Polydimethylpolyphenylsiloxanes by catalytic condensation

THE technical use of organosilicon polymers has brought about the necessity~ of investigating their properties at high temperatures. The properties of po]ydimethylpblyphenylsiloxane {L), obtained by catalytic polymerization from phenyltrichlorosilane and dimethyldichtorosilane, are described in this paper. Polymer I I contained 25 per cent more triiunctional monomer than I. Polymer I I I differed from I in containing 5 per cent of a tetrafunctional component; polymer IV differed from polymer II in the same way. Polymer V contained polya]uminomethylphenylsiloxane. Investigation of the propelX, ies was carried out on the free films and on films on a metal substrate. Experiment has shown that the mechanical properties of polymer films depends on their composition and they va~, markedly with temperature. Polymer II, containing more of the trifunctional monomer, is rather stronger at room temperature than I but the strength of both polymers falls sharply with increasing temperature (Fig. 1, curves I and II). The introduction of 5 per cent of a tetrafunctional crosslinking agent increases the initial mechanical strength a little (polymer II]), lowers the elongation in the original state from 40-50 to 15 per ceut and increases it to 60-70 per cent at high temperatures. The mechanical strength falls considerably more slowly with increase in temperature (curve III). The introduction of a crosslinking agent with polymer II results in a decrease in the elongation at break from 20 to 10 per cent. in the original state, and at 160-180 the elongation is 60-70 per cent. The mechanical strength of polymer IV falls considerably less with increasing temperature than does that of the original polymer II. The addition of polyaluminomethylphenylsiloxanes reduces still fnrther the effect of temperature on mechanical strength (curve V). The elongation at break does not exceed 15-20 per cent. Figure 2 shows the thermomechanical properties of these polymers. The curves indicate that polymer II has a higher glass temperatm~ (T~) than polymer I. The glass temperatures of polymers I I I V are also higher. The deformations found in the study of the thermomechanical properties are in complete agreement