JP2022154044A - Organopolysiloxane prepolymer and cured body thereof - Google Patents

Abstract

To provide a condensation type organopolysiloxane prepolymer capable of obtaining an elastic material which is soft and well extendible and has a high elasticity recovery rate and to provide a cured body of the same.SOLUTION: There is provided a condensation type organopolysiloxane prepolymer which is prepared by condensation reaction of the following (A) with the following (B) in an amount more than 1 mol based on 1 mol of the following (A). (A) A polydimethlsiloxane having silanol groups at both terminals, which has a molecular weight of 30000 or more and a molecular weight distribution index (Mw/Mn; Mw is a weight average molecular weight and Mn is a number average molecular weight) of 1.3 or more. (B) An oligomer of tetraalkoxysilane and/or a product of a complete or partial hydrolysis and a condensate of the oligomer.SELECTED DRAWING: None

Description

The present invention relates generally to organopolysiloxane prepolymers and cured bodies thereof.

Cured bodies of organosiloxane compositions are known to have poor hysteresis characteristics. For example, Japanese Patent Application Laid-Open No. 9-328615 (Patent Document 1) discloses a curable organosiloxane composition having an improved hysteresis characteristic, which has a viscosity of 20 to 200 Pa s at 25° C. Diorganovinylsiloxy-terminated polydiorganosiloxanes containing no terminal silicon-bonded ethylenically unsaturated hydrocarbon groups; viscosity at 25° C. of 0.1-200 Pa·s and 1-5% of the non-terminal repeat units of the siloxane. diorganovinylsiloxy-terminated polydiorganosiloxane having vinyl groups; 10-30 wt% reinforcing silica filler treated with hexamethyldisilazane and 1,1,3,3-tetramethyl-1,3-divinyldisilazane compositions containing organohydrogensiloxa crosslinkers having at least 10 silicon-bonded hydrogen atoms per molecule are proposed;

In addition, Japanese Patent Application Laid-Open No. 2011-241401 (Patent Document 2) proposes an elastic material having an organic bond as a main skeleton for the purpose of improving "settling".

JP-A-9-328615 Japanese Unexamined Patent Application Publication No. 2011-241401

However, although the cured body of the curable organosiloxane composition described in Patent Document 1 contains silica fine particles for the purpose of improving hysteresis, it is difficult to apply when producing a conductive coating film, and hysteresis is reduced. The improvement is not sufficient for applications such as sensors.

In addition, if organic bonds are used as the main skeleton as described in Patent Literature 2, it can be made soft, but the heat resistance and weather resistance are inferior due to the low bond energy. Moreover, the hysteresis loss of the elastic material disclosed in Patent Document 2 exceeds 10%, which is not sufficient. This is because the organic bond energy is low, and the bonds are often broken by external stress, and it is difficult to sufficiently improve "settling".

In general, elastic materials with low hardness, high elongation, and low elastic modulus are weak against repeated deformation and are easily distorted.

Accordingly, an object of the present invention is to provide a condensed organopolysiloxane prepolymer capable of obtaining an elastic material that is soft, stretches well, and has a high elastic recovery rate and that can be cured for use in precision actuators and sensors. It is to provide the body.

The condensation-type organopolysiloxane prepolymer according to the present invention is prepared by condensation reaction of (A) below and (B) below in an amount of more than 1 mol per 1 mol of (A) below. is.
(A) Polydimethylsiloxane having silanol groups at both ends, having a molecular weight (Mn) of 30,000 or more, and having a molecular weight distribution index (Mw/Mn; Mw is the weight average molecular weight and Mn is the number average molecular weight) 1.3 or more.
(B) Oligomers of tetraalkoxysilanes and/or complete or partial hydrolysates or condensates of said oligomers.

In the condensed organopolysiloxane prepolymer according to the present invention, (A) preferably has a number average molecular weight (Mn) of 70,000 or less.

In the condensed organopolysiloxane prepolymer according to the present invention, (B) preferably has a linear tetramer to decamer and has a methoxy group or an ethoxy group as an alkoxy group.

In the condensed organopolysiloxane prepolymer according to the present invention, (B) is preferably blended in an amount of more than 1 mol and not more than 2 mol per 1 mol of (A). In other words,

An electrode material according to the present invention contains any of the condensed organopolysiloxane prepolymers described above.

An insulating material according to the present invention comprises any of the condensed organopolysiloxane prepolymers described above.

A cured product according to the present invention is a cured product of any one of the condensation-type organopolysiloxane prepolymers described above.

A cured product according to the present invention is a cured product obtained by curing any of the condensation-type organopolysiloxane prepolymers described above and a curing agent, wherein the amount of alkoxy groups in the curing agent is It is preferably not more than 10% by weight of the total ethylsilicate amount of the polymer and hardener.

The cured body according to the present invention preferably has an elastic modulus of 1.5 MPa·s or less, an elongation of 200% or more, and an elastic recovery of 90% or more.

As described above, according to the present invention, it is possible to provide a condensed organopolysiloxane prepolymer and a cured product thereof, which can be used to obtain an elastic material that is soft, stretches well, and has a high elastic recovery rate. The condensed organopolysiloxane prepolymer obtained in the present invention has a helical structure of inorganic bonds as a skeleton, and has extremely few cross-linking points to achieve both mechanical resistance and flexibility, resulting in an elastic body with high restoring force. Obtainable.

The condensed organopolysiloxane prepolymer according to the present invention is described in detail below.

<Polydimethylsiloxane (A) having silanol groups at both ends>
The condensation-type organopolysiloxane prepolymer of the present invention uses polydimethylsiloxane (PDMS) having reactive silanol groups at both ends as one raw material. Various raw materials are conceivable, such as those having silanol groups at both ends and branched molecular chains, those having a plurality of silanol groups at the ends, and those having other reactive functional groups. The chemical formula of (A) is shown in (1).
H—(O—Si(CH ₃ ) ₂ ) _m —OH (1)

The silanol-terminated polydimethylsiloxane is preferably linear and has a number average molecular weight (Mn) of 30,000 or more and preferably 70,000 or less. m in (1) is preferably an integer that satisfies the above molecular weight. Mw/Mn is 1.3 or more, preferably 1.5 or more.

When the number average molecular weight is less than 30,000, the cured organopolysiloxane obtained by curing the synthesized condensed organopolysiloxane prepolymer becomes hard. On the other hand, if the number average molecular weight exceeds 70,000, the reaction becomes very difficult. Therefore, the number average molecular weight of PDMS having a terminal silanol group as a raw material is 30,000 or more, preferably 70,000 or less, more preferably 60,000 or less, and 55,000 or less. is more preferred.

The molecular weight distribution index Mw/Mn is 1.3 or more, preferably 1.5 or more. It is generally difficult to narrow the molecular weight of the silicone raw material due to the influence of variations in temperature distribution depending on the size of the reactor when polymerization proceeds. General-purpose silicones generally have a molecular weight of 1.3 or more, and those with a high molecular weight have a molecular weight of 1.5 or more. PDMS having a molecular weight distribution index Mw/Mn of less than 1.3 due to living polymerization or the like is also commercially available, but in the present invention, PDMS having such a narrow molecular weight distribution has a low elastic recovery rate.

If the Mw/Mn is small, the transparency and homogeneity to light will be good, and the curing reaction will be completed quickly. From the viewpoint of resistance in the UV region, it is preferably 1.5 or more. On the contrary, if the Mw/Mn is large, the transparency will be significantly deteriorated, so the Mw/Mn is preferably 3.0 or less, more preferably 2.5 or less.

<Oligomer of tetraalkoxysilane and/or complete or partial hydrolyzate or condensate of this oligomer (B)>
Silane oligomers having an alkoxy group are generally known compounds such as methyl silicate and ethyl silicate, and can be easily obtained. The general structural formula of the oligomer, alkylsilicate, is as follows.
RO—(Si(OR) ₂ —O) _n —R (2)

Here, R is a methyl group or an ethyl group. In the case of a methyl group, although the reaction proceeds rapidly, methanol may be generated as a by-product, so it is desirable to use an ethyl group. Preferably, n is 4 to 10 (tetramer to decamer). When n exceeds 10 (10-mer), the reactivity with PDMS is reduced, and synthesis may require a high temperature and a long time. If n is less than 4 (tetramer), the polycondensation of the alkyl silicate alone may proceed to form cluster particles, which may lead to a decrease in light transmittance. From the viewpoint of reactivity due to steric hindrance, the oligomer (B) is preferably linear.

As will be described later, in the condensed organopolysiloxane prepolymer of the present invention, a tetraalkoxysilane oligomer and/or a complete or partial hydrolyzate or condensate of this oligomer (B) has silanol groups at both ends. is used in an amount equal to or less than the polydimethylsiloxane (A) having

<Organometallic compound (C)>
For the preparation of the condensed organopolysiloxane prepolymer of the present invention, it is preferable to proceed with the synthesis using an organometallic compound as a condensation catalyst. There are no restrictions on the condensation catalyst, but Sn-based catalysts, which are the easiest to use and can be added in a low amount, are effective. Metal-based catalysts include Ti-based, Al-based, Zn-based, Zr-based, Bi-based, and other organometallic compounds other than Sn-based catalysts, but they have low reactivity, reduced heat resistance of the cured product when it remains, and coloration. Sn-based catalysts can be used most effectively because problems such as

As the Sn-based catalyst, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin bisacetylacetonate and the like are generally used. Depending on the synthesis conditions, the Sn-based catalyst can promote an effective condensation reaction even in a small amount, and the blending amount can be suppressed to 500 ppm or less relative to the solid content.

<Measurement of average molecular weight>
The average molecular weight of PDMS (A) was measured by gel permeation chromatography (GPC), and the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) was defined as the molecular weight distribution index. Using polystyrene as a standard sample, polystyrene equivalent molecular weight was measured. The polystyrene equivalent molecular weight measurement by the GPC method shall be performed under the following measurement conditions.
a) Measuring equipment: Tosoh GPC HLC-8320PC
b) Columns with Mn of 30,000 or less: TSKgel guard Column Super HZ-H, TSKgel Super HZM-H × 2 c) Columns with Mn of 30,000 or more: TSKgel guard Column Super MP (HZ)-N, TSKgel Multipore HZ-N × 3 Book d) Oven temperature: 40°C
e) Eluent: Tetrahydrofuran (THF) 1.0 mL/min
f) standard sample: polystyrene g) injection volume: 100 μL
h) Concentration: 0.05g/10mL
i) Sample preparation: THF to which 0.2% by mass of 2,6-di-tert-butyl-p-phenol (BHT) has been added is used as a solvent and stirred at room temperature to dissolve.
j) Correction: Molecular weight calculation is performed by correcting the deviation of the BHT peak between calibration curve measurement and sample measurement.

<Preparation of condensed organopolysiloxane prepolymer>
In preparing the condensed organopolysiloxane prepolymer of the present invention, the condensed organopolysiloxane prepolymer is preferably synthesized in the presence of the organometallic compound (C).

A polydimethylsiloxane (A) having silanol groups at both ends and a silane oligomer (B) having an alkoxy group are prepared by mixing 1 mol of polydimethylsiloxane (A) in which the silane oligomer (B) having an alkoxy group has a silanol group at both ends. In formulations where the molar ratio is adjusted to be greater than 1 mol per mol, heating causes a condensation reaction by dealcoholization (or dehydration with a complete or partial hydrolyzate of (B)). This reaction is controlled in several hours to several tens of hours to form a condensed organopolysiloxane prepolymer. For the synthesis, a reaction vessel (flask with multiple insertion ports) equipped with a stirrer, thermometer, and dropping line is used. If the stirring device has the effect of homogeneously mixing high-viscosity liquid raw materials that contribute to the reaction, such as a rotary stirrer with stirring blades, a magnetic stirrer, a twin-screw planetary stirring device, and an ultrasonic cleaning device, it is particularly limited. no. However, a rotary stirrer, magnetic stirrer, or the like is desirable because it is associated with temperature control, atmosphere control, component dropping line, and the like. Uniformity of synthesis temperature is important. The synthesis temperature is appropriately set between 60 and 140.degree. It is individually set according to the type of raw materials, blending ratio, synthesis equipment, etc., such as when reacting at low temperature for a long time or when synthesizing at high temperature in a short time. For the synthesis atmosphere, nitrogen gas, for example, is used as an inert gas, and the reaction vessel is sufficiently filled with nitrogen gas having a constant water content. At this time, the nitrogen gas can be used not only from the nitrogen gas production apparatus but also from cylinders and liquid nitrogen.

Regarding the molar ratio (blending ratio) of the polydimethylsiloxane (A) having silanol groups at both ends and the silane oligomer (B) having an alkoxy group, (B) is more than 1 mol per 1 mol of (A). Adjusted over a large amount range. When the molar ratio of (A) and (B) is within the above range and the condensation reaction is carried out under conditions suitable for condensation, gelation is less likely to occur during or after the reaction, and no low-molecular-weight siloxane remains. A stable prepolymer is obtained.

The molar ratio referred to here is the number average molecular weight (Mn) of PDMS measured by gel permeation chromatography (GPC method) using polystyrene as a standard substance and tetrahydrofuran as an eluent, and the ratio of the oligomer of tetraalkoxysilane. Molar ratio calculated based on purity and average molecular weight.

Furthermore, the cured product obtained from the condensed organopolysiloxane prepolymer of the present invention is excellent in heat resistance and weather resistance, so that it can be used in a heat resistance range of 200° C. or higher and in outdoor exposure conditions.

In addition, the elastic modulus can be lowered by reducing the number of crosslinked sites when the silane oligomer (B) having an alkoxy group is cured. For example, by using a curing agent whose terminals are not all alkoxy groups but partially methyl groups, the number of crosslinked sites can be reduced. More specifically, for example, the amount of alkoxy groups in the curing agent is 10% by weight or less, preferably 8% by weight or less, of the total amount of ethyl silicate in the mixture containing the condensed organopolysiloxane prepolymer and the curing agent, More preferably, by adjusting the content to 1% by weight or less, the number of crosslinked sites can be reduced.

By compounding the condensed organopolysiloxane prepolymer of the present invention with a conductive material such as carbon, a stretchable electrode, a stretchable transparent insulating film, or a stretchable electrode paint can be produced.

EXAMPLES The present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. The toluene content in PDMS in the examples was measured by gas chromatography.

[Examples 1 to 4]
[Preparation of condensed organopolysiloxane prepolymer]
A reactor equipped with a stirrer, a thermometer and a dropping line was sufficiently filled with nitrogen gas. At this time, nitrogen gas produced by a nitrogen gas production apparatus (UNX-200 manufactured by Japan Unix) was used.

Next, PDMS (A) having silanol groups at both ends, a tetraalkoxysilane oligomer (B), and an organometallic compound (C) were placed in the reaction vessel sufficiently filled with the nitrogen gas. and stirred until homogeneous. As the oligomer (B), a product distilled by an evaporator (130° C. for 2 hours) was used. After that, the mixture was naturally cooled to room temperature to obtain a condensed organopolysiloxane prepolymer.

The raw materials used were as follows.
PDMS (A) having silanol groups at both ends: Momentive YF3057 (number average molecular weight (Mn) 33,735, Mw / Mn = 1.58), NuSil PRO-2815 (number average molecular weight (Mn) 56 ,000, Mw/Mn=1.91).
Tetraalkoxysilane oligomer (B): Ethylsilicate 40 manufactured by Tama Kagaku Kogyo Co., Ltd. (tetraethoxysilane linear tetra- to hexa-mer oligomer, average molecular weight = 745, 36 wt% alkoxy groups, at 130°C purified by distillation for 2 hours).
Organometallic compound (C): Dibutyltin dilaurate manufactured by Tokyo Chemical Industry Co., Ltd.

[Preparation of curing agent]
A tetra- to hexa-mer silicate oligomer (Ethyl Silicate 40 manufactured by Tama Kagaku Kogyo Co., Ltd., the same as (B) above) was placed in a sealable plastic container that can be equipped with a stirring and degassing device. 2, 4: X-40-9246 manufactured by Shin-Etsu Chemical Co., Ltd., alkoxy group 13 wt%), zinc 2-ethylhexanoate (Nikka Octix zinc 18% manufactured by Nippon Kagaku Sangyo Co., Ltd.), 3-aminopropyltriethoxysilane ( KBE-903 manufactured by Shin-Etsu Chemical Co., Ltd.) was added in the amount shown in Table 1 and sufficiently stirred, then tert-butyl alcohol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added in the amount shown in Table 1 and further stirred. was used as the curing agent.

The alkoxy group content of the silicate oligomer was measured by the following method. A measurement sample was prepared by weighing 1.2 to 1.5 g of silicate oligomer into an aluminum cup. Using a constant temperature dryer (ONW-300 manufactured by AS ONE), the measurement sample was heated at 100° C. for 1 hour (condition 1) to remove the solvent (ethanol or water) contained in the silicate oligomer. The sample weight (W ₁ ) after heating under Condition 1 was measured. Thereafter, the sample was further heated at 200° C. for 3 hours (condition 2) to react and volatilize the alkoxy groups in the silicate oligomer. The sample weight (W ₂ ) after heating under Condition 2 was measured. Assuming that all the alkoxy groups of the silicate oligomer could be removed by heating under Condition 2, the content of alkoxy groups was calculated from the following formula.
Alkoxy group content (wt%) = [(W2 _- W1) _/ W1] x ₁₀₀

[Comparative Examples 1 and 2]
Instead of PDMS (A) having silanol groups at both ends of Examples 1 to 4, PDMS (a) having silanol groups at both ends: JNC FM9927A (number average molecular weight (Mn) 30,900, Mw / Mn = 1.08) and XF3905 manufactured by Momentive (number average molecular weight (Mn) 20,000, Mw/Mn = 1.48) was used. A siloxane prepolymer and curing agent were prepared. The amount of each raw material was as shown in Table 2.

[Preparation of condensed organopolysiloxane prepolymer cured body (sheet)]
10 parts by weight of the cured product was blended with 100 parts by weight of the above prepolymer (main agent) to prepare a sol. The resulting sol was applied to a TPX film and baked at 150° C. for 2 hours. The obtained cured body was peeled off from the TPX film to obtain a sheet of 500 μm.

[Evaluation of elastic modulus and elongation]
A tensile test was performed according to JIS K6251 to measure the elastic modulus and elongation of the sheet. A No. 7 dumbbell test piece specified in JIS K6251 was prepared as a test sample from the 500 μm sheet. Using a tensile tester ("Autograph AG-I" manufactured by Shimadzu Corporation), the test sample was subjected to a tensile test with the initial _L0 set to 20 mm and a strain rate of 100 mm / min. and the elongation at break was measured.

[Evaluation of elastic recovery rate]
A No. 7 dumbbell test piece was prepared in the same manner as above, and the elastic recovery rate was evaluated. Using a tensile tester ("Autograph AG-I" manufactured by Shimadzu Corporation), the initial _L0 was set to 20 mm, and the strain was stretched from 0% to 100% at a speed of 100 mm/min. , 10 cycles of contraction from 100% to 0%. The elastic recovery rate was calculated from the following formula, with L ₁ being the length when the first stress was generated and L ₁₀ (mm) being the length when the 10th stress was generated.
Elastic recovery rate (%) = [(L ₁₀ - L ₁ ) / A] × 100 (A in the formula is the stretched length)

From the results shown in Table 3, it was found that the cured product obtained from the condensed organopolysiloxane prepolymer of the present invention was soft, stretched well, and had a high elastic recovery rate.

[Change example]
The above examples are not limited to this, and organometallic compounds of different types and properties may be used.

It should be considered that the embodiments and examples disclosed above are illustrative in all respects and not restrictive. The scope of the present invention is defined by the scope of the claims rather than the above-described embodiments and examples, and includes all modifications and variations within the scope and meaning equivalent to the scope of the claims.

Claims (9)

A condensed organopolysiloxane prepolymer prepared by subjecting (A) below to a condensation reaction with (B) below in an amount greater than 1 mol per 1 mol of (A) below.
(A) Polydimethylsiloxane having silanol groups at both ends, having a molecular weight (Mn) of 30,000 or more, and having a molecular weight distribution index (Mw/Mn; Mw is the weight average molecular weight and Mn is the number average molecular weight) 1.3 or more.
(B) Oligomers of tetraalkoxysilanes and/or complete or partial hydrolysates or condensates of said oligomers. 2. The condensed organopolysiloxane prepolymer according to claim 1, wherein (A) has a number average molecular weight (Mn) of 70,000 or less. 3. The condensed organopolysiloxane prepolymer according to claim 1, wherein (B) is a linear tetramer to decamer and has a methoxy group or an ethoxy group as an alkoxy group. 4. The condensed organopolysiloxane prepolymer according to any one of claims 1 to 3, wherein (B) is blended in more than 1 mol and 2 mol or less per 1 mol of (A). . An electrode material comprising the condensed organopolysiloxane prepolymer according to any one of claims 1 to 4. An insulating material comprising the condensed organopolysiloxane prepolymer of any one of claims 1-4. A cured product of the condensed organopolysiloxane prepolymer according to any one of claims 1 to 4. A cured product obtained by curing a mixture containing the condensed organopolysiloxane prepolymer according to any one of claims 1 to 4 and a curing agent, wherein the curing agent comprises an alkoxy group, the 8. The cured body according to claim 7, containing 10% by weight or less of ethyl silicate in the mixture. 9. The cured body according to claim 7, which has an elastic modulus of 1.5 MPa·s or less, an elongation of 200% or more, and an elastic recovery rate of 90% or more.