SynopsisThe manner in which a series of silcarboranylene-siloxsne polymers behave in air at elevated temperatures was investigated by thermogravimetric, isothermogravimetric, and differential thermal analyses techniques. Results indicate that methyl pendant groups on the polymers undergo thermal and oxidative degradations a t temperatures under 600OC. Final weight losses of the polymers, however, are significantly lower than that shown by dimethylsiloxanes. The reduced volatility is attributed to the inhibition of thermooxidation by the m-carboranylene group in the polymer molecules. This protective influence decreases apparently as the distance between the carborane nucleus and the methyl groups increases.
SynopsisThis study covers the results of synthesis and investigation of thermal stabilities of several organometallosiloxanes and organometal compounds containing Group IV elements. Investigations indicate, in general, that heat resistanceis related to the dissoci* tion energies of the M-0 bonds, the number of organic groups connected to the metal atom, and the structure of the molecule as a whole. More specifically, the substitution of Ge-4 and Sn-0 bonds for some Si-0 linkages in organosiloxanes produces a reduction in heat stability. The influence of the G e -4 bond to decrease the resistance of siloxanes is less than that of the Sn-0 linkage; an increase in the number of S n -4 linkages producing a corresponding decrease in heat stability of the organosiloxane. The resistances of the germoxysiloxanes to heat degradation are less than that which would be expected from indications given by the relative stabilities of more simple organometallic compounds.
SynopsisPolysiloxanes containing carboranylbutyl and methyl pendant groups were investigated, to determine their resistance to thermal decomposition when heated in air. Results indicate that the copolymers degrade through Si-C as well as Si-0 bond rupture. A t 300°C. thermooxidative scission of pendant groups was the predominant reaction, whereas S i 4 and Si-C bond rupture occurred at 500°C. Variations in the behavior of the copolymers studied suggest that the carborane nucleus provides some inhibiting influence on their thermal decomposition. T h i s is mainly attributed to steric hindrance effects rather than polarity factors. Chain extension with tin octoate caused a reduction of thermal stability, probably because of the addition of S n 4 bonds to the molecules.
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