WO2013127989A1

WO2013127989A1 - Self-healing elastomeric material

Info

Publication number: WO2013127989A1
Application number: PCT/EP2013/054147
Authority: WO
Inventors: Ibon Odriozola; Alaitz REKONDO; Roberto Martín; Germán Cabañero
Original assignee: Fundación Cidetec
Priority date: 2012-03-02
Filing date: 2013-03-01
Publication date: 2013-09-06
Also published as: EP2820087A1

Abstract

A self-healing elastomeric material comprising at least a) a crosslinked diorgano polysiloxane and b) a polymer or bitumen is described. Several procedures for the preparation of the self-healing elastomeric materials of the invention as well as uses thereof are also described.

Description

SELF-HEALING ELASTOMERIC MATERIAL

The present invention relates to the field of polymeric materials, and to elastomeric materials specifically. Particularly, the invention refers to a self- healing elastomer material and methods for its preparation.

BACKGROUND ART

Self-healing materials are generating great interest due to the wide range of potential applications they have shown. A self-healing polymer must possess the ability to form multiple bonding interactions in and around a damaged area, creating links between the different components that comprise its structure. Up to date, four strategies have been developed to achieve this challenge: (a) encapsulation of reactive monomers that are released after a breaking of capsules, (b) formation of new covalent irreversible bonds in the damaged area, (c) supramolecular self-assembling, and (d) reversible covalent bond formation. Encapsulation of monomers has been successfully used in some applications, but is limited by the irreversible nature of the self-healing mechanism, since reparation can occurs only once in each site. The same reasoning can be applied to irreversible covalent bonds that are generated in the damaged area. A particularly interesting approach for generating self-healing polymers is to introduce reversible cross-linking points in the polymeric network. Thus, cross-linking points which break when the material undergoes fracture may be reformed, recovering the integrity of the material. Still, most of the covalent reversible systems developed up to date, require the application of heat, light or other source of source for the healing reaction to take place, a fact which considerably limits their practical application.

Manufacturing of elastomers capable of self-repair is an area that is

becoming a matter of great interest in recent years. This is because these materials could have great potential for making self-healing roads, dumping systems, etc. Today there are few elastomeric materials with self-healing properties described in the literature. One of the most significant ones is perhaps the one developed by Cordier and colleagues (Cordier P., "Self- healing and thermo-reversible rubber from supramolecular assembly", Nature, 2008, vol. 451 (7181 ), p. 977-980). This material has a high self-healing power, however, it does not present high thermal stability, which limits their usefulness in applications requiring high temperatures, as for example the production of bitumen. Currently the product is being exploited by Arkema (France), under the brand Reverlink ®.

Other frequent limitations of existing self-healing elastomeric materials are the poor mechanical properties and its incompatibility with other materials along with the difficulty of their synthesis.

While up to date several self-healing elastomers have already been

described in the literature, searching for a polymer system that overcomes all these limitations continues. The possibility of obtaining a self-healing elastomeric system capable of being compatible with a wide range of organic and polymeric materials, would provide an enormous advantage with respect to the present elastomeric materials.

SUMMARY OF THE INVENTION

The present invention concerns an elastomeric material capable of self- healing.

Therefore, the first aspect of the present invention relates to a self-healing elastomeric material comprising a diorgano polysiloxane cross-linked by means of borate ester reversible bonds, hereinafter Component A, and at least one polymer, at least one bitumen or mixture of polymer and bitumen, hereinafter component B. The component A is a diorgano polysiloxane containing terminal hydroxyl groups which are functionalized in a borate ester form so having a cross- linked structure by these reversible borate ester linkages.

The resulting material of the invention is especially suitable for preparing self- healing elastomeric material compounds.

According to a preferred embodiment, the diorgano polysiloxane has a kinematic viscosity comprised from 2.5·10^"4 to 2.5·10^"2 m²/s a 25 °C, being the most preferred comprised from 2.5·10^"4 to 2·10³ m²/s.

Particularly preferred is the use of a polydimethylsiloxane with a kinematic viscosity comprised from 5·10^"4 to 10·10^"4 m²/s at 25 °C.

According to one embodiment of the present invention the diorgano

polysiloxane containing terminal hydroxyl groups is a (C-fC₆) alkyl- polysiloxane, (Ci-C₆) alkyl-(C₅-C₆) arylpolysiloxane or (C₅-C₆) straight chain aryl-polysiloxane containing terminal hydroxyl groups, preferably selected from the group consisting of a poly-dimethylsiloxane, a poly-diethylsiloxane, a poly-dipropylsiloxane a poly-dibutylsiloxane a poly-diphenylsiloxane or poly- methylphenylsiloxane containing terminal hydroxyl groups, being the most preferred a poly-dimethylsiloxane (PDMS) containing terminal hydroxyl groups.

Particularly preferred is the use of a PDMS containing terminal hydroxyl groups with a kinematic viscosity comprised from 5·10^"4 to 1 O10^"4 m²/s. Being even most preferred a hydroxyl-terminated PDMS having a kinematic viscosity of 7.5·10^"4 m²/s.

Advantageously, the introduction of a diorgano poly-siloxane reversibly cross- linked by borate ester bonds (component A), provides a three-dimensional network which is mixed with the component B, obtaining a homogeneous material with the consistency of an elastomer. The result is a surprising material with self-healing capability and which does not undergo phase separation.

One particular embodiment of the invention provides a self-repairing material comprising at least one poly-dimethylsiloxane polymer chain functionalized with two terminal hydroxyl groups (OH), in which 10-100% of such terminal hydroxyl groups are in the form of borate ester forming a three-dimensional network. Thus preferably, at least comprised from 50 to 100% of the hydroxyl terminations are in borate ester form, and most preferably comprised from 80 to 100%.

According to a particular embodiment of the present invention, the amount of component A in the elastomeric material is comprised from 5 to 95% being these percentages in weight relative to the total material . Preferably 10-85 wt%, more preferred from 20-80 wt%. Even more preferred is an amount comprised from 40-75% weight of the total component of the material .

Regarding the amount of component B, according to a particular embodiment of the present invention, this component quantity is comprised from 95 to 5% weight in the final elastomeric material, preferably 90-15%, and more preferably comprised from 80 to 20% in weight. Even more preferred is an amount in the range comprised from 60 to 25% in weight of component B with respect to the total material .

Thus, in a particularly preferred embodiment according to the present invention, the amount of diorgano polysiloxane containing terminal hydroxyl groups functionalized as borate esters (component A) is between 40-75% in weight relative to the total weight of elastomeric material, and the amount of polymer, bitumen or mixture of bitumen and polymer (component B) is comprised from 60 to 25% in weight relative to the total weight of elastomeric material.

Regarding the ratio of diorgano polysiloxane - borated compound in component A, according to a particular embodiment of the present invention the quantity of diorgano polysiloxane is comprised from 80 to 99% of the total weight in component A. Preferably 85-98% and more preferably comprised from 90 to 95%. While the borated compound (boric acid, boric anhydride, borate (C C₄) alkyl ester, (C C₄) alkyl and (C₅-C₆) and aryl boronic acid and their (Ci-C₄)alkyl esters, a metallic borate being the metal selected from K, Na, Li, Ca, Mg and borax) is present in an amount ranging from 20 to 1 % weight of the total of component A, preferably 15-2% and more preferably comprised from 10 to 5% in relation to the total weight of component A.

In some cases, when the proportion of component B in the self-healing material is over 25%, it is necessary to apply a pressure for such reparation to occur. The magnitude of such pressure depends on the final composition of the material, typical pressures being comprised from 0.1 to 10 MPa.

As mentioned above, the component B of the elastomeric material, according to the present invention, comprises at least one polymer, at least one bitumen or mixture of polymer and bitumen.

According to one embodiment of the present invention, the polymer or mixture of polymers used as component B is selected from the known polymers useful in the preparation of construction and structural materials. According to a preferred embodiment of the present invention, the polymer of component B is selected from: polyethylene (PE, high density polyethylene HDPE, low density polyethylene LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polycarbonate (PC), polyesters, polyethers, polyacrylates, polymethacrylates, polyurethanes, polyureas, polytetrafluoroethylene (Teflon or PTFE), styrene-butadiene-styrene (SBS), styrene-ethylene-butylene- styrene (SEBS), natural rubber, nitrile butadiene rubber (NBR),

polybutadiene, polyisoprene, polychloroprene, ethylene-propylene-diene (EPDM), polyvinyl alcohol, polylactic acid (PLA), polyvinylacetate (PVAc), ethylene-vinyl acetate (EVA), polyacetals, polyvinyl ketones, polyamides, polyacrylamides, polymethacrylamides, polycaprolactone, polyacrylonitrile (PAN), acrylonitrile-styrene copolymers (ABS), styrene-acrylonitrile

copolymers (SAN), polysulfones, polyimides, polyditiazoles,

polybenzothiazoles, polyanhydrides, polythiophenes, cellulose derivatives, phenolic resins, melamine-formaldehyde, urea-formaldehyde, silicones and mixtures thereof.

In a particular embodiment, the polymers present in component B are silicon- free polymers.

According to a more preferred embodiment of the present invention, the polymers may be present in component B are selected from:

polyethylene (PE), high density polyethylene (HDPE), low density

polyethylene (LDPE), ultrahigh molecular weight polyethylene (UHMWPE), polypropylene (PP), polytetrafluoroethylene (PTFE), polystyrene (PS), polyvinylchloride (PVC), styrene-butadiene copolymers (SBS), styrene- ethylene-butylene-styrene (SEBS), thermoplastic polyurethane (TPU), polyvinyl acetate (PVAc), polyvinyl alcohol copolymers, acrylonitrile- butadiene-styrene (ABS) copolymers, ethylene-propylene-diene (EPDM), natural rubber, nitrile butadiene rubber, polybutadiene, polyisoprene, polychloroprene and mixtures thereof. Particularly preferred is the use of polyethylene (PE), high density

polyethylene (HDPE), low density polyethylene (LDPE), polyethylene of ultrahigh molecular weight (UHMWPE), polypropylene (PP),

polytetrafluoroethylene (PTFE), styrene butadiene-styrene copolymers (SBS), styrene-ethylene-butylene-styrene copolymers (SEBS), thermoplastic polyurethane (TPU), ethylene-propylene-diene copolymers (EPDM), natural rubber, polyisoprene and mixtures thereof. According to another embodiment, component B comprises at least one bitumen, or mixtures made from the above polymers and copolymers and bitumen.

In the preparation of component A, a boron derivative may be used selected from boric acid, boric anhydride, borate (Ci-C₄)alkyl ester, (Ci-C₄)alkyl and (C₅-C₆)aryl boronic acids and their (Ci-C₄)alkyl esters, a metallic borate being the metal selected from K, Na, Li, Ca, Mg and sodium tetraborate (borax). Preferably, the boron derivative is selected from boric acid, borax and sodium borate.

The present invention also relates to processes for the preparation of self- healing elastomeric materials as defined above. Thus, the invention relates to a process for preparing self-healing elastomer material of the invention, the method comprising the following steps:

a) mixing the diorgano polysiloxane-containing terminal hydroxyl groups with the polymer, the bitumen or mixture of polymer and bitumen at a temperature comprised from room temperature to 250 °C;

b) adding a boron derivative selected from boric acid, boric anhydride, borate (Ci-C₄)alkyl ester, (Ci-C₄)alkyl and (C₅-C₆)aryl boronic acids and therir (d- C₄)alkyl esters, a metallic borate being the metal selected from K, Na, Li, Ca,

Mg and borax;

c) stirring of the resulting mixture until a homogeneous elastomeric material is obtained. According to a particular embodiment of the present invention, the

preparation process is carried out at a temperature comprised from room temperature to 50 °C. In a more preferred embodiment, the process is carried out at room temperature.

According to a particular embodiment, the method is carried out at a temperature comprised from 150 to 200 °C.

Another aspect of the invention refers to an alternative method for preparing the self-healing elastomer material of the invention, the method comprising the following steps:

a) heating the polymer, the bitumen or mixture of polymer and bitumen at a temperature comprised from 100 to 250 °C, preferably 150-200 °C;

b) adding the diorgano polysiloxane previously crosslinked with a boron derivative selected among boric acid, boric anhydride, borate (Ci-C₄)alkyl ester, (Ci-C₄)alkyl and (C₅-C₆)aryl boronic acids and their (Ci-C₄)alkyl esters, a metallic borate the metal being selected from K, Na, Li, Ca, Mg and borax, stirring the mixture until obtaining of an homogeneous mass.

This alternative procedure avoids the direct use of boric acid or borax, substances whose handling is being subjected to regulation due to their toxicity.

It is obvious for experienced readers that, in the process for preparing the elastomeric material of the invention, would be possible to interchange the order of steps a) and b). The self-healing polymeric material of the invention may also be defined by its own preparation procedure. In this sense, a self-healing material obtainable by the process of the invention is also considered part of the invention.

A third aspect the invention relates to the use of self-healing elastomeric material as defined above as an additive or component in the preparation of asphalt.

Further aspects of the present invention relate to the use of self-healing elastomeric material as defined above in the manufacture of anti-vibration systems, magneto-rheological elastomers, adhesives, construction materials, insulation, etc. In another aspect the invention relates to an item made with the self-healing elastomeric material of the invention.

In still another aspect the invention relates to a method for manufacturing an item as defined above, the method comprising manufacturing the item from the self-healing elastomer material of the invention.

The term "three-dimensional network" refers to a cross-linked polymer containing borate ester linkages and refers to the self-healing final product.

The term "polymer chain" refers to a straight or branched large molecule or macromolecule composed of many monomers linked to each other.

The borate ester linkages mentioned above refer to a chemical bonding that happens between the terminal hydroxyl groups (OH) present in the diorgano polysiloxanes and the borate groups coming from borated compound (boric acid, boric anhydride, borate (Ci-C₄)alkyl ester, (Ci-C₄)alkyl and (C₅-C₆)aryl boronic acids and their (Ci-C₄)alkyl esters, a metallic borate the metal being selected from K, Na, Li, Ca, Mg and borax).

Bitumen is, as defined in ASTM (American Society for Testing and Materials) a material consisting of dark brown or black color comprising a mixture of bituminous products, which are found in nature or are obtained in petroleum processing. Technically, the bitumen is a petroleum fraction which distills above 535 °C and is formed by chemical compounds with molecular weights above 600 Da. Thus, according to the present invention, the term "asphaltic bitumen" refers to bitumen as defined above having the characteristics and properties suitable for use in paving. It is important to note that the terminology used to refer to various bituminous products can create some confusion, since in Europe is called with the word "bitumen" or "asphalt" to what is known in the United States with the word "asphalt". However, in Europe the word asphalt immediately suggests the asphaltic mixture of bitumen with mineral aggregates. In the context of the present invention, the terms asphalt and bitumen are used as used in Europe.

The term "thermoplastic polyurethane" refers to a linear elastomeric polymer, and therefore, thermoplastic, obtained by reacting polyols, diisocyanates and short chain diols.

As mentioned above, the self-healing elastomer material of the invention can be prepared simply by reacting, in the presence of a component B, at least one diorgano polysiloxane functionalized with at least two hydroxyl groups, with at least one boron compound, preferably in the form of boric, borate or tetraborate (borax). The process may be carried out either at room

temperature or at higher temperatures, depending on the nature of the component B in each case.

In a particular embodiment, component B is a thermoplastic polymer such as styrene-butadiene-styrene (SBS), and the process may be carried out at a temperature above the melting temperature of said polymer, thereby achieving a more homogeneous final material with better performances.

The derivative of boron should be added in sufficient quantity to cross-link at least part of the chains of diorgano polysiloxane containing terminal hydroxyl groups. Preferably, to cross-link all the polymer chains from the diorgano polysiloxane compound.

For a polydimethylsiloxane (PDMS) with viscosity 7.5·10^"4 m²/s, the optimum amount of boric acid is 5% weight, relative to the amount of PDMS. Preferably the derivative of boron is boric acid, a borate or borax. The boron compound may be added in solution.

The formation of the elastomer can be conducted in the presence of a suitable solvent such as water or an organic solvent. In this case, the boron derivative can be dissolved or dispersed in the solvent and this mixture can be added to the diorgano polysiloxane of component B. Alternatively, the boron derivative in powder form can be added to a solution of diorgano polysiloxane and component B in a suitable solvent.

Among suitable organic solvents, are included but not limited N,N- dimethylformamide (DMF), dimethylsulfoxide (DMSO). The organic solvent may be removed when the reaction is considered finished to obtain the final elastomeric material. In a particular embodiment, a PDMS (7.5·10^"4 m²/s, 71 .25 wt%) is mixed with a styrene-butadiene-styrene (SBS, 25 wt%) previously melted at 200 °C and to the said mixture boric acid is added (3.75 wt%). The result is an

elastomeric material which does not flow, but has the capacity to heal itself by applying pressure at room temperature for 16 hours. It has been observed that the resulting elastomeric material also has the capacity to heal itseft by simple contact at room temperature in less than 1 hour. In another particular embodiment, a PDMS (7.5·10^"4 m²/s, 47.5%) is mixed with bitumen (50 wt%) at 200 °C and boric acid is added to the said mixture (2.5% by weight). The result is an elastomeric material capable of self-healing by applying pressure at room temperature for 16 hours. The performance of self-healing depends on the ratio between component A and component B, and the nature of the latter. The higher the proportion of component A, the better the performance of self-repair material, but it will provide greater fluidity. The reversible cross-linking borate esters provide a tridimensional-shaped network with constant exchange, thus conferring great self-healing power to the resulting material.

In case of breakage, the self-healing procedure in the polymeric network of the invention, can occur in a short period of time and sometimes without any external stimulus. Thus, when the elastomeric material is cut into two pieces it self-heals repaired again, sometimes in a matter of seconds, only placing the two parts in contact with each other. Furthermore, the ability of the self- healing material of the invention does not depend on the number of breakage/repair cycles to which it is subjected, the procedure may be repeated many times without observing any decrease in the self-healing power.

The self-healing elastomeric material of the invention may have application in different areas such as the manufacture of building materials, asphalt, anti- vibration systems, gaskets, magneto-rheological elastomers, adhesives, insulation, etc. Therefore, these uses are also part of the invention. In a particular embodiment, the elastomeric material of the invention can be used as additive for the production of bitumen with self-healing properties. Throughout the description and claims the word "comprise" and variations of the word, are not intended to exclude other technical features, additives, components, or steps. Furthermore, the word "comprise" encompasses the case of "consisting of. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided by way of illustration, and they are not intended to be limiting of the present invention. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.1 shows pictures of the different stages that make up the general procedure of the hot synthesis (200 °C) of self-healing elastomeric materials. The polymeric material in pellet form (a) was added to the internal mixer (preheated to 200 °C) to observe their complete melting (b). Thereafter the polydimethylsiloxane (PDMS) was added obtaining a completely

heterogeneous mixture (c). Finally, boric acid was added and the mixture was kept under mechanical mixing until the formation of a material with

homogeneous appearance (d).

Fig. 2 represents the self-healing procedure of the elastomeric material containing 25%SBS and obtained according to Example 4. The cylindrical elastomeric material (a) was cut in half (b). Then the two halves were placed next to each other (c) and allowed to stand in contact for 1 hour. After this time the material was completely restored into one piece (d).

Fig.3 represents the self-healing procedure of the elastomeric material obtained according to Example 5.

Fig.4 represents the self-healing procedure of the elastomeric material obtained according to Example 7. Fig.5 represents the self-healing procedure of the elastomeric material obtained according to Example 9. Fig.6 shows scanning electron microscopy (SEM) micrographs of the elastomeric materials obtained according to Examples 4 and 8.

EXAMPLES EXAMPLE 1 . General procedure for the hot synthesis of self-healing elastomeric materials

A polymeric material (Fig. 1 a), a bitumen or a mixture thereof was placed into an internal mixer (preheated to 200 °C) until obtaining a uniform melt (Fig. 1 b). Hydroxyl-terminated polydimethylsiloxane (PDMS) with a viscosity of 7.5·10^"4 m²/s was then added, obtaining a completely heterogeneous mixture (Fig. 1 c). Then boric acid was added (5% in weight with respect to PDMS) and the mixture was kept under stirring until the formation of a homogeneous material (Fig.l d). Finally, the resulting material was allowed to cool to room temperature.

EXAMPLE 2. General procedure for the hot synthesis of self-healing elastomeric materials starting from previously cross-linked silicone with boric acid

A polymeric material, a bitumen or a mixture thereof was placed into an internal mixer (preheated to 200 °C) until obtaining a uniform melt.

Simultaneously, hydroxyl-terminated polydimethylsiloxane (PDMS) with a viscosity of 7.5·10^"4 m²/s and a boric acid 5 wt% solution in DMSO (0.5 mL) were mixed manually in a beaker with the aid of a spatula. After

approximately 5 minutes of stirring, formation of an elastomeric material occurred as a result of cross-linkage between hydroxyl groups coming from PDMS and boric acid. Then the cross-linked elastomer was added to the internal mixer and the mixture was kept under stirring until formation of an homogeneous material. Finally the resulting material was allowed to cool to room temperature. EXAMPLE 3. General procedure for the room-temperature synthesis of self- healing elastomeric materials

In a beaker, a polymeric material (in powder form) and hydroxyl-terminated polydimethylsiloxane (PDMS) with a viscosity of 7.5·10^"4 m²/s were added. After mixing manually with the aid of a spatula, a solution of boric acid (5 wt% with respect to PDMS) in DMSO (0.5 ml_) was added with additional stirring. Approximately 5 minutes after of agitation, formation of the elastomeric material occurred, to give a homogeneous solid.

EXAMPLE 4. Synthesis of SBS-25% silicone elastomer

The material was prepared following the procedure described in Example 1 : - SBS (KRATON D1 184CM): 12.5 g

- PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma-Aldrich): 35.6 g

- Boric acid (Sigma Aldrich): 1 .9 g

The procedure rendered a yellowish elastomer. In order to test its self-healing capacity, a cylindrical probe was prepared using a plastic syringe as template. Then it was broken in half, and the two halves were immediately put in contact again and left to stand for 1 hour. After this time the self-healing elastomer was completely repaired, the fracture zone not being able to observe (Fig. 2). This operation may be repeated several times without observing any loss in self-healing power.

EXAMPLE 5. Synthesis of SBS-50% silicone elastomer

The material was prepared following the procedure described in Example 1 :

- SBS (KRATON D1 184CM): 25 g

- PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma-Aldrich): 23.75 g

- Boric acid (Sigma Aldrich): 1 .25 g

A brown elastomer was obtained. To test the self-healing ability of the resulting elastomeric material, the same procedure described in Example 4 was repeated. After 1 hour the piece was not entirely self-repaired and it took a longer healing time (12 hours) to obtain a complete self-reparation (Fig. 3).

EXAMPLE 6. Synthesis of SBS-50% silicone elastomer using silicone previously cross-linked with boric acid

The procedure described in Example 2 was followed:

- SBS (KRATON D1 184CM): 25 g

- PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma-Aldrich) 23.75 g

- Boric acid (Sigma Aldrich) 1 .25 g in DMSO (2 ml_)

A yellowish elastomer was obtained. To test the self-healing ability of the resulting elastomeric material, the same procedure described in Example 4 was repeated. After 12 hours of contact a complete self-healed material was obtained.

EXAMPLE 7. Room-temperature synthesis of SBS-25% silicone elastomer The procedure described in Example 3 was followed:

- SBS (KRATON D1 184CM): 1 .25 g

- PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma-Aldrich): 3.56 g

- Boric acid (Sigma Aldrich) 0.19 g in DMSO (0.5 mL) A yellowish elastomer was obtained. To test the self-healing power of the resulting elastomeric material a cylindrical specimen was prepared and cut it in half with a "cutter". Immediately after, the two sides were again contacted. After 1 hour one cannot differentiate the fracture zone corroborating the total capacity of the elastomer to self-heal (Fig. 4).

The following Examples 8 and 9 refer to elastomeric materials obtained at room temperature and according to the general procedure described in Example 3. These elastomeric materials were synthesized from a mixture of Teflon (PTFE) powder and hydroxyl-terminated polydimethylsiloxane subsequently cross-linked with boric acid.

EXAMPLES 8-9. Room-temperature synthesis of Teflon-Silicone elastomeric materials Similarly to Example 7, the elastomeric materials of Examples 8 and 9 were obtained using the following amounts of each reagent:

- PTFE powder (1 micron) (1 .25 g, Sigma Aldrich), PDMS (hydroxyl- terminated, viscosity 7.5·10^"4 m²/s, Sigma-Aldrich) (3.56 g) and a solution of boric acid (0.19 g) in DMSO (0.5 ml_); and

- PTFE powder (1 micron) (2.5 g), PDMS (hydroxyl-terminated, viscosity 7.5Ί 0^"4 m²/s, Sigma-Aldrich) (2.375 g) and a solution of boric acid (0.125 g) in DMSO (0.5 ml_).

To test the self-healing ability of the resulting elastomeric materials, cylindrical samples were prepared and cut in half with a knife. Immediately after, the two parts were contacted. After 1 hour, one cannot differentiate the fracture zone, corroborating the total capacity of the self-healing elastomers (Fig. 5). This procedure was repeated several times with no evidence of the cut/reparation site or loss in the capacity of self-healing elastomeric materials

The following Examples 10-19 relate to the production of elastomeric materials at 200 °C according to the general procedure described in Example 1 . The elastomeric materials were synthesized from a mixture of a polymeric material or bitumen in the molten state and hydroxyl-terminated poly- dimethylsiloxane which was subsequently cross-linked with boric acid. EXAMPLES 10-1 1 . 200 °C Synthesis of TPU-Silicone elastomeric materials

Similarly to Examples 4 and 5, the elastomeric materials of Examples 10 and 1 1 were obtained using the following amounts of each reagent:

- TPU pellets (12.5 g; DESMOPAN 445, Bayer), PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma-Aldrich) (35.6 g) and boric acid (1 .9 g).

- TPU pellets (25 g), PDMS (hydroxyl-terminated, viscosity 7.5Ί 0^"4 m²/s, Sigma-Aldrich) (23.75 g) and boric acid (1 .25 g).

To test the self-healing ability of the resulting elastomeric materials the same break-repair assay in the above Examples was performed, verifying that the elastomeric material of Example 10 containing 25% TPU self-heals completely after 1 hour of "resting", while the material from Example 1 1 and containing 50% TPU needs 12 hours to achieve the same degree of self- reparation.

EXAMPLES 12-13. Synthesis of PP-Silicone elastomeric materials at 200 °C Similarly to Examples 4 and 5, the elastomeric materials of Examples 12 and 13 were obtained using the following amounts of each reagent:

- PP pellets (12.5 g), PDMS (hydroxyl-terminated, viscosity 7.5Ί 0^"4 m²/s, Sigma-Aldrich) (35.6 g) and boric acid (1 .9 g); and

- PP pellets (25g), PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma- Aldrich) (23.75 g) and boric acid (1 .25 g)

To test the self-healing ability of the resulting elastomeric materials, the same break-repair assay in the above Examples was carried out, obtaining the same results.

EXAMPLES 14-15. Synthesis of PE-Silicone elastomeric materials at 200 °C.

Similarly to Examples 4 and 5, the elastomeric materials of Examples 14 and 15 were obtained using the following amounts of each reagent:

- PE pellets (12.5 g), PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma-Aldrich) (35.6 g) and boric acid (1 .9g); and

- PE pellets (25 g), PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma-Aldrich) (23.75 g) and boric acid (1 .25 g).

To test the self-healing ability of the resulting elastomeric materials, the same break-repair assay in the above Examples was carried out, obtaining the same results. EXAMPLES 16-17. Synthesis of EPDM-silicone elastomeric materials at 200°

C

Similarly to Examples 4 and 5, the elastomeric materials of Examples 16 and 17 were obtained using the following amounts of each reagent:

- EPDM (12.5 g), PDMS (hydroxyl-terminated, viscosity 7.5Ί 0^"4 m²/s, Sigma-

Aldrich) (35.6 g) and boric acid (1 .9 g); and

- EPDM (25 g), PDMS (hydroxyl-terminated, viscosity 7.5Ί 0^"4 m²/s, Sigma- Aldrich) (23.75 g) and boric acid (1 .25 g). To test the self-healing ability of the resulting elastomeric materials, the same break-repair assay in the above Examples was carried out, obtaining the same results. EXAMPLES 18-19. Synthesis of Bitumen-Silicone elastomeric materials at 200 °C Similarly to Examples 4 and 5, the elastomeric materials of Examples 18 and 19 were obtained using the following amounts of each reagent:

- Bitumen (12.5 g), PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma-Aldrich) (35.6 g) and boric acid (1 .9 g); and

- Bitumen (25 g), PDMS (hydroxyl-terminated, viscosity 7.5·10^"4 m²/s, Sigma- Aldrich) (23.75 g) and boric acid (1 .25 g).

To test the self-healing ability of the resulting elastomeric materials, the same break-repair assay in the above Examples was carried, out obtaining the same results.

EXAMPLE 20. SEM analysis

SEM characterization was carried out in order to analyze the miscibility of silicone and the different organic polymer matrixes added in the elastomeric materials prepared in Examples 4 and 8. Samples of each material were prepared cutting a planar foil and depositing it on conductive adhesive tape. Subsequently, they were subjected to a sputtering process for coating with a gold layer thickness of 7-10 nm. Finally, images of elastomeric materials were recorded using scanning electron microscopy (SEM), proving that in both cases there is a homogeneous distribution of the organic load in the silicone matrix (Fig. 6a and b).

Claims

1 . Self-healing elastomeric material comprising: a) a diorgano polysiloxane containing terminal hydroxyl groups functionalized in form of borate ester, and b) a polymer, a bitumen or mixture of polymer and bitumen.

2. Elastomeric material according to claim 1 , wherein the diorgano

polysiloxane is a polydimethylsiloxane containing terminal hydroxyl groups.

3. Elastomeric material according to any of the claims 1 -2, wherein the diorgano polysiloxane has a viscosity comprised from 2.5·10^"4 to 2.5·10^"2 m²/s at 25 °C.

4. Elastomeric material according to any of the claims 1 -3, wherein the diorgano polysiloxane has a viscosity comprised from 2.5·10^"4 to 2·10³ m²/s at 25 °C.

5. Elastomeric material according to any of the claims 2-4, wherein the amount of diorgano polysiloxane containing terminal hydroxyl groups functionalized in the form of borate ester is comprised from 40 to 90% weight, relative to the total weight of the material; and the amount of polymer, bitumen or mixture of polymer and bitumen is comprised from 60 to 10% weight relative to the total weight of the material.

6. Elastomeric material according to any of the claims 1 -5, wherein the polymer is selected from polyethylene, high density polyethylene, low density polyethylene, ultrahigh molecular weight polyethylene, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, polyesters, polyethers, polyacrylates, polymethacrylates, polyurethanes, polyureas,

polytetrafluoroethylene, styrene-butadiene-styrene copolymers, styrene- ethylene-butylene-styrene copolymers, natural rubber, nitrile butadiene rubber, polybutadiene, polyisoprene, polychloroprene, ethylene-propylene- diene copolymers, polyvinyl alcohol, polylactic acid, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyacetals, polyvinyl ketones,

polyamides, polyacrylamides, poly-methacrylamides, polycaprolactone, polyacrylonitrile, acrylonitrile-butadiene styrene copolymers, styrene- acrylonitrile copolymers, polysulfones, polyimides, polyditiazoles, polybenzothiazoles, poly-anhydrides, poly-thiophenes, cellulose derivatives, phenolic resins, melannine-fornnaldehyde resins, urea-formaldehyde, silicones and mixtures thereof.

7. Elastomeric material according to any of the claims 1 -6, wherein the polymer is selected from polyethylene, high density polyethylene, low density polyethylene, ultrahigh molecular weight polyethylene, polypropylene, poly- tetrafluoroethylene, polystyrene, polyvinyl chloride, styrene-butadiene-styrene copolymers, styrene-ethylene-butylene-styrene copolymers, thermoplastic polyurethane, polyvinyl acetate, polyvinyl alcohol, acrylonitrile-butadiene- styrene copolymer, ethylene-propylene-diene copolymers, natural rubber, nitrile butadiene rubber, poly-butadiene, poly-isoprene, poly-chloroprene and mixtures thereof.

8. Elastomeric material according to any of the claims 1 -7, wherein the polymer is selected from polyethylene, high density polyethylene, low density polyethylene, ultrahigh molecular weight polyethylene, polypropylene, polytetrafluoroethylene, styrene-butadiene-styrene copolymers, styrene- ethylene -butylene-styrene copolymers, thermoplastic polyurethane, ethylene- propylene-diene copolymers, natural rubber, polyisoprene and mixtures thereof.

9. Elastomeric material according to any of the claims 1 -5, which comprises a polydimethylsiloxane containing terminal hydroxyl groups functionalized in the form of borate ester and an asphaltic bitumen.

10. Process for the preparation of an elastomeric self-healing material as defined in a any of the claims 1 -9, the process comprising:

a) mixing the diorgano polysiloxane containing terminal hydroxyl groups with the polymer, bitumen or mixture of asphaltic bitumen and polymer at a temperature in the range from room temperature to 250 °C;

b) adding a boron derivative selected from boric acid, boric anhydride, borate (Ci-C₄)alkyl ester, (Ci-C₄)alkyl and (C₅-C₆)aryl boronic acids and their

(Ci-C₄)alkyl esters, a metallic borate being the metal selected from K, Na, Li, Ca, Mg and borax;

c) stirring the resulting mixture until a homogeneous elastomeric material is obtained.

1 1 . Process according to claim 10, wherein the mixing is carried out at a temperature comprised from room temperature to 50 °C.

12. Process according to claim 10, wherein the mixing is carried out at a temperature comprised from 150 to 200 °C.

13. Process for the preparation of a self-healing elastomeric material as defined in any of the claims 1 -9, comprising mixing a diorgano polysiloxane containing terminal hydroxyl groups previously cross-linked with a boron derivative with a polymer, bitumen or the mixture of polymer and bitumen previously heated at a temperature comprised from 150 to 250 °C, and stirring the resulting mixture until a homogeneous elastomeric material is obtained.

14. Process according to any of the claims 10-13, wherein the diorgano polysiloxane is a polydimethylsiloxane containing terminal hydroxyl groups.

15. Process according to any of the claims 10-14, wherein the polymer is selected from polyethylene, high density polyethylene, low density

polyethylene, ultra-high molecular weight polyethylene, polypropylene, polystyrene, polyvinyl chloride, polycarbonatepolyesters, polyethers, polyacrylates, polymethacrylates, polyurethanes, polyureas,

polytetrafluoroethylene, styrene-butadiene-styrenecopolymers, styrene- ethylene-butylene-styrene copolymers, natural rubber, nitrile butadiene rubber, polybutadiene, polyisoprene, polychloroprene, ethylene-propylene- diene copolymers, polyvinyl alcohol, polylactic acid, polyvinyl acetate copolymers, ethylene-vinyl acetate copolymers, polyacetals, polyvinyl ketones, polyamides, polyacrylamides, polymethacrylamides,

polycaprolactone, polyacrylonitrile, acrylonitrile-butadiene-styrene

copolymers, styrene-acrylonitrile copolymers, polysulfones, polyimides, polyditiazoles, polybenzothiazoles, polyanhydrides, polythiophenes, cellulose derivatives, phenolic resins, melamine-formaldehyde resins, urea- formaldehyde, silicones and mixtures thereof.

16. Process according to any of the claims 10-15, wherein the polymer is selected from polyethylene, high density polyethylene, low density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polytetrafluoroethylene, polystyrene, polyvinylchloride, styrene-butadiene- styrene copolymers, styrene-ethylene-butylene-styrene copolymers, thermoplastic polyurethane, polyvinyl acetate, polyvinyl alcohol, acrylonitrile- butadiene-styrene copolymers, ethylene-propylene-diene copolymers, natural rubber, nitrile butadiene rubber, polybutadiene, polyisoprene,

polychloroprene and mixtures thereof.

17. Process according to any of the claims 10-16, wherein the polymer is selected from polyethylene, high density polyethylene, low density

polyethylene, ultra-high molecular weight polyethylene, polypropylene, polytetrafluoroethylene, styrene-butadiene-styrene copolymers, styrene- ethylene-butylene-styrene copolymers, thermoplastic polyurethane, ethylene- propylene-diene copolymers, natural rubber, polyisoprene and mixtures thereof.

18. Use of the self-healing elastomeric material as defined in any one of the claims 1 -9, for the production of bitumen.

19. Use of the self-healing elastomeric material as defined in any one of claims 1 -9, as an anti-vibration system, magneto-rheological elastomer, adhesive, or insulating material for construction.

20. Article made from the self-healing elastomeric material as defined in any one of the claims 1 -9.