Method for the preparation of an organopolysiloxane

An oligomer or a mixture of organopolysiloxane oligomers is polymerized in the presence of a strong acid, e.g. trifluoromethane sulfonic acid, as the catalyst to give an organopolysiloxane containing a considerable amount of silanolic hydroxy groups at the molecular chain ends. Thereafter, the mixture is admixed with water and a hexaorganodisilazane or triorganosilyl amine compound in combination so as to neutralize the acid catalyst by the ammonia produced by the hydrolysis of the disilazane or silyl amine compound with simultaneous silylation of the terminal hydroxy groups. Thus, the organopolysiloxane contains a greatly decreased amount of the residual silanolic hydroxy groups at the molecular chain ends to be imparted with remarkably improved heat stability.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for the preparation of an 
organopolysiloxane or, more particularly, to a method for the preparation 
of an organopolysiloxane by the ring-opening or equilibration 
polymerization of organopolysiloxane oligomers in the presence of an acid 
catalyst, in which the amount of residual silanolic terminals is greatly 
decreased so as to impart the organopolysiloxane with improved heat 
stability and curing characteristics. 
It is well known in the art of silicones that a high-polymeric 
organopolysiloxane can be prepared by the polymerization of 
organopolysiloxane oligomers in the presence of a strong acid or strong 
basic compound as the catalyst. When a strong acid is used as the 
catalyst, it is usual that completion of the polymerization is followed by 
the neutralization of the acid in the mixture after washing with water by 
the addition of an alkaline compound such as sodium carbonate, sodium 
hydrogencarbonate or ammonium carbonate. 
A problem in such a process of neutralization by the addition of the 
alkaline compound is that the neutralization is complete taking a 
considerably long time because the above mentioned neutralizing agents are 
each solid. Moreover, the organopolysiloxane prepared in the above 
described method contains a considerably large amount of silanolic hydroxy 
groups at many of the molecular chain ends badly affecting the heat 
stability and curing characteristics of the organopolysiloxane 
When the polymerization is performed in the presence of an alkaline 
compound as the catalyst, the alkalinity after completion of the 
polymerization reaction is neutralized usually using an ammonium halide, 
alpha-halohydrin and the like while neutralization with such a 
neutralizing agent can hardly be complete in addition to the problem that 
the thus neutralized organopolysiloxane necessarily contains more or less 
of halogen as an impurity to cause various adverse influences. 
Alternatively, a method has been proposed in Japanese Patent Kokai 
60-49033 that the residual alkaline catalyst is neutralized by the 
addition of a triorgano halosilane and a hexaorgano disilazane. This 
method, however, is disadvantageous in respect of the low yield of the 
desired organopolysiloxane. 
SUMMARY OF THE INVENTION 
The present invention accordingly has an object to provide a method for the 
preparation of an organopolysiloxane by the acid-catalyzed polymerization 
of organopolysiloxane oligomers without the above described problems and 
disadvantages in the prior art methods. 
Thus, the method for the preparation of an organopolysiloxane provided by 
the present invention comprises: 
(a) polymerizing organopolysiloxane oligomers in a mixture containing a 
strong acid as a catalyst to give an organopolysiloxane; and 
(b) admixing the mixture with water and an organosilicon compound selected 
from the class consisting of hexaorganodisilazanes represented by the 
general formula 
EQU (R.sup.1.sub.3 Si).sub.2 NH, (I) 
and triorganosilyl amine compounds represented by the general formula 
EQU R.sup.1.sub.3 SiNHR.sub.2, (II) 
in which each of the groups denoted by R.sup.1 and R.sup.2 is, 
independently from the others, a substituted or unsubstituted monovalent 
hydrocarbon group, in an amount sufficient to neutralize the strong acid 
as the catalyst and to silylate the terminal silanol groups at the 
molecular chain ends of the organopolysiloxane. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As is understood from the above given summarizing description, the most 
characteristic feature of the inventive method is in the step for the 
neutralization of the acid catalyst after completion of the polymerization 
reaction to form an organopolysiloxane. Namely, the neutralization is 
performed by admixing the polymerization mixture with a combination of 
water and a hexaorgano disilazane of the general formula (I) or a 
triorganosilyl amine of the formula (II) so that the residual acid 
catalyst is neutralized by the ammonia produced by the reaction of the 
disilazane or silyl amine compound with water while the triorganosilyl 
groups produced by this reaction serve as a silylating agent of the 
silanol groups which otherwise may remain as such at the molecular chain 
ends of the organopolysiloxane formed by the polymerization of the 
starting organopolysiloxane oligomers so that the organopolysiloxane 
product prepared by this method contains only a greatly decreased amount 
of the residual terminal silanol groups. 
The above described method of the invention is of course applicable to the 
preparation of any type of organopolysiloxanes including a 
vinylsilyl-terminated diorganopolysiloxane which can be obtained when the 
starting mixture of the oligomers contains an organopolysiloxane oligomer 
providing vinylsilyl terminal groups and a diorganopolysiloxane having a 
trifluoropropyl silyl group which can be obtained when the starting 
mixture contains an organopolysiloxane oligomer providing such a silyl 
group. 
The starting material used in the inventive method is an oligomer or a 
mixture of organopolysiloxane oligomers. Such an oligomeric mixture is 
usually prepared by the (co)hydrolysis of one or a combination of two 
kinds or more of various organohalosilanes represented by the general 
fromula R.sup.1.sub.n SiX.sub.4-n, in which R.sup.1 has the same meaning 
as defined above, X is a halogen atom and n is a positive integer of 1, 2 
or 3, and composed of several kinds of oligomeric organopolysiloxanes 
having a cyclic, straightly linear or branched chain-like molecular 
structure. It is usual in order to adequately control the average degree 
of polymerization of the organopolysiloxane product that the starting 
oligomeric mixture should contain a suitable amount of the species capable 
of providing the terminal groups of the molecular chain ends of the 
organopolysiloxane molecules such as hexaorgano disiloxanes, octaorgano 
trisiloxanes and other low-molecular linear diorganopolysiloxanes as the 
chain-terminating agent. 
The first step of the inventive method is the polymerization of the above 
mentioned oligomer or oligomeric mixture in the presence of a strong acid 
as the catalyst. Suitable strong acids include trifluoromethane sulfonic 
acid, sulfuric acid, hydrochloric acid, nitric acid and the like, of which 
trifluoromethane sulfonic acid is preferred. The polymerization reaction 
can be performed at room temperature or at an elevated temperature in the 
absence of any solvent or in a diluted condition with an organic solvent. 
The polymerization is a ring-opening or equilibration reaction including 
the siloxane rearrangement and a high-polymeric organopolysiloxane is 
produced by the repetition of the condensation reaction between the 
reactive terminal groups fromed in the presence of the acid catalyst such 
as silanol groups, silyl ester groups, silyl halide groups and the like. 
After completion of the above described polymerization in the first step of 
the inventive method, the reaction mixture is admixed with water and a 
hexaorgano disilazane of the general formula (I) or a triorganosilyl amine 
compound of the general formula (II). The groups denoted by R.sup.1 and 
R.sup.2 in the general formulas are each a monovalent hydrocarbon group 
exemplified by alkyl groups, e.g. methyl, ethyl, propyl and butyl groups, 
alkenyl groups, e.g. vinyl and allyl groups, aryl groups, e.g. phenyl and 
tolyl groups, and cycloalkyl groups, e.g. cyclohexyl group, as well as 
those substituted groups obtained by the replacement of a part or all of 
the hydrogen atoms in the above named hydrocarbon groups with substituent 
atoms and/or groups such as halogen atoms, cyano groups and the like. Each 
of the groups R.sup.1 and R.sup.2 can be selected from the above 
exemplified groups independently from the others. Particular examples of 
the hexaorgano disilazane and triorganosilyl amine compound include: 
hexamethyl disilazane; 1,3-divinyl-1,1,3,3-tetramethyl disilazane; 
1,3-diphenyl-1,1,3,3-tetramethyl disilazane; trimethylsilyl methyl amine; 
vinyldimethylsilyl methyl amine; phenyldimethylsilyl n-propyl amine; and 
the like. 
In order to completely neutralize the acid catalyst, the amount of the 
disilazane or silyl amine compound added to the polymerization mixture 
should be at least equimolar to the residual acid in the mixture or, 
usually, in the range from 1 to 5 moles or, preferably, from 1.2 to 2.0 
moles per mole of the acid. When the disilazane or silyl amine compound is 
added to the mixture together with water, a reaction takes place to 
produce ammonia which serves as a neutralizing agent of the acid catalyst 
while the disilazane or silyl amine compound is converted into an 
organosilane compound having a triorganosilyl group of the formula 
R.sup.1.sub.3 Si--. Such an organosilane compound has an activity as a 
silylating agent which silylates the terminal silanol groups at the 
molecular chain ends of the organopolysiloxane produced by the 
polymerization. Therefore, the organopolysiloxane product obtained by the 
inventive method contains a greatly decreased amount of residual terminal 
hydroxy groups or has an increased percentage of the molecular chain ends 
terminated with triorganosilyl groups. 
In practicing the second step of the inventive method, water is first added 
to the polymerization mixture followed by the addition of the disilazane 
or silyl amine compound although the order of their addition is not 
particularly limitative and they can be added in a reverse order or 
simultaneously. The reaction of neutralization and silylation can proceed 
even at room temperature to be completed within about two hours. After 
completion of the reactions, the reaction mixture is heated, if necessary, 
under reduced pressure to remove the excessive amounts of water and the 
disilazane or silyl amine compound together with the solvnet, if used, and 
the low-boiling matters formed in the course of the polymerization. 
Finally, the mixture is filtered to remove the precipitated ammonium salt 
of the acid catalyst and the desired organopolysiloxane product is 
obtained. The disilazane or silyl amine compound used in the 
neutralization and silylation should preferably have a boiling point of 
200.degree. C. or below because, as is mentioned above, the excess amount 
thereof after completion of the reaction must be completely removed by 
distillation. 
Although the above described method of the present invention is applicable 
to the preparation of organopolysiloxanes of any types, typical 
organopolysiloxanes, to the preparation of which the inventive method is 
applied most successfully, include those expressed by the following 
structural formulas (1) to (6), in which n, x and y are each a positive 
integer, denoting methyl, vinyl, phenyl and 3,3,3-trifluoropropyl groups 
by the symbols of Me, Vi, Ph and Fp, respectively: 
EQU Me.sub.3 Si--O--SiMe.sub.2 --O].sub.n SiMe.sub.3 ; (1) 
EQU ViMe.sub.2 Si--O--SiMe.sub.2 --O].sub.n SiMe.sub.2 Vi; (2) 
EQU ViMe.sub.2 Si--O--SiMe.sub.2 --O].sub.x [SiPh.sub.2 --O].sub.y SiMe.sub.2 
Vi; (3) 
EQU Me.sub.3 Si--O--SiMe.sub.2 --O].sub.n SiMe.sub.2 Vi; (4) 
EQU Me.sub.3 Si--O--SiMeFp--O].sub.n SiMe.sub.3 ; and (5) 
EQU ViMe.sub.2 Si--O--SiMe.sub.2 --O].sub.x [SiMeFp--O].sub.y SiMe.sub.2 Vi.(6)

In the following, the method of the present invention is illustrated in 
more detail by way of examples, in which the values of viscosity are all 
those obtained by the measurement at 25.degree. C. 
EXAMPLE 1 
A mixture of 710 g of octamethyl cyclotetrasiloxane and 6.5 g of hexamethyl 
disiloxane was cooled to 5.degree. C. and admixed with 32 g of 
concentrated sulfuric acid. After agitation for 4 hours at 40.degree. C., 
the mixture was admixed with 14 g of water followed by further continued 
agitation for additional 30 minutes. The depleted acid was removed from 
the organopolysiloxane by phase separation. 
In the next place, the reaction mixture after separation from the acid 
layer was admixed with 32 g of trimethylsilyl methyl amine to effect 
neutralization of the residual acid catalyst and silylation of the 
terminal silanol groups at the molecular chain ends of the 
organopolysiloxane under agitation at room temperature for 2 hours. 
Thereafter, the mixture was heated at 180.degree. C. for 6 hours under a 
reduced pressure of 20 mmHg to remove the low-boiling matters by 
distillation followed by filtration to remove the ammonium salt of the 
acid. The product thus obtained in a yield of 86% was a clear 
dimethylpolysiloxane having a viscosity of 960 centistokes and terminated 
at both molecular chain ends each with a trimethyl silyl group. The 
content of silanolic hydroxy groups in this product was only 10 ppm by 
weight. 
For comparison, the same experimental procedure as above was repeated 
except that the neutralization of the acid catalyst was performed, intead 
of the admixture of trimethylsilyl methyl amine, by repeating washing with 
water to give a dimethylpolysiloxane having a viscosity of 1120 
centistokes in a yield of 86%. This dimethylpolysiloxane product contained 
170 ppm by weight of silanolic hydroxy groups. 
EXAMPLE 2 
A mixture of 805 g of 1,3,5-trimethyl-1,3,5-tri(3,3,3-trifluoropropyl) 
cyclotrisiloxane, 163 g of octamethyl cyclotetrasiloxane and 7.5 g of 
1,3-divinyl-1,1,3,3-tetramethyl disiloxane was admixed with 0.97 g of 
trifluoromethane sulfonic acid and agitated at 25.degree. C. for 5 hours 
to effect the polymerization reaction of the polysiloxanes. Thereafter, 
the mixture was admixed with a varied amount of water followed by 
agitation at room temperature for 30 minutes and then with a varied amount 
of 1,3-divinyl-1,1,3,3-tetramethyl disilazane followed by agitation for 
additional 2 hours to effect the neutralization and silylation. 
Thereafter, the mixture was heated at 200.degree. C. for 6 hours under a 
reduced pressure of 1 mmHg to remove the low-boiling matters by 
distillation followed by filtration to remove the ammonium salt of the 
acid catalyst. The thus obtained product was a clear methyl 
trifluoropropyl polysiloxane terminated at both molecular chain ends each 
with a vinyl dimethyl silyl groups and having a specific gravity of 1.23. 
Table 1 below shows the amounts of water and the disilazane compound added 
to the mixture in moles per mole of the acid catalyst, viscosity of the 
organopolysiloxane product in centistokes and content of non-volatile 
matters after heating for 3 hours at 105.degree. C. 
A room temperature-curable organopolysiloxane composition was prepared by 
uniformly blending 100 parts by weight of the thus prepared methyl 
trifluoropropyl polysiloxane, 0.04 part by weight of 
1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane, 3 parts by 
weight of an organohydrogen polysiloxane composed of the Me.sub.2 
HSiO.sub.0.5 units, (CF.sub.3 CH.sub.2 CH.sub.2)MeSiO units and SiO.sub.2 
units in a molar ratio of 3:2.5:1 and chloroplatinic acid modified with an 
alcohol in an amount of 12 ppm by weight based on the overall amount of 
the above named polysiloxane components. The thus prepared room 
temperature-curable organopolysiloxane composition was cured by standing 
at 25.degree. C. for 16 hours and the cured composition was examined for 
the hardness according to JIS and surface tackiness to give the results 
shown in Table 1. 
TABLE 1 
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Water added, moles 
Disilazane added, moles 
Organopolysiloxane 
Cured Composition 
per moles of 
per moles of 
Viscosity, 
Non-volatile 
Hardness, 
Surface 
acid catalyst 
acid catalyst 
centistokes 
matter, % 
JIS tackiness 
__________________________________________________________________________ 
6 5 3600 98 5 yes 
5 2 3700 98 8 no 
2 2 3600 99 10 no 
0 2 3700 99 5 yes 
__________________________________________________________________________ 
EXAMPLE 3 AND COMATIVE EXAMPLES 1 AND 2 
A clear methyl trifluoropropyl polysiloxane having a viscosity of 3660 
centistokes was prepared in the same manner as in Example 2 except that 
the amounts of water and the disilazane compound were 0.4 g and 6 g, 
respectively. This organopolysiloxane was processed into a room 
temperature-curable composition in the same formulation as in Example 2 
and the curing characteristics of the composition were examined to give 
the results shown in Table 2 below (Example 3). 
In Comparative Example 1, the same experimental procedure as above was 
repeated except that the neutralization of the acid catalyst was 
performed, in place of the addition of water and the disilazane compound, 
by adding 54 g of sodium carbonate to the reaction mixture after 
completion of the polymerization reaction. The mixture was agitated for 12 
hours and then filtered to remove the sodium salt of the acid catalyst 
followed by stripping at 200.degree. C. for 6 hours to remove the 
low-boiling matter. The thus obtained methyl trifluoropropyl polysiloxane 
terminated at both molecular chain ends each with a vinyl dimethyl silyl 
group had a viscosity of 4970 centistokes. 
In Comparative Example 2, the same experimetal procedure as in Example 3 
was further repeated except that the neutralization of the acid catalyst 
was performed by adding 2 g of ammonia water to the reaction mixture 
followed by agitation for 30 minutes to give a methyl trifluoropropyl 
polysiloxane terminated at both molecular chain ends each with a vinyl 
dimethyl silyl group, which had a viscosity of 3990 centistokes. 
These three methyl trifluoropropyl polysiloxanes each had a specific 
gravity of 1.23 at 25.degree. C. and a refractive index n.sub.D.sup.25 of 
1.384. Table 2 below shows the yield of the polysiloxane product by the 
stripping of the low-boiling matter, content of non-volatile matter in the 
polysiloxane product after heating for 3 hours at 150.degree. C., content 
of vinyl groups in moles per 100 g and content of silanolic hydroxy groups 
in ppm by weight for each of the methyl trifluoropropyl polysiloxanes. 
Each of these three polysiloxane products was compounded into a room 
temperature-curable organopolysiloxane composition in the same formulation 
as in Example 2 and the curing behavior of the compositions was examined 
by standing at 25.degree. C. for 16 hours. The results were that the cured 
composition prepared from the organopolysiloxane obtained in Example 3 had 
a hardness of 10 by the JIS scale while the composition prepared from the 
organopolysiloxane obtained in Comparative Example 1 was gelled to give no 
cured composition and the cured composition from the polysiloxane obtained 
in Comparative Example 2 had no measurable hardness. 
TABLE 2 
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Non-volatile matter 
Content of 
Content of silanolic 
Yield by 
after 3 hours at 
vinyl groups, 
hydroxy groups, 
stripping, % 
150.degree. C., % 
moles/100 g 
ppm by weight 
__________________________________________________________________________ 
Example 3 
88 98 0.0082 9 
Comparative 
88 98 0.0077 120 
Example 1 
Comparative 
84 97 0.0080 100 
Example 2 
__________________________________________________________________________ 
EXAMPLE 4 AND COMATIVE EXAMPLE 3 
To a mixture of 4680 g of 1,3,5-trimethyl-1,3,5-tri(3,3,3-trifluoropropyl) 
cyclotrisiloxane and 56 g of 1,3-divinyl-1,1,3,3-tetramethyl disiloxane 
were added 2.4 g of trifluoromethane sulfonic acid and the mixture was 
agitated for 5 hours at 35.degree. C. to effect the polymerization 
reaction. Thereafter, the mixture was admixed with 0.6 g of water followed 
by agitation for 30 minutes and then with 6 g of 
1,3-divinyl-1,1,3,3-tetramethyl disilazane followed by agitation for 
additional 2 hours to effect neutralization and silylation. The mixture 
was then heated at 200.degree. C. for 6 hours under a reduced pressure of 
1 mmHg to remove the low boiling matter by distillation followed by 
filtration to remove the precipitated ammonium salt of the acid catalyst. 
The product thus obtained in a yield of 80% was a clear methyl 
trifluoropropyl polysiloxane terminated at both molecular chain ends each 
with a vinyl dimethyl silyl group and had a viscosity of 5500 centistokes. 
For comparison (Comparative Example 3), the same starting polysiloxane 
mixture as above was admixed with 0.45 g of calcium hydroxide as the 
catalyst for the polymerization and heated at 70.degree. C. for 16 hours 
to effect polymerization. Thereafter, the alkalinity of the mixture after 
cooling was neutralized by the addition of a mixture of 0.49 g of vinyl 
dimethyl chlorosilane and 4.4 g of hexamethyl disilazane and agitation for 
2 hours followed by heating at 180.degree. C. for 6 hours under a reduced 
pressure of 1 mmHg to remove the low-boiling matter and then filtration to 
remove the precipitated salt to give a clear and viscous product of a 
methyl trifluoropropyl polysiloxane having a viscosity of 4800 
centistokes. The yield of the product was 60% indicating that the 
inventive method was much more advantageous in respect of the yield of the 
product. 
EXAMPLE 5 
A mixture composed of 7100 g of octamethyl cyclotetrasiloxane, 32 g of 
hexamethyl disiloxane and 37 g of 1,3-divinyl-l,l,3,3-tetramethyl 
disiloxane was admixed with 1.8 g of trifluoromethane sulfonic acid as the 
catalyst and agitated for 6 hours at 25.degree. C. to effect the 
polymerization reaction. Thereafter, the mixture was admixed with 0.2 g of 
water followed by agitation for 30 minutes and then with 4.0 g of 
hexamethyl disilazane followed by agitation for additional 2 hours to 
effect neutralization and silylation. The mixture was then heated at 
180.degree. C. for 6 hours under a reduced pressure of 20 mmHg to remove 
the low-boiling matter and filtered to remove the precipitated ammonium 
salt of the acid catalyst. The clear and viscous product obtained in this 
manner in a yield of 86% was a dimethylpolysiloxane having a viscosity of 
990 centistokes and terminated at both molecular chain ends each with a 
vinyl dimethyl silyl group. The content of vinyl groups therein was 0.0028 
mole per 100 g and the content of the silanolic hydroxy groups was 10 ppm 
by weight.