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2,934,550 Patented Apr. 26, 1960 United States Patent Office 2 1. phenyl or vinyl groups. By “high molecular weight" I mean of molecular weight not less than about 1000. 2,934,550 The material reacted may be in the form of a poly PREPARATION OF CYCLIC METHYLPOLYSILox. siloxane elastomer composition which will, of course, nor ANES BY REACTING ORGANOPOLYSILOXANES mally contain one or more fillers, pigments, etc, or may PHORUSWITH HALDES OF ALUMINUM oR PHOS be in the form of a polysiloxane gum such as is used in the preparation of polysiloxane elastomers. Partially James Jack, Troon, Scotland, assignor to Imperial Chemi cured polysiloxane compositions may also be used and in tionAff." of Great Britain 9 EEE, England, a corpora addition, other high molecular weight linear polysiloxanes 0 may be treated by this process. The advantages of the No Drawing. Application December 8, 1958 process are, however, of most value in the recovery of Serial No. 778,609 elastomersHalides ofand aluminium gums. and phosphorus which may be Claims priority, application Great Britain used in this process include aluminium chloride, alumin January 17, 1958 ium fluoride, aluminium bromide, phosphorus trichlo 5 ride, phosphorus pentachloride and phosphorus oxychlo 8 Claims. (CI. 260-448.2) ride. Aluminium chloride is, however, preferred, since This invention relates to the treatment of high molecu it is relatively inexpensive and does not tend to contami lar weight Substantially linear polysiloxanes and to the nate the products. preparation of low molecular weight cyclic polysiloxanes 20 The process of my invention is normally carried out therefrom. by heating the reactants together in a vessel adapted for High molecular weight linear organopolysiloxanes, for distilation and the low molecular weight cyclic poly example, such as polysiloxane elastomers and gums used siloxanes are distilled off as the reaction proceeds, the for the production thereof, are widely known and used. reaction being complete when there is no further distilla In the fabrication of articles from these materials, there 25 tion, usually after a few hours. It is normally preferred is of necessity, a certain amount of waste, for example, to operate at temperatures above 250 C. and it is further flash from moulding, prematurely or partially cured ma preferred to operate within the range 280 to 350° C. terial, e.g. arising from stock stored beyond its useful The quantity of aluminium orphosphorus halides which shelf life and the like. Since this material is relatively may be used may vary widely, but should not exceed 'expensive any such waste adds considerably to the cost 30 30% by weight of the polysiloxane, Quantities of the of the final fabricated article and it is most desirable to order of 3 to 30% by weight of the polysiloxanes in the material to be treated are usually adequate. It is, how beutilizable able to form convert and suchto do waste this by material a process to nota readily involving re ever, preferred to use 5 to 15%. undue expenditure. One method which has been pro My invention is further illustrated by the following posed for this purpose, is to treat a polysiloxane elas 35 examples in which all parts and percentages are by tomer or gum with an anhydrous halogen acid to form a weight. liquid product. The uses of this product are, however Example 1 limited and it is first necessary to remove or neutralise 75 parts of a polysiloxane composition consisting of the halogen acid present. It has also been proposed to 100 parts of a trimethylsily end-stopped dimethylpoly use a treatment with steam for this purpose. These 40 siloxane gum, 35 parts of a fume. silica ("Aerosil” FK3), :methods, however, suffer from various disadvantages, 3 parts of (tetramethylethylenedioxy)-dimethylsilane and e.g. the product obtained is not always in its most useful 3 parts of a paste containing 50% benzoyl peroxide...in form and can frequently be used for only limited ap a polysiloxane oil ("Luperco" A.G.E.) were reacted plications. with 3.8 parts of aluminium chloride by heating and There has also been a proposal to prepare cyclic com 5 stirring at 300° C. for 3 hours in a vessel adapted for pounds of the general formula (RSiOAICl) where distillation. During this period, 41.7 parts of liquiddis each R is the same or different and is a methyl, ethyl, tilled off. This liquid contained 0.5 part of hexamethyl or phenyl group by reacting substantially completely CO cyclotrisiloxane, 26.8 parts of octamethylcyclo tetrasilox densed organosiloxanes containing polymeric units of the ane, 6.9 parts of decamethylcyclopentasiloxane and 3.5 general formula R2SiO with aluminium chloride - under 50 parts of duodecamethylcyclohexasiloxane. The weights 'substantially anhydrous conditions. In these compounds the silicon and aluminium atoms are linked through an of distillate produced after one and two hours reaction "oxygen atom giving the linkage -Si-O-Al-. These were 35.7 and 40.1 parts respectively. compounds are crystalline solids, the alkyl compounds Example 2 being capable of purification by distillation while the aryl 75 parts of the polysiloxane composition used in Ex -compounds are not readily distilled but are best purified ample 1 were reacted with 37 parts of anhydrous alumin by recrystallization and all are hydrolysed by water to ium chloride by heating at 350° C. 49.3 parts of distil give siloxanes and hydrated aluminium chlorides. late were collected from this reaction during a period of According to the present invention a process for the 2 hours. This distillate contained 0.885 part of hydrogen production of low molecular weight cyclic methyl poly 60 chloride and 1.13 parts of hexamethylcyclotrisiloxane, Isiloxanes comprises reacting together a high molecular 32.6 parts of octamethylcyclotetrasiloxane, 8.1 parts of weight substantially linear methyl polysiloxane with a decamethylcyclopentasiloxane and 3.4 parts of duodeca substance from the class consisting of halides of alumin methylcyclohexasiloxane. - - - - ium and halides of phosphorus in an amount not more than 30% by weight at an elevated temperature under 65 Example 3 substantially anhydrous conditions and simultaneously 75 parts of the polysiloxane composition used in Ex distilling off the so produced cyclic polysiloxanes. ample 1 were heated with 1.88 parts of aluminium chloride The methylpolysiloxanes to be treated may also con at 300° C. for 5 hours in a vessel adapted for distillation. tain other groups such as e.g. phenyl or vinyl groups but After 3 hours 14.3 parts of liquid had distilled of and the low molecular weight cyclic polysiloxanes obtained 70 after 5 hours, 18.6 parts had been collected. The final by the process of my invention will not contain any product contained 0.48 part of hexamethylcyclotrisilox 2,934,550 3 4. ade, 10.1 parts of octamethylcyclopentasiloxane and 2.06 Example 10 parts of duodecamethylcyclohexasiloxane. A siloxane composition of the kind used in Example 5 Example 4 was cured to an elastomer by heating for 10 minutes at 75 parts of partially cured siloxane gum composition 135 C. under pressure of 600 lb./sq. in. followed by consisting of 100 parts of a trimethylsilyl end-stopped di heating for 1 hour in an oven at 150° C. and for 24 methylpolysiloxane gum, 35 parts of a fume silica hours at 250° C. 75 parts of the elastomer so obtained ("Aerosil' FK3), 3 parts of (tetramethylethylenedioxy) were heated with 3.75 parts of aluminium chloride at 300 dimethylsilane, 3 parts of a paste consisting of 50% C. for 4.5 hours in a vessel adapted for distillation. Dur benzoyl peroxide in a polysiloxane oil ("Luperco' O ing this period, 41.5 parts of liquid distilled off. This A.G.E.) and 1 part of ferric oxide were reacted with 3.8 liquid contained 2.8 parts of hexamethylcyclotrisiloxane, parts of phosphorus pentachloride by heating under reflux 24.6 parts of octamethylcyclotetrasiloxane, 5.3 parts of for 1 hour and thereafter heating at 300° C. for 3 hours. decamethylcyclopentasiloxane and 2.0 parts of duodeca After 1, 2 and 3 hours' heating at 300° C., 31.2, 43.0 and methylcyclohexasiloxane. 45.0 parts respectively of distillate were collected. The Example II final distillate contained 26.6 parts of octamethylcyclo 75 parts of a product obtained by hydrolysis of dimeth tetrasiloxane, 9.2 parts of decamethylcyclopentasiloxane yldichlorsilane with water were heated with 3.75 parts and 2.3 parts of duodecamethylcyclohexasiloxane. of aluminium chloride at 300° C. in a vessel adapted for - Example 5 20 distillation and the volatile products distilled off and neu 75 parts of a siloxane composition similar to that of tralised. This product was re-distilled to give 46 parts of Example 4 were reacted with 7.5 parts of aluminium chlo a liquid containing 0.4 part hexamethylcyclotrisiloxane. ride by heating at 300° C. for 1 hour in a vessel adapted 39.8 parts octamethylcyclotetrasiloxane and 5.8 parts for distillation. During this period, 45.5 parts of distill decamethylcyclopentasiloxane. late collected. This distillate contained 1.05 parts of 25 Example 12 hexamethylcyclotrisiloxane, 30.4 parts of octamethylcy 75 parts of a partially cured polysiloxane composi clotetrasiloxane, 9.5 parts of decamethylcyclopentasilox tion prepared from a composition consisting of 100 ane, 3.1 parts of duodecamethylcyclohexasiloxane. parts of a polysiloxane gum containing methyl and Example 6 phenyl groups in the molar ratio of 15:1 and having a 30 ratio of methyl plus phenyl groups to silicon atoms 75 parts of the siloxane composition used in Example 5 of 2:1, 45 parts of a silica aerosol (“Santocel' CS) and were heated with 3.75 parts of aluminium bromide at 3.3 parts of a paste consisting of 50% benzoyl peroxide 300 C.