DE1770140C - Process for polymerizing cyclic organosilicon compounds - Google Patents

Description

in which each R is a hydrogen atom, a monovalent hydrocarbon radical or a monovalent halohydrocarbon radical and m has a value of 3 or 4, or

(b) the general formula

R ₂ 'Si - CH ₂ - CH ₂ - Si R' _t ,

I ο!

in which each R is a monovalent hydrocarbon radical, a monovalent halogenated hydrocarbon radical or a low molecular weight alkoxy radical represents

in the presence of a basic catalyst and a polar organic solvent at a temperature of up to 160 ° C _1, which is characterized in that the polymerization is terminated before equilibrium is reached at a stage in which the ratio for the polymeric product Mw: Mn is less than 1, 6 is. (Mw and Mn correspond to the definition given in the previous paragraph.)

The Mn values can be determined osmometrically and the Mw values by measuring the light scattering. The ratio Mw: Mn can also be determined by gel permeation chromatography. Such methods are z. B. described in "Principles of Polymer Chemistry", P. J Flory (!>) 53), Chapter 7, and "Waters Associates Manual".

There can be cyclic trisiloxanes and cyclic kirasiloxanes according to the teaching of the present Eri; ihing can be polymerized in order to arrive at organosils. In general: ■ <but it is possible to use a smaller Mw : A /; t-Veri. To achieve iinis with the cyclic trisiloxanes, i ,, \ i therefore the use of such materials is often of particular advantage.

For the process according to the invention it is also possible to use cyclic silarylene siloxanes which can be polymerized to form anosilicon polymers in which the silicon atoms are bonded to one another via ethyne residues and "iicrstol" atoms.

η of the general formula under which the cyclic starting materials coming in ί n ': n. B. alkyl such as VtMhyl, ethyl, propyl, nonyl and octadecyl, also, '■ kenyl such as vinyl, allyl and butenyl, and aryl such as i'k-nyl, ToIyI and xylyl mean. Each R can also represent a hydrogen atom or a monovalent halogenated hydrocarbon radical, ■ / .. B. chloromethyl, bromophenyl and trifluoropropyl! The radical R 'in the cyclic silethylene siloxane can mean the same organic radicals as are given for R, and can also represent alkoxy groups with 1 to 6 carbon atoms.

Organosilicon polymers and copolymers, the monovalent hydrocarbon radicals or Contain halogenated hydrocarbon residues, especially methyl, vinyl, phenyl and trifluoropropyl residues, are usually of considerable technical importance, and those for the purposes of the present Invention preferred cyclic organosilicon materials in question are those having such Contains leftovers. The cyclic organosilicon compound is preferably the cyclotrisoxane. If so desired Mixtures of cyclic organosilicon compounds can be used to make so to arrive at copolymeric siloxanes, and if desired, R can also have more than one meaning in any particular cyclic material.

The cyclic siloxanes useful for the purposes of the present invention therefore include Hexamethylcyclotrisiloxane, methylphynylcyclotrisiloxane, methyl- (trilluorpropyl) -cyclotrisiloxane and Mixtures of the same. If desired, it can also be used together with the cyclic organosilicon material a compound may be incorporated which acts as a source of the terminal polymeric product Units is used, for example hexamethyldisiloxane.

Anyone can serve as the basic catalyst! which is known to be able to catalytically accelerate the polymerization of cyclic siloxanes. Such catalysts can be summarized by the symbol AB, where A z. B. denotes an alkali metal atom, an i | uaternary ammonium radical or a quaternary phosphonium radical and B represents, for example, a hydroxy radical, an alkoxy radical, an alkyl radical, an alkenyl radical, an aryl radical or a silanolate radical, / .. B. the radical of the formula OSiX .. or

[OSiX ₂ ] "O,

wherein each X represents an alkyl group or an aryl group and ρ represents an integer.

Specific examples of useful tools Catalysts are therefore potassium hydroxide, sodium phenolate, potassium trimethylsilanolut, tetramethylammonium silanolate, Benzyhrimelhykirsimonium SilanoIat, // - Hydroxyäthyltrimethylammunium-Siloxanolat, Tetramethylammonium butylate, tetraethylammonium hydroxide, tetramethylphosphoniuin silanolates, Butyl lithium and vinyl lithium. The alkyl, alkenyl or aryllithium compounds, especially Lithium butyl, are normally preferred because they give better control of the polymerization process than is usually possible with the more active silanolate compounds.

In the general given for the catalysts Formula AB, the anion B can be monovalent, bivalent or polyvalent. Therefore belong to The basic catalysts which can be used also include, for example, the dilithium salts of disiloxanols.

The basic catalyst can be used in such amounts as are usually used in the be known polymerization of cyclic organosilicon compounds are used. the the amount actually used depends in each individual case on the nature of the catalyst. As a rule However, Kalalysatorverbindungen are from 0.01 to 5 percent by weight, based on the weight of the cyclic Material, sufficient, although of course also quantities outside this range can be applied if desired.

The polymerization reaction is started by adding the cyclic siloxane or the mixture of the cyclic siloxanes and the basic catalyst at the desired temperature door brings in contact. The polymerization can expediently take place at temperatures between 0 ° and 40 ° C. be performed. However, temperatures of. 20'C or below applied the minimum temperature being mainly from the freezing point of any of the components of the Reaction mixture is determined. As the temperature rises, it has been found to expand the molecular weight distribution in the Product a, and therefore it is recommended that the inventive method at temperatures below about 160 ° C.

The process according to the invention is carried out in the presence an organic solvent, such as toluene or xylene, carried out, which the thorough and rapid dispersion of the catalyst unteisliit / t. In those cases in which the catalyst causes the formation of alkali cations, it has proven to be special Proven to be beneficial, polar solvents / 11

use, the strong solvalization of said cations and the existence of the active ones Enable silanolate centers as free ions.

Furthermore, in certain cases a lower Mir: Mn ratio can be achieved if there is an excess on a soluble salt of the cation with a polar solvent is used to facilitate the formation to suppress free ions and to ensure that the polymerization only from free ion pairs takes place.

Examples of suitable polar solvents which can be used are dimethyl sulfoxide, dimethylformamide, hexamethylphosphorotriamide, tetramethylurea, tetrahydrofuran, dimethoxyethane and acetonitrile. Dimethyl sulfoxide and hexamethylphosphorotriamide are the preferred polar solvents in which the catalyst ^{gives rise to the formation of potassium (K H} ) ions. Tetrahydrofuran, dimethyl sulfoxide and dimethoxyethane, however, are preferred when the cation consists of lithium (Li ¹ ).

The Mw: M / i ratio in the polymerization product depends to a considerable extent on this The degree to which the polymerization is allowed to proceed. To Mw: M / i ratios of below To achieve 1.6, it is necessary to stop the polymerization before the equilibrium state is reached and before the reaction, which redistributes the siloxane bonds in the polymer comprises and causes an expansion of the molecular weight distribution of the polymerization product, has reached a noticeable extent.

The desired polymerization time depends e.g. B. on the nature of the catalyst, the solvent and on the type of cyclic siloxane used and varies from seconds to to hours.

In most cases it has proven to achieve Mir: M / 7 ratios below about 1.2 proved necessary to stop the polymerization process at the stage at which 50 percent by weight or less of the cyclic starting material has been converted to the polymeric product.

The completion of the Polymerisatiorsprozcsses can can be achieved by neutralizing the catalyst with a weakly acidic compound, and one known method is to add solid carbon dioxide to the polymerization mixture. The separation of the desired polymer from the solvent and from the unreacted cyclic polymer remaining in the reaction product Starting material can be obtained by any convenient or known working technique, e.g. B. by Precipitation with, if necessary, subsequent freeze-drying, or more advantageously by distillation, which can, if desired, be carried out under reduced pressure.

With the help of the eiTmdimgsjK'ischemcn procedure it has been shown to be possible by an enveloping Polymcrisiitionspro / .cß Oiganosiliconpolymerisate in which the molecular weights are linked is at least as narrow as that which one can only get through using known methods Closing the cumbersome fractionation process achieved.

The method is useful for elucidating OrgauosiliciiiinpolN im lisaliu, those of lui llu-liläliigcn Liquids with molecular weights from about Kl (K) to non-flowable, toluene-soluble gums with molecular weights of 2-10 ° or more.

The polymers prepared according to the process of the present invention can be used for all those Purposes can be used for which the known linear siloxane or silethylene siloxane polymers commonly used. For example, they can be used either on their own or in

ίο community with other siloxanes, solvents or other ingredients in bulk for coating paper and textiles or - with fillers and vulcanizing agents combined - for manufacture of organopolysiloxane rubbers or in the formation of lubricating greases and compounds will. The polymers have flow properties that are similar to the behavior of Newtonian liquids approach, and they are therefore particularly useful as hydraulic fluids and damping media technically useful.

The following examples, in which the term "Me" means the methyl radical, are intended to encompass the invention explain in more detail.

example 1

Hexamethylcyclotrisiloxane (14.0 g) was dissolved in about 30 ml of toluene, and then the solution with more Toluene made up to a total volume of 50 ml. 1 ml of a ca-

Added lium silanolate catalyst solution, which had been prepared by refluxing a mixture of cyclic mixed dimethylsiloxanes (148 g), potassium hydroxide (28 g) and toluene (200 ml) for 24 hours and stripping off the released water using a Dean and Stark separator. The offset with the catalyst mixture was then filled in a glass dilatometer ml of a capacity of 40, which is then sealed and placed in a bath maintained at 20 ⁰ C water bath Wuide. After 50 minutes the contents of the dilatometer contracted by 0.061 ml, which corresponded to a 10% conversion of the cyclic silicon oxane into the polysiloxane. _{Solid CO 2} was then added to the contents of the dilatometer, the mixture was filtered and the polymeric siloxane was isolated by precipitation with excess methanol and subsequent freeze-drying.

The weight average molecular weight was 76,500 while the number average the molecular weight was 59,300 giving a Mii ': Mu ratio of 1.29.

Example 2

Hexamethylcyclotrisiloxane (14 g) was dissolved in about 30 ml of toluene and the mixture was then made up to a total volume of 50 ml with more toluene and dried over calcium hydride overnight. 0.05 g KOSiMe. Was then added directly to this solution. The silanolate dissolved rapidly and the mixture was then transferred to a dilatometer, which was sealed and placed in a water bath kept at 20 ° C. The Üüatometerinhall pulled After 28 minutes, 0.064 ml together, which corresponded to a approximately 10 ⁿ / Nigen Umwandhing of the cyclic starting material to the polymeric siloxane. The catalyst was then neutralized by adding solid (X), the mixture was filtered and the polymeric siloxane was isolated

by precipitation with excess methanol and subsequent freeze-drying.

The Mtv value was determined to be 24,610 and the M / j value to be 19,160, which is a We: Mu ratio of 1.28 resulted.

Example 3

50 ml of a solution of octamethylcyclotetrasiloxane (14 g) in toluene was dried over calcium hydride. 1 ml of a solution of 0.607 g KOSiMc., In 50 ml dimethyl sulfoxide was added to the filtered solution given. This mixture was used to fill a glass dilatometer, which then closed and placed in a water bath regulated to 20 ° C. The ones with the Treatments carried out in solutions were carried out inside a drying chamber. the Dilatomclerinhaltc had contracted after 5 hours by 0.055 ml, and the The reaction was then terminated by adding solid CO. The polymer was as in previous examples isolated.

The Mw was 66,000 and the M / j was 46,200, resulting in an A: M / j ratio of 1.43.

Example 4

To 50 ml of a dried solution of Hxamethylcyclotrisiloxan (which had been prepared as in Example 2) 0.05 ml of a solution of KOSiMc., in dimethyl sulfide (0.607 g KOSiMc., in 25 ml of dimethyl sulfoxide). The mixture was filled into a dilatometer, which was then closed and placed in a water bath kept at 20 ° C. After 34 minutes the Dilatometcrine content contracted by 0.059 ml, and the polymerization was then stopped by adding solid carbon dioxide. The polymer was isolated in the manner described in the previous example

The Mtv and M / i values for the polymeric product are 49,600 and 34,500, respectively, which corresponded to an Mtr : Wn ratio of 1.44.

Example 5

To 50 ml of a dried solution of hexamethylcyclotrisoxane in toluene was added 0.05 ml of a catalyst solution consisting of 0.219 g KOSiMe., And 2.4129 g KI, dissolved in 10 ml dimethyl sulfoxide. A dilatometer was filled with this mixture, which was then placed in a water bath kept ^{at 20 ° C.} After 4 ¹ 2 hours, the mixture had contracted to 0.064 ml, and the reaction was abgehrochen by adding \ on solid carbon dioxide and the polymer is isolated as described in the previous examples manner.

The measured JUw and M / j values were 26,350 and 21,560, respectively, which corresponded to a 717m: M / 7 ratio of 1.22 .

Example 6

0.005 ml of a solution of 12.8 g of n-butyllithium in 100 ml of η-hexane were added at 20 ° C. to 100 ml of a solution of hexamethylcydotrisiloxane (40 g) in tetrahydrofuran. The polymerization reaction was allowed to proceed for 280 minutes at 20 ° C., after which time it was terminated by adding solid carbon dioxide.

The reaction product contained 28 weight percent of a polydimethylsiloxane of molecular weight 147,000 and a Mir: Mn ratio of 1.05.

Example 7

20 ml of a solution of 40 g of hexamethylcyelotrisiloxane, dissolved in 60 g of toluene, were dried over calcium hydride for 24 hours, then filtered and heated to 100 ° C. in an oil bath been ml Dimcthylsulfoxyd added and the polymerization was stopped after 5 minutes at the end of this period were 40 ⁽ "n of Hcxamcthylcyclotrisiloxans in a polydimethylsiloxane converted whose number average was of molecular weight 100,000 and its with ·:. M / i-Vcrhällnis less than 1.4 was.

Example K

A 4 () "solution of hexamethylcyclolrisiloxane in toluene was dried for several days over a molecular sieve type 4 A (Linde). 20 ml

»5 of this solution were placed in a 50 ml flask and then with 0.02 ml of a 0.15 g solution Tetramethylammonium silanolate in 25 ml of dimethyl sulfoxide are added, the filling under anhydrous Conditions in a protective chamber that can be operated with gloves. The polymerization was allowed to proceed for 2 minutes at 25 ° C. and then stopped. As found was 70 "/" of the hexamethylcyclotrisiloxane converted into a polydimethylsiloxane.

Its molecular weight was 2,800,000 and its Mm: M / 7 ratio was less than 1: 1.

Example 9

A 40% solution of methyl (trilluoropropyl) cyclotrisiloxane in tetrahydrofuran was dried over a molecular sieve type 4 A (Linde) for 24 hours. 0.02 ml of a solution of 12.8 g of n-butyllithium in 100 ml of n-hexane were added to 20 ml of this solution added at 20 ° C. The polymerization was allowed to proceed for 40 minutes and thereafter 30% of the cyclic siloxane is converted into a polymer which has an Mw: Mn ratio of less than 1.4.

Example 10

To 25 ml of a solution of Hxamethylcyclotrisiloxan (10 g) in tetrahydrofuran was added 0.04 ml of a 2 η solution of lithium vinyl in tetrahydrofuran. Polymerization of the cyclic siloxane then began and was allowed to proceed for 90 minutes, after which time solid carbon dioxide was added to terminate the reaction. Analysis of the reaction product by gas-liquid chromatography indicated that it consisted of 34 weight percent of a polydimethylsiloxane with the remainder consisting of tetrahydrofuran and unreacted cyclic siloxane. Further analysis of the product using GcI permeation chromatography indicated that the polydimethylsiloxane had a molecular weight SSn of 38,000 and an Mw: Mn ratio of 1.21.

10

A small siloxane set in and was left for 15 minutes long expire and then ended by adding solid carbon dioxide.

Analysis of the reaction product revealed that 38% of a polymethylvinylsiloxane was present therein, which had a molecular weight Mn of 18,000 and an Mw: Mn value of 1.35.

Example 13

ίο One gives 300 μΐ of a 2.3 molar solution of n-Butyllithium to 100 ml of a solution containing 40 g of 2,2,5,5-tetramethyl-1-oxa-2,5-disiIacyclopentan der formula

CH ₂ CH ₂

Example 11

40 ml of a (), 3 molar solution of the lithium salt of the tetramethyldisiloxane-1,3-diol were added to 2 liters of a solution of hexamethylcyclotrisiloxane (800 g) placed in tetrahydrofuran. The reaction was allowed to proceed for 115 minutes and they was then stopped by adding solid carbon dioxide.

The reaction product was found by gas-liquid chromatography and gel permeation chromatography to contain 35 weight percent of a silanol-capped polydimethylsiloxane having a molecular weight Mn of 56,000 and an Mw: Mn ratio of 1.26.

Example 12 contains j _{n rc} j _nem tetrahydrofuran (this solution was

0.10 ml of a 2 η solution of Lilhiumbutyl in previously dried over Linde molecular sieve type 4A

Tetrahydrofuran were added to 100 ml of tetrahydrofuran, ao). The polymerization reaction is allowed to

the 40 g of methyl vinyl cyclotrisiloxane run until 43% of the monomer has been consumed

UCU CU - rucni ι ^{sma <} · the reaction is ended with carbon dioxide.

U ^ n ₃ »_n ₂ - v.nsiuj _a j ^ _iso , _jerte p _{oIymerisat has a} Jf _{n =} 26,400

contained, admitted. The polymerization of the eye and a ratio of Mw: Mn <1.30.

Claims (1)

Claim: Process for polymerizing a cyclic organosilicon compound (a) of the general formula (RjSiO) _n,. (R - hydrogen monovalent hydrocarbon radical or monovalent halogenated hydrocarbon radical; m - 3 or 4) or (b) the general formula R ₂ 'Si - CH ₂ - CH ₂
r \ Si (R '- monovalent hydrocarbon, monovalent halogenated hydrocarbon residue or low molecular weight alkoxy radical) in the presence of a basic catalyst and a polar organic solvent at a temperature of up to 160 ^° C., characterized in that the polymerization is terminated before equilibrium is reached at a stage at which the Mw : ~ ffln ratio for the polymeric product is less than 1 .6 (Mw - weight average molecular weight; Mn = number average molecular weight). The present invention relates to a method for polymerizing cyclic organosilicon compounds, and it relates in particular to the production of organosilicon polymers, which have a molecular weight distribution that is kept within narrow limits. The polymerization of cyclic organosiloxanes in the presence of basic catalysts to give high molecular weight linear organopolysiloxanes has long been known. Among those proposed for this purpose and catalysts used include alkali hydroxides, quaternary ammonium hydroxides, quaternary phosphonium compounds and alkali silanolates. The method by which this polymerization reaction takes place is - as has been established is - in the stepwise addition of cyclic siioxane units to an active silanolate center, for example according to the equation B (RR "SiO)"R'R"SiO-A ⁺ (- (R'R" SiO) _ro - * - B (R'R "SiO)"_{> m} R'R "SiO-A ^ in which R 'and R "represent the silicon-bonded organic radicals in the cyclic siloxane, m and η are integers and A and B represent the cation and the anion which have been formed by the dissociation of the catalyst .. The active silanolate center can, as shown above, as a non-isolated ion pair, as a solvated ion pair or as free ions. There is a dynamic equilibrium between these various forms of active siliconolite / center, and the polymerization of the cyclic organosiloxane proceeds at rates that are different for each type of center. The formation of the active silanolate center can take place in situ following the addition of the basic catalyst to the cyclic siloxane, or it can have been preformed, e.g. B. by reacting an alkali metal with a triorganosilanol.
In connection with the one just described ίο Polymerization mechanism it is also known that side reactions during the polymerization process occur that redistribute the siloxane bonds between the active silanolate centers and the polymeric product. One effect of this rearrangement is that the spectrum of molecular weights of the silicon oxane polymers in the product is expanded. An analogous expansion of the molecular weight distribution is also achieved by the depolymerization reaction and caused by transfer reactions which occur in the system in the presence of water take place. For this reason, the known processes for polymerizing cyclic organosiloxanes provide to the technically desirable linear polymers products that consist of organosiloxane, which have a very broad distribution of molecular weights and by a ratio from (weight average molecular weight) to (number average molecular weight) are marked, which is often well above 2. To get products that are improved and more have desired molecular weight distributions, it has hitherto been unavoidable, the polymerization product subject to cumbersome and costly fractionation processes. It has now been found that by modifying the known polymerization process described above, it is possible to obtain a polymeric product which has a molecular weight distribution which is remarkably narrower than that of products which have been prepared by known procedures, and one thus can obtain polymeric organosilicon products without the use of costly fractionation processes, in which products the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is substantially less than 2.0. What is claimed is a process for polymerizing a cyclic organosilicon compound (a) of the general formula (R ₂ SiO) _1n ,