Randall Gene Schmidt

Impact of End-Tethered Polyhedral Nanoparticles on the Mobility of Poly(dimethylsiloxane)

A series of dumbbell-shaped nanocomposite materials of poly(dimethylsiloxanes) (PDMSs) and polyhedral oligomeric silsesquioxanes (POSSs) were synthesized through hydrosilylation reactions of allyl- and vinyl-POSS and hydride-terminated PDMS. The chemical structures of the dumbbell-shaped materials, so-called POSS-PDMS-POSS triblocks, were characterized by (1)H NMR and FT-IR spectroscopy. The molecular weights of the triblock polymers were determined by gel permeation chromatography (GPC). Their size was analyzed by small-angle neutron scattering (SANS) and pulsed-field gradient stimulated echo (PFG STE) NMR experiments. The impact of POSS on the molecular mobility of the PDMS middle chain was observed by using (1)H spin-spin (T2) relaxation NMR. In contrast to the PDMS melts, the triblocks showed an increase in mobility with increasing molecular weight over the range studied due to the reduced relative concentration of constraints imposed by the end-tethered nanoparticles. The triblock systems were used to compare the impact of tethered nanoparticles on the mobility of the linear component compared to the mobility of the polymer in conventional blended nanocomposites. The tethered nanoparticles were found to provide more reinforcement than physically dispersed particles especially at high molecular weights (low particle concentration). The physical blends showed an apparent percolation threshold behavior.

Siloxanes and Silicones (Advances in Silicone Technologies 2000–15)

Abstract Silicone materials and product technologies have steadily advanced since the turn of the 21st century with the majority of advances driven by new application needs. Established silicone manufacturers or specialty formulators have primarily been responsible for the developments of new materials. The most significant advances have been in the development of silicone materials with enhanced adhesive, optical, thermal management, and aesthetics. The impact of these new materials technologies are seen in lower assembly processing temperatures, extended lifetimes of photovoltaic systems and energy efficient light emitting diode lighting devices, and improved feel of personal care and beauty products. In addition to leveraging the inherent properties of silicones, advances have been made by introducing new chemistries, such as dual cure systems and alpha silanes that speed cure rates and chemically bond to a wider range of substrates. New delivery options such as hot melts and swollen elastomers provide rapid green strength adhesives and add a “velvety” feel to beauty care products, respectively.