylsiloxane thin films were prepared by the phosphoric acid (1 mol %) catalyzed condensation of alpha'w-bis(hydroxy)oligodimethylsiloxane (P) and tetrakis(hydroxydimethylsiloxy)silane (Q). Other acid catalysts were evaluated. P and Q were prepared by the Pd-catalyzed oxidation of the corresponding Si-H compounds with water. The starting materials were characterized by IR and H-1, C-13, and Si-29 NMR. A thermal cure was achieved with H3PO4 in 24 h and with poly(phosphoric acid) in 3 h at 110-120 degrees C. Dynamic mechanical analysis was used to determine the glass-transition temperatures and to evaluate the mechanical properties of the films. Their thermal stabilities (>= 300 degrees C) in air and N-2 were determined by thermogravimetric analysis. Small amounts of non-crosslinked P were recovered from the films by Soxhlet extractions with CH2Cl2 and analyzed by IR, gel permeation chromatography, and Si-29 NMR. The crosslink densities were evaluated by the CH2Cl2 absorption capacities of the films. The surface propel-ties of the films were determined by static and dynamic contact-angle measurements. Electrochemical impedance spectroscopy was carried out to evaluate the corrosion-protective proper-ties of the coatings on mild steel as a function of the exposure time to 0.5 N NaCl. The biofoul-release properties of the films were evaluated with sporelings from mature Ulva linza plants and barnacles. (c) 2006 Wiley Periodicals, Inc.