OH-terminated polysiloxanes

Scheme 1 Thermal depolymerization of an OH-terminated polysiloxane in inert environment.

Scheme 2 Mechanism of in situ cross-linking of OH-terminated polysiloxanes by methyltrimethoxy silane.

Table 2 Commercially available asymmetrically substituted, OH-terminated polysiloxane phases, designed for gas chromatography, working temperatures (on glass) 350-370°C...

Figure 8 FID chromatogram of antioxidants and UV stabilizers. Column PS-089, 20m x 0.3mm, glass. Carrier gas H2. (Reproduced from Blum W and Damasceno L (1987) High temperature glass capillary gas chromatography using OH-terminated polysiloxane stationary phases. Separation of antioxidants and UV stabilizers. Journal of High Resolution Chromatography and Chromatography Communications 10 472-476.)...

Linear polysiloxanes obtained by the hydrolysis of dichlorosilanes are of relatively low molecular weight they can, however, be condensed further through the terminal OH groups by thermal after-treatment. 

The use of the building block isocyanatomethyl-dimethylmonomethoxy silane allows the ready synthesis of mono-silanol-terminated hydrocarbon polymers. These then can be used in the same way as their polysiloxane congeners in RTV-2 applications. The advantages that the vulcanizates then have mainly depend on the performance properties which the base polymer HO-P-OH introduces into the RTV-2 system. 

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