Siloxanes phenyl groups

The most commonly used siloxane modifiers are those having phenyl, trifluoro-propyl and cyanopropyl substituents. Introduction of phenyl units into the polydimethylsiloxane backbone either in the form of methylphenylsiloxane or diphenyl-siloxane increases the thermal and oxidative stability, glass transition temperature and the organic solubility characteristics of the resulting copolymers. At low levels (5-10 percent by weight) of incorporation, bulky phenyl groups also break up the regularity of polydimethylsiloxane chains and inhibit the crystallization (Tc... 

The phenyl modified polymers show a significant decrease In weight loss compared to their all methyl analog (6). In a study of the thermal breakdown of phenyl substituted carborane-slloxane polymers, It has been reported that the presence of phenyl groups In carborane-siloxanes leads to cross-linking and less loss of weight ( ) ... 

Table II provides a summary of the results on the characteristics of aminopropyl terminated poly(dimethyl-diphenyl)-siloxane oligomers synthesized. These reactions were conducted in bulk at 160°C with K0H as the initiator. As can be seen from Table II the stoichiometric number average molecular weights sought and obtained are in very good agreement. The level of diphenylsiloxane incorporation was determined by UV spectroscopy. There is no absorption of dimethylsiloxane backbone in the spectral range of 240 to 280 nm. On the other hand, phenyl groups absorb very strongly over these wavelengths (Figure 3). For quantitative analysis we have used the absorption peak at 270 nm as the reference.

The unique hormonal activity of siloxanes is limited to methylaryl-substituted, linear di- and trisiloxanes and cyclic tri- and tetrasiloxanes (67, 75, 76, 81). In general, at least one arylsilicon grouping is necessary for activity. The substitution of an alkyl group for a phenyl group either decreases the activity markedly or eliminates it entirely. Cyclosiloxanes... 

Furthermore, at the increase of cyclic fragment volume, i.e. at transition from organocyclotetra-siloxane fragment to organocyclopenta- and organocyclohexasiloxane ones, at the same length of di-methylsiloxane unit induces a decrease of thermal oxidative stability of the copolymers, which, in turn, is explained by increase of the mass part of phenyl groups. 

Efforts to generate a 1-phosphaallene with a less bulky phenyl group at the P atom via a siloxane elimination from a phosphapropene gave the diphosphetane [Eq. (58)], easily imaginable as a dimer of the... 

Boehm and his co-authors [15,17] paied attention to the fact that C4HgLi and CeHsLi could also react with the starting silica surface to form attached n-butyl and phenyl groups (0.04-0.13 mmol/g). In all probability, this occurs due to the breaking of siloxane bonds on the silica matrix surface ... 

It is common practice to incorporate phenylmethyl or diphenyl substituents along the siloxane chain for improving thermal and oxidative stability of the polymer relative to polydimethylsiloxane. The presence of the phenyl group brings about a strengthening of the siloxane bond and can also improve... 

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