Self-healing rubber containing a poly(glycerol monomethacrylate)-boronic acid ester complex

Abstract

The present invention relates to a method for preparing a rubber composition, which includes polymerizing glycerol monomethacrylate, crosslinking poly(glycerol monomethacrylate) obtained by boric acid to form a poly(glycerol monomethacrylate)-dynamic boronic acid ester complex, and compounding the complex with an additive. The present invention further relates to a rubber composition, a cured rubber composition, and a self-healing tire using the rubber composition.

Description

Technical Field

[0001] The present invention relates to the field of self-healing rubbers. In particular, the present invention relates to a rubber composition comprising a dynamic poly(glycerol monomethacrylate)-boronic acid ester complex, a method for preparing the rubber composition, and the use of the rubber composition in a self-healing tire.

Background Art

[0002] Self-healing natural rubber is known in the prior art. C. Xu et al., "Design of Self-Healing Supramolecular Rubbers by Introducing Ionic Cross-Links into Natural Rubber via a Controller Vulcanization", ACS Appl. Mater. Interfaces 2016, 8, 17728-17737, DOI: 10.1021 / acsami.6b05941 describes a controlled peroxide-induced vulcanization that produces ionic cross-links in natural rubber by polymerization of zinc dimethacrylate. In Ch. Xu et al., "Self-Healing Natural Rubber with Tailorable Mechanical Properties based Ionic Supramolecular Hybrid Network", ACS Appl. Mater. Interfaces 2017, 9, 29363-29373, DOI: 10.1021 / acsami.7b09997, the authors aimed to improve the properties of self-healing natural rubber by in-situ polymerization reaction of excess zinc oxide (ZnO) and methacrylic acid in natural rubber to form zinc dimethacrylate. Self-healing natural rubber is known from the aforementioned publications, but has insufficient mechanical strength.

[0003] In the coincidence-induced self-assembly (PISA) system, the use of a methacrylate-based macromonomer as a "sulfur-free" RAFT agent is described in "Toward Sulfur-Free RAFT Polymerization Induced Self-Assembly" by A. Lotierzo et al., ACS Macro Lett. 2017, 6, 1438 - 1443, DOI: 10.1021 / acsmacrolett.7b00857. The preparation of polymers containing boronic ester-type dynamic covalent bonds is described in "Recyclable Polymers with Boronic Ester Dynamic Bonds Prepared by Miniemulsion Polymerization" by S. Tajbakhsh et al., ACS Appl. Polym. Mater. 2021, 3, 3402 - 3415, DOI: 10.1021 / acsapm.1c00368.

[0004] Y. Chen et al. describe a thiol-containing boronic ester used to crosslink self-healing styrene-butadiene rubber (SBR) in "Covalently Cross-Linked Elastomers with Self-Healing and Malleable Abilities Enabled by Boronic Ester Bonds", ACS Appl. Mater. Interfaces 2018, 10, 24224 - 24231, DOI: 10.1021 / acsami.8b09863. Furthermore, in "Mechanically Robust, Self-Healable, and Reprocessable Elastomers Enabled by Dynamic Dual Cross-Links", Macromolecules 2019, 52, 3805 - 3812, DOI: 10.1021 / acs.macromol.9b00419, Y. Chen et al. describe the covalent cross-linking of epoxidized natural rubber (ENR) using a boronic ester-type cross-linking agent with dithiol by the chemical reaction of epoxy groups and thiol groups.

[0005] N. Yang et al., "Polyvinyl Alcohol / Silk Fibroin / Borax Hydrogel Ionotronics: A Highly Stretchable, Self-Healable, and Biocompatible Sensing Platform", ACS Appl. Mater. Interfaces 2019, 11, 23632 - 23638, DOI: 10.1021 / acsami.9b06920 reported a biocompatible ionic hydrogel fabricated from polyvinyl alcohol, silk fibroin, and borax, and this hydrogel can be used as a sensing platform for monitoring the movement of the surrounding body.

Prior Art Documents

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] One object of the present invention was to provide a rubber composition that simultaneously provides improved self-healing properties in the cured state and high mechanical strength, enabling its use in tires.

Means for Solving the Problems

[0008] Surprisingly, it has been found that by using a composite prepared by cross-linking an oligomer or polymer of glycerol monomethacrylate with borax in a rubber composition, the trade-off between the self-healing efficiency and mechanical strength of the cured rubber is solved. The cured rubber is self-healable and at the same time achieves high mechanical strength enabling its use in tires.

[0009] Accordingly, the present invention is a method for preparing a rubber composition, (A) polymerizing glycerol monomethacrylate in the presence of a Co(II) complex as a catalytic chain transfer agent to obtain a poly(glycerol monomethacrylate) which is an oligomer or polymer of glycerol monomethacrylate having a number average molecular weight (M n ) in the range of 160 - 3200 g / mol and preferably a dispersity D of 4 or less, and (B) cross-linking the poly(glycerol monomethacrylate) with borax to obtain a poly(glycerol monomethacrylate)-dynamic boronic acid ester complex, (C) Preparing the rubber composition by blending a poly(glycerol monomethacrylate)-dynamic boronic acid ester complex with a vulcanization activator system, a diene rubber, sulfur, and a vulcanization accelerator refers to a method that includes at least

[0010] As used herein, the term "poly(glycerol monomethacrylate)" or the abbreviation "pGMMA" means an ω-vinyl oligomer or polymer of glycerol monomethacrylate. As used herein, the term "poly(glycerol monomethacrylate)" is used interchangeably with the term "poly(glycerol monomethacrylate) oligomer".

[0011] In a preferred embodiment of the method, in step (A), the molecular weight of poly(glycerol monomethacrylate) is controlled by the ratio to the Co(II) complex of glycerol monomethacrylate, and in particular, a ratio of glycerol monomethacrylate to the Co(II) complex of 10 6 :10 to 10 6 :180 is used.

[0012] In another preferred embodiment of the method, the Co(II) complex is cobaloxime boron fluoride, and in particular, the Co(II) complex is bis[(difluoroboryl)dimethylglyoximato]cobalt(II).

[0013] In a more preferred embodiment, in step (B), poly(glycerol monomethacrylate) is mixed with borax in a weight ratio of 1.0:0.05 to 1.0:0.4.

[0014] In a preferred embodiment of the present method, in step (C), the poly(glycerol monomethacrylate)-boronic acid ester complex is compounded with a vulcanization activator system that is zinc oxide and an organic acid. In a more preferred embodiment, the organic acid used is stearic acid, and stearic acid combines with zinc oxide during processing to form a vulcanization activator complex. In another preferred embodiment of the present method, the vulcanization activator system is a poly(zinc methacrylate)-zinc oxide activator (p(ZnMA) / ZnO) complex. Preferably, the organic acid used is an ω-vinyl oligomer of methacrylic acid, and the ω-vinyl oligomer of methacrylic acid is mixed with zinc oxide to form a poly(zinc methacrylate)-zinc oxide activator (p(ZnMA) / ZnO) complex, and then compounded with a diene rubber, sulfur, and a vulcanization accelerator.

[0015] In a further preferred embodiment, the poly(glycerol monomethacrylate) has a number average molecular weight (M n ) in the range of 160 to 3200 g / mol, preferably 320 to 2400 g / mol. In other preferred embodiments, the poly(glycerol monomethacrylate) has a dispersity D of 4 or less, preferably 2 or less.

[0016] In other preferred embodiments, in step (C), the diene rubber is selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, and combinations thereof.

[0017] In an exemplary embodiment, in step (C), the vulcanization accelerator is based on a sulfenamide compound and / or a thiazole compound.

[0018] In other preferred embodiments, in step (C), a filler is further used, and in particular, the filler is used in an amount of 5.0 to 80 phr relative to 100 phr of the diene rubber.

[0019] The present invention relates to a rubber composition, - Polymerizing glycerol monomethacrylate in the presence of a Co(II) complex as a catalytic chain transfer agent to obtain a poly(glycerol monomethacrylate) which is an oligomer or polymer of glycerol monomethacrylate having a number average molecular weight (M n ) in the range of 160 to 3200 g / mol, and a poly(glycerol monomethacrylate)-dynamic boronic acid ester complex obtained by crosslinking the poly(glycerol monomethacrylate) with borax, - A vulcanization activator system, - A diene rubber, - Sulfur, - A vulcanization accelerator and further relates to a rubber composition containing.

[0020] A preferred rubber composition of the present invention is - Polymerizing glycerol monomethacrylate in the presence of a Co(II) complex as a catalytic chain transfer agent to obtain a poly(glycerol monomethacrylate) which is an oligomer or polymer of glycerol monomethacrylate having a number average molecular weight (M n ) in the range of 160 to 3200 g / mol, and a poly(glycerol monomethacrylate)-dynamic boronic acid ester complex obtained by crosslinking the poly(glycerol monomethacrylate) with borax, - Zinc oxide and an organic acid, preferably zinc oxide and stearic acid, - A diene rubber, - Sulfur, - A vulcanization accelerator and contains.

[0021] An even more preferred rubber composition is - Polymerizing glycerol monomethacrylate in the presence of a Co(II) complex as a catalytic chain transfer agent to obtain a poly(glycerol monomethacrylate) which is an oligomer or polymer of glycerol monomethacrylate having a number average molecular weight (M nObtain poly(glycerol monomethacrylate), which is an oligomer or polymer of glycerol monomethacrylate having - A poly(zinc methacrylate) / zinc oxide activator (p(ZnMA) / ZnO) composite, - A diene rubber, - Sulfur, - A vulcanization accelerator is included.

[0022] In a preferred embodiment, the rubber composition preferably contains a filler in an amount of 5.0 to 80 phr based on 100 phr of the diene rubber.

[0023] The present invention further provides a cured rubber or a cured rubber composition that can be obtained by curing the above rubber composition.

[0024] Furthermore, the present invention provides a self-healing tire comprising a tire part, preferably a tread, manufactured by using the above rubber composition.

[0025] All references to the unit "phr" herein refer to parts by weight per 100 parts by weight of rubber.

[0026] The term "molecular weight" as used herein, such as the number average molecular weight (M n ), refers to the measurement by size exclusion chromatography (SEC), preferably 1 the measurement further by performing 1H nuclear magnetic resonance (NMR) spectroscopy.

[0027] The term "dispersion degree" as used herein refers to the molecular weight distribution D and is determined from the following formula [Equation 1] D = M w / M n (where M w is the weight average molecular weight and Mn which is the number average molecular weight).

[0028] Preferred embodiments of the present invention are described in the following description, examples, drawings and claims.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0030] The rubber composition according to the present invention is curable and contains at least a diene rubber, a poly(glycerol monomethacrylate)-dynamic boronic acid ester complex, a vulcanization activator system, sulfur, a vulcanization accelerator and preferably a filler. Preferably, the vulcanization activator system is zinc oxide (ZnO) and an organic acid. In a preferred embodiment, the organic acid is stearic acid. In another preferred embodiment, the organic acid is an ω-vinyl oligomer of methacrylic acid.

[0031] The diene rubber is preferably selected from natural rubber (NR), styrene-butadiene rubber (SBR), isoprene rubber, butadiene rubber (BR) or a combination thereof. Preferably, natural rubber (NR), styrene-butadiene rubber (SBR) or a combination thereof is used. A suitable formulation is 80 to 90% by weight of natural rubber and 20 to 10% by weight of styrene-butadiene rubber based on 100% by weight of the rubber.

[0032] According to the present invention, the poly(glycerol monomethacrylate)-dynamic boronic acid ester complex has a number average molecular weight (M n ) in the range of 160 to 3200 g / mol, particularly when the degree of dispersion (D) is 4 or less. Preferably, M n is in the range of 240 to 2400 g / mol when the degree of dispersion (D) is 2 or less, and more preferably, M n is in the range of 240 to 1600 when the degree of dispersion (D) is less than 2. A molecular weight in the range of 160 to 3200 g / mol corresponds to a degree of polymerization of 2 to 40.

[0033] Poly(glycerol monomethacrylate) is produced by oligomerization or polymerization of glycerol monomethacrylate by catalytic chain transfer (CCT) using a cobalt(II) complex as a catalyst, and the degree of polymerization or molecular weight of poly(glycerol monomethacrylate) can be controlled by the ratio of the monomer (glycerol monomethacrylate) to the catalyst.

[0034] An exemplary embodiment of the polymerization using bis[(difluoroboryl)dimethylglyoximato]cobalt(II) (CoBF) as a catalyst is shown in Figure 1, where n represents the number of monomer units. Preferably, n is 2 to 15.

[0035] The cobalt(II) complex or catalyst can be any cobalt complex known in the art for catalytic chain transfer polymerization (CCTP). Suitable catalysts are described, for example, in European Patent Application Publication No. EP1295922 (A2), U.S. Patent No. 9090724 (B2) and U.S. Patent No. 9580529 (B2). Preferably, bis[(difluoroboryl)dimethylglyoximato]cobalt(II) is used as the catalyst.

[0036] As shown in Figure 1, boric acid is used to crosslink poly(glycerol monomethacrylate) to form a dynamic boronic acid ester. This reaction is preferably carried out in deionized water, preferably at ambient temperature. In a preferred embodiment, water is then removed by lyophilization.

[0037] The poly(glycerol monomethacrylate)-dynamic boronic acid ester composite contains a network structure of dynamic boronic acid esters that imparts self-healing properties to the cured rubber when added to the rubber composition.

[0038] Since ZnO acts as a vulcanization accelerator, it is generally used as an additive in rubber compositions for tires. In a preferred embodiment of the present invention, when ZnO is added together with stearic acid, zinc stearate salt is formed in situ. In the present invention, ZnO can be used in the form of zinc stearate or in the form of p(ZnMA) / ZnO. When using p(ZnMA) / ZnO, this composite can be formed by combining an ω-unsaturated oligomer of methacrylic acid with ZnO in water and then lyophilizing to form a dry composite before mixing.

[0039] Suitable fillers for the rubber composition are not limited and are known in the field of tire manufacturing. Exemplary fillers are carbon black, silica, and combinations thereof. Carbon black and silica with specific surface areas are both commercially available and can be used. The filler is generally used in an amount of 5 phr to 80 phr, preferably 5 phr to 50 phr, more preferably 10 phr to 40 phr.

[0040] In the present invention, sulfur is used as a crosslinking agent during vulcanization. Sulfur causes covalent crosslinking to occur in the cured rubber composition, contributing to the mechanical strength of the cured rubber.

[0041] Suitable vulcanization accelerators are based on sulfenamide compounds and / or thiazole compounds. Preferably, N-cyclohexyl-2-benzothiazole sulfenamide (known as CBS) or tetramethylthiuram monosulfide is used.

[0042] The rubber composition can include further additives, in particular additives commonly used in the field of tire manufacturing. Such additives are lubricants, pigments, activators, softeners, plasticizers, antioxidants, fatty acids (stearic acid). Generally, the total amount of these additives is 10% by weight or less or 10 phr or less based on 100% by weight of the rubber composition.

[0043] The present invention also provides a cured rubber composition or cured rubber obtained after curing the curable rubber composition of the present invention. Curing can be carried out as known in the art without limitation. A suitable curing temperature ranges from 150 to 160 °C.

[0044] The rubber composition of the present invention is particularly used for manufacturing one or more tire parts or one or more rubber components of a self-healing tire including a tread compound or a case compound. In particular, the rubber composition is preferably used for the tread or tread portion of a self-healing tire. Accordingly, the present invention further provides a tire part manufactured by using the self-healing rubber composition of the present invention, more preferably a self-healing tire including a tread. The manufacture of tire parts from the rubber composition in a suitable device is carried out as known in the art.

[0045] The rubber composition of the present invention imparts self-healing properties and high mechanical strength to the tire.

[0046] The following examples illustrate the present invention without limiting the scope of protection.

Examples

[0047] (Examples 1 to 4) Examples 1 to 4 refer to different rubber compositions showing the effect of poly(glycerol monomethacrylate)-dynamic boronic acid ester composites on the self-healing property and mechanical properties of rubber after curing.

[0048] The compounding formulations used are shown in Table 1 below, and the numerical values are in phr. The comparative compounding formulation was CV1, which contained components that were the same in other respects but did not contain pGMMA-boric acid in corresponding amounts.

Table 1

[0049] The above components were compounded at 40 °C and 50 rpm in a Haake PolyLab twin-screw compounding device. The curing characteristics and optimum curing time (t 90 ) of the compound were measured using a Montech M3000 moving die rheometer (MDR). Then, the sample was cured in a Collin P200 hot press at a pressure of 150 bar and a temperature of 150 °C up to the t 90 curing time to form a 9×9 cm film with a thickness of 1 mm. 2

[0050] ​Figure 2 shows (a) the curing curves of the formulations in Table 1 obtained using MDR, and (b) the tensile tests of CV1 and the formulations in Table 1. The mechanical properties were evaluated by measuring stress (MPa) versus stroke strain (%) at a strain rate of 100 mm / min using an AGS-X tensile tester manufactured by Shimadzu Corporation. The results are shown in Figure 2 in comparison with the formulation without pGMMA-boric acid (CV1).

[0051] Figure 3 further shows the self-healing test from the perspective of the recovery %. These results were obtained by repeating the tensile test using specimens taken from each sample that was cut in half with a scalpel, then only 4 mm × 3 mm area was overlapped, and then placed under the influence of a 20 N weight at 80 °C for 30 minutes or 2 hours. Next, the value of the recovery % was calculated from the value obtained from the cut specimen relative to the uncut specimen.

[0052] The values of stress recovery and strain recovery of the cured rubbers of Examples 1 to 4 are shown in Table 2 below.

Table 2

[0053] Figure 4 shows the DMA analysis of CV1 and the formulations in Table 1. These results were measured in the temperature range of -80 to 100 °C at 1% strain and a frequency of 5 Hz using Tritec2000 DMA in tension mode.

[0054] (Examples 5 and 6) Examples 5 and 6 refer to rubber compositions showing the effect of pGMMA-boric acid on rubber compositions further containing a pZnMA / ZnO salt (a salt of pMAA and ZnO with a pre-formed weight ratio of 1:1) as a curing activator. The formulations used are shown in Table 3 below.

Table 3

[0055] The above components were compounded in the same manner as described in Examples 1 to 4.

[0056] The mechanical properties were evaluated by measuring stress (MPa) versus stroke strain (%) at a strain rate of 100 mm / min using an AGS-X tensile tester manufactured by Shimadzu Corporation. The results are shown in Fig. 5.

[0057] (Examples 7 to 9) Examples 7 to 9 refer to rubber compositions showing the effect of adding carbon black N234 to compound PG20 as shown in Examples 1 to 4. The detailed compositions are shown in Table 4.

Table 4

[0058] The components shown in Table 4 were compounded as described in Examples 1 to 4. The mechanical properties were evaluated again by measuring stress (MPa) versus stroke strain (%) at a strain rate of 100 mm / min using an AGS-X tensile tester manufactured by Shimadzu Corporation. The results are shown in Fig. 6. Furthermore, the self-healing efficiency was evaluated using the same method as described in Examples 1 to 4 and is shown in Table 5.

Table 5

[0059] The results obtained show that the addition of the dynamic boronic ester complex has a beneficial effect on the self-healing property and mechanical properties of the cured rubber.

Claims

1. A method for preparing a rubber composition, comprising: (A) Polymerizing glycerol monomethacrylate in the presence of a Co(II) complex as a chain transfer agent for the catalyst to obtain a poly(glycerol monomethacrylate) which is an oligomer or polymer of glycerol monomethacrylate having a number average molecular weight (M ｎ ) in the range of 160 to 3200 g / mol and preferably a dispersity D of 4 or less; (B) crosslinking the poly(glycerol monomethacrylate) with boric acid to obtain a poly(glycerol monomethacrylate)-dynamic boronic acid ester complex; (C) compounding the poly(glycerol monomethacrylate)-dynamic boronic acid ester complex with a vulcanization activator system, a diene rubber, sulfur, and a vulcanization accelerator to prepare the rubber composition. A method comprising at least the above steps.

2. The method according to claim 1, wherein in step (A), the molecular weight of the poly(glycerol monomethacrylate) is controlled by the ratio to the Co(II) complex of glycerol monomethacrylate, in particular 10 ６ : 10 to 10 ６ : A method in which a ratio to the Co(II) complex of glycerol monomethacrylate of 180 is used.

3. The method according to claim 1 or 2, wherein the Co(II) complex is cobalt boroxime fluoride, and in particular, the Co(II) complex is bis[(difluoroboryl)dimethylglyoximato]cobalt(II).

4. The method according to any one of claims 1 to 3, wherein in step (B), the poly(glycerol monomethacrylate) is mixed with boric acid at a weight ratio of 1.0:0.05 to 1.0:0.

4.

5. The method according to any one of claims 1 to 4, wherein in step (C), the vulcanization activator system is zinc oxide and an organic acid, and preferably, the vulcanization activator system is zinc oxide and stearic acid.

6. The method according to any one of claims 1 to 4, wherein in step (C), the vulcanization activator system is a poly(zinc methacrylate)-zinc oxide (p(ZnMA) / ZnO) complex.

7. The method according to any one of claims 1 to 6, wherein in step (C), the diene rubber is selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, and combinations thereof.

8. The method according to any one of claims 1 to 7, wherein in step (C), the amount of the poly(glycerol monomethacrylate)-dynamic boronic acid ester complex is 5.0 to 40 phr based on 100 phr of the diene rubber.

9. The method according to any one of claims 1 to 8, wherein in step (C), a filler is further used, and in particular, the filler is used in an amount of 5.0 to 80 phr based on 100 phr of the diene rubber.

10. A rubber composition comprising: - Polymerize glycerol monomethacrylate in the presence of a Co(II) complex as a chain transfer agent for the catalyst to obtain a poly(glycerol monomethacrylate) which is an oligomer or polymer of glycerol monomethacrylate having a number average molecular weight (M ｎ n) in the range of 160 to 3200 g / mol, and a poly(glycerol monomethacrylate)-dynamic boronic acid ester complex obtained by crosslinking the poly(glycerol monomethacrylate) with borax. - a vulcanization activator system; - a diene rubber; - sulfur; and - a vulcanization accelerator. A rubber composition containing the above components.

11. The rubber composition according to claim 10, wherein the vulcanization activator system is zinc oxide and an organic acid, and preferably, the vulcanization activator system is zinc oxide and stearic acid.

12. The rubber composition according to claim 10, wherein the vulcanization activator system is a poly(zinc methacrylate)-zinc oxide (p(ZnMA) / ZnO) complex.

13. The rubber composition according to any one of claims 10 to 12, further comprising a filler in an amount of 5.0 to 80 phr, particularly with respect to 100 phr of the diene rubber.

14. A cured rubber composition obtainable by curing the rubber composition prepared by the method according to any one of claims 1 to 9 or the rubber composition according to any one of claims 10 to 13.

15. A self-healing tire comprising a tire component, preferably a tread, prepared from the rubber composition prepared by the method according to any one of claims 1 to 9 or the rubber composition according to any one of claims 10 to 13.

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