Novel tricomponent membranes containing poly(ethylene glycol)/poly(pentamethylcyclopentasiloxane)/poly(dimethylsiloxane) domains

The synthesis and characterization of novel tricomponent networks consisting of well-defined poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) strands crosslinked and reinforced by poly(pentamethylcyclopentasiloxane) (PD5) domains are described. Network synthesis occurred by dissolving alpha,omega-diallyl PEG and alpha,omega-divinyl PDMS prepolymers in a common solvent (toluene), introducing a stoichiometric excess of pentamethylcyclopentasiloxane (D5H) to the charge, inducing the cohydrosilation of the prepolymers by Karstedt's catalyst and completing network formation by the addition of water. Water in the presence of the Pt-based catalyst oxidizes the SiH groups of D5H to SiOH functions that immediately polycondense and bring about crosslinking. The progress of cohydrosilation and polycondensation was followed by monitoring the disappearance of the SiH and SiOH functions by Fourier transform infrared spectroscopy. Because cohydrosilation and polycondensation are essentially quantitative, overall network composition can be controlled by calculating the stoichiometry of the three network constituents. The very low quantities of extractable (Sol) fractions corroborate efficient crosslinking. The networks swell in both water and hexanes. Differential scanning calorimetry showed three thermal transitions assigned, respectively, to PEG (melting temperature: 46-60 degreesC depending on composition), PDMS [glass-transition temperature (T-g) = similar to-121 degreesC], and PD5 (T-g = similar to-159 degreesC) and indicated a phase-separated tricomponent nanoarchitecture. The low T-g of the PD5 phase is unprecedented. The strength and elongation of PEG/PD5/PDMS networks can be controlled by overall network composition. The synthesis of networks exhibiting sufficient mechanical properties (tensile stress: 2-5 MPa, elongation: 100-800%) for various possible applications has been demonstrated. (C) 2002 Wiley Periodicals, Inc.