DE959946C - Heat-vulcanizable organopolysiloxane compound - Google Patents

Description

ISSUED MARCH 14, 1957

D 17148 IVb / 39b

It is known to vulcanize vulcanizable compositions containing organopolysiloxanes by heating with small amounts of organic peroxides. This process has mainly been introduced in technology because these peroxides are inactive at room temperature, ^{but enable rapid vulcanization at temperatures from 0} to 150 °, and the vulcanizable compounds processed with peroxides are therefore easy to transport without premature Hardening occurs and can be quickly processed into objects. The siloxane elastomers cured with peroxides, however, have certain disadvantages which it appears to be desirable to eliminate.

In the previously used siloxane elastomers consisting of dimethylsiloxane, or from compounds of dimethylsiloxanes and phenylmethyl or from diphenylsiloxanes, it is necessary to harden after a preliminary vulcanization for 24 hours at 250 ⁰ to siloxane elastomers useful to obtain suitable characteristics. This hardening is particularly necessary when silicone rubber with a

tolerable pressure elasticity adjustment are produced target. The loss of pressure elasticity is z. B. in the elastomers previously used Heating at 125 ° 100% for 5 minutes. As a result Due to this high loss, the silicone rubber cannot be used in this hardness state. After heating at 250 ° for 24 hours, the loss of pressure elasticity is approximately 50 to 60%. In 90 out of 100 cases with the use of silicone rubber with loss of compressive elasticity in this amount can be expected.

In order to reduce the loss of pressure elasticity, it is necessary to use certain additives. The best way to do this is to use mercury oxide, which is, however, poisonous.

Another disadvantage of peroxide cured siloxane elastomers is the significant decrease in tensile strength and elongation during? the 24-hour ^| en hardening

ao 250 ⁰ . However, in order to limit the loss of pressure elasticity to a minimum, one is forced to accept these disadvantages. The decrease in tensile strength and elongation is due to the initial vulcanization

«5 Remaining peroxide and its decomposition products traced back. These remaining substances vulcanize the polysiloxane during the required curing time, with crosslinking of the elastomer. Will the Amount of peroxide is significantly reduced, so the previously used methyl and Phenylsiloxane elastomers not cured.

It has now been found that the above difficulties can be overcome by less than 0.5 parts by weight of peroxide for vulcanizing the polysiloxanes, which also have a small amounts of copolymerized alkenylsiloxanes are used.

It is known to incorporate vinylmethyl and divinylsiloxanes into siloxane elastomers. the The use of vinylsiloxanes somewhat improves the loss of compression elasticity of these produced in this way Elastomers versus' elastomers that only contain methyl groups. The compressive elasticity

♦ 5 loss increases, however, if the proportion of peroxide vulcanizing agent becomes less, e.g. B. is the compression elasticity loss at 0.5 parts of benzoyl peroxide higher than 1 part benzoyl peroxide. Unexpectedly it has been found that there is a very considerable reduction in the loss of compressive elasticity by using smaller amounts of peroxide for certain alkenyl radicals Siloxanes can achieve. The combination of a small amount of vinyl group containing Siloxanes and a small amount of peroxide produce results that are completely in contrast to the previously known stand ·.

The present invention now relates to improved compositions vulcanizable with peroxides, which can be vulcanized in a shorter time and which also make the production without any special additives of elastomers that have only a small loss of compressive elasticity, and therefore superior to all previously known siloxane elastomers due to their physical properties are.

The vulcanizable compositions according to the invention are characterized by a content of (1) an organosiloxane copolymer whose viscosity at 25 ° is at least 1,000,000 cSt and! that essentially consists of 99.5 to 99.982 mol percent of siloxane units of the formula R ₂ Si 0, in which R represents a methyl or phenyl radical and at least 50% of the R groups should be methyl radicals, and 0.018 to 0.5 mol percent of siloxane units of the formula R 'R "is composed of Si O, where R' is an alkenyl radical with 2 to 6 carbon atoms and R" is an alkenyl radical with 2 to 6 carbon atoms or a methyl or phenyl radical, by a content of (2) 0.075 to 0 , 4 percent by weight, based on the weight of the copolymer, of an aromatic acyl peroxide, and ¹ (3) optionally by a content of a filler, e.g. B. a silica filler, in an amount of 10 to 100 parts by weight per 100 parts by weight of the copolymer.

The copolymers can in the usual manner, such as. B. by joint hydrolysis of the corresponding chlorosilanes or by catalytic «copolymerization of the corresponding siloxanes. The copolymerization is expediently carried out with an alkaline catalyst, such as alkali metal hydroxide. If desired, acidic catalysts can also be used. Suitable for the inventive vulcanizable masses copolymers are liquid, with a viscosity of about 1000 000 cSt at 25 ^0, non-flowing, solid, benzene-soluble polysiloxanes. In general, the higher the degree of polymerization, the better the elastomers obtained therefrom.

These copolymers essentially consist of a small amount of alkenylsiloxanes, together with phenyl and methyl siloxanes as the main component. If the proportion of alkenylsiloxane is below 0.018 mol percent, it is explained the vulcanization with the amount of peroxide according to the invention is not satisfactory ' if the proportion is more than 5 mole percent, elastomers with inferior properties are obtained.

The copolymer consists mainly of dimethylsiloxane, phenylmethylsiloxane or from compounds of dimethylsiloxane and phenylmethylsiloxane and / or diphenylsiloxane. It however, at least 50% of the organic groups should be methyl radicals. So z. B. the maximum amount of diphenylsiloxane used in conjunction with dimethylsiloxane can, 50 mole percent.

The alkenyl lao siloxanes to be used according to the invention have either one or two of the Silicon-bonded alkenyl groups with 2 to 6 carbon atoms. So there are alkenylsiloxanes like z. B. vinylmethylsiloxane, divinylsiloxane, allylmethylsiloxane, Diallylsiloxane and hexenylphenylsiloxane, into consideration. These alkenylsiloxanes can

by hydrolysis of the corresponding chlorosilanes, which are produced by reaction of the corresponding alkenyl Grignard reagents with chlorosilanes.
Any peroxide containing at least one aromatic acyl radical can be used in accordance with the invention. Peroxides containing two aromatic acyl radicals can also -vie ζ. B. dinaphithoyl, benzoyl peroxide, substituted benzoyl peroxides such as bis-p-chlorobenzoyl peroxides, bis-2, 4-dichlorobenzoyl peroxides and bisp-methylbenzoyl peroxides, or peroxides which contain only one aromatic acyl radical, such as. B. benzoylacetyl, benzoyl lauroyl, tertiary butyl perbenzoate and substituted tertiary butyl perbenzoates, such as tertiary butyl p-chloroperbenzoate, can be used. The most suitable peroxides are benzoyl peroxide, halogenated benzoyl peroxides and tertiary butyl perbenzoate. If so desired

A combination of two or more of the above-mentioned peroxides can also be used.

It can be calculated from 0.075 to 4 percent by weight based on the weight of the copolymeric siloxane, of peroxide can be used. If less than

* 5 0.075 percent by weight is only a proportionate weak vulcanization, more than 4 percent by weight results in inferior products.

The vulcanizable compositions according to the invention can be ground and cured together with other substances in the usual way. In general, the copolymer and vulcanizing agent, optionally with a filler, are ground in a mill. The mixture is heated for 5 to 10 minutes at 110 to 150 ^0th The properties of the rubber produced in this way correspond to the requirements placed on silicone rubber in 90 out of 100 cases. If the pressure loss of elasticity, however, be very small, you can achieve this by hardening for 24 hours at 250 ^0th A product is then obtained, the loss of compressive elasticity of which is 5% or less.

Suitable fillers are, for. B. titanium earth, zinc oxide, diatomaceous earth, clays and with methylchlorosilanes treated carbon black. About 10 to 300 parts by weight of filler are used, based on weight on 100 parts by weight of siloxane. The best physical Properties are obtained by using so-called »reinforcing« silica fillers, ζ. B. obtained from silica aerogels and by burning volatile silicon compounds Silica. In general, 10 to 100 parts by weight of silica fillers are used to 100 parts by weight of siloxane.

In addition to the fillers, the vulcanizable compositions according to the invention can contain additives such as Pigments, oxidation-retarding substances and additives, the special properties of the products made with them Elastomers such as B. change the resistance to solvents. The products made from the vulcanizable compositions according to the invention are for the general usual areas of application for SiI-oxane elastomers, z. B. as a sealing material for electrical insulation, suitable for hot air ducts and antifreeze.

All copolymers used in the examples were made in the following ways:

Octamethylcyclotetrasiloxane was mixed with a cyclic tetramer containing alkenyl radicals. The mixed cyclic products were polymerized by heating with potassium hydroxide in a ratio of 1 potassium atom per 5000 silicon atoms at a temperature of 150-165 ⁰ for 30 minutes. The polymer was then heated for ι hour in an oven at 150 ^0th The solid benzene-soluble substances obtained in this way had a plasticity of 90 to 100 as measured by the Williams plastometer.

The cyclic substances containing alkenyl groups used in the examples can be used in exist in two forms, as a tetrasiloxane with one alkenyl and one phenyl or methyl radical each per silicon atom or as tetrasiloxane in which each of 3 silicon atoms has two methyl radicals and the other silicon atom contains a vinyl and a phenyl radical bonded. In the former case it is a cyclic tetramer of a certain siloxane (e.g. the cyclic tetramer a phenylvinylsiloxane). These tetramers can be produced by hydrolysis of the corresponding dichlorosilanes can be prepared in a dilute solvent, with the majority of the hydrolyzate is condensed to the cyclic tetramer. In the second case it became the cyclic product by hydrolysis of a mixture of vinylphenyldfothorsiian and dimethyldichlorosilane in a molar ratio of 1: 4. The mixed ones Chlorosilanes were in a solvent consisting of 3 parts by volume of diethyl ether and 1 part by volume Tetrahydrofuran, dissolved. Then a solution of 75%> the theoretical amount of water in the same amount of tetrahydrofuran added to the chlorosilane solution. After the hydrolysis was complete, the product became acid-free washed and distilled to give the desired cyclic material.

The progress achieved mainly by the present invention lies in the improvement of the compressive elastic properties of the siloxane elastomers. To determine the loss of compressive elasticity, a sample is compressed to 70% of its normal thickness, below this. Pressure is heated to a given temperature and then cooled while releasing the pressure. This method is equivalent to the American ASTM test procedure (D-395-49 T, method B) with the difference that the sample gesetzt..wird 22 hours at 150 ⁰ under pressure. The thickness of the sample after such a treatment compared to the original thickness indicates the degree to which the sample returns to its original thickness after the test described. A high loss of pressure elasticity is therefore synonymous

with a large permanent set, and a low loss of compressive elasticity indicates that the Product has largely regained its original thickness.

Example ι

A number of copolymers were prepared by copolymerizing octamethylcyclotetrasiloxane and the mol percent of ι -phenyl-i-vinylhexamethylcyclotetrasiloxane given in the table. The copolymer used in each test consisted of a benzene-soluble, non-flowing material, the plasticity of which was between 90 and 100, measured with the WHliams plastometer. In each case, 100 parts by weight of the copolymer with 40 parts by weight of silica obtained by combustion of volatile silicon compounds, 0.5 part by weight of ferric oxide and the various in the table were given. Parts by weight of tertiary butyl perbenzoate processed. The amounts given in parts by weight are calculated on the basis of 10.0 parts by weight of this polymer. The mixture was processed in a rubber mill. When a uniform mixture was obtained, the material was ^{heated to 150 °} in a press for 10 minutes. Each sample was then cured for 24 hours at 250 ^0th The following results were obtained:

Table I 'samples heated ^{to 150 0 for 10 minutes}

Mole percent vinyl
phenylsiloxane Parts by weight
tertiary butyl
perbenzoate Durometer
value tensile strenght
in kg / cm ² Elongation at break
in% Compressive elasticity
loss O, Ol8
0.071
0.140
0.405 0.233
0.1
0.1
0.1 33
37
37
45 86.1
98.0
90.3
91.3 980
975
830
760 100
62
43
42

Samples 24 hours at 250 ⁰ Tensile strength
speed
in kg / cm ² fracture
strain heated Durometer
value . 35.5
84.0
84.0
84.0 705
755
690
600 pressure
elasticity
loss 50
49
51
52 44
20th
15th
17th

Example 2

Octamethylcyclotetrasiloxane and 0.14 mole percent cyclic tetramers from vinylmethylsiloxane were copolymerized in the manner described above. The resulting copolymer was a benzene-soluble, non-flowing material; 100 parts by weight of the copolymer were ground with 0.5 parts by weight of ferric oxide, 40 parts by weight of silica obtained by combustion of volatile silicon compounds and 0.233 parts by weight of benzoyl peroxide. This product was heated in a press for 5 minutes at 125 ^0, whereby the following results were obtained: Durbmeterwert 46, tensile strength of 78.5 kg / cm ^2, elongation at break 685 ° / o, pressure loss of elasticity 50%. After 24 hours of curing at 240 ^0: 55 durometer, tensile strength 70 kg / cm ^2, elongation at break 605%, pressure loss of elasticity 14%.

Example 3

A benzene-soluble, non-flowing copolymer was obtained by copolymerizing the cyclic tetramers from dimethylsiloxane and

Example 4

0.14 mole percent cyclic tetramers made from allylmethylsiloxane. 100 parts by weight of the copolymer were ground with 40 parts by weight of silica obtained by incineration of volatile silicon compounds, 0.5 part by weight of ferric oxide and 0.233 part by weight of tertiary butyl perbenzoate. This vulcanizable composition was heated for 10 minutes at 150 ⁰ in a press, whereby the following results were obtained: 37 durometer, tensile strength 72.2 kg / cm ^2, elongation at break 520%, pressure loss of elasticity 47%. After 24 hours of curing at 250 ^0: 55 durometer, tensile strength 60.9 kg / cm ^2, elongation at break 320%, pressure loss of elasticity 15 ° / ".

A non-flowing, benzene-soluble copolymer was produced by copolymerizing the cyclic tetramers of 5 mol percent phenylmethylsiloxane, 94.86 mol percent dimethylsiloxane and 0.14 mol percent vinylphenylsiloxane. The copolymer was processed further as in Example 2. Elongation at break 51% 33 durometer, tensile strength 73.5 kg / cm ^2, 725%, Druckelastitätsverlust: a 5-minute cure at 125 ⁰ gave the following results. After curing for 24 hours at 250 °: durometer value 51, tensile strength 63.7 kg / cm ² , elongation at break 695%, loss of compressive elasticity 21%. iao

Example 5

A copolymer consisting of dimethylsiloxane and 0.14 mole percent vinylphenylsiloxane, was produced according to Example 1. A non-flowing, benzene-soluble product was obtained. 100 ge

Parts by weight of this copolymer were ground with 40 parts by weight of silica obtained by incineration of volatile silicon compounds and 0.5 part by weight of ferric oxide. The Mi-S research then came in a hot air oven where it was heated 1V2 hours to 200 ^0th After the mixture had cooled, it was ground with 0.233 parts by weight of benzoyl peroxide. Then, the vulcanizable composition was vulcanized by heating at 150 for 5 minutes ^0th The results were: Durometer value 40, tensile strength 100.8 kg / cm ² , elongation at break 545%, loss of compressive elasticity 38%. After 24 hours of heating at 250 ^0: 44 durometer, tensile strength 106.4 kg / cm ^2, elongation at break 480%, pressure loss of elasticity 5 ° / o.

A sample prepared from this mass was heated 70 hours at 150 ⁰ in accordance with ASTM test method; it was found that the

no pressure loss of elasticity substantially the same as was in the 22 hours heating auf'150 ^0th

Example 6

This example shows the difference between

as the properties of one of the inventive vulcanizable mass produced elastomers and one of the commercially available dimethylsiloxane elastomers.

The vulcanizable composition No. 1 was obtained by grinding 100 parts by weight of a benzene-soluble, non-flowing copolymer consisting of dimethylsiloxane and 0.14 mole percent vinylphenylsiloxane, with 35 parts by weight of silica obtained by combustion of volatile silicon compounds, 0.5 part by weight of ferric oxide and 0.233 parts by weight of benzoyl peroxide obtained from a uniform mixture. The product was first heated for 5 minutes at 125 ⁰ and for 24 hours at 250 ^0th Elastomer No. 1 was obtained.

The vulcanizable composition No. 2 was made by grinding benzene-soluble, non-flowing Dimethylpolysiloxane in the same way and with the same amounts of volatile by combustion Silicon compounds obtained from silicic acid, ferric oxide and benzoyl peroxide, as they are in used in the manufacture of vulcanizable composition No. 1.

The vulcanizable composition No. 3 contains the same components as No. 2, the only difference being that 1.5 parts by weight of benzoyl peroxide were used for vulcanization. Nos. 2 and 3 were heated for 5 minutes at 125 ⁰ and then for 24 hours at 250 ^0, it gave the elastomers Nos. 2 and 3.

The results are shown in Table II.

Elastomer Hardening Durometer
value tensile strenght
in kg / cm ^a Elongation at break Pressure elasticity
loss of power I. 5 minutes at 125 ⁰
24 hours at 250 ⁰ 46
50 87.1
64.3 920
780 • Φ00
-Φ Η 2 5 minutes at 125 ⁰
24 hours at 250 ⁰ 25th
35 5.6
4.4 900
215 IOO
100 3 5 minutes at 125 ⁰
24 hours at 250 ⁰ 44
61 82.9
55.5 975
420 95
64

The reduction in the elongation at break 140% after aging at the elastomer no. 1 versus 555 ⁰ / ° of the Dimethylelastomeren no. 3 is remarkable. In addition, the compression elasticity loss of elastomer No. 1 was only V2 to V ₃ compared to that of dimethylsiloxane elastomer No. 3.

Example 7

A copolymeric siloxane, the dimethylsiloxane and 0.14 mole percent vinylphenylsiloxane was prepared according to Example 1. The copolymer obtained was not soluble in benzene fluent and was further processed as follows:

100 parts by weight of copolymer, 40 parts by weight of silica obtained by burning volatile silicon compounds, 2 parts by weight of ferric oxide and 0.28 parts by weight of bis-2,4-dichlorobenzoyl peroxide were ground in a mill and 5 minutes at 112 ^° , then 24 hours

Table II

heated at 250 ^0. As a result, there was obtained an elastomer whose durometer value was 50, tensile strength 91.8 kg / cm ² , elongation at break 580% and the loss of compressive elasticity was 7%.

Example 8

A non-flowing, benzene-soluble polysiloxane containing dimethylsiloxane and 0.14 mole percent copolymerized vinylphenylsiloxane was ground in an amount of 100 parts by weight with 100 parts by weight of Ti O ₂ and 0.4 parts by weight of benzoyl peroxide.

A non-flowing, benzene-soluble dimethylpolysiloxane was ground in a mill with 100 parts by weight of TiO ₂ and 1.5 parts by weight of benzoyl peroxide.

Each of the two above-mentioned mixtures is first heated for 5 minutes on 125 ⁰ and then for 24 hours at 250 ^0th The physical properties of the resulting products can be seen from Table III.

Hardening Table III tensile strenght
in kg / cm ² Elongation at break
ia% Pressure elasticity
loss of power Siloxane 5 minutes at 125 ⁰
24 hours at 250 ⁰
5 minutes at 125 ⁰
24 hours at 250 ⁰ Durometer
value 21.8
31.2
l6, O
I8.3 770
355
240
130 66
19th
79
59 Mixed poly
merisat
Dimethyl
siloxane 23
27
37
42

Example 9

Three elastomers were made as follows:

(1) 100 parts by weight of the copolymeric SiIoxane of Example 8 with 90 parts by weight of diatomaceous earth and 0.4 parts by weight of benzoyl peroxide to marry.

(2) 100 parts by weight of the dimethylsiloxane of Example 8 were mixed with 90 parts by weight of diatomaceous earth and 1.5 parts by weight of benzoyl peroxide.

(3) Another 100 parts by weight of the same dimethylpolysiloxane were ground with 90 parts by weight of diatomaceous earth and 3 parts by weight of benzoyl peroxide.

Each of the three samples was heated in a press for 5 minutes at 125 ⁰ and then for 24 hours at. The properties of the elastomers produced from these vulcanizable compositions are shown in Table IV.

Table IV

Siloxane Hardening Durometer
value tensile strenght
in kg / cm ² Elongation at break
ia ° / o Pressure elasticity
loss of power I. 5 minutes at 125 ' ⁰
24 hours at 250 ⁰ 56
70 21.5
48.0 240
190 41
25th 2 5 minutes at 125 ⁰
24 hours at 250 ⁰ Vt Ol
O OJ 24.0
44.1 H OJ
Oi (O
Oi O 100
92 3 5 minutes at 125 ⁰
24 hours at 250 ⁰ 56
74 27.1
50.0 25O
I3O 100
90

Claims (4)

Patent claims: i. Organopolysiloxane mass vulcanizable by heat, characterized by a content of (1} an organosiloxane copolymer whose viscosity at 25 ^{0 is} at least ι 000,000 cSt and which consists essentially of 99.5 to 99.982 mol percent of siloxane units of the formula R ₂ Si O, whereR is a Represents methyl or phenyl radicals and at least 50% of the R groups should be methyl radicals, and 0.018 to 0.5 mol percent of siloxane units of the formula R'R "is composed of SiO, where R 'is an alkenyl radical with 2 to 6 carbon atoms and R" represent an alkenyl radical with 2 to 6 carbon atoms or a methyl or phenyl radical, by a content of (2) 0.075 ° i ^s ° A weight percent, based on the weight of the copolymer of an aromatic acyl peroxide, and (3) optionally by a content on a filler, for example a silica filler, in one Amount from 10 to 100 parts by weight per 100 parts by weight of the copolymer. 2. Heat vulcanizable organopolysiloxane composition according to claim 1, characterized in that the aromatic acyl peroxide Benzoyl peroxide, its halogenated derivative or tertiary butyl perbenzoate. 3. Heat vulcanizable organopolysiloxane composition according to claim 1, characterized in that the 0.018 to 0.5 mole percent Siloxane units of the formula R'R "SiO from vinylmethyl and vinylphenylsiloxane units exist. 4. Heat-vulcanizable organopolysiloxane composition according to claim 1, characterized in that the siloxane of the formula R ₂ Si O is dimethylsiloxane. Considered publications:
"Industrial and Engineering Chemistry", 40 (1948), pp. 2078 and 2079.