WO1990009411A2

WO1990009411A2 - Modification of addition-crosslinkable silicon elastomers with block copolymerizates containing polysiloxane segments

Info

Publication number: WO1990009411A2
Application number: PCT/EP1990/000257
Authority: WO
Inventors: Herbert Eck; Gerald Fleischmann; Alfred Prasse
Original assignee: Wacker-Chemie Gmbh
Priority date: 1989-02-17
Filing date: 1990-02-16
Publication date: 1990-08-23
Also published as: DE3904939A1; WO1990009411A3

Abstract

The mechanical properties of addition-crosslinkable silicon elastomers are improved by diluting them with block copolymerizates of type AB, ABA or BAB consisting of organopolymer segments A and polysiloxane sections B or with mixtures of such block copolymers and organopolymers. The mixtures contain 30 to 99 wt.% of addition-crosslinkable silicon elastomer, 1 to 70 wt.% of block copolymer and 0 to 55 wt.% of organic homo- or copolymer. The mixtures are used mainly as embedding materials, impression materials or for moulding materials. Another field of application is the manufacture of solvent-free coating materials.

Description

Modification of addition-crosslinkable silicone elastomers with block copolymers containing duck polysiloxane

The invention relates to the modification of addition-crosslinkable silicone elastomers with block copolymers, consisting of polysiloxane segments and organopolymer sections, or with mixtures of such block copolymers and organopolymers.

A large number of attempts are known from the patent literature to produce homogeneous mixtures of silicone elastomers and organopolymers. This is based on the effort to develop compositions which have the advantageous properties of both polymer groups in combination. On the one hand, such polymer compositions should combine the surface properties (release properties), weather resistance, water repellency and antistatic properties of silicone polymers, and on the other hand the superior mechanical properties (hardness, tensile strength) of thermoplastic polymers.

A simple mixing of both polymer components, as described in DE-A 29 49 000 (US Pat. No. 4,252,915) using the example of a mixture of ethylene-vinyl acetate copolymer and polydiorganosiloxane, is problematic because of the intolerance of the polymers there is a tendency for the polymer phases to separate. DE-A 24 05 828 (US-A 4,032,499) describes a procedure in which the polymerization of the organopoly phase occurs in the silicone matrix, the organomonomers being partially grafted onto the organopolysiloxanes. The advantageous properties of the masses produced in this way are explained above all by the rod shape of the organocopolyer and by the partial grafting onto the silicone matrix. Since the rods convert into spherical particles at elevated temperature, which results in a permanent decrease in the mechanical properties, these products are in need of improvement.

Another possibility for the production of silicone organopolymer compositions is the production of so-called semi-IPNs (semi-interpenetrated networks = stable mixture of two plastics which are not connected to one another, one of which is cross-linked) analogously to DE-A 3314355 (US -A 4500688). For this purpose, the melt of the organic thermoplastic is mixed with the still liquid silicone. In this state, the silicone component is crosslinked, an irreversible interlacing of the uncrosslinked organic and the crosslinked silicone polymer taking place.

DE-A 21 42 597 (US-A 3,686,356) relates to a process for modifying vinyl thermoplastic with polyorganosiloxanes, with up to 50% of a graft or block copolymer of vinyl and siloxane units being added to obtain a homogeneous mixture. In order to ensure the miscibility of the polyorganosiloxane with the other two components, it is taught to use only moderately crosslinkable polyorganosiloxanes, since crosslinked polyorganosiloxanes are immiscible. In contrast, the task of the present invention was to modify addition-crosslinkable silicone rubber compositions in such a way that their mechanical properties are improved. This has been achieved, especially in the light of DE-A 21 42 597, surprisingly by adding block copolymers of polysiloxane and organopolymer segments, optionally additionally thermoplastic organopolymers, to the addition-crosslinkable organopolysiloxanes.

The invention relates to a process for modifying addition-crosslinkable silicone elastomers by mixing with block copolymers containing polysiloxane segments, characterized in that the mixture contains the following components:

(I) 30-99% by weight of addition-crosslinkable silicone rubber,

(II) 1-70% by weight of a block copolymer of the AB, ABA or BAB type, where A stands for a homo- or copolymeric organic radical and B for a mono- or divalent polysiloxane segment which is well compatible with component I,

(III) 0-55% by weight of an organic homo- or copolymer,

where the percentages add up to 100%.

Component (I) of the mixture, the addition-crosslinkable silicone rubber, is composed of 2 components (a) and (b) which, when mixed in the presence of a catalyst component, form the addition-crosslinked silicone elastomer. Component (a) is a diorganopolysiloxane, each with a triorganosiloxane unit having at least one vinyl group as the terminal group, which can preferably be described using the following general formula:

(CH ₂ = CH) ₁ _3SiRo-2θ (R ₂ SiO) _x SiR ₀ _2 (CH = CH2) ι-3 (a)

The radicals R are preferably monovalent, unbranched or branched, optionally substituted hydrocarbon radicals free of aliphatic multiple bonds. The radicals R in the above formula can have the same or different meanings within the scope of the definition just given. Examples of radicals R are: methyl, ethyl, propyl, butyl, hexyl, octyl, dodecyl, phenyl and trifluoropropyl. Preferably at least 50% of the radicals R are methyl groups. x has values such that the viscosity of the diorganopolysiloxane units is between 10 and 10 ⁶ cP, preferably between 500 and 10 ⁶ cP, at 25 ° C.

Component (b) is an organopolysiloxane of the general formula:

R ₂ R'SiO (SiRR ^, 0) _y SiR ₂ R '(b)

where R 'is H or R, R has the meaning given above, and each molecule has at least 3 Si-H functions. The number y is chosen so that the viscosity of the organopolysiloxane units 5-10 ⁵ cP, preferred wise 25-25000 cps at 25 C ^β.

To produce the addition-crosslinked silicone rubber compositions, components (a) and (b) are mixed in such a ratio that the molar ratio of the Si-H units of component (b) to the SiCH = CH2 units of the component (a) is at least 1. Preferably choose one Ratio of 1: 1 to 1: 3, the range 1: 1 to 1: 2 is particularly preferred.

The catalysts described for this in the literature can be used as catalysts for the addition crosslinking, that is to say the addition of the SiH groups of component (b) to the vinyl groups of component (a). Examples include: platinum on supports such as SiO ₂ or activated carbon; Platinum compounds such as platinum (IV) chloric acid; Platinum complexes of platinum (IV) chloric acid with other organic, including organosilicon, or inorganic compounds, for example ketones or 1,3-divinyltetramethyldisiloxane ^" ; cobalt or manganese carbonyls; and rhodium compounds.

Xu- The catalysts are used in an amount of 0.5-500 ppm, preferably 1-100 ppm, based on the total weight of the elastomer composition to be crosslinked. The catalyst is preferably admixed with component (a).

In the mixture according to the invention, component (I), the addition-crosslinked silicone elastomer to be modified, is used in an amount of 30 to 99% by weight, preferably 50 to 98% by weight, based on the total weight of the mixture.

Component (II) to be used according to the invention is a block copolymer of the AB, ABA or BAB type.

The organopolymer segment A stands for organic homo- or copolymers. The homopolymers are preferably composed of the following monomers: methacrylic acid esters, acrylic acid esters, vinyl esters, such as vinyl acetate, vinyl chloride, styrene or other substituted vinylbenzenes, methacrylonitrile, acrylonitrile, methacrylamide, acrylamide, N-vinylamides, such as, for example, N-methylvinylacetamide, N-vinylpyrrolidone or Maleic acid ester. Copolymers with the above monomer units can also contain, as co onomer units, ethylene, propylene and compounds which contain an allyl function, such as, for example, allyl chloride, allyl bromide, allyl esters, trimethylallylsilane, trialkoxy- ( _7- oxypropyl (meth) acrylic acid ester) silane.

The average molecular weight of A is between 500 and five million, preferably between 1000 and 100000.

The polysiloxane segments B are mono- or bivalent polysiloxanes with an average molecular weight of 500 to 10 ⁶ , preferably 1000 to 100000, which are well compatible with component (I). The polysiloxane units B preferably correspond to the general formula:

X- (SiR ₂ 0) _y -SiR ₂ -X

where R stands for preferably monovalent, unbranched or branched, optionally substituted, hydrocarbon radicals free of aliphatic single bonds. The radicals R in the above formula can have the same or different meanings, y is chosen so that the average molecular weight of the polysiloxane units B is in the range described above. X is the link to the organopolymer blocks A, where an X, in the case of the block copolymers AB or BAB, can have the same meaning as R. X preferably has the meaning -O-, -NR-, -s- or is a divalent, unbranched or branched, optionally substituted hydrocarbon radical free of aliphatic multiple bonds, which is connected to block A via 0, S, NR.

The block copolymer can be prepared, for example, by anionic polymerization of the organic monomer and subsequent reaction with a suitable mono- or difunctional siloxane as a proton donor. Such a procedure is described in DE-A 19 15 789.

Such block copolymers are also accessible by radical polymerization of the organic block in the presence of mercaptoethanol or mercaptoacetic acid and subsequent reaction of the prepolymer with ter inal, with amino or carboxy groups, mono- or bis-substituted polysiloxanes (DE- A 36 06 983, DE-A 36 06 984).

The reaction of siloxane, which carries a terminal alkenyl group, with vinyl monomer gives an organopolymer with a terminal alkenyl-substituted siloxane unit. By further reaction of this intermediate compound with a polysiloxane with one or two SiH end groups, in the presence of a transition metal catalyst, block copolymers with organopolymer and polysiloxane segments are also accessible.

Production by the process of DE-A 38 28 862 is particularly advantageous. In a first process step, trialkylsilylacetic acid alkenyl ester is added to a polyorgano-H-siloxane in the presence of a transition metal in the presence of an aprotic solvent and with the exclusion of moisture -Catalyst of the 8th subgroup of the PSE, added. In a second process stage, the organic monomer, which must have a nitrile or carbonyl group in the a-position to the C = C double bond, is then polymerized on in accordance with the principle of group transfer polymerization, in the presence of nucleophilic or electrophilic catalysts . Component (II), the block copolymer of the AB, ABA or BAB type, is used in the mixture according to the invention in an amount of 1 to 70% by weight, preferably 2 to 50% by weight, based on the total weight of the mixture . The amount to be used depends on the application properties of the silicone elastomer to be modified (component (I)).

If it appears advantageous for technical reasons, organic homopolymers and copolymers (component (III)), insofar as they are compatible with the organopolymer segments of the block copolymer, can be added to the mixture consisting of component (I) and component (II ), incorporated homogeneously.

Suitable polymers are homo- and copolymers of the following monomers:

Methacrylic acid esters, acrylic acid esters, vinyl esters, such as vinyl acetate, vinyl chloride, styrene and substituted vinyl benzenes, methacrylonitrile, acrylonitrile, methacrylamides, acrylamides, vinyl la ide, such as N-methylvinylacetamide, N-vinylpyrrolidone, ethylene, propylene, allyl chloride, allyl bromide, allyl bromide, allyl bromide,

The average molecular weight of these organopolymers should preferably be more than 10,000, in particular up to 10 ⁷ .

Component (III) can be added in an amount of preferably 0 to 55% by weight, based on the total weight of the mixture.

The mixing of the individual components, as well as the additives to be added to the mixture according to the invention, is carried out, depending on their consistency, in appropriate mixing units such as stirred kettles, kneaders or extruders. If all components are liquid at room temperature or if you work with solvents, the mixture is prepared in stirred tanks. Otherwise you work in the melt, for example in extruders, plasticizers and similar devices.

In general, the procedure is such that the block copolymer (II), if appropriate together with the organopolymer (III), is initially taken to prepare the mixture. Then the a component of the silicone elastomer (I) is mixed in together with the hydrosilylation catalyst and finally the b component. Of (I) is incorporated.

In a preferred embodiment, the desired amount of component (II), the block copolymer, optionally together with the organopolymer (component (III)), is first diluted or dissolved in a solvent to prepare the mixture. The a component of the silicone elastomer (component I) is then stirred into this solution together with the catalyst. After admixing the b component of the silicone elastomer, the solvent is removed in vacuo.

The addition-crosslinking silicone elastomers to be modified can optionally also contain additives to improve their property profile or to improve processability.

The physical properties of the rubbers are influenced, for example, by the addition of diorganopolysiloxanes of the following formula:

R ₂ HSiO (SiR ₂ 0) ₂ ; SiR2CH = CH ₂ where the radicals R have the meanings already mentioned, that is to say preferably monovalent, unbranched or branched, optionally substituted hydrocarbon radicals free from aliphatic multiple bonds, z has a value such that the viscosity at 25 ° C. is 50 to 10000 cP, preferably 300 to 5000 cP.

Suitable reinforcing fillers are, for example, silica, hydrophobized silica, chalk, hydrophobized chalk or activated carbon. The reinforcing fillers should have a specific surface area of> 30 m ² / g, preferably> 50 m ² / g.

In addition to the additives just mentioned, other substances can also be used which have hitherto also been used in the production of compositions which can be crosslinked to form elastic structures, based on organopolysiloxanes containing vinyl groups, at least three Si-bonded hydrogen atoms per molecule and organopolysiloxanes and the addition of Si bound hydrogen on catalysts promoting vinyl groups, could also be used.

Examples include fillers with a surface area of less than 30 m ² / g, such as calcium carbonate, quartz powder or diatomaceous earth.

Pigments, such as iron oxide red, or soluble dyes can be added.

Suitable plasticizers are organopolysiloxanes which contain no aliphatic multiple bonds or Si-bonded hydrogen; such as dimethylpolysiloxanes that are endblocked at room temperature by trimethylsiloxy groups.

Common additives are agents to improve the adhesion processing of the elastomers on substrates on which they were produced; for example glycidyloxypropyltrialkoxysilane, tetramethyltetra (glycidyloxypropyl) cyclotetrasiloxane or methacryloxypropyltrialkoxysilane.

Resin-like organopolysiloxanes can also be added. These compounds are copolymers of Si0 _4/2 -., (CH ₃₎ ₃ Si0 _1/2 and (CH ₃₎ ₂ (CH ₂ = CH) Si0 _1/2 units, 5.1 to 5.3% by weight of the vinyl groups and a total of 0.6 to 1.0 jy2 SiO "units per SiO contain ₄ / ~ unit (CH ₃₎ ₃ Si0 _1/2 and _(CH3) ₂ (CH2 = CH).

Common additives are also retarding agents such as benzotriazole and open-chain diorganopolysiloxanes with vinyl units arranged within the chain. Such additives are described in US-A 3,699,073.

These additives just described can be mixed with the components I to III in any order. They are preferably only added when components (I) to (III) are homogeneously mixed.

The mixtures claimed here make it possible to specifically modify the material properties of addition-crosslinked silicone elastomers by admixing block copolymers from silicone and organopolymer segments. The combination according to the invention of addition-crosslinked silicone elastomers and silicone-organopolymer block copolymers also enables the production of homogeneous mixtures of addition-crosslinked silicone elastomer and organic polymers.

With the mixtures according to the invention, one obtains Foxmmasseπ, in terms of their material properties, specifically in terms of their mechanical strength, elasticity, hardness, permeability to gases and liquids, pure silicone elastomer molding compositions are superior.

Examples of applications for the mixtures according to the invention are:

The use as casting or embedding compounds for sealing electronic components. The production of impression or impression materials, as well as the production of moldings.

The use as an insulating agent or as a solvent-free coating for fabrics of all kinds.

The following examples serve to further explain the invention.

Example 1:

A) Preparation of the block copolymer

a, ω-bis (3-trimethylsilyl acetoxypropyl) poly dimethyl siloxane

100 g of polydimethylsiloxane having 1 H atom in the terminal units and having an average molecular weight of 15,000, dissolved in 100 ml of anhydrous toluene, were treated with 0.345 g (2 mol) of trimethylsilyl acetic acid allyl ester and 1 mg of platinum in the form of a Pt complex compound ((acac-C7H ₈₎ Pt (acac)), wherein acac represents the acetylacetonate, and the mixture heated for 5 hours at 80 ° C and then the solvent at 80 ^β C and 100 Pa was stripped then excess trimethylsilyl acetic acid allyl ester was removed at 80 ° C. under 0.1 Pa. Poly (dimethylsiloxane-g- (tert-butyl acrylate-co-undecenyl acrylate))

The polydimethylsiloxane modified with the trimethylsilylacetoxypropyl groups was added at 40 ° C. to 90 g (702 mmol) of tert-butyl acrylate, 10 g (45 mmol) of undecenyl acrylate and 0.25 mmol (1 ml of a 0.25 M solution in tetrahydrofuran) tetrabutylammonium fluoride. An exothermic reaction occurred after a few minutes. The mixture was heated to 60 ° C. for 5 hours, a viscous, white block copolymer being formed. The product was purified by removing volatile impurities in a high vacuum. The yield of block copolymer was quantitative.

B) Preparation of the mixture with the silicone elastomer

RTV-ME 625, an addition-crosslinking silicone rubber from Wacker-Chemie GmbH, was used as the silicone elastomer to produce the mixture. The A component of this silicone rubber is a CH ₂ = CHSi (CH ₃₎ 2 ~ endgestoppertes polydimethylsiloxane (having an average molecular weight of 88000), the b-component, a co-condensate of whore ^* thyldi- alkoxysilane and Methyldialkoxy-H-silane (having a average molecular weight of 37,000). Component a is the Pt catalyst (platinum-l, 3-divinyl-l, l, 3,3-tetramethyl-disiloxane complex) in an amount of 20 ppm Pt, based on the total weight of the elastomer composition.

6 g of the block copolymer were placed in 7 ml of toluene and 54 g of the a component were stirred in at 1800 rpm using a propeller stirrer, then 6 g of the b component were stirred in and the solvent was removed in vacuo. C) testing

For testing, the mixture was poured into a film. For this purpose, the mixture was poured into a cleaned PE mold greased with petroleum jelly and evacuated. After heating to 70 ° C. for 20 minutes, the mold was removed from the mold and baked at 70 ° C. for a further 20 hours.

The tensile strength was determined in accordance with DIN 53504-S3A, the elongation at break in accordance with DIN 53504-S3A, the tear propagation resistance in accordance with ASTM D624 (Form B) and the hardness Shore A in accordance with DIN 53505.

The composition of the block copolymer, the composition of the mixture and the results of the testing of the mechanical properties are shown in Table 1.

Example 2:

The block copolymer was prepared analogously to Example 1, with the difference that 90 g of methyl methacrylate and 10 g of allyl methacrylate were used as organic monomers.

The preparation of the mixture with the silicone elastomer and the testing were carried out analogously to Example 1.

Example 3:

A) Preparation of the block copolymer

Preparation of an allyloxy group-terminated polyethylene acrylate:

To a solution of 1.3 g (10 mmol) of allyloxytrimethylsiloxane in 150 ml of dry tert-butyl methyl ether, 2 ml of a 0.25 M solution of tetra-n-butylammonium fluoride in THF. was added and metered in with stirring and cooling 75 ml (690 mmol) acrylic acid ethyl ester, that the reaction temperature does not exceed 50 C ^β. After completion of the addition is allowed to react for a further 4 hours, then removed the Lösungs¬ medium in a vacuum and then the product is dried at 80 ^β C and 0.1 Pa. The yield is 67.6 g (98%) viscous powder with an average molecular weight of 7000.

Preparation of the silicone-acrylate block copolymer: 50 g of the polymer obtained are dissolved in 100 ml of dry toluene and 0.5 mg of platinum in the form of a Pt complex compound ((acac-C ₇ Hs) Pt (acac)), in which acac is the acetylace - Tonatrest means, admitted. After the solution has been heated to 80 ° C., 47 g of a polydimethylsiloxane (average molecular weight 15,000) with SiH end groups are added dropwise with vigorous stirring within 3 hours. After a 4-hour after-reaction and evaporation of the solvent, a viscous, uniform, viscous silicone-ethyl acrylate block copolymer was obtained.

The preparation of the mixture with the silicone elastomer RTV-ME 625 and the testing of the mechanical properties was carried out analogously to Example 1. The composition of the mixture and the test results are listed in Table 1.

Example 4:

The block copolymer was produced analogously to Example 1.

The block copolymer (component II) was also admixed to the silicone elastomer (component I) analogously Example 1, with the difference that, in addition to the block copolymer, 12 g of poly (butyl methacrylate-co-methacrylic ester) 13.0 ^R (from Roehm GmbH), = 15% by weight, based on the total weight of the mixture, as component III were submitted.

The composition of the mixture and the test results are shown in Table 1.

Example 5:

The procedure was analogous to Example 4, except that instead of 15% by weight of component III, only 8% by weight was used.

Comparative Example 1:

Analogously to the procedure in Example 1, a film was cast which consisted only of addition-crosslinked silicone elastomer RTV-ME 625. The tensile strength, elongation at break, tear propagation resistance and Shore A hardness were determined with this film analogously to Example 1. The results are shown in Table 1.

TABLE 1 :

Addition of 15% by weight of poly (butyl methacrylate-co-methacrylic ester)

** = addition of 8% by weight of poly (butyl methacrylate-co-methacrylic ester)

Claims

1. A process for modifying addition-crosslinkable silicone elastomers by mixing with block copolymers containing polysiloxane segments, characterized in that the mixture contains the following components:

(I) 30-99% by weight of an addition-crosslinkable silicone elastomer,

(II) 1-70% by weight of a block copolymer of the AB, ABA or BAB type, where A is a homo- or copolymeric organic radical and B is a mono- or divalent polysiloxane segment,

(III) 0-55% by weight of an organic homopolymer or copolymer,

where the percentages add up to 100%.

2. The method according to claim 1, characterized in that

(I) is composed of a component (a) with the general formula:

(CH ₂ = CH) _1- -. ₃ SiRo-2θ (R2SiO) _x SiR ₀ -2 (CH = CH ₂ ) ι- ₃ where the radicals R are monovalent, unbranched or branched hydrocarbon radicals free of aliphatic multiple bonds, the radicals R can be the same or different, and x has values such that the viscosity of (a) is between 10 and 10 ⁶ cP, and a component (b) with the general formula: R2R ^, SiO (SiRR-O) ySiR ₂ R where R 'is H or R, R has the meaning given above, each molecule has at least 3 SiH functions and y has values such that the viscosity is between 5 and 10 ⁵ cP, and

(II) is composed of organopolymer segments A, consisting of simply ethylenically unsaturated monomer units _/ with a molecular weight between 500 and five million, and polysiloxane segments B of the general formula: X- (SiR ₂ 0) _y -SiR ₂ -X where the radicals R have the abovementioned meaning and can be the same or different, an X in the case of the block copolymers AB or BAB can have the same meaning as R, or X has the meaning -O-, -NR-, -S- or is a divalent, unbranched or branched, optionally substituted, hydrocarbon radical free from aliphatic multiple bonds, which is connected to block A via O, S, or NR and y is selected such that the average molecular weight of B is between 500 and 10 is ⁶ , and

(III) is an organic homo- or copolymer of mono-ethylenically unsaturated monomers.

3. The method according to claim 1 or 2, characterized gekennzeich¬ net that the block copolymer (II) is presented for the preparation of the mixture, then the a component of the silicone elastomer (I) is added together with the hydrosilylation catalyst and only after that the b component of (I) is admixed.

Process according to Claim 1, 2 or 3, characterized in that component (III) is initially introduced together with the block copolymer (II).

Process according to Claim 1, 2, 3 or 4, characterized in that additives to be incorporated into the mixture are only incorporated after components (I) to (III) have been mixed in.

Use of mixtures according to claims 1 to 5 for the production of casting or embedding compounds.

7. Use of mixtures according to claims 1 to 5 for the production of molding compositions, impression, or Abformmas¬ sen.

8. Use of mixtures according to claims 1 to 5 for the production of solvent-free coating compositions.