Ideal tetrafunctional amphiphilic PEG/PDMS conetworks by a dual-purpose extender/crosslinker. II. Characterization and properties of water-swollen membranes

Select characteristics and properties of a series of ideal tetrafunctional amphiphilic conetworks consisting of random poly(ethylene glycol) (PEG) and polydimethylsiloxane (PDMS) segments crosslinked by a novel dual-purpose crosslinker/extender were determined. The overall composition of the conetworks was varied in the 16-40% PEG range, and membranes were prepared by polymerizing/crosslinking charges in molds. Membranes were characterized by equilibrium swelling (both in water and n-heptane) and by determining their oxygen permeabilities and select mechanical properties. Swelling in water increases, whereas in heptane it decreases with increasing PEG content. Significant swelling in both solvents indicates bicontinuous (bipercolating) PEG and PDMS phases. Bicontinuity is reached with similar to 13% PEG in the conetworks. The oxygen permeabilities of optically clear water-swollen membranes containing 24, 32, and 40 wt % PEG are similar to 350, similar to 245 and similar to 185 barrers, respectively, i.e., oxygen permeability decreases by increasing the hydrophilic constituent. These oxygen permeabilities are far superior to those of contemporary soft contact lenses. The tensile strengths and moduli of water-swollen membranes decrease, while elongations increase, with increasing PEG content. Dry membranes exhibit first order transitions at -52 and similar to 46 degrees C indicating phase-separated crystalline PDMS and PEG domains, respectively. Both dry and water-swollen membranes are optically clear, indicating the presence of PEG and PDMS domains with dimensions well below the wavelength of visible light. (c) 2005 Wiley Periodicals, Inc.