Method for making silarylenesiloxane-polydiorganosiloxane block polymers

A method is provided for making silarylenesiloxane-polydiorganosiloxane block polymers, based on the reaction between a silarylenesilanediol and a silanol terminated polydiorganosiloxane in the presence of a condensation catalyst in the form of an amine salt of certain carboxylic acids. A carbonyl containing organic compound, such as phthalic anhydride, is employed prior to a subsequent devolatilization step to facilitate the removal of amine-carboxylic acid catalyst residues.

The present invention relates to a method for making 
silarylenesiloxane-polydiorganosiloxane block polymer, based on the 
intercondensation of silarylenesilanediol and silanol terminated 
polydiorganosiloxane. More particularly, the present invention relates to 
the use of a carbonyl compound, such as an organic aldehyde, organic acid 
anhydride, etc., organic ketone, to facilitate the removal of residual 
amine-carboxylic acid condensation catalyst from 
silarylenesiloxane-polydiorganosiloxane block polymer which can interfere 
with the thermal stability of the block polymer. 
Prior to the present invention, as shown by Merker U.S. Pat. No. 3,202,634, 
silarylenesiloxane-polydiorganosiloxane block polymers consisting 
essentially of silarylenesiloxy blocks of the formula, 
##STR1## 
CHEMICALLY COMBINED WITH POLYDIORGANOSILOXANE BLOCKS, 
##STR2## 
WHERE R is a monovalent organic radical, Z is a divalent aromatic organic 
radical, a has an average value greater than 3, and b has an average value 
greater than 10, was prepared by effecting the intercondensation of a 
silanol terminated polydiorganosiloxane of the formula, 
##STR3## 
with a silarylenesilanediol, 
##STR4## 
using an amine-carboxylic acid condensation catalyst. It was found that 
amine-carboxylic acid catalyst residues adversely affect the heat 
stability of the resulting silicone block polymer. A procedure which was 
employed to effect the removal of such amine-carboxylic acid catalyst 
residues from the block polymer was by pouring the block polymer solution 
into methanol to effect block polymer precipitation. Prior to the 
precipitation step, the viscous block polymer solution was also further 
diluted with additional organic solvent, such as benzene, toluene, 
chloroform or methylene chloride. As a result, large volumes of solvent 
were necessary which were difficult to salvage. The precipitation 
procedure therefore was economically unattractive. 
The present invention is based on the discovery that block polymers 
consisting essentially of units of formula (1) chemically combined with 
units of formula (2) can be made substantially free of amine 
carboxylic-acid residues by the intercondensation of silanol fluid of 
formula (3) with silarylenesilanediol of formula (4) without the need of a 
precipitation step, or the use of large volumes of organic solvent, by 
adding water to the mixture after the initial condensation reaction and 
azeotroping the water therefrom, followed by the use of an organic 
carbonyl compound or precursor thereof, defined more particularly below, 
and thereafter devolatilizing the mixture to effect the stripping of 
remaining catalyst residues from the block polymer. 
There is provided by the present invention a method for making 
silarylenesiloxane-polydiorganosiloxane block polymer consisting 
essentially of chemically combined units of formulas (1) and (2), and 
referred to hereinafter as "block polymer", which comprises, 
(1) refluxing a mixture comprising silarylene silanediol of formula (4) and 
a silanol terminated polydiorganosiloxane of formula (3) in an inert 
organic solvent in the presence of an effective amount of an amine salt of 
a carboxylic acid, selected from the class consisting of formic, acetic 
and propionic, 
(2) additional 0.01 to 1 part of water, per part of mixture to the mixture 
or (1), 
(3) azeotroping the mixture of (2) until it is substantially free of water, 
(4) adding an effective amount of an organic carbonyl compound, or 
precursor thereof, to the mixture of (3) and 
(4) devolatilizing the mixture of (4) at temperatures up to 175.degree. C. 
Included by the monovalent organic radicals shown by R of formula 1-4 are, 
for example, C.sub.(1-8) alkyl radicals, such as methyl, ethyl, propyl, 
butyl, pentyl, etc.; aryl radicals, such as phenyl, naphthyl; alkaryl 
radicals, such as tolyl, xylyl; unsaturated aliphatic radicals such as 
vinyl, allyl, propenyl; and halogenated derivatives thereof, such as 
chlorophenyl, 3,3,3-tri-fluoropropyl, etc. Included by the divalent 
aromatic radicals shown by Z of formulas 1 and 3 are are, for example, 
divalent aromatic hydrocarbon radicals, such as phenylene, tolylene, 
xylene, naphthylene, 4,4'-biphenylene 4,4'-diphenylene ether, etc.; 
halogenated divalent aromatic hydrocarbon radicals, such as 
chlorophenylene, bromonaphthylene, etc. In formulas 1-4, where R and Z 
respectively can represent more than 1 radical, these radicals can be all 
the same or can be different as previously defined. 
Included in the organic carbonyl compounds which can be used in the 
practice of the present invention to minimize the effect of 
amine-carboxylic acid catalyst residues on the heat stability of the block 
polymers made in accordance with the method of the present invention are, 
for example, cyclic organic anhydrides, such as phthalic anhydride, maleic 
anhydride, succinic anhydride, polyanhydrides, such as 
##STR5## 
where a can be 0 or 1, and X is selected from 
##STR6## 
where X is as previous defined, etc.; anhydride containing polymers 
consisting essentially of units such as 
##STR7## 
organic aldehydes and ketones, such as benzaldehyde and other aromatic 
aldehydes, caproaldehyde and other aliphatic aldehydes; acetophenone, 
propiophenone, and other aliphatic-aromatic ketones, benzophenone and 
other aromatic ketone, cyclohexanone, heptanone and other cycloaliphatic 
ketones; polyketones, such as benzil 
##STR8## 
In addition to the above described carbonyl compounds, precursors of such 
carbonyl compounds also can be utilized as the organic carbonyl compound 
which can be added to the reaction mixture, such as polycarboxylic acids, 
such as phthalic acid, maleic acid, succinic acid, etc.; acetals and 
ketals, such as benzaldehyde diethyl ketal, acetophenone diethylene ketal, 
##STR9## 
Included in the silarylenesilanediols of formula (4) are compounds such as 
##STR10## 
Included by the silanol terminated polydiorganosiloxane of formula (3) are 
polymers where b of formulas 2 and 4 is an integer having a value of from 
5-10,000 inclusive, and preferably, an average of from 10-1,000 inclusive. 
In the practice of the invention the block polymer can be made by effecting 
reaction between the silarylenesilanediol, and the silanol terminated 
polydiorganosiloxane in the presence of an inert organic solvent and a 
non-rearranging catalyst, such as an amine-carboxylic acid. To facilitate 
the removal of the amine-carboxylic acid catalyst residues from the 
mixture, water can be added thereto. The water and the organic solvent can 
then be azeotroped from the mixture. There can then be added to the 
mixture, the organic carbonyl reactant followed by stripping the mixture 
of volatiles. 
The intercondensation reaction can be conducted at a temperature in the 
range of from 25.degree. to 150.degree. C. and preferably from 80.degree. 
to 120.degree. C. Reaction times can vary widely depending upon the nature 
of the reactants, the temperature of the reaction, such factors as degree 
of agitation etc. Generally, however, the reaction can be completed 
anywhere from 4 hours or less to as long as 24 hours or more. 
The amine-carboxylic acid catalyst can be formed in situ utilizing 
substantially equal moler amounts of amine and carboxylic acid. However, 
excesses of either components can be utilized without adverse results. 
Preferably, organic primary amines can be used, such as C.sub.(1-8) alkyl 
amines, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl amines, 
etc. Carboxylic acids which can be used are preferably formic, acetic, 
propionic, etc. If desired, preformed amine-carboxylic acid condensation 
catalysts can be used, such as a variety shown in Hyde, U.S. Pat. No. 
3,160,601, Merker U.S. Pat. No. 3,202,634 and Fork U.S. Pat. No. 
3,032,530. 
Experience has shown that about 0.01 to 5% by weight of the 
amine-carboxylic acid catalyst will provide for effective results. 
Organic solvents which can be used in the practice of the invention are, 
for example, any inert organic solvent including non-polar organic 
solvents, such as benzene, toluene, xylene, ethylbenzene. Other inert 
organic solvents which can be used are polar aprotic organic solvents, 
such as chloroform, chlorobenzene, chlorotoluene, etc. 
The amount of water that can be added to the mixture after the initial 
intercondensation reaction can vary widely, such as from 0.01 parts to 1 
part of water per part of mixture. It has been found that effective 
results can be achieved if from 0.1% to 1% by weight of carbonyl compound, 
based on the weight of reaction mixture is used in the practice of the 
invention. 
The final stripping or devolatilization of the block polymer after the 
carbonyl compound has been added can be achieved after 0.5 to 8.0 hours, 
at temperatures in the range of from 150.degree. to 175.degree. C. 
In order that those skilled in the art will be better able to practice the 
invention, the following example is given by way of illustration and not 
by way of limitation. All parts are by weight.

EXAMPLE 1. 
A mixture of 220 parts of p-bis(dimethylhydroxysilyl) benzene, 300 parts of 
a 60 centistoke silanol terminated polydimethylsiloxane fluid, 250 parts 
of toluene, 4 parts of tert-butyl amine, and 5 parts of formic acid was 
refluxed for 6 hours. There was added to the resulting mixture, 100 parts 
of water. The mixture was thoroughly stirred and then azeotroped dry. 
There was added 8 parts of phthalic anhydride to the resulting mixture and 
the mixture was refluxed for 30 minutes. The resulting mixture was then 
devolatilized over a 12 hour period at a temperature of 115.degree. C. at 
30 Torr. A stiff white gum was obtained. Based on method of preparation, 
the resulting white gum was a block polymer consisting essentially of 
diphenylenesiloxane units chemically combined with blocks of 
polydimethylsiloxy units. 
The above procedure was repeated except that the block polymer was 
recovered without the use of a carbonyl reactant, such as phthalic 
anhydride in the reaction mixture. In another reaction free of carbonyl 
reactant, block polymer was recovered by also precipitating it from a 
reaction mixture by direct addition of methanol to the reaction mixture. 
Additional block polymer was recovered from reaction mixtures containing 
different amine-carboxylic acids and carbonyl reactants other than 
phthalic anhydride. The block polymer was then evaluated for thermal 
stability in accordance with thermal gravemitric analysis (TGA) in air and 
under a nitrogen atmosphere over a period of 1.5 hours to determine the 
temperature required to effect the loss of 10% by weight of the block 
polymer. The following results were obtained where the catalyst was 
prepared in situ in the reaction mixture by employing substantially equal 
molar amounts of the acid and the amine "t" is tert, "o" is ortho and "n" 
is normal: 
______________________________________ 
T(.degree. C.) 
Carbonyl In Situ- for 10% WT Loss 
Reactant Catalyst Air N.sub.2 
______________________________________ 
None HCO.sub.2 H/t-C.sub.4 H.sub.9 NH.sub.2 
340 345 
None + 
Precipitated 
HCO.sub.2 H/t-C.sub.4 H.sub.9 NH.sub.2 
435 435 
Maleic 
Anhydride HCO.sub.2 H/t-C.sub. 4 H.sub.9 NH.sub.2 
395 375 
Phthalic 
Anhydride HCO.sub.2 H/t-C.sub.4 H.sub.9 NH.sub.2 
430 425 
Succinic 
Anhydride HCO.sub.2 H/n-C.sub.6 H.sub.13 NH.sub.2 
390 370 
Benzil HCO.sub.2 H/o-C.sub.6 H.sub.4 (NH.sub.2).sub.2 
405 405 
Benzoaldehyde 
HCO.sub.2 H/n-C.sub.6 H.sub.13 NH.sub.2 
390 395 
______________________________________ 
The above results show that improved thermal stability can be achieved with 
the block polymer of the present invention if it is precipitated from 
solution as generally practiced in accordance with the prior art, or a 
carbonyl additive is employed in the reaction mixture in accordance with 
the practice of the present invention. In instances where precipitation 
was not employed, or the carbonyl compound was not utilized in the 
reaction mixture, the thermal stability of the block polymer was adversely 
affected. 
Although the above example is limited to only a few of the very many 
variables which can be employed in the practice of the method of the 
present invention, it should be understood that the present invention is 
directed to the use of a much broader class of organic carbonyl compounds 
and amine-carboxylic acid catalysts as well as silarylenesilanediols and 
silanol terminated polydiorganosiloxanes as shown in the description 
preceding these examples.