Low Modulus Dry Silicone-Gel Materials by Photoinduced Thiol-Ene Chemistry

The curing behavior of telechelic vinyl-functionalized poly(dimethylsiloxane) (PDMS) with poly(dimethylsiloxane-co-propylmercaptomethylsiloxane) using photoinitiated radical thiol-ene polyaddition was studied, by means of rheology, mechanical analysis of the cured elastomeric products, and high resolution magic angle spinning NMR (HR-MAS). Postpolymerization modification of a hydroxy-functionalized PDMS-derivative (OH-PDMS) yielded a telechelic thiol-functionalized PDMS-derivative, which was subsequently used as chain extender for the preparation of dry silicone-gel materials with elastic moduli between 30 and 500 kPa. The rate of thiol-ene polyaddition of the chain extender proved to be similar to that of the cross-linking process using multifunctional PDMS-based thiols. HR-MAS analysis of the loosely cross-linked thiol-ene PDMS networks and their fluoride-solubilized counterparts proved a highly efficient cross-linking with an optimal cure at 1:1 thiol to ene stoichiometric ratios. Using mechanical analysis, it was shown that the low molecular weight thiol-functionalized chain extender was efficiently incorporated in the PDMS polymer network.