Silicon based polymer systems changes

Poly(hydrosilane)s are stable compounds and can be manipulated in the air only for a short period since they are oxygen sensitive. In order to study the oxidation products, a xylene solution of poly(phenylhydrosilane)(Mw = 2340, Mw/Mn = 1.72) was refluxed (140 °C) for 12 h in a system exposed to the air [15]. Only minor changes were observed by GPC analysis whereas FTIR showed characteristic absorptions due to siloxane-type structures on the polymer backbone. A detailed NMR analysis, based on H NMR, Si INEPT and H- Si HMQC spectroscopies, indicated that the oxidized material contains the units 7-10 shown in Scheme 8.2. In particular, units 7,8 and 9+10 were present in relative percentages of 27%, 54% and 19%, respectively, which mean that more than 70% of the catenated silicons were altered. It has also been reported that silyl hydroperoxides and peroxides are not found as products in the autoxidation of poly(phenylhy-drosilane) [16]. 

Chemomechanical systems based on a synthetic polymer network gel are the only artificial systems able to convert chemical energy directly into mechanical work. Gels are soft with respect to their environments. Machines made of metal or silicon operate as closed systems. They do not adapt to changes in their operating conditions unless a separate sensor system or a human operator is at the controls. 

Concentrated phosphoric acid (90-100% based on ortho phosphoric acid) is used as electrolyte in this fuel cell, that operates at 150 to 190°C. Some of the pressurized systems are reported to work upto 220°C. At lower temperatures, phosphoric acid is a poor ionic conductor (Der-tau and Chang, 1989), and CO poisoning of the Pt electrocatalyst in the anode becomes severe. The relative stability of concentrated phosphoric acid is high compared to other common acids consequently the PAFC is capable of operating at the high end of the acid temperature range (100 to 220°C). In addition, the use of concentrated acid minimizes the water vapor pressure and hence water management in the cell is not as difficult as it is for polymer electrolyte fuel cell (PEMFC). The matrix, that is universally used to retain the acid, is silicon carbide. The electrocatalyst typically used in both the anode and cathode is Pt loaded on carbon. 

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