Silicone polymers phenyl groups

PMQ Silicone rubbers having both methyl and phenyl groups on the polymer chain. 

The TT-electron system-substituted organodisilanes such as aryl-, alkenyl-, and alkynyldisilanes are photoactive under ultraviolet irradiation, and their photochemical behavior has been extensively studied (1). However, much less interest has been shown in the photochemistry of polymers bearing TT-electron substituted disilanyl units (2-4). In this paper, we report the synthesis and photochemical behavior of polysiloxanes involving phenyl(trimethylsilyl)-siloxy units and silicon polymers in which the alternate arrangement of a disilanylene unit and a phenylene group is found regularly in the polymer backbone. We also describe lithographic applications of a double-layer system of the latter polymers. 

The replacement of 5-10% of the methyl groups on the silicon atom with phenyl groups gives polymers which exhibit superior low temperature properties. Brittleness temperatures of approximately -117 °C can be achieved compared to the approximately -70 °C for the VMQ types. The ISO designation for the phenyl modified silicones is either PMQ or PVMQ depending on whether the grade is vinyl modified. 

The polymers thus formed are very heat-resistant. Polyphenylsilsesquioxane, for example, starts to decompose above 600 °C. At 900 °C only loss of phenyl groups occurs, the silicon-oxygen framework of the macromolecule remaining intact . This sharply differs the above polymers from linear and branched polyphenylsilses-quioxanes. 

Polysilanes have also been modified by removal of aryl groups under acidic conditions, to give Si-functional polymers. Phenyl or other aryl groups on silicon can be selectively replaced by halogens, upon treatment with a hydrogen halide and a Lewis acid. 

Although a transition metal was not involved, the dehydrocoupling of the secondary hydrosilane, 1,1-dihydrotetraphenylsilole, to polymers with Mw values ranging from 4000 to 6000 (polydispersities ranged between 1.1 and 1.2) in the presence of catalytic quantities of Red-Al, L(N or K)-Selectride or Super-Hydride has been reported.1353 This is the only currently published example of polymeric material produced from a secondary silane. It is interesting that this secondary silane is a heterocyclic system where steric interactions (from substituents at silicon) have been reduced, although the fact that there are phenyl groups on the a-carbon, makes this a rather extraordinary result. 

Table 2.6 shows a series of silicone polymer stationary phases from the OV series. These are dimethylsiloxane polymers, with a varying percentage of the methyl groups replaced by phenyl groups. It turns out that the Rohrschneider constants closely follow this increase in phenyl group percentage. The constants therefore appear to be a reliable indication of the polarity of the stationary phase. 

Finally, the sum of the first five McReynolds values has been used to compare the polarities of silicone polymers on OT columns. It has already been stated that the polarity of the silicone polymers can be increased by increasing the percentage of phenyl groups in the polymer. Figure 8.17 shows a plot for five polymers on bonded fused silica WCOT columns (except for SP-2250, which is from packed column data). The increasing McReynolds values clearly show the validity of this method of specifying stationary phase polarity. 

After treatment with water to dissolve out the magnesium salts, and after evaporation of the ether which generally is used as solvent, sticky resinous polymers are left. Their rather low melting point (about 100°) suggests that the phenylene-silicon chains are rather short, and probably they are terminated by methyl groups or by phenyl groups derived from the hydrolysis of structures like Si—CeH4MgBr. 

Hybrid graft copolymers having silicon-based polymer backbones were also prepared by the metal-mediated radical polymerizations of styrene. The phenyl groups of poly[(methylphenyl)silylene] were bromomethylated and then employed as the grafting points of polystyrene (G-16).294,441 Polysiloxane can be employed also as a backbone (G-17) by introduction of benzyl chloride units into the pendant vinyl-functionalized poly(dimethylsiloxane).409... 

Other silicone liquid phases are available in which the methyl groups are replaced to various extents by other groups. Enhanced selectivity may be obtained by chemical modification of the silicone polymer by the introduction of a polyester which, unfortimately, reduces the thermal breakdown temperature. Ethylene glycol succinate is commonly used as the polyester for these modifications. The silicone part may also be substituted by phenyl or cyanoethyl, etc. Table 3 shows some of these liquid phases which are available commercially. 

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