Base catalyzed preparation of polyorganosiloxanes with controlled low levels of hydroxy substitution

摘要

The described process uses a Lewis base as a catalyst to effect the condensation of hydroxy end-substituted polyorganosiloxanes, in the presence of triorganosilyl endblocker to control polymer chain length. The inventors have discovered that within a base catalyst concentration range where the cation concentration is about 1x10-3 to 2x10-1 mole percent in relation to the silicon atoms present, the partial pressure of water can be controlled at a constant value to produce polyorganosiloxane polymers with a reproducible and predictable level of hydroxy substitution.