Anhydrous process for preparation of polyorganosiloxanes

The present invention is an anhydrous process for preparing organosiloxy end-blocked polyorganosiloxanes from chlorine end-terminated polyorganosiloxanes. The process comprises contacting an anhydrous mixture comprising a chlorine end-terminated polyorganosiloxane and an organodisiloxane with a rearrangement catalyst, where the rearrangement catalyst facilitates a chlorine and organosiloxy exchange between the chlorine end-terminated polyorganosiloxane and the organodisiloxane forming a organochlorosilane as a by-product. The organochlorosilane is continuously removed from the process providing a means by which the chlorine displaced from the chlorine end-terminated polyorganosiloxane can be effectively removed from the organosiloxy end-blocked polyorganosiloxanes in a useable form. The present process is especially useful for the rearrangement of chlorine end-terminated polyorganosiloxanes having one or more hydrogen atoms bonded to silicon to organosiloxy end-blocked polyorganohydrosiloxanes.

BACKGROUND OF INVENTION 
The present invention is an anhydrous process for the rearrangement of 
chlorine end-terminated polyorganosiloxanes to form organosiloxy 
end-blocked polyorganosiloxanes. The process is especially useful for the 
rearrangement of chlorine end-terminated polyorganosiloxanes having one or 
more hydrogen atoms bonded to silicon. The process comprises contacting a 
mixture comprising a chlorine end-terminated polyorganosiloxane and an 
organodisiloxane with a rearrangement catalyst. The rearrangement catalyst 
is effective in facilitating a chlorine and organosiloxy exchange between 
the chlorine end-terminated polyorganosiloxane and the organodisiloxane 
and may further effect rearrangement of the silicon to oxygen bonds within 
the chlorine end-terminated polyorganosiloxane and the silicon to oxygen 
bonds within the organosiloxy end-blocked polyorganosiloxanes. In the 
present process, the organodisiloxane serves as a source of (1) an 
organosiloxy end-blocker which displaces the chlorines of the chlorine 
end-terminated polyorganosiloxanes and (2) an organosilyl component which 
binds with the displaced chlorine to form a volatile organochlorosilane. 
The volatile organochlorosilane is continuously removed from the process. 
Since the early work of Hyde, U.S. Pat. No. 2,457,677, issued Dec. 28, 
1948, it has been known that diorganodihalosilanes in the presence of 
water hydrolyze to form a mixture of cyclic diorganosiloxanes and 
short-chained linear diorganosiloxanes along with hydrogen chloride as a 
by-product. Hyde also observed in this patent that the presence of a 
triorganosilane in the process could result in polydiorganosiloxanes that 
were triorganosiloxy end-blocked. 
Hyde, U.S. Pat. No. 2,467,976, issued Apr. 19, 1949, teaches that the 
viscosity of polydimethylsiloxanes produced by the hydrolysis of 
diorganodichlorosilanes could be increased by refluxing the 
polydimethylsiloxanes with hydrochloric acid effecting rearrangement of 
silicon to oxygen bonds within the polydimethylsiloxanes. In U.S. Pat. No. 
2,779,776, Hyde further teaches that the acid concentration is important 
in determining the equilibrium viscosity of the polydimethylsiloxane 
products. 
Wilcock, U.S. Pat. No. 2,491,843, issued Dec. 20, 1949, described 
processes, similar to those described by Hyde, for the production of 
polyorganohydrosiloxanes. 
The hydrolysis of diorganodichlorosilanes to form a mixture of cyclic 
siloxanes and short-chain linear siloxanes with the liberation of chlorine 
continues to be an important first step in commercial processes for 
producing higher molecular weight polyorganosiloxanes. However, the 
chlorine displaced from the diorganodichlorosilanes during the hydrolysis 
process creates several problems. For example, it is known that residual 
chloride present in polyorganosiloxane fluids can reduce shelf-life of the 
fluids by effecting viscosity changes. Therefore, any process for 
producing higher molecular weight polyorganosiloxanes from a hydrolyzate 
must be capable of controlling the level of chlorine present in the 
polyorganosiloxanes. A second problem is disposition of the displaced 
chlorine after recovery from the process. Because of the economic value of 
chlorine and the cost of disposal of chlorine, it is preferred to recover 
the chlorine for use in the same or different processes. Several processes 
have been described to deal with these problems but each suffers from 
various shortcomings. 
For example, in one process, the hydrolysis is run in the presence of a 
stoichiometric excess of water, resulting in the production of 
cyclosiloxanes, short-chained hydroxyl terminated polysiloxanes, and 
aqueous hydrogen chloride. The partitioning of the chlorine into the 
aqueous phase is an exothermic process requiring that the reactor be 
cooled to maintain a desired temperature. Furthermore recovery of the 
chlorine from the process in the form of anhydrous hydrogen chloride must 
typically be accomplished by an energy intensive distillation of a 
HCl-H.sub.2 O azeotrope. 
In another process, as exemplified by Hajjar, U.S. Pat. No. 4,609,751, 
issued Sep. 2, 1968, the process is run with about a stoichiometric 
equivalence of water with the consequential generation of anhydrous 
hydrogen chloride. The resultant product is cyclosiloxanes and chlorine 
end-terminated polyorganosiloxanes. Although this process provides a 
satisfactory solution to the recovery of displaced chlorine, to assure 
satisfactory low-levels of chlorine in the final polyorganosiloxane 
product a multi-step process is typically required. The 
chlorine-terminated polyorganosiloxanes are typically washed with one or 
more portions of water to form hydroxyl-terminated polyorganosiloxanes and 
a weak aqueous hydrogen chloride solution which can be returned to the 
process. These hydroxyl-terminated polyorganosiloxanes can then be further 
processed to produce long-chain polyorganosiloxanes. This additional wash 
step increases the cost of producing long-chain polyorganosiloxanes. 
An additional problem associated with the described processes is that the 
process conditions can be sufficiently severe to cause reaction of desired 
silicon-bonded hydrogen when present in the polyorganosiloxanes. 
Therefore, these process are not entirely suitable for the production of 
polyorganohydrosiloxanes. 
Therefore, an objective of the present invention is to provide a process 
for converting chlorine-end terminated polyorganosiloxanes to 
polyorganosiloxanes without first converting the end-terminal chlorine to 
end-terminal hydroxyl. A second objective is to provide a process for 
making polyorganosiloxanes end-blocked with organosiloxy groups. A third 
objective is to provide a process where the polyorganosiloxanes have an 
acceptably low level of residual chloride. A fourth objective is to 
provide a process where the chlorine displaced from the 
chlorine-terminated polyorganosiloxane is recovered in a form suitable for 
use in other processes. A fifth objective of the present invention is to 
provide a process where chlorine end-terminated polyorganohydrosiloxanes 
can be processed to form polyorganohydrosiloxanes without significant 
reaction of the silicon-bonded hydrogen. 
SUMMARY OF INVENTION 
The present invention is an anhydrous process for preparing organosiloxy 
end-blocked polyorganosiloxanes from chlorine end-terminated 
polyorganosiloxanes. The process comprises contacting an anhydrous mixture 
comprising a chlorine end-terminated polyorganosiloxane and an 
organodisiloxane with a rearrangement catalyst, where the rearrangement 
catalyst facilitates a chlorine and organosiloxy exchange between the 
chlorine end-terminated polyorganosiloxane and the organodisiloxane 
forming a organochlorosilane as a by-product. The organochlorosilane is 
continuously removed from the process providing a means by which the 
chlorine displaced from the chlorine end-terminated polyorganosiloxane can 
be effectively removed from the organosiloxy end-blocked 
polyorganosiloxanes in a useable form. The present process is especially 
useful for the rearrangement of chlorine end-terminated 
polyorganosiloxanes having one or more hydrogen atoms bonded to silicon to 
organosiloxy end-blocked polyorganohydrosiloxanes.

DESCRIPTION OF INVENTION The present invention is an anhydrous process for 
the preparation of organosiloxy end-blocked polyorganosiloxanes. The 
process comprises: 
(A) contacting an anhydrous mixture comprising a chlorine end-terminated 
polyorganosiloxanes described by formula 
EQU Cl(R.sub.2 SiO).sub.x SiR.sub.2 Cl ; and (1) 
an organodisiloxane described by formula 
EQU R.sub.3 SiOSiR.sub.3 ; (2) 
with a rearrangement catalyst effective in facilitating a chlorine and 
organosiloxy exchange between the chlorine end-terminated 
polyorganosiloxane and the organodisiloxane where organochlorosilane is 
formed by the exchange; 
(B) continuously removing the organochlorosilane from the process: and 
(C) recovering organosiloxy end-blocked polyorganosiloxanes described by 
formula 
EQU R.sub.3 SiO(R.sub.2 SiO).sub.y SiR.sub.3 ; (3) 
where each R is independently selected from a group consisting of hydrogen 
atom, alkyls comprising one to 20 carbon atoms, cycloalkyls comprising 
four to 20 carbon atoms, alkenyls comprising two to 20 carbon atoms, and 
aryls; x=1 to 1000; and y=1 to 1,001. 
The present process can be conducted as a batch, semi-batch, or continuous 
process. Contact of the anhydrous mixture of the present process with the 
rearrangement catalyst can be effect in standard type reactors for 
conducting such reactions. The reactor may be, for example, a stirred-tank 
reactor, a fixed-bed reactor, or a fluidized-bed reactor. 
The present process is conducted as an anhydrous process. By anhydrous, it 
is meant that the present process does not require the presence of water. 
For purpose of the present process, an anhydrous mixture is one containing 
ten weight percent or less of water. Preferred is an anhydrous mixture 
containing one weight percent or less of water. 
The anhydrous mixture useful in the present process comprises a chlorine 
end-terminated polyorganosiloxane and a organodisiloxane. Chlorine 
end-terminated polyorganosiloxanes useful in the present invention are 
described by formula (1). The chlorine end-terminated polyorganosiloxane 
has substituents R, where each R is independently selected from a group 
consisting of hydrogen atom, alkyls comprising one to 20 carbon atoms, 
cycloalkyls comprising four to 20 carbon atoms, alkenyls comprising two to 
20 carbon atoms, and aryls. The substituent R can be, for example, methyl, 
ethyl, propyl, tert-butyl, isobutyl, cyclopentyl, cyclohexyl, cycloheptyl, 
vinyl, allyl, hexenyl, pentenyl, phenyl, xylyl, and naphthyl. The chlorine 
end-terminated polyorganosiloxane can have x number of divalent siloxy 
units of formula --R.sub.2 SiO--, where R is as previously described, and 
x=1 to 1000. Preferred are chlorine end-terminated polyorganosiloxanes 
where x=10 to 200. 
The present process is particularly useful for converting chlorine 
end-terminated polyorganosiloxanes to organosiloxy end-blocked 
polyorganosiloxanes where at least one R substituent is a hydrogen atom. 
The reason for this preference is the reactive nature of the hydrogen to 
silicon bond. Unlike standard practices for converting chlorine 
end-terminated polyorganosiloxanes to polyorganosiloxanes, the present 
process has minimal effect on the hydrogen to silicon bond. Therefore, 
organosiloxy end-blocked polyorganohydrosiloxanes in high yield can be 
prepared by the present process. Even more preferred are those chlorine 
end-terminated polyorganosiloxanes where the ratio of hydrogen atoms on 
the silicon atom to organic substituents on the silicon atom is within a 
range of about 0.001:1 to about 1:1. 
In a preferred process, the chlorine end-terminated polyorganosiloxanes are 
the product of a hydrolysis process where an organodichlorosilane or 
diorganodichlorosilane is hydrolyzed in a near stoichiometric equivalence 
of water. By "near stoichiometric equivalence," it is meant about 0.8 to 
1.2 mole of water is added to the hydrolysis process for each mole of 
organodichlorosilane diorganodichlorosilane. The product of the hydrolysis 
process may be used in the present process as a mixture of cyclic 
siloxanes and chlorine end-terminated polyorganosiloxanes or the chlorine 
end-terminated polyorganosiloxanes may be separated from the cyclic 
siloxanes prior to use. 
The anhydrous mixture useful in the present invention also contains an 
organodisiloxane as described by formula (2). The organodisiloxane 
contains substituents R, where R is as previously described for the 
chlorine end-terminated polyorganosiloxane. For the organodisiloxane, it 
is preferred that R be selected from a group consisting of hydrogen atom 
and methyl and that no more than one hydrogen atom be bonded to each 
silicon. The most preferred organodisiloxane is hexamethyldisiloxane. 
The amount of organodisiloxane employed in the process will depended upon 
the initial degree of polymerization of the chlorine end-terminated 
polyorganosiloxane and the desired degree of polymerization of the 
organosiloxy end-blocked polyorganosiloxane. Generally, the larger the 
amount of organodisiloxane employed in the process, the smaller the degree 
of polymerization of the organosiloxy end-blocked polyorganosiloxane. A 
useful amount of organodisiloxane is within a range of about 0.001 mole to 
10.0 mole per mole of chlorine added to the process as the end-terminal 
chlorine of the chlorine end-terminated polyorganosiloxane. A preferred 
amount of organodisiloxane is within a range of about 0.1 to 2.0 moles per 
mole of chlorine added to the process as the end-terminated 
polyorganosiloxane. 
The anhydrous mixture comprising a chlorine end-terminated 
polyorganosiloxane and an organodisiloxane is contacted with a 
rearrangement catalyst. By "rearrangement catalyst" it is meant those 
catalyst which facilitate the replacement of the end-terminal chlorine of 
the chlorine end-terminated polyorganosiloxane with an organosiloxy group 
originating from the organodisiloxane. In addition, the rearrangement 
catalyst may effect rearrangement of internal siloxane bonds, i.e. silicon 
to oxygen bonds, of the chlorine end-terminated polyorganosiloxanes and 
organosiloxy end-blocked polyorganosiloxanes. In a preferred process, the 
rearrangement catalyst effects rearrangement of siloxane bonds of the 
chlorine end-terminated polyorganosiloxanes and of the organosiloxy 
end-blocked polyorganosiloxanes to form organosiloxy end-blocked 
polyorganosiloxanes having a higher degree of polymerization than the 
chlorine end-terminated polyorganosiloxanes added to the process. 
The rearrangement catalyst can be either a homogeneous catalyst or a 
heterogeneous catalyst. Examples of useful homogeneous rearrangement 
catalysts are: trifluoromethane sulfonic acid, methanesulfonic acid, and 
trifluoroacetic acid. 
Preferred is when the rearrangement catalyst is a heterogeneous catalyst. 
Even more preferred is when the rearrangement catalyst is a heterogeneous 
catalyst selected from a group consisting of acid clays, sulfonic acid 
resins, and activated carbon. The heterogeneous rearrangement catalyst can 
be in the form of, for example, particles, powders, flakes, chips, or 
pellets. Any activated carbon capable of facilitating the replacement of 
the end-terminal chlorine of the chlorine end-terminated 
polyorganosiloxane with an organosiloxy group originating from the 
organodisiloxane can be employed in the present process. The activated 
carbon useful in the present process can be of the thermal or chemically 
activated type. 
Any acid clay capable of facilitating the replacement of the end-terminal 
chlorine of the chlorine end-terminated polyorganosiloxane with an 
organosiloxy group originating from the organodisiloxane can be employed 
in the present process. The acid clays can be, for example, those produced 
from halloysites, kaolinites, and bentonites composed of montmorillonite; 
where the clay is treated with an acid solution, for example, sulfuric 
acid. 
Any sulfonic acid resin capable of facilitating the replacement of the 
end-terminal chlorine of the chlorine end-terminated polyorganosiloxane 
with an organosiloxy group originating from the organodisiloxane can be 
employed in the present process. The sulfonic acid resin can be, for 
example, a synthetic resin having --SO.sub.3 H or --SO.sub.2 OH groups 
attached thereto. The sulfonic acid resin can be for example. Amberlyst 
A15 (Rhom and Haas, Philadelphia, Pa.) or Dowex DR2040 (The Dow Chemical 
Company, Midland, Mich.). 
The amount of rearrangement catalyst employed in the present process can be 
varied within wide limits in relation to the chlorine end-terminated 
polyorganosiloxane added to the process. The amount of rearrangement 
catalyst will depend upon such factors as the type of catalyst, the 
specific chlorine end-terminated polyorganosiloxane and organodisiloxane 
to be rearranged, the process temperature, and whether the process is run 
as a batch, semi-batch, or continuous process. Examples of useful amount 
of catalyst are given in the Examples provided herein. 
Rearrangement of the chlorine end-terminated polyorganosiloxane with the 
organodisiloxane results in the organodisiloxane being split into (1) an 
organosiloxy group which is exchanged for a chlorine of the chlorine 
end-terminated polyorganosiloxane and (2) a silyl group which serves as a 
receptor for chlorine to form a chlorosilane which is volatile under 
process conditions. 
The chlorosilane is continuously removed from the process as it is being 
formed. The chlorosilane can be removed from the process by standard means 
for separating a gas from a liquid or liquid and solid mixture. The 
chlorosilane may by removed from the process, for example, by means of a 
vacuum to draw the chlorosilane into an appropriate storage container or 
into a process where the chlorosilane serves as a feed. 
Polyorganosiloxanes as described by formula (3) are recovered from the 
process. By the term "recovered" it is meant that the polyorganosiloxanes 
are appropriately isolated, contained, and stored for their intended use. 
Preferred polyorganosiloxanes are those in which each substituent R is 
methyl. Even more preferred are those polyorganosiloxanes in which each 
substituent R is selected from a group consisting of hydrogen and methyl 
and no more than one hydrogen is bonded to each silicon atom. 
The following examples are provided to illustrate the present process. 
These examples are not intended to limit the scope of the claims provided 
herein. 
EXAMPLE 1 
About 200 g of chlorine end-terminated polymethylhydrosiloxane was added to 
a flask containing 10 g of a sulfonic acid resin (Amberlyst A-15 Rhom and 
Haas, Philadelphia, Pa.). Nitrogen was bubbled through the flask contents 
at a slow rate to remove trimethylchlorosilane formed during the process. 
About 50 mL of hexamethyldisiloxane was added to the flask over a period 
of three hours. The content of the flask was kept at a temperature of 
about 25.degree. C. The nitrogen was allowed to continue to bubble through 
the flask contents for an additional 16 hours. The flask contents was 
analyzed by nuclear magnetic resonance and found to comprise 17.8 mole % 
Me.sub.3 SiO.sub.1/2, 82.0 mole % MeHSiO.sub.2/2, and 0.15 mole % 
MeSiO.sub.3/2. Acid content of the flask contents was determined by 
titration and equated to 99 ppm HCl. 
EXAMPLE 2 
A 3.6 m by 2.5 cm I.D. teflon reactor was packed with about 227 g of 
activated carbon (Type: WSIV, Calgon, Philadelphia, Pa.). A mixture 
comprising 500 g of chlorine end-terminated polymethylhydrosiloxanes and 
38 g of hexamethyldisiloxane was fed to the reactor at a rate of 2.1 
g/min. The reactor was maintained at a temperature of about 45.degree. C. 
and a pressure of about 300 mmHg. During conduct of the process a wet 
nitrogen purge was fed to the reactor counter to the flow of the siloxanes 
to facilitate removal of trimethylchlorosilane from the process as it was 
formed. The wet nitrogen purge was created by passing dry nitrogen gas 
through a 25.degree. C. water bath at a rate of 20 mL/min. prior to the 
passing of the nitrogen gas into the reactor. A sample of the reactor 
product was analyzed at the times given in Table 1 for acid content by 
titration. The results are presented in Table 1 as ppm HCl. 
TABLE 1 
______________________________________ 
Chlorine Content of Polyorganohydrosiloxane 
Sampling Time (h) 
ppm HCl 
______________________________________ 
2.25 20 
2.75 12 
4.00 11 
______________________________________ 
The product was determined to have an Mn of 4590 relative to polystyrene by 
gel-permeation chromatography. 
EXAMPLE 3 
The process described in Example 2 was repeated using a mixture of 500 g of 
chlorine end-terminated polyorganohydrosiloxane and 76.3 g of 
hexamethyldisiloxane to the reactor. All other process conditions were the 
same as given for Example 1. A sample of the reactor product was analyzed 
at the times given in Table 2 for acid content by titration. The results 
are presented in Table 2 as ppm HCl. 
TABLE 2 
______________________________________ 
Chlorine Content of Polyorganohydrosiloxane 
Sampling Time (h) 
ppm HCl 
______________________________________ 
0.8 2.1 
1.8 1.7 
2.8 1.7 
______________________________________ 
The product was determined to have an Mn of 3134 relative to polystyrene by 
gel-permeation chromatography.