Process for the preparation of 1-monoalkyl-dimethylsilylpropyne polymers

A process for the preparation of 1-monoalkyl (C.sub.1 -C.sub.4)dimethylsilyl-1-propyne polymers which comprises polymerizing a 1-monoalkyl (C.sub.1 -C.sub.4)dimethylsilyl-1-propyne monomer in the presence of a compound of a transition metal and a member selected from .alpha.,.omega.-dihydropolydialkylsiloxanes and polyalkyldihydrosiloxanes in a solvent inert for the polymerization. The polymerization reaction proceeds at low temperatures in an efficient manner. The membrane of the resultant polymer has a high gas transmission and suffers little degradation when placed under severe temperature conditions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process for the polymerization of 1-monoalkyl 
(C.sub.1 -C.sub.4)dimethylsilyl-1-propynes. 
2. Description of the Prior Art 
A variety of processes for the preparation of polymers of acetylene 
compounds have been known and investigated. These processes commonly have 
several problems such as a difficulty in obtaining high molecular weight 
polymers and a low yield. 
On the other hand, few studies on the polymerization of 
1-monoalkyldimethylsilyl-1-propynes which are one of di-substituted 
acetylene compounds have been made since they have poor reactivity. In 
recent years, however, Higashimura et al developed catalysts effective for 
obtaining high molecular weight polymers of the propynes, which is known 
from U.S. Pat. No. 4,755,193 and Japanese Laid-open Patent Application No. 
59-155409. In these publications, it is stated that polymers of 
1-monoalkyl(C.sub.1 -C.sub.4)dimethylsilyl-1-propynes are obtained by 
polymerization of 1-monoalkyl(C.sub.1 -C.sub.4)dimethylsilyl-1-propynes in 
the presence of a transition metal compound of Group V of the Periodic 
Table. In this process, a relatively high polymerization temperature is 
used ranging from 30.degree. to 100.degree. C., within which a higher 
temperature is favored and a long reaction time of from 12 to 36 hours is 
necessary. The 1-trimethylsilyl-1-propyne polymer obtained by the above 
process has very high gas permeability but its characteristic properties 
degraded considerable. This is reported by Higashimura et al (Journal of 
Applied Polymer Science: JAPS, Vol. 30, pp., 1605-1616, 1985). According 
to this literature, when the polymer is thermally treated at 100.degree. 
C. for about 5 hours, the oxygen permeability coefficient (Po.sub.2) 
reduced to 1/5 of the initial value. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the invention to provide a process for the 
polymerization of 1-monoalkyl(C.sub.1 -C.sub.4)dimethylsilyl-1-propyne 
which overcomes the drawbacks of the prior art process and wherein the 
resultant polymer exhibits stable gas permeability with a much reduced 
degree of degradation of the characteristic properties. 
It is another object of the invention to provide a process for the 
preparation of 1-monoalkyl (C.sub.1 -C.sub.4)dimethylsilyl-1-propyne 
polymers wherein the polymers are efficiently obtained at relatively low 
temperatures within a time shorter than in the prior art process. 
The process of the invention comprises polymerizing a 1-monoalkyl(C.sub.1 
-C.sub.4)dimethylsilyl-1-propyne compound in the presence of a compound of 
a transition metal of Group V of the Periodic Table and an 
.alpha.,.omega.-dihydropolydialkylsiloxane and/or a 
polyalkyldihydrosiloxane in a solvent inert for the polymerization. 
Preferably, the compound of the transition metal and the 
.alpha.,.omega.-dihydropolydialkylsiloxane and/or a 
polyalkyldihydrosiloxane is thermally treated and the resultant reaction 
product is used for the polymerization.

DETAILED DESCRIPTION AND EMBODIMENTS OF THE INVENTION 
The starting propyne monomers used in the present invention are 
1-monoalkyldimethylsilyl-1-propynes whose monoalkyl moiety has from 1 to 4 
carbon atoms and include, for example, 1-trimethylsilyl-1-propyne, 
1-ethyldimethylsilyl-1-propyne, 1-n-propyldimethylsilyl-1-propyne and the 
like. 
The compounds of transition metals of Group V include, for example, halides 
of the transition metals such as bromides and chlorides of niobium, 
tantalum and the like. Specific examples include TaCl.sub.5, NbCl.sub.5, 
TaBr.sub.5, NbBr.sub.5 and the like. Of these, TaCl.sub.5 and TaBr.sub.5 
are preferred. The compound is usually used in an amount of from 0.01 to 
10 mole %, preferably from 0.05 to 5 mole % of the starting monomer. 
The .alpha.,.omega.-dihydropolydialkylsiloxane used in combination with the 
transition metal compound should preferably be a hydrosiloxane compound 
having a hydrogen atom at both ends and represented by the following 
general formula 
##STR1## 
wherein each R represents an alkyl group having from 1 to 8 carbon atoms, 
and n is an integer of from 1 to 6. Examples of the alkyl group include a 
methyl group, an ethyl group, a propyl group, a butyl group, a pentyl 
group, a hexyl group, a heptyl group and an octyl group. Preferably, the R 
of the formula is a methyl group. 
The polyalkyldihydrosiloxane should preferably be a siloxane polymer having 
the hydrogen atom bonded directly to the silicon atom or atoms of 
intermediate siloxane units and represented by the following general 
formula 
##STR2## 
wherein each R' represents an alkyl group having from 1 to 8 carbon atoms 
and m is an integer of not less than 1. The alkyl group represented by R' 
is the same as used in the .alpha.,.omega.-dihydropolydialkylsiloxane. The 
polymer of the above formula wherein the terminal trialkylsilyl group is 
absent, thereby forming a cyclic polymer, may also be used. 
These .alpha.,.omega.-dihydropolydialkylsiloxanes and 
polyalkyldihydrosiloxanes are commercially available from Shin-Etsu Co., 
Ltd., Chisso Co., Ltd. and Toray Silicone Co., Ltd. of Japan. These 
siloxane compounds and/or polymers may be used singly or in combination. 
The amount of the .alpha.,.omega.-dihydropolydialkylsiloxane and/or 
polyalkyldihydrosiloxane is not critical but is preferably as small as 
possible in order to minimize its incorporation as an impurity into a 
final polymer product. In general, the amount is from 1 to 10 mole %, as 
the hydrogen atom or atoms bonded directly to the silicon atom or atoms, 
based on the monomer. 
The polymerization reaction is performed in a solvent. Examples of the 
solvent include aromatic hydrocarbons such as benzene, toluene, xylene and 
the like, halogenated hydrocarbon such as 1,2-dichloroethane, carbon 
tetrachloride, chloroform, 1,2,3-trichloropropane, trichloroethylene, 
chlorobenzene and the like, alicyclic hydrocarbons such as cyclohexane, 
cyclohexene and the like, and mixtures thereof. The monomer concentration 
at the polymerization reaction is generally from 0.1 to 2 moles per liter 
of the solvent, preferably from 0.3 to 1 mole per liter of the solvent. 
The order of addition of the solvent, monomer, compound of a transition 
metal of Group V and .alpha.,.omega.-dihydropolydialkylsiloxane and 
polyalkyldihydrosiloxane is not critical. In general, a transition metal 
compound and an .alpha.,.omega.-dihydropolydialkylsiloxane and/or 
polyalkyldihydrosiloxane are first added to a solvent in predetermined 
amounts and heated to about 60.degree. C. for 5 to 15 minutes. During this 
treatment, it is assumed that the transfer metal is reduced with the 
hydrogen bonded to the silicon atoms of the siloxane compound or polymer, 
thereby forming a reaction product serving as a polymerization initiator. 
Thereafter, the mixture is cooled down to about 0.degree. C., to which a 
predetermined amount of monomer is added. The polymerization reaction may 
proceed at temperatures not higher than 0.degree. C. and is completed in 
about 1 hour to several hours at a temperature of 30.degree. C. The 
reaction temperature is generally in the range of from 0.degree. to 
80.degree. C., preferably from 30.degree. to 70.degree. C. Higher 
temperatures may be used but are not favorable in economy. 
Alternatively, an .alpha.,.omega.-dihydropolydialkylsiloxane and/or 
polyalkyldihydrosiloxane may be added after keeping a solution of the 
monomer and the transition metal compound at a given temperature 
sufficient to cause the reaction between the transition metal and the 
siloxane. 
The reaction solution obtained after completion of the polymerization may 
be purified by a so-called re-precipitation technique wherein the solution 
is added to a large amount of a poor solvent thereby precipitating the 
resultant polymer. Examples of the poor solvent include alcohols such as 
methanol, ethanol and the like. 
It will be noted that although the polymerization may be effected in an 
atmosphere of air, it is usually effected in an atmosphere of an inert gas 
such as nitrogen. 
The polymer obtained by the polymerization process of the invention becomes 
very high in molecular weight, e.g. not only the polymerization reaction 
solution becomes very viscous, but also the reaction may proceed to an 
extent where a solid product is obtained. In the latter case, the reaction 
system is diluted with a solvent and subjected to re-precipitation. 
The gel permeation chromatography of the polymer reveals that its weight 
average molecular weight (Mw) is about 1,000,000 or over. 
The polymer obtained by the above process is film-forming. When the film 
obtained from the polymer is thermally treated at 100.degree. C. for 5 
hours as reported by Higashimura et al set out before, the oxygen 
permeability coefficient undergoes little degradation of the oxygen 
permeability coefficient. The reason for this is not clear. Several 
factors may be considered including a structural change of the polymer 
because of the presence of a .alpha.,.omega.-dihydropolydialkylsiloxane 
and/or polyalkyldihydrosiloxane in the reaction system, a change in the 
cis-trans structure of the double bonds in the propyne compound owing to 
the polymerization reaction at low temperatures, e.g. at room temperature, 
and a very high degree of polymerization taking place. Anyway, the final 
polymer product has a high gas permeability and a very small degree of 
characteristic degradation, thus being useful in practical applications. 
The polymers obtained by the process of the invention will have utility 
not only as a gas permeation membrane, but also as electronic and 
insulating materials. 
The present invention is more particularly described by way of examples. 
EXAMPLES 1 TO 6 
200 ml of purified toluene, 2 mmols of tantalum pentachloride (TaCl.sub.5) 
as a compound of a metal of Group V and 0.5 g of a 
polyalkyldihydrosiloxane (SH-1107, available from Toray Silicone Co., 
Ltd.) were charged in an atmosphere of dry nitrogen into a three-necked 
flask equipped with an agitator, a thermometer and a separating funnel and 
having a capacity of 300 ml, followed by heating to 60.degree. C. for 10 
minutes. Thereafter, the mixture was cooled down to 0.degree. C. (ice 
bath), to which 0.2 moles of 1-trimethylsilyl-1-propyne was added, 
followed by polymerization reaction for 3 hours under agitation. A very 
viscous polymer solution was charged into a large amount of methanol to 
obtain a polymer precipitate. 
The thus obtained polymer was purified by re-precipitation, after which the 
molecular weight and gas permeation characteristic were measured. As a 
result, the weight average molecular weight was 1,200,000 when determined 
gel permeation chromatography using polystyrene as a reference and the 
oxygen gas permeability coefficient was 1.46.times.10.sup.-6 
cc.multidot.cm/cm.sup.2 .multidot.sec.multidot.cmHg. 
The above procedure was repeated using different transition metal compounds 
and/or different polyalkyldihydrosiloxanes as Examples 2 to 6. The results 
are shown in Table below. 
TABLE 
__________________________________________________________________________ 
Transition Weight Average 
Metal Polymethyl- 
Molecular Weight 
Example 
Compound 
hydrosiloxane 
--Mw .sup.--Po.sub.2 *.sup.1 
__________________________________________________________________________ 
1 TaCl.sub.5 
SH-1107 1,200,000 
1.46 .times. 10.sup.-6 
2 NbCl.sub.5 
SH-1107 1,200,000 
8.6 .times. 10.sup.-7 
3 NbBr.sub.5 
SH-1107 1,000,000 
7.6 .times. 10.sup.-7 
4 TaCl.sub.5 
KF-99*.sup.2 
1,500,000 
1.6 .times. 10.sup.-6 
5 TaCl.sub.5 
##STR3## 1,100,000 
1.2 .times. 10.sup.-6 
6 TaCl.sub.5 
PS 120*.sup.3 
2,000,000 
2.0 .times. 10.sup.-6 
__________________________________________________________________________ 
Note 
*.sup.1 oxygen permeability coefficient (cc .multidot. cm/cm.sup.2 
.multidot. sec .multidot. cmHg) 
*.sup.2 KF 99 is polymethylhydrosiloxane available from SinEtsu Silicone 
Co., Ltd. 
*.sup.3 PS 120 is a polymethylhydrosiloxane available from Chisso Co., 
Ltd. 
Similar results were obtained when the general procedure of the above 
examples was repeated using polydimethylsiloxane terminated with hydrogen 
at both ends (PS-537, available from Petrarch System Inc. of U.S.A.).