Abstract:
Organopolysiloxanes are polymerized in the presence of an alkaline catalyst and a complex oxygen, sulfur or nitrogen heterocyclic compound.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for the preparation of high molecular weight organopolysiloxanes by polymerization and rearrangement of low molecular weight organopolysiloxane compounds, especially those which are cyclic. 
     2. Description of the Prior Art 
     It is known to the art that it is possible to polymerize and to rearrange low molecular weight organopolysiloxanes in order to convert them into high molecular weight products by using basic catalysts, such as, for example, alkali metal hydroxides, alkali metal silanolates and alcoholates, or quaternary ammonium hydroxides (NOLL -- Chemistry and Technology of Silicones -- 1968 Ed. p. 206). Various techniques have been proposed with a view towards speeding up the polymerization rate, for example, via the use of nitrites or amides (French Pat. Nos. 1,354,443 an 1,359,414). It has also been proposed to associate an aminophosphine oxide (French Pat. No. 1,474,899), or a complex of an alkali metal with a triaminophosphine oxide (French Pat. No. 1,474,900), with the basic catalyst. 
     Additionally, Boileau et al. have shown (POLYMER LETTERS, 12, p. 217-220 -- 1974) that it was possible to rapidly polymerize hexamethylcyclotrisiloxane, in the presence of potassium hydroxide complexed with a macroheterobicyclic ether (complexes termed cryptates). Boileau et al. have carried out the reaction in benzene, using a large quantity of alkaline catalyst and of &#34;cryptate&#34;, relative to the quantity of cyclic siloxane employed. 
     SUMMARY OF THE INVENTION 
     It has now been found that it is possible to speed up, very substantially, the bulk polymerization of low molecular weight siloxanes, in the presence of a small quantity of an alkaline catalyst, by associating a monocyclic or polycyclic macrocyclic compound with the alkaline catalyst. More precisely, the subject of the invention is a process for the preparation of high molecular weight organopolysiloxanes by polymerization of siloxanes which consist of at least 50% by weight of cyclic siloxanes of the formula (A) 
     
         --r.sub.1 r.sub.2 si--O--.sub.n 
    
     in which the symbol &#34;n&#34; represents an integer which is at least equal to 4, the symbol &#34;R 1  &#34; represents a hydrocarbon radical containing 1 to 12 carbon atoms, which may be unsubstituted or substituted by one or more atoms or radicals such as halogen atoms, amino groups or cyano groups, and the symbol &#34;R 2  &#34; represents a radical such as defined for &#34;R 1  &#34;, or an --OR 3  group, &#34;R 3  &#34; being a hydrogen atom or a radical such as &#34;R 1  &#34;, this process being characterized in that the polymerization is carried out in bulk, in the presence of: 
     (A) 0.005 TO 1 MILLIMOL OF AN ALKALINE CATALYST PER 100 GRAMS OF SILOXANE, AND 
     (B) FROM 0.05 TO 5 MOLS, PER MOL OF ALKALINE CATALYST, OF A MONOCYCLIC OR POLYCYCLIC COMPOUND, OR MIXTURE OF SUCH COMPOUNDS, COMPRISING AT LEAST THREE ATOMS OR GROUPS OF ATOMS SELECTED FROM AMONG --O--, --S--, ##STR1## or --NH-- and from 9 to 60 carbon atoms, the atoms or groups mentioned above being connected together via hydrocarbon groups which comprise at least two carbon atoms. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The cyclic compounds mentioned above can contain one type of heteroatom only (O, S or N); or, alternatively, can also contain two or three types of heteroatoms. Among these compounds, there may specially be mentioned the monocyclic polyethers (I) of the formula 
     
         --R--O--.sub.a 
    
     in which &#34;a&#34; is a number from 3 to 20, and the symbol &#34;R&#34; represents a --CH 2  --CH 2  -- or --CH 2  --CH 2  --CH 2  -- radical or a radical selected from among the ##STR2## radicals, it being possible for the said cyclic radicals to be substituted, especially by an alkyl radical having up to 12 carbon atoms, the number of units in which &#34;R&#34; represents one of the above-mentioned cyclic radicals preferably being, at the most, equal to 2 in the macrocyclic polyether. These cyclic polyethers are usually termed crown-ethers. 
     The cyclic compound can also be a monocyclic polythioether (II) of the formula 
     
         --R--S--.sub.a 
    
     in which &#34;a&#34;0 is a number from 3 to 20 and &#34;R&#34; represents a --CH 2  --CH 2  -- or --CH 2  --CH 2  --CH 2  -- radical or a radical selected from among the ##STR3## radicals, which may be substituted with an alkyl radical having up to 12 carbon atoms, the number of units in which &#34;R&#34; represents one of the cyclical radicals being no greater than 2. 
     The cyclic compound can also be a monocyclic polyamine (III) containing from 4 to 8 N atoms or NH groups, connected especially by --CH 2  --CH 2  --, --CH 2  --CH 2  --CH 2  -- or --CH--CH--CH-- radicals. 
     The cyclic compound can also be selected from among the monocyclic or polycyclic compounds (IV) containing at least two different types of atoms or groups chosen from among --O--, --S-- and --NH--, connected by --R-- radicals, with &#34;R&#34; having the meaning indicated above, and the total number of these atoms or groups being at most equal to 8. 
     The cyclic compound can also be selected from among the nitrogen-containing bicyclic compounds (V) corresponding to the general formula ##STR4## in which the symbols Σ, Σ&#39; and Σ&#34;, which may be identical or different, represent groups of the formula --R&#39;--T-- p  R&#39;--, where T represents --O-- or --S--, p is equal to 1, 2 or 3 and R&#39; represents a --CH 2  --CH 2  -- group, it being possible, in addition, for T to represent a valence bond in one of the bridges represented by the symbols Σ, Σ&#39; and Σ&#34;, and it also being possible, alternatively, for R&#39; to represent, once, a ##STR5## radical in one or two of these bridges. 
     By way of specific examples of cyclic compounds belonging to the groups defined above, there may be mentioned the products whose formulae are indicated below: ##STR6## 
     The preparation and the study of the different types of macrocyclic compounds, such as those mentioned above, has been the subject of numerous publications. In particular the works of Pedersen (J.A.C.S., 89, 7017-1967, 89, 2495-19067), Vogtle et al. (Chemiker Zeitung, 97 (11) 1973 p. 600-61°), Ditrich, Lehn et al. (Tetrahedron Letters, 15, pp. 1225-1228 -- 1973, Tetrahedron, 29 pp. 1629-1658 -- 1973), and Leveque and Rosset (Analusis, 2 p. 218 -- 1973), and Christensen et al. (Science, 174 no 4008 -- 1971), the disclosures of each of which are hereby incorporated by reference; each teach the synthesis of compounds which are useful for the purpose of the invention. 
     The symbols &#34;R 1  &#34; and &#34;R 2  &#34; of the polysiloxanes of the formula (A) preferably represent radicals chosen from among the alkyl radicals having 1 to 4 carbon atoms, particularly the methyl radical; alkenyl radicals having up to 8 carbon atoms, in particular the vinyl radical; a cycloaliphatic radical, preferably cycloalkyl of up to 10 carbon atoms, especially the cyclohexyl radical; or an aryl radical having from 6 to 10 carbon atoms, in particular a phenyl radical. 
     The radicals represented by the symbol OR 3  can especially be selected from among the methoxy, ethoxy or propoxy radicals. 
     It must be understood that, in the same cyclic siloxane, the various symbols &#34;R 1  &#34; and &#34;R 2  &#34; can likewise represent different radicals, for example methyl and ethyl or methyl and phenyl radicals. 
     By way of illustration of the siloxanes of the formula (A), there may particularly be mentioned: octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, octaphenylcyclotetrasiloxane, pentamethylpentaethylcyclopentasiloxane and 1,1-hexamethyldiphenyl-cyclotetrasiloxane. 
     These cyclic siloxanes or mixture of siloxanes represent at least about 50% by weight, and preferably more than about 70% by weight, of the polysiloxanes subjected to polymerization. The remainder may consist of linear polysiloxanes of the formula (B) ##STR7## in which &#34;q&#34; represents an integer ranging from 1 to about 100, and the different symbols &#34;R 1  &#34; and &#34;R 2  &#34; have the meaning given above, it being possible for the radicals bonded to the same silicon atom to be different from one another. 
     The following products constitute examples of such siloxanes of the formula (B): divinyltetramethyldisiloxane, tetravinyldimethyldisiloxane, α,ω-dihydroxy-dimethylpolysiloxanes, α,ω-dialkoxy-dimethylpolysiloxanes, tetraphenyldisiloxane-diol and tetradecamethylhexasiloxane. 
     The invention further includes incorporating silanes such as for example, methyltriethoxysilane, vinyltri(methoxyethoxy) silane, phenyltriethoxysilane, vinylmethyldiethoxysilane, diphenyldimethoxysilane, or tetraethoxysilane, or of a cyclic trisiloxane such as hexamethylcyclotrisiloxane, with the cyclic siloxane of the formula (A) and, optionally, with the linear siloxane of the formula (B), in small amounts, representing for example up to 10% by weight of the siloxane (A) or of the mixture A + B. 
     In the process according to the invention, it is possible to use various alkaline catalysts, which are used for the polymerization of low molecular weight polysiloxanes (See for example NOLL, Chemistry and Technology of Silicones, p. 227). Catalysts which may be used are alkali metal hydroxides, in particular lithium hydroxide, potassium hydroxide, sodium hydroxide and cesium hydroxide; alkali metal silanolates, in particular potassium or sodium silanolates; alkali metal alkoxides, and alkali metal siliconates, especially potassium dimethylsiliconate, may be used. 
     Among other advantages, the process according to the invention has is the requirement that only a very small quantity of alkaline catalyst (for a given rate of polymerization), be used in association with the macrocyclic compound. Thus, in order to carry out this process, it is possible to use quantities of alkaline catalyst which are as low as between about 0.005 and about 1 millimol, and preferably about 0.01 to about 0.5 millimol, per 100 g of siloxane, and from about 0.05 to about 5 mols and, preferably about 0.1 to about 2 mols, of macrocyclic compound per mol of alkaline catalyst. The polymerization temperature can be within the usual temperature range, i.e., generally between about 25° and 200° C. Under these conditions, the disclosed technique makes it possible to substantially reduce the duration of the polymerization reaction, for a given degree of conversion. By using the present process, under the right circumstances, reductions in time relative to polymerizations carried out with the alkaline catalysts alone, can amount to 50 to 75 %. 
     The technique described above is of considerable interest in both the continuous and batch polymerization of siloxanes on an industrial scale. The macrocyclic compound does not break down and does not alter the mechanical properties and the heat-stability of the polymerized organosilicon products. Thus, organosilicon rubbers prepared by following the process according to the invention and having, for example, methyl, ethyl, vinyl and phenyl groups bonded to the silicon atom, when mixed with the usual fillers and then cross-linked using a peroxide, give elastomers having excellent mechanical properties. 
    
    
     In order to further illustrate the present invention and the advantages thereof, the following specific examples are given, it being understood that same are intended only as illustrative and in nowise limitative. 
     EXAMPLES 1 to 3 
     1,040 g of octamethylcyclotetrasiloxane and the macrocyclic compound (&#34;crown-ether&#34; identified below) were charged into a 2 liter stainless steel reactor. The temperature of the mixture was raised progressively up to 120° C. The mixture was stirred and a stream of nitrogen was passed through the reactor (flow-rate 50 l/hour). The temperature was further increased to 173° C. while the siloxane, carried by the stream of nitrogen, was condensed; when 42 cm 3  of distillate had been collected, [40 g of octamethylcyclotetrasiloxane] bubbling of the nitrogen was stopped and the temperature of the mixture was lowered to 160° C. Tetradecamethylhexasiloxane (hereinafter termed &#34;blocking agent&#34;), 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl-cyclotetrasiloxane (hereinafter termed vinylated fluid) and subsequently the alkaline catalyst/KOH, which was in the form of potassium dimethylsiliconate, were then introduced into the reactor. 
     When the degree of conversion into high boiling point compounds (products which do not distil during the devolatilization process) attained the desired value, the polymerization was stopped by bubbling CO 2  through the mixture at a flow rate of 40 l/hour for 5 minutes and then cooled to 25° C. 
     Thereafter, the polymer mixture was neutralized, as is conventional, by using silylated phosphoric acid as the neutralizing agent. Finally, remaining monomers, which were present in equilibrium with the polymers, together with light cyclosiloxanes were removed by heating at a temperature of 180° C. while under a reduced pressure of 0.5 mm of mercury to purify the polysiloxane rubber. 
     In each of these examples, the product of the following formula was used as the crown-ether: ##STR8## (chemical name: 2.3-(3&#39;-nonyl-benzo)-1,4,7,10,13,16-hexaoxacyclooctadecane, also called 3&#39;-nonyl-benzo-18-crown-6). 
     By way of comparison, a control test using no crown-ether was also run. 
     The quantities of reagents used and the results obtained will be indicated in the table which follows: 
     
         ______________________________________TEST         1       2       3     CONTROL______________________________________Blocking agent (g)        1.12    1.12    1.05  1.1Vinylated fluid (g)        2.54    2.4     2.44  2.4KOH (mg)     8       8       8     10Crown-ether (mg)        84      67      48    --Mols of crown-ether        1.22    0.97    0.7   --Mols of KOHPolymerizationtemperature  160° C.                160° C.                        160° C.                              160° C.Duration of the        1/2 Hour                1/2 Hour                        1/2 Hour                              21/2polymerization                     Hoursand degree ofconversion (DC)        85.6%   87.4%   88.4% 80.7%.sup.1______________________________________ .sup.1 After half an hour, the degree of conversion is less than 50%. .sup.2 The degree of conversion was determined according to the formula ##STR9## which has distilled during the devolatilization process and P the weight of monomer introduced (octamethylcyclotetrasiloxane). The quantity of alkaline catalyst is expressed in mg of KOH. 
    
     EXAMPLE 4 
     In order to illustrate the properties of the elastomers derived from the rubbers obtained in accordance with the invention, compositions were prepared comprising: 100 g of rubber, 44 g of pyrogenic silica with a high specific surface area (260 m 2  /g), 0.4 g of iron octoate, 0.85 g of diphenyldimethoxysilane, 0.85 g of an α,ω-dihydroxy-dimethylpolysiloxamic oil of viscosity 50 cp. at 25° C., and 0.9 g of 2,4-dichloro-benzoyl peroxide. 
     &#34;Vulcanization&#34; of this composition was carried out by heating for 8 minutes at 110° C. under a pressure of 65 bars. 
     The table which follows sets forth the various measurements which were carried out on samples cut from the above elastomers. 
     
         ______________________________________             TEST RUBBER                           CON-             1     3       TROL______________________________________   SHORE A hardness                 (a)   59    59    61After   Tensile strength at                 (b)   84    79.5  83recuring   break (Kg/cm.sup.2)for 16  Elongation at (b)hours at   break (%)           290   285   300250° C.   Tear strength (c)   19.5  18.7  21   (Kg/cm.sup.2)   Compression set                 (d)   28    30    23   SHORE A hardness                 (a)   67    67    67After   Tensile strength atrecurring   break (Kg/cm.sup.2) 54    not   57for 7   Elongation at (b)days at break (%)           160   meas- 164250° C.   Tear strength (c)   12    ured  11   (Kg/cm)______________________________________ (a) standard ASTM specification D 2,240 (b) standard ASTM specification D 412 (c) standard ASTM specification D 624 (d) standard ASTM specification D 395 - 70 hours/150° C/25% 
    
     EXAMPLES 5 and 6 
     The tests of Examples 1 to 3 were repeated. However, instead of using octamethylcyclotetrasiloxane (Me 2  SiO) 4  alone, the following combinations of silanes having Formula (A) were used: 
     5. a mixture of octamethylcyclotetrasiloxane and octaphenylcyclotetrasiloxane (φ 2  SiO) 4 . 
     6. a mixture of octamethylcyclotetrasiloxane and diphenylhexamethylcyclotetrasiloxane (φ 2  SiO) (Me 2  SiO) 3 . 
     The operating conditions and the results are shown in the following table: 
     
         ______________________________________Test       5       CONTROL    6     CONTROL______________________________________(Me.sub.2 SiO).sub.4 (g)      860     850        570   570(φ.sub.2 SiO).sub.4 (g)      150     150        --    --(φ.sub.2 SiO)(Me.sub.2 SiO).sub.3 (g)      --      --         430   430Blocking agent (g)       1.04   0.9         0.39 0.39Vinylated fluid (g)      2.8     2.8        2.3   2.34KOH (mg)    14      20        9.6    20Crown-ether (mg)      143     --          60   --Mols of crown-ethermols of KOH      1.2     --          0.73 --______________________________________Polymerization      160° C.              160° C.                         160° C.                               160° C.temperature______________________________________Durationof polymerization(hours)    1.5      3         1.5    3Degree ofconversion %       89      85         87   89.5______________________________________ 
    
     EXAMPLES 7 and 8 
     The test of Example 1 was repeated, operating at a lower polymerization temperature: 
     
         ______________________________________TEST              7       8______________________________________(For 1,000 g of octamethyl-cyclotetrasiloxane)Blocking agent (g)             1.34    1.36Vinylated fluid (g)             2.53    2.35KOH (mg)          10      12Crown-ether (mg)  86      190Mols of crown-ethermols of KOH       1       1.8Polymerization temperature             130     100Duration of polymerization             2 hours 1 hour 30 minutesDegree of conversion             89.6    71             (x)     (xx)______________________________________ (x)using no crown-ether, a degree of conversion of 88% was obtained over period of 6 hours 45 minutes. (xx)using no crown-ether, a degree of conversion of 88% was obtained over a period of 45 hours. 
    
     EXAMPLES 9 and 10 
     The test of Example 1 was repeated, using the product of the following formula as the crown-ether: ##STR10## 
     The following table illustrates the operating conditions and the results achieved: 
     
         ______________________________________           Example 9 Example 10______________________________________Octamethylcyclotetrasiloxane             1,000 g     1,000 gCrown-ether (mg)  5.2         42.1Blocking agent  (g)             1.150       1.193Vinylated fluid  (g)             2.600       2.520Catalyst (KOH) (mg)             9           7.4Mols of crown-ether             0.123       1.2mols of KOH______________________________________Temperature       160° C.                         160° C.______________________________________Duration of polymerization and             1/2 Hour    1/4 Hourdegree of conversion             87.8        86.4______________________________________ 
    
     EXAMPLES 11 to 14 
     The test of example 1 was repeated, using the product of the following formula as the macrocyclic ether: ##STR11## (4,7,13,16,21,24-hexaoxa-1,10-diaza bicyclo (8,8,8) hexacosane. 
     The following table illustrates the operating conditions and the results achieved: 
     
         ______________________________________          EX. 11                EX. 12  EX. 13  EX. 14______________________________________Octamethylcyclotetrasiloxane            1,000 g 1,000 g 1,000 g                                  1,000 gMacrocyclic ether   (mg)            6.9     4.6     12.7  53.2Blocking agent   (g)            1.240   1.192   1.160 1.172Vinylated fluid  2.410   2.630   2.480 2.520Catalyst (KOH)   (mg)            11.1    8.6     11.3  8.8Mols of macrocyclic ether            0.092   0.12    9.167 0.9Mols of KOH______________________________________Temperature      160° C                    160° C                            160° C                                  160° C______________________________________Duration of polymerization and            10mn    20mn    10mn  15mndegree of conversion            85.5    87.4    86.7  88.1______________________________________ 
    
     While the invention has been described and illustrated with reference to certain preferred embodiments thereof, those skilled in the art will appreciate that various changes, modifications and substitutions therein can be made without departing from the spirit of the invention. It is intented, therefore, that the invention be limited only by the scope of the claims which follow.