Method for preparing novel fluorinated organosiloxane copolymers

DETAILED DESCRIPTION OF THE INVENTION The resinous benzene-soluble organosiloxane copolymers prepared using the present method consist essentially of (a) repeating units of the formulae SiO.
sub.
4/2 ; R(CH.
sub.
3).
sub.
2 SiO.
sub.
1/2 ; and units of the general formula R'CH.
sub.
2 CH.
sub.
2 Si(R").
sub.
n O.
sub.
(3-n)/2 where R represents a saturated or ethylenically unsaturated hydrocarbon radical containing from 1 to 4 carbon atoms or a phenyl radical, R' represents a monovalent organic group containing at least 4 perfluorinated carbon atoms, R" represents an alkyl radical containing from 1 to 3 carbon atoms or a phenyl radical and n is 0, 1 or 2; (b) silicon-bonded hydroxyl groups and, optionally (c) (CH.
sub.
3).
sub.
2 SiO units.
The molar ratio of all units in the copolymer other than silicon-bonded hydroxyl groups and SiO.
sub.
4/2 units to said SiO.
sub.
4/2 units is from 0.
7:1 to 1.
1:1, inclusive, and the concentration of silicon-bonded hydroxyl groups in said copolymer is from 0 to 4.
0% by weight.
In preferred embodiments of the present copolymers, R is methyl and the molar ratio of (CH.
sub.
3).
sub.
3 SiO.
sub.
1/2 units to said fluorine-containing units is such that (a) the surface tension exhibited by a 10% by weight solution of the copolymer in a hydroxyl endblocked polydimethylsiloxane exhibiting a viscosity of 0.
08 Pa.
multidot.
s at 25.
degree.
C.
is less than 2.
2.
times.
10.
sup.
-4 newtons per cm at 25.
degree.
C.
when in contact with air, and (b) optical clarity is achieved by the addition to said solution of from 0 to 100 percent by weight of o-xylene.
These copolymers are claimed in an application for Letters Patent entitled "Novel Fluorinated Organosiloxane Copolymers" that is being filed concurrently herewith in the names of Chi-Long Lee, Thomas Fay-Oy Lim and Antony Pope Wright.
This invention provides a method for preparing the aforementioned novel fluorinated organosiloxane copolymers, said method comprising the steps of (I) heating at a temperature of from 50.
degree.
C.
to the boiling point thereof a liquid reaction mixture comprising, (A) a fluorinated silane of the formula R'CH