Reprocessable polymer composition with dynamic crosslinking

Abstract

Polysiloxane-based polymers with reversible crosslinking are provided using at least one dynamic bond activator that promotes Si-O bonds between adjacent silicon-oxygen backbone elastomers within the polymer network. The polymer is capable of undergoing reversible cross-linking and de-cross-linking processes, allowing reprocessing. The polymer composition is formed from a silicon-oxygen backbone elastomer that produces a polymer network. A non-agglomerating filler is dispersed within and bonded to the polymer network. The catalyst promotes the condensation reaction. The crosslinker may be one or more silanes comprising one or more methoxyl or ethoxyl groups. At least one dynamic bond activator facilitates Si-O bond exchange between adjacent silicon-oxygen backbone elastomers of the polymer network. The polymer composition has properties of a thermoset polymer in bulk form under ambient conditions and is capable of remodeling to a viscoelastic liquid at a temperature greater than about 170 DEG C.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 514,804, filed on July 21, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] The present invention relates to polymer compositions having a covalently bonded network that can be altered by heat-activated bond exchange that produces dynamic crosslinks. The polymer compositions are capable of being reprocessed in that they can be reshaped by reheating. Background Art

[0003] Silicone accounts for a large portion of the polymer market. The annual production in China is about 370K tons, with a compound annual growth rate (CAGR) of 6.1% in the global market from 2019 to 2025, and is expected to reach $2.01 billion by 2025. Compared with elastomers such as thermoplastic polyurethane (TPU), silicone rubber is widely used in general consumer goods projects and food contact articles due to its high tensile strength, thermal stability and food contact safety.

[0004] With this large production volume, a large amount of silicone waste and waste is generated by manufacturing or end users. This has a negative impact on both production costs and the environment, because commercial silicones are not reprocessable due to their thermosetting properties. The waste rate from demoulding during manufacturing can be as high as 5%, which causes a loss of 4 million to 11 million yuan per year. Although the recycling cost of silicone is 4 to 7 yuan per kilogram at present, the development of reprocessable silicone-like materials will not only represent a solution to save production costs, but also provide a sustainable solution because recycling equipment and resources can be saved.

[0005] Conventional methods for reprocessing silicone scrap and waste involve physical or chemical degradation, or sometimes a combination of both. These methods include: 1) Mechanical grinding into fillers used as reinforcing materials in composite materials; 2) Downgrading to industrial lubricants, such as those developed by Dow Corning by depolymerizing polydimethylsiloxane (PDMS) (WO 2014130948A1); 3) Hydrothermal methods for reforming silicone rubbers with significantly inferior mechanical properties.

[0006] These low value-added processes add additional production cost and time, are unsustainable, and do not leverage the strength of silicone rubber for high value-added applications.

[0007] "Thermoplastic silicone elastomers" are commercially available, for example, Thermoplastic Silicone Vulcanizate TPSiV sold by DuPont. The product is formed by dispersing a crosslinked silicone rubber (vulcanized silicone modules including PDMS) into a thermoplastic continuous phase of a thermoplastic polyurethane TPU using an in-situ platinum hydrosilylation catalyst. The composite is said to be reprocessable by melting and remolding. In most cases, the silicone content is less than 50% w / w, and the manufacturing process requires anhydrous conditions to obtain good quality TPSiV with high tensile strength. In addition, TPSiV cannot be used in food contact applications because amines or amides from the TPU may reside in the composite.

[0008] There is a need for a new polymer elastomer using a silicon-oxygen backbone that can be thermally reprocessed at temperatures beyond the desired application range while maintaining the advantages of commercial silicones with high tensile strength, thermal stability and food contact safety for high value-added applications. The present invention addresses this need. Summary of the invention

[0009] The present invention provides a novel polymer system based on silicon-oxygen backbone elastomers that promote changes in material topology through thermally activated bond exchange reactions: at its reprocessable temperature, the polymer system of the present invention flows as a viscoelastic liquid, while at low temperatures, the bond exchange reactions are immeasurably slow and, therefore, the polymer system of the present invention behaves like a thermosetting elastomer.

[0010] In order to achieve material properties similar to commercial silicone rubbers, namely high tensile strength, thermal stability and food contact safety, the present invention involves: 1) selecting different chain lengths and branching of PDMS polymers for the polymer networks of the present invention, thereby enabling adjustment to high tensile strength; 2) developing and selecting new cross-linking agents for PDMS-based polymer networks, thereby allowing selection of optimal reprocessing temperatures; and 3) using high silicon-oxygen polymer content and avoiding the use of TPU in the formulation, which ensures food contact compliance.

[0011] The present invention provides polysiloxane-based polymers with reversible crosslinking using at least one dynamic bond activator that promotes Si-O bonds between adjacent silicon-oxygen backbone elastomers within the polymer network. These polymers are designed to have the ability to undergo reversible crosslinking and decrosslinking processes, thereby allowing reprocessing.

[0012] In one aspect, the invention provides a polymer composition having a covalently bonded network that can be altered by heat-activated bond exchange that produces dynamic crosslinking. The polymer composition is formed by a silicon-oxygen backbone elastomer that produces a polymer network. Non-agglomerated fillers are dispersed within the polymer network and bonded to the polymer network. Catalysts promote condensation reactions. Crosslinking agents are used for crosslinking and can be one or more silanes containing one or more methoxy or ethoxy groups.

[0013] At least one dynamic bond activator promotes Si-O bonds between adjacent silicon-oxygen backbone elastomers of the polymer network such that dynamic crosslinks formed between the adjacent silicon-oxygen backbone elastomers produce a three-dimensional crosslinked polymer network.

[0014] The polymer composition has the properties of a thermosetting polymer in bulk form at ambient conditions and can be reshaped into a viscoelastic liquid at a temperature greater than about 170° C. In some embodiments, the viscoelastic liquid retains at least 60% of the tensile strength and at least 70% of the elongation at break at ambient conditions.

[0015] In one aspect, the silicon-oxygen backbone elastomer is selected from one or more of trimethylsilyl-terminated polydimethylsiloxane and silanol-terminated polydimethylsiloxane.

[0016] In one aspect, the silicon-oxygen backbone elastomer has a molecular weight of 5,970 to 139,000 g / mol and a viscosity of 100 to 150,000 cSt and is present in the composition in an amount of 49.6 to 65.6 wt%.

[0017] In one aspect, the filler comprises fumed silica, calcium carbonate, or zinc oxide in an amount of 24.9 to 36.9 wt%.

[0018] In one aspect, the at least one dynamic bond activator is an ionic salt selected from an ammonium salt or a phosphonium salt, and the amount of the ionic salt is 0.09 to 2.5 wt%.

[0019] In one aspect, the dynamic bond activator is tetrabutylphosphonium hydroxide.

[0020] In one aspect, the at least one catalyst comprises dibutyltin dilaurate or dibutyltin dioctoate in an amount of 0.12 to 2.3 wt%.

[0021] In one aspect, the crosslinking agent is a silane having an ethoxy group or a silane having a methoxy group in an amount of 2.7 to 25.0 wt%.

[0022] In one aspect, the crosslinking agent is selected from one or more of 1,2-bis(triethoxysilyl)ethane, poly(dimethoxysiloxane), poly(diethoxysiloxane), and tetraethyl silicate.

[0023] The present invention further provides a method for preparing the polymer composition, wherein a first silicon-oxygen main chain elastomer is combined with a filler and a crosslinker to form a first mixture. A second silicon-oxygen main chain elastomer is combined with a filler and a catalyst to form a second mixture. The first mixture is combined with the second mixture to form a third mixture, wherein the first mixture is combined with the second mixture in a weight ratio of 1.1:1 to 8.3:1. The third mixture is combined with at least one dynamic bond activator to form a fourth mixture, and the fourth mixture is cured to form the polymer composition. The solvent can be removed in a vacuum at a temperature of 50 to 80°C by an optional heating step. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The mechanism of polymer reprocessability is schematically depicted.

[0025] Figure 2 The reactions involved in the formation of the polymer compositions of the present invention are depicted. DETAILED DESCRIPTION

[0026] Silicon-oxygen backbone elastomers, such as polysiloxanes, have repeating units of siloxane (-Si-O-) bonds. These polymers have excellent thermal stability, chemical resistance, and flexibility, which makes them useful in a variety of applications. By incorporating Si-O bonds between adjacent backbone chains, various mechanical properties can be improved without sacrificing the polymer's ability to be remolded and reprocessed.

[0027] The reprocessability of these polymers is particularly valuable in reducing waste and promoting sustainability. By breaking and reforming the crosslinks, the material can be repeatedly processed, molded, and reshaped without any significant degradation of its properties. This reprocessability opens up the possibility for efficient material reuse and reduces the need to produce new polymers.

[0028] The polymer composition is formed by a silicon-oxygen main chain elastomer that produces a polymer network. In one aspect, the silicon-oxygen main chain elastomer has a molecular weight of 5,970 to 139,000 g / mol and a viscosity of 100 to 150,000 cSt and is present in the composition in an amount of 49.6 to 65.6 wt%. Specifically, these silicon-oxygen main chain elastomers can be one or more of trimethylsilyl-terminated polydimethylsiloxane (PDMS) and silanol-terminated polydimethylsiloxane (PDMS).

[0029] The non-agglomerated filler is dispersed within and bonded to the polymer network.In one aspect, the filler comprises fumed silica, calcium carbonate, or zinc oxide in an amount of 24.9 to 36.9 wt%.

[0030] The catalyst promotes the condensation reaction, such as dibutyltin dilaurate or dibutyltin dioctoate in an amount of 0.12 to 2.3 wt%. The crosslinking agent is used for crosslinking and can be one or more silanes containing one or more methoxy groups or ethoxy groups. In one aspect, the crosslinking agent is a silane with ethoxy groups or a silane with methoxy groups in an amount of 2.7 to 25.0 wt%. Examples of suitable crosslinking agents include one or more of 1,2-bis(triethoxysilyl)ethane, poly(dimethoxysiloxane), poly(diethoxysiloxane) and tetraethyl silicate.

[0031] The present invention uses a dynamic activator to promote Si-O bonds between adjacent silicon-oxygen backbone elastomers of the polymer network. These bonds can be in the form of silyl ether groups, which can be tailored to achieve specific properties or optimize their reprocessing. The ability to reversibly break and reform crosslinks between adjacent Si-O backbone elastomers creates a polymer system that flows as a viscoelastic liquid at high temperatures, while at low temperatures the bond exchange reactions are immeasurably slow and therefore the polymer system behaves like a thermosetting elastomer. This phenomenon is demonstrated in Figure 1 Thus, a reprocessable polysiloxane-based polymer with reversible crosslinking is formed, which allows the polymer to be processed and reshaped without significant loss of its inherent properties. Due to the formation of dynamic crosslinks between adjacent Si-O backbone elastomers, a three-dimensional crosslinked polymer network is formed, which has increased strength and elasticity while being re-formable under external stimuli such as heating.

[0032] As used herein, the expression "dynamic bond activator" refers to any material that, when incorporated into a polymer network, can promote reversible connections or crosslinks between polymer chains that can break and reform in response to changes in temperature, pH, or the presence of specific chemicals. Dynamic bonds enable polymers to exhibit self-healing properties, adaptability, and enhanced mechanical properties.

[0033] Types of dynamic bonds include reversible covalent bonds, as well as non-covalent interactions such as hydrogen bonds, ionic interactions, and metal-ligand coordination.

[0034] Dynamic bond activators may be able to help polymers self-repair after damage, as well as enable polymers to adapt to environmental changes and mechanical stresses. That is, after an activation event, the polymer regains its structural integrity and mechanical properties, often with minimal external intervention.

[0035] In the present invention, dynamic bond activators are capable of promoting Si-O bonds between adjacent silicon-oxygen backbone elastomers of a polymer network. These bonds can be in the form of silyl ether groups, which can be tailored to achieve specific properties or optimize polymer reprocessing. The ability to reversibly break and reform crosslinks between adjacent Si-O backbone elastomers creates a polymer system that flows as a viscoelastic liquid at high temperatures, while at low temperatures the bond exchange reactions are immeasurably slow and, therefore, the polymer system behaves like a thermosetting elastomer. This phenomenon is demonstrated in Figure 1 Thus, a reprocessable polysiloxane-based polymer with reversible crosslinking is formed, which allows the polymer to be processed and reshaped without significant loss of its intrinsic properties.

[0036] In one aspect, the at least one dynamic bond activator can be an ionic salt. Examples of such ionic salts include ammonium salts or phosphonium salts. The amount used can be about 0.09 to 2.5wt%. A specific example of a dynamic bond activator is tetrabutylphosphonium hydroxide. When tetrabutylphosphonium hydroxide is used as a dynamic bond activator, the Si-O bond formed by the exchange between adjacent silicon-oxygen main chain elastomers is a silyl ether. Another specific example of a dynamic bond activator is potassium trimethylsilanol. The silyl ether exchange between different siloxane chains produces reversible crosslinking between different main chain polymer chains, thereby forming a three-dimensional network. The resulting network structure provides mechanical strength and stability for the material.

[0037] Figure 2 The reactions involved in forming a polymer composition are shown. Polysiloxanes undergo a condensation reaction with a crosslinker and a filler in the presence of a catalyst. In this case, the dynamic bond activator tetrabutylphosphonium hydroxide triggers the silyl ether exchange between different siloxane chains. Figure 2 The formation and breakdown of bonds that produce a three-dimensional network are demonstrated.

[0038] The polymer composition has the properties of a thermosetting polymer under ambient conditions in bulk form and is capable of being reshaped into a viscoelastic liquid at a temperature greater than about 170° C. while retaining at least 60% of the tensile strength and at least 70% of the elongation at break at room temperature.

[0039] The present invention further provides a method for preparing a polymer composition, wherein a first silicon-oxygen main chain elastomer is combined with a filler and a crosslinking agent to form a first mixture. A second silicon-oxygen main chain elastomer is combined with a filler and a catalyst to form a second mixture. The first mixture is combined with the second mixture to form a third mixture, wherein the first mixture is combined with the second mixture in a weight ratio of 1.1:1 to 8.3:1. The third mixture is combined with at least one dynamic bond activator to form a fourth mixture, and the fourth mixture is cured to form a polymer composition. The solvent can be removed in a vacuum at a temperature of 50 to 80°C by an optional heating step.

[0040] Examples:

[0041] Various compositions, including comparative compositions, were prepared and tested. The ingredients and their properties are described below, followed by methods for preparing the compositions. Finally, Tables 1-6 give a summary of the experiments, ingredients, and properties of the prepared compositions.

[0042] Silanol-terminated PDMS

[0043] Polydimethylsiloxane (PDMS) having terminal silanol (SiOH) groups is used to form the Si—O backbone elastomeric component to form a polymer network through condensation of the terminal silanol groups. Table 1: Silanol-terminated PDMS Silanol-terminated PDMS Molecular weight Viscosity(cSt) DMS-S33 43,500 3,500 DMS-S45 110,000 50,000 DMS-S51 139,000 90,000 to 150,000

[0044] filler

[0045] The filler enhances the mechanical strength of the polymer composition, including tensile strength, elongation at break and tear strength. The filler comprises fumed silica and zinc oxide. In the examples, hexamethyldisilazane treated silica is used as a filler compared to untreated silica, because the treatment replaces the OH groups on the silica surface, thereby increasing hydrophobicity and promoting good anti-settling properties of the filler without unnecessarily increasing the viscosity of the silicone formulation during the manufacturing process.

[0046] Crosslinking agent

[0047] The crosslinking agent helps to form a polymer network with the silanol-terminated PDMS. Silanes with ethoxy or methoxy groups are selected to condense with the silanol-terminated PDMS. In the presence of silanol-terminated PDMS, the ethoxy or methoxy groups are eliminated as ethanol or methanol during the condensation reaction. Poly(diethoxysiloxane) (including 40% to 42% SiO2, abbreviated as PSI-021) and / or 1,2-bis(triethoxysilyl)ethane are used in the examples.

[0048] Trimethylsilyl-terminated PDMS

[0049] Polydimethylsiloxane (PDMS) with terminal trimethylsilyl groups is an additive for viscosity adjustment, and these trimethylsilyl-terminated PDMS chains can penetrate into the condensed and cross-linked PDMS network to provide flexibility to the resulting material.

[0050] Table 2: Trimethylsilyl-terminated PDMS Trimethylsilyl-terminated PDMS Molecular weight Viscosity(cSt) DMS-T21 5,970 100 DMS-T31 28,000 1,000 DMS-T46 116,500 60,000

[0051] catalyst

[0052] Dibutyltin dilaurate is used in the condensation system involving silanol-terminated PDMS and its crosslinker.

[0053] Dynamic Bond Activator

[0054] Ionic salts such as ammonium or phosphonium salts are selected to achieve reprocessability. In these examples, tetrabutylphosphonium hydroxide (40%) was used.

[0055] Manufacturing Process

[0056] A planetary centrifugal mixer is typically used to mix the compositions of the examples. A crosslinker is added to the silanol terminated PDMS and mixed at 2000 rpm for 20 seconds, and then hexamethyldisilazane treated fumed silica is added at 2000 rpm for 2 minutes to form a first mixture.

[0057] Dibutyltin dilaurate was added to the trimethylsilyl terminated PDMS and mixed at 2000 rpm for 20 seconds, and then the hexamethyldisilazane treated fumed silica was mixed at 2000 rpm for 2 minutes to form a second mixture.

[0058] The second mixture was added to the first mixture in the weight ratios indicated in Tables 3-6 (5 minutes, 2000 rpm) to form a third mixture.

[0059] The dynamic bond activator was added to the third mixture and mixed (5 minutes, 2000 rpm) to form a fourth mixture.

[0060] The fourth mixture was poured into a mold and then placed in a temperature and humidity controlled room (25 degrees Celsius, 95% RH).

[0061] The resulting cured polymer was placed in a vacuum oven at 60°C for 4 hours as an optional post-cure step.

[0062] Mechanical properties

[0063] According to ASTM International standards, samples were cut into standard test specimen sizes (in the shape of dumbbells).

[0064] Reprocessability

[0065] The samples were reprocessed in the as-molded condition for 6 hours at 170° C. The reprocessed silicone was cut into standard test specimen sizes for measuring mechanical properties.

[0066] Tables 3, 4, 5 and 6 depict various compositions formed from the Examples and their measured mechanical properties.

[0067] As is well known, the mechanical properties of silicone rubber depend on the viscosity of the composition and the total solid content in the composition. By adjusting the ratio of the amount of the components in the first mixture relative to the amount of the components in the second mixture, the viscosity and the total solid content can be optimized. As shown in Table 3, various compositions were formed in Examples 1 to 4, and the range of their tensile strength was 1.17 to 5MPa. The range of the Shore A hardness of these compositions was 20 to 50 units. Comparing Examples 1 to 4 with Example 5, increasing the amount of fumed silica treated with hexamethyldisilazane in the composition increased the total solid content of the composition, and increased the tensile strength from 4.21MPa to 5MPa to 6.03MPa.

[0068] It is expected that silanol-terminated PDMS with high molecular weight (such as those of DMS-S51 in Table 4) will have more polymer chain entanglements; while silanol-terminated PDMS with low molecular weight (such as those of DMS-S33) will have higher crosslink density and high density. According to common knowledge in the art, the composition including DMS-S51 should have high elongation at break in the flexible rubber form. However, comparing Example 1 in Table 3 with Example 6 in Table 4, this is not the case (the elongation at break of Example 1 is 1178%, while the elongation at break of Example 6 is 570%). Referring to Examples 7, 8, 9, and 10 in Table 5, using a low molecular weight silanol-terminated PDMS (DMS-S33), the elongation at break can be adjusted by adding a suitable amount of trimethylsilyl-terminated PDMS and a crosslinking agent (poly(diethoxysiloxane) (including 40% to 42% SiO2, abbreviated as PSI-021) and 1,2-bis(triethoxysilyl)ethane). The trimethylsilyl-terminated PDMS chain can penetrate into the condensed and crosslinked PDMS network to provide flexibility to the resulting material. Comparing Examples 7 and 8 in Table 5 with Examples 13 and 14 in Table 6, the use of 1,2-bis(triethoxysilyl)ethane as a cross-linking agent reduces the elongation at break from 357% to 69.1%; comparing Examples 7 and 10, the use of a trimethylsilyl-terminated PDMS (DMS-T21) with a low molecular weight in Table 2 instead of a trimethylsilyl-terminated PDMS (DMS-T31) with a higher molecular weight reduces the elongation at break from 357% to 170%.

[0069] Referring to Comparative Examples 16 and 17 in which the first mixture and the second mixture were combined at a weight ratio of 24:1, these compositions lacked the property of being remodeled into a viscoelastic liquid at a temperature greater than about 170°C.

[0070] Example 5 in Table 3, Example 6 in Table 4, Examples 8 and 9 in Table 5, and Examples 14 and 15 in Table 6 have the characteristics of thermosetting polymers under ambient conditions and can be reshaped into viscoelastic liquids at a temperature greater than about 170°C, while retaining a tensile strength of no more than 60% and an elongation at break of no more than 70% at room temperature. Table 3 Table 4 Table 5: Table 6

[0071] Industrial Applicability

[0072] By using a dynamic bond activator that promotes the exchange of Si-O between adjacent silicon-oxygen main chains, the polymer of the present invention can be reformed and reshaped when heated. However, under ambient conditions, the polymer exhibits typical properties of thermosetting materials. The polymer has a stable cross-linked structure that can maintain its shape and mechanical properties. In one aspect, when heated to a temperature above about 170°C, the dynamic bond activator promotes the exchange of Si-O bonds. This process makes the polymer behave like a viscoelastic liquid, thereby enabling reshaping and reprocessing. Importantly, the reshaping process does not significantly reduce the properties of the material. On the contrary, at least some of the polymer compositions retain at least 60% of their tensile strength and at least 70% of their elongation at break compared to their environmental properties after reshaping. The retention of this mechanical property ensures that the material retains functionality and reliability after thermal processing. Therefore, the polymer can be used in many applications that require recyclability and reprocessability. These applications include reusable molds and seals, including molds and seals that may need to be periodically reformed. The material of the present invention is food contact safe and can be used in silicone food storage containers. The polymer can be used in self-healing materials and flexible electronic devices. Medical devices may also be made from the polymers because they are biocompatible and can be sterilized or remodeled.

[0073] The foregoing description of the present invention has been provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations will be apparent to those skilled in the art.

[0074] The embodiment was chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated.

[0075] As used herein and not otherwise defined, the terms "substantially," "substantially," "approximately," and "about" are used to describe and explain small variations. When used in conjunction with an event or circumstance, the terms may encompass instances where the event or circumstance occurs precisely as well as instances where the event or circumstance nearly occurs. For example, when used in conjunction with a numerical value, the terms may encompass a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0076] As used herein, the singular terms "a / an" and "the" may include plural referents unless the context clearly indicates otherwise. In the description of some embodiments, another component disposed "on" or "over" a component may include a situation where the former component is directly located on (e.g., physically in contact with) the latter component, as well as a situation where one or more intermediate components are positioned between the former component and the latter component.

[0077] Although the present disclosure has been described and shown with reference to the specific embodiments of the present disclosure, these descriptions and illustrations are not restrictive. It should be understood by those skilled in the art that various changes can be made and equivalents can be substituted without departing from the true spirit and scope of the present disclosure as defined by the appended claims. The illustrations may not necessarily be drawn to scale. Due to manufacturing processes and tolerances, there may be differences between the artistic demonstrations in the present disclosure and the actual equipment. There may be other embodiments of the present disclosure that are not specifically shown. The specification and the drawings should be considered illustrative rather than restrictive. Modifications may be made to make specific situations, materials, material compositions, methods or processes suitable for the goals, spirit and scope of the present disclosure. All such modifications are intended to fall within the scope of the appended claims. Although the methods disclosed herein have been described with reference to specific operations performed in a specific order, it should be understood that these operations can be combined, subdivided or rearranged to form equivalent methods without departing from the teachings of the present disclosure. Therefore, unless explicitly indicated herein, the order and grouping of operations are not limited.

Claims

1. A polymer composition having a covalently bonded network that can be altered by heat-activated bond exchange producing dynamic crosslinks, characterized in that The polymer composition comprises: A silicon-oxygen backbone elastomer for producing a polymer network; a non-agglomerated filler dispersed within and bonded to the polymer network; A catalyst for promoting the condensation reaction; a crosslinking agent selected from one or more silanes containing one or more methoxy or ethoxy groups; at least one dynamic bond activator, the at least one dynamic bond activator promoting Si-O bond exchange between adjacent silicon-oxygen backbone elastomers of the polymer network such that dynamic crosslinks formed between the adjacent silicon-oxygen backbone elastomers produce a three-dimensional crosslinked polymer network; The polymer composition has the characteristics of a thermosetting polymer under ambient conditions in bulk form and can be reshaped into a viscoelastic liquid at a temperature greater than 170°C.

2. The polymer composition according to claim 1, characterized in that The silicon-oxygen main chain elastomer is selected from one or more of trimethylsilyl-terminated polydimethylsiloxane and silanol-terminated polydimethylsiloxane.

3. The polymer composition according to claim 2, characterized in that The silicon-oxygen backbone elastomer has a molecular weight of 5,970 to 139,000 g / mol and a viscosity of 100 to 150,000 cSt, and is present in the composition in an amount of 49.6 to 65.6 wt%.

4. The polymer composition according to claim 2, characterized in that The filler includes hexamethyldisilazane treated silica in an amount of 24.9 to 36.9 wt%.

5. The polymer composition according to claim 1, characterized in that The at least one dynamic bond activator is an ionic salt selected from ammonium salts or phosphonium salts, and the amount of the ionic salt is 0.09 to 2.5 wt%.

6. The polymer composition according to claim 5, characterized in that The at least one dynamic bond activator is tetrabutylphosphonium hydroxide.

7. The polymer composition according to claim 1, characterized in that The at least one catalyst includes dibutyltin dilaurate or dibutyltin dioctoate in an amount of 0.12 to 2.3 wt%.

8. The polymer composition according to claim 1, characterized in that The crosslinking agent includes silane having an ethoxy group and silane having a methoxy group in an amount of 2.7 to 25.0 wt %.

9. The polymer composition according to claim 8, characterized in that The crosslinking agent is selected from one or more of 1,2-bis(triethoxysilyl)ethane, poly(dimethoxysiloxane), poly(diethoxysiloxane) and tetraethyl silicate.

10. The polymer composition according to claim 1, characterized in that The reshaped polymer composition retains at least 60% of the tensile strength and at least 70% of the elongation at break at room temperature.

11. A method for preparing the polymer composition according to claim 1, characterized in that The method comprises: combining a first silicon-oxygen backbone elastomer with a filler and a crosslinker to form a first mixture; combining a second silicon-oxygen backbone elastomer with a filler and a catalyst to form a second mixture; combining the first mixture with the second mixture to form a third mixture, wherein the first mixture and the second mixture are combined in a weight ratio of 1.1:1 to 8.3:1; combining the third mixture with at least one dynamic bond activator to form a fourth mixture; and The fourth mixture is cured to form the polymer composition.

12. The method according to claim 11, characterized in that Further comprising heating the polymer composition at a temperature of 50 to 80° C. in a vacuum.

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