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

Claim 1

A process for preparing polyorganosiloxanes containing a controlled low-level of hydroxy substitution, the process comprising: (A) contacting a mixture comprising low molecular weight polyorganosiloxanes of formula ##STR3## and a source of triorganosilyl endblocker of formula R.sup.1.sub.3 Si--, with a Lewis base catalyst; where each X is independently selected from a group consisting of cations of the Lewis base catalyst and hydroxyl radicals; each R is independently selected from a group consisting of monovalent hydrocarbon radicals of one to six carbon atoms and 1,1,1-trifluoropropyl radical; each R 1 is independently selected from a group consisting of hydrocarbon radicals of one to six carbon atoms and 1,1,1-trifluoropropyl radical; and a is an average value of one to about 2,000; (B) controlling partial pressure of water in the process at a constant value within a range of about zero to 1,000 mmHg. (C) controlling temperature of the contacted mixtures and Lewis base catalyst at a value within a range of 40° C. to 300° C.; and (D) recovering product polyorganosiloxanes of formula ##STR4## where the product polyorganosiloxanes have a potential value for hydroxy substitution within a range of about zero to 1,000 ppm; where R is as previously described and R 2 is selected from a group consisting of R 1 and hydroxyl; and b is an average value within a range of a to about 2,000.