ITMI20101223A1 - POLYURETHANE COMPOSITION FROM RENEWABLE RAW MATERIALS TO PREPARE SYNTHETIC SKINS - Google Patents

Description

Polyurethane composition from renewable raw materials to prepare synthetic leathers

The present invention relates to a polyurethane composition from renewable raw materials for preparing synthetic leathers.

Synthetic leathers (also called "eco-leathers", or "faux-leathers") are flexible materials obtained from textile substrates coupled to one or more layers of a polymer, generally of the polyurethane type, to give the surface a similar appearance to that of leather of animal origin. The textile substrate is generally a natural, synthetic or blended fiber substrate (for example, cotton, polyester or cotton / polyester fibers).

Synthetic leathers are used in sectors, such as furniture, clothing, leather goods and vehicle interior upholstery, where they are used to replace precious leathers (for example, leather and animal skins) or other materials with a lower cost. high or unsuitable for certain applications.

Polyurethanes are polymers obtained from the reaction of a diisocyanate or polyisocyanate (often referred to as component "A") with a polyol (component "B") and with the aid of other components which, in addition to favoring the reaction (catalysts), contribute to giving the polymer particular properties.

The properties of polyurethane materials can be extremely varied. By appropriately selecting components A and B, as well as the additional auxiliary components, it is possible to obtain polyurethane materials having mechanical characteristics, resistance to hydrolysis, resistance to chemical agents, and even very different fire behavior. The wide variety of uses of these materials is based on this versatility.

Some uses of polyurethanes, divided by categories, are listed below:

- rigid expanded polyurethanes, used as thermal insulators for construction, refrigeration, packaging and transport;

- Semi-rigid expanded polyurethane, used in the automotive industry and for safety applications;

- flexible polyurethane foam, used as padding for furniture, cars, toys;

- compact polyurethanes and elastomers, used as soles for footwear, synthetic leather, sports articles, yarns, bottoms for athletic tracks;

- polyurethanes for paints, used for furniture, the automotive industry and in the construction field;

- polyurethanes for adhesives, used in the wood and building industries;

- special polyurethanes, used for applications in the medical or electronic fields.

In the production of polyurethanes according to the state of the art, the polyisocyanic component can be a polymeric compound of the aromatic, cycloaliphatic or aliphatic type.

Examples of isocyanates used in the state of the art, alone or in mixture, are: methyldiphenyl-2,4'-diisocyanate (2,4'-MDI), methyldiphenyl-4,4'-diisocyanate (4,4'-MDI) , toluene-2,4-diisocyanate (2,4-TDI) toluene-2,6-diisocyanate (2,6-TDI), naphthalen-1,5-diisocyanate (NDI), isophorondisocyanate (IPDI), hexamethylene-1, 6-diisocyanate (HDI), tetramethylen-1,4-diisocyanate, hexahydroxotoluene diisocyanate, 3,3 <1> -dimethyl-4,4 <1> -diphenyl-diisocyanate, triisocyanates and polyisocyanates of MDI (pMDI). The polyisocyanates can be used singly or in mixture. Polyisocyanate blends have on average 1.8 to 2.2 isocyanate groups (NCOs) for each polyisocyanate molecule.

Isocyanates can also be used in modified form (prepolymers). The prepolymers are produced by reacting a stoichiometric excess of polyisocyanates with reactive substances towards the isocyanate groups (for example, polyol compounds).

Polyol compounds are compounds that contain two or more functional groups capable of reacting with the NCO groups of isocyanates (-OH, -SH groups, etc.). These functional groups are also referred to in the following description as "isocyanator-reactive" groups.

The polyols used in the preparation of the polyurethanes can be of different types, for example polyether polyols, polyester polyols and polylactone polyols.

Polyether polyols include polymers of ethylene oxide, tetrahydrofuran, propylene oxide or their mixtures, either as physical mixtures or as ordered or random copolymers. These polyols can be linear or branched, generally with a nominal functionality, referred to the reaction with the isocyanate groups, lower than 6 and equivalent weight from 250 to 10000. In the polyether polyols at least 70% of the hydroxyl groups consist of secondary hydroxyl groups.

Polyether polyols are prepared by reacting the corresponding oxide with an appropriate molecule (initiator). Examples of initiators are water, ammonia, aniline, polyalcohols such as ethylene glycol, propylene glycol, hexamethylene glycol, glycerin, trimethylol propane, trimethylol ethane, or compounds with higher molecular weight , pentaerythritol, pentan-1, 2,3,4,5-pentol (xylitol - also called arabitol), sorbitol and mannitol. Other polyether polyols include polytetramethylene oxide polyols which are prepared by a chemical reaction that opens the tetrahydrofuran ring and terminated with water.

Polyester polyols are usually prepared by an esterification process using a molar excess of aliphatic glycol together with a dicarboxylic acid.

The most used glycols include: ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-pentanediol, 1,4-butanediol and other isomers, 1,5-pentanediol and other isomers, 1,6-hexanediol and other isomers , isomers of decanediol and isomers of dodecanediol.

The most widely used dicarboxylic acids include: maleic acid, mayionic acid, succinic acid, glutaric acid, adipic acid, dimethyl-1,6-hexanoic acid, pimelic acid, suberic acid and dodecanedioic acid.

Polylactone polyols are usually prepared by reaction of a monomer of a lactone with a proton initiator. Suitable lactones for the preparation of these polyols include: valerolactone, caprolactone and methylcaprolactone. The initiators normally used include: ethylene glycol, diethylene glycol, propanediol, 1,6-hexanediol, 1,4-butanediol and trimethylolpropane.

For the production of polyurethanes one or more catalysts are usually used, such as for example tertiary amines, organometallic compounds or their mixtures. Examples of organometallic catalysts are dibutyl tin dilaurate (DBTL), dibutyl tin diacetate, dibutyl tin sulfide, stannous octoate, lead octoate and nickel acetylacetonate.

The catalysts are generally used in concentrations ranging from about 0.001 to about 2 parts per 100 parts of formulation (polyurethane polymerizable composition).

Specific examples of tertiary amines used as catalysts include alkyl morpholines, dimethylpiperazine, triethylenediamine, which are used in concentrations ranging from about 0.01 to about 3 parts per 100 parts of formulation.

In the present description, the terms "formulated" and "polymerizable polyurethane composition" refer to the mixture of polyol compounds, polyisocyanates, solvents and additives (in the fluid state) which, following polymerization under suitable operating conditions, gives rise to a polyurethane polymer .

The terms "polyurethane" and "polyurethane polymer" refer, on the other hand, to the solid product obtained following the polymerization of a polymerizable polyurethane composition.

Additional components used in the preparation of polyurethane polymers are chain extenders and crosslinking agents. These components are compounds having two or more isocyanate-reactive groups.

As chain extenders or cross-linking agents, hydroxyl-terminated compounds, primary amines and secondary amines can be used. Generally, these components have an equivalent weight of isocyanate-reactive groups ranging from 30 to 400. Other examples of chain extenders are: propylene and ethylene glycols, diols of C2-C12 hydrocarbon chains, amino-terminated polyethers, substituted piperazines, 1,5-diamino-3-methylpentane, isophorondiamine, ethylenediamine, hexamethylenediamine, hydrazine or mixtures thereof.

Other additives often used in the formulation of polymerizable polyurethane compositions are surfactants. Generally, one or more surfactants are used in an overall concentration ranging from 0.1 to about 3 parts of surfactant per 100 parts of formulation.

For certain applications, the polymerizable polyurethane compositions can also comprise a chemical type blowing agent, such as water, or a physical type, such as air, nitrogen, argon or other gas.

In the state of the art, polyurethanes with suitable characteristics to be used in the preparation of synthetic leathers are obtained starting from polymerizable compositions formulated exclusively with chemical compounds obtained from petroleum transformation processes.

Although polymerizable polyurethane compositions based on chemical compounds deriving from raw materials of vegetable origin, ie from renewable sources, are known, the polyurethanes obtainable from these compositions (also known as "bio-polyurethanes") possess characteristics that do not allow the preparation of synthetic leathers with adequate performance characteristics.

In particular, the bio-polyurethanes of the state of the art, once applied to the textile substrate in a production process of a synthetic leather, do not give the synthetic leather adequate characteristics in terms of 100% elastic modulus, percentage elongation, resistance to hydrolysis, resistance to solvents and aging. More specifically, with the bio-polyurethanes of the state of the art it is not possible to obtain synthetic leathers having one or more layers of polymer with the following characteristics:

- elastic modulus at 100% variable from 0.5 MPa to 35.0 MPa (ASTM D638, ISO 527)

- percentage elongation up to 900% (ASTM D638, ISO 527).

Furthermore, the synthetic leathers that can be made with state-of-the-art biopolyurethanes do not possess adequate resistance to hydrolysis and solvents for the uses to which they are generally intended.

Document US 20050239915, for example, describes polyurethanes obtained from polymerizable compositions containing polyols obtained from castor oil or soybean oil. The polyurethanes described in US 20050239915, however, have characteristics such that they can be used for the production of insulating materials and packaging, but are not suitable for producing synthetic leather.

In consideration of the state of the art described above and the growing awareness at industrial level with regard to environmental issues, the need to identify alternative raw materials is strongly felt also in the synthetic leather production sector that allow to avoid, or at least reduce, the consumption of chemical compounds produced by the petrochemical industry, in particular for the preparation of polyurethanes.

The object of the present invention is to overcome the drawbacks highlighted in the state of the art. In particular, it is an object of the present invention to identify a polymerizable polyurethane composition based on renewable raw materials suitable for producing synthetic leathers.

A first object of the present invention is a polymerizable polyurethane composition for preparing synthetic leathers comprising the following components:

i) 50-80% by weight, preferably 55-75% by weight, based on the weight of the dry polyurethane polymer, of one or more polyols,

ii) 10-40% by weight, preferably 15-35% by weight, based on the weight of the dry polyurethane polymer, of one or more isocyanates or polyisocyanates,

iii) 0-10% by weight, referred to the weight of the dry polyurethane polymer, of one or more additives,

iv) a solvent,

characterized in that said component i) consists of one or more polyols obtained from renewable raw materials of vegetable origin, said one or more polyols having a nominal functionality of isocyanate-reactive groups in the range 1.99-2.01, preferably equal at 2.0, and a number average molecular weight comprised in the range of 200-4000 UMA, preferably between 500 and 2000 UMA.

A second object of the present invention is a multilayer product comprising a paper support such as release paper coupled to one or more layers, the same or different, of a polyurethane obtained by polymerization of the aforementioned polymerizable polyurethane composition.

A third object of the present invention is a synthetic leather comprising one or more layers of a polyurethane obtained by polymerization of the aforementioned polymerizable polyurethane composition.

A further object of the present invention is the use of the aforesaid synthetic leather to produce coverings for furniture or leather goods, such as shoes, bags, suitcases and belts.

The Applicant has surprisingly found that it is possible to prepare polymerizable polyurethane compositions to be used in the preparation processes of synthetic leathers, resorting to raw materials of vegetable origin. In particular, the Applicant has found that it is possible to prepare the above compositions using exclusively polyols obtained from vegetable oils, thus avoiding the use of polyols derived from petroleum.

According to the present invention, the polyols used are obtained from the transformation of vegetable oils, ie from the transformation of renewable raw materials. In particular, polyols are obtained from vegetable oils, such as castor oil, rapeseed oil, soybean oil, rapeseed oil, olive oil, coconut oil, linseed oil, cotton, peanut oil, almond oil, cashew oil.

The polyols obtained from these vegetable oils can be used to prepare the polymerizable polyurethane compositions (and the related polyurethanes) of the present invention either alone or in mixture.

In order to obtain polyurethane polymers of a quality suitable for the production of synthetic leathers, the polyols must have a nominal functionality (fn) in the range 1.99-2.01, preferably equal to 2.0, and a number average molecular weight included between 200 and 4000 UMA, preferably between 500 and 2000 UMA.

For the purposes of the present invention, the term "nominal functionality" means the number of isocyanate-reactive groups present in a polyol, ie the number of functional groups capable of reacting with the NCO groups of an isocyanate. The parameter fn can be calculated on the basis of the stoichiometry of the synthesis reaction of the polyol itself.

It has been surprisingly found, in fact, that only by using polyols of vegetable origin that possess the aforementioned characteristics of nominal functionality (fn = 1.99-2.01) and average molecular weight (200-4000 UMA) it is possible to prepare polyurethane polymers, from coupling in the form of layers to textile substrates to produce synthetic leathers, having suitable performance characteristics for the subsequent uses to which such leathers are intended. In particular, with the above compositions it is possible to prepare polyurethane polymer layers each having the following performance characteristics:

- elastic modulus at 100% variable from 0.5 MPa to 35.0 MPa (ASTM D638, ISO 527),

- percentage elongation up to 900% (ASTM D638, ISO 527.

Furthermore, the synthetic leathers comprising the polyurethane polymers object of the present invention possess excellent resistance to hydrolysis and solvents.

The polyols usable in the present invention are compounds preferably having a nominal functionality equal to 2.0, ie compounds containing two isocyanate-reactive groups per molecule.

The isocyanate-reactive groups therein of the polyols are preferably of proton nature; for example, the isocyanate-reactive groups can be OH groups and / or SH groups and / or primary amino groups and / or secondary amino groups.

The polyols can be of the polyester, polyether or polycarbonate type.

Polyols are made from castor oil, soybean oil, rapeseed oil, olive oil, coconut oil, linseed oil, cottonseed oil, peanut oil, almond oil, cashew nuts and their mixtures. Preferably, polyols obtained from castor oil are used.

The vegetable oils from which the above polyols are prepared can contain completely saturated, mono-unsaturated or poly-unsaturated fatty acids. Fatty acids can also have conjugated or cumulated double bonds.

Generally, vegetable oils are transformed into polyols usable for the purposes of the present invention by transesterification reactions with lower molecular weight polyols, such as glycerin (1,2,3-propantriol), pent aeritrol (2,2-dihydroxymethyl-1 , 3-propanediol).

It is also possible to obtain polyols through other transformation reactions of vegetable oils, including reduction and amination reactions.

The reactions and production techniques of polyols by transformation of vegetable oils through transesterification, reduction or amination reactions are known to those skilled in the art.

Furthermore, polyols of vegetable origin having the characteristics described above and, therefore, usable for preparing the polymerizable compositions of the present invention, are commercially available.

The isocyanate compounds usable as component ii) in the polymerizable polyurethane compositions of the present invention are compounds having two or more isocyanate groups (polyisocyanates), of the type known in the state of the art.

Preferably, isocyanates of the aromatic, cycloaliphatic or aliphatic type are used.

Preferably, the isocyanates are selected from the group consisting of methyl diphenyl-2,4'-diisocyanate (2,4'-MDI), methyldiphenyl-4,4'-diisocyanate (4,4'-MDI), toluene-2,4 -diisocyanate (2,4-TDI), toluene-2,6-diisocyanate (2,6-TDI), naphthalen-1,5-diisocyanate (NDI), isophorondisocyanate (IPDI), hexamethylene-1,6-diisocyanate (HDI ), tetramethylen-1,4-diisocyanate, 3,3'-dimethyl 4,4'-diphenyl-diisocyanate, triisocyanates, MDI polyisocyanates (pMDI) and their mixtures. More preferably, the isocyanate is the MDI compound.

Polyisocyanates can be used either alone or in a mixture. Mixtures of polyisocyanates have on average 1.8 to 2.2 NCO groups for each polyisocyanate molecule.

The polyisocyanates can also be in the form of isocyanate-terminated prepolymers. These prepolymers are produced by reacting a stoichiometric excess of polyisocyanates with reactive substances towards the isocyanate groups (for example, polyol compounds).

The polymerizable polyurethane compositions of the present invention contain component i) (polyol) in an amount variable in the range 50-80% by weight referred to the weight of the dry polyurethane polymer, preferably in the range 55-75% by weight.

Component ii) (isocyanate) is present in the composition in a variable amount in the range 10-40% by weight referred to the weight of the dry polyurethane polymer, preferably in the range 15-35% by weight.

The polymerizable polyurethane compositions can also contain other additive components (component iii)), such as for example catalysts, chain extenders and cross-linking agents.

The catalysts can be of the known type and generally used in the sector of the production of polyurethanes, in particular of polyurethanes for the production of synthetic leathers (for example, tertiary amines, organometallic compounds and their mixtures). However, in a preferred embodiment of the present invention, the polymerizable polyurethane compositions and the related polyurethanes obtainable therefrom do not contain catalysts.

Since the catalysts generally used in the state of the art are obtained, in part or totally, starting from raw materials or intermediates derived from synthesis products of fossil origin (petroleum), their absence in the polymerizable compositions and in the polyurethanes of the present invention reduces further the overall environmental impact of these materials and of the synthetic leathers obtained with them. Furthermore, the absence of catalysts helps to reduce the consumption of raw materials and the production costs of synthetic leathers.

The chain extenders and the crosslinking agents are of the type known in the state of the art. Generally, compounds having two or more isocyanator-reactive groups are used. Preferably, hydroxyl terminated compounds, primary or secondary amines are used. These compounds have an equivalent weight of isocyanate-reactive groups varying in the range of 30-400.

The chain extenders, the crosslinking agents and the catalysts (the latter when present) are added to the polymerizable composition in quantities lower than 10% by weight with respect to the weight of the dry polyurethane polymer.

The polymerizable polyurethane compositions of the present invention and the polyurethanes obtainable therefrom may also contain other additives of the type generally used in the production of polyurethane polymers, such as, for example, surfactants, pigments and expanding chemical agents.

The polymerizable polyurethane compositions object of the present invention can be prepared using the techniques and equipment known in the state of the art.

The preparation involves mixing the various components in a suitable solvent, under stirring and in conditions of absence of humidity (anhydrous environment).

The solvent is selected from those generally used in the production of polyurethane polymers, such as for example: dimethylformamide (DMF), ethyl acetate, toluene.

Typically, a fraction of the isocyanate is mixed with the remaining components and the solvent at a temperature of about 40 ° C (+/- 2 ° C) until their total dissolution. Subsequently, the temperature is raised to about 75 ° C (+/- 2 ° C) and the remaining isocyanate is gradually added to the mixture (inviscosamento phase).

During its preparation, to ensure anhydrous conditions, the mixture can be kept under a flow of inert gas (for example, nitrogen).

At the end of the inviscosimento phase, the polymerizable composition, which is still sufficiently fluid to be spread, is brought back to room temperature and is ready for its subsequent use.

The polymerizable polyurethane compositions object of the present invention can be used in the conventional production processes of synthetic leathers.

Generally, these processes involve the application, by spreading the polymerizable composition on a paper support (called "release paper") which gives the design to the synthetic leather. The paper support comprising the coated polymerizable composition is then subjected to drying (generally at a temperature in the range from 100 to 200 ° C).

The drying, in addition to allowing the complete evaporation of the solvent, causes the complete cross-linking of the polyurethane composition with the formation of a layer of polyurethane polymer (10-150 μπι thickness) supported on the release paper suitable for the production of synthetic leather.

The spreading step on the release paper can be repeated obtaining a multilayer product having layers of polyurethane polymer, of the same or different composition, of the desired thickness (generally in the range from 50 to 500 μπι).

The polyurethane layer supported on the release paper (or the aforementioned multilayer product) is then coupled by lamination to a textile substrate in natural, synthetic or mixed fiber (for example, cotton, polyester or cotton / polyester fibers), while recovering the release card that can be reused.

In the lamination process, to make the polyurethane layer adhere to the textile substrate, a layer of a second polyurethane polymer is used as an adhesive. The adhesive polymer layer is obtained by polymerization of a polymerizable polyurethane composition of the type described in the present invention, that is, prepared using renewable raw materials.

The conditions of use of the polymerizable polyurethane compositions and of the related polyurethanes obtainable from them in the production processes of synthetic leathers (for example, quantity of composition to be applied, drying times and temperature, etc.) are variable and can be easily determined by a skilled in the art according to the aesthetic effect and the characteristics to be obtained for synthetic leather.

The synthetic leathers comprising the polyurethanes object of the present invention can be subjected to surface finishing treatments, before subsequent uses. These treatments are generally carried out to modify the "hand" or feel of the leathers.

Synthetic leathers produced with one or more layers of the polyurethane polymers object of the present invention are particularly suitable for producing coatings for furniture or leather goods, such as shoes, bags, suitcases and belts.

The polymerizable compositions and the related polyurethanes object of the present invention solve the current total dependence of the synthetic leather production sector on the petrochemical industry.

The present invention, in fact, makes it possible to produce polyurethane polymers which, for an amount ranging from 50% to 80% by weight, consist of compounds derived from renewable raw materials of vegetable origin.

The following exemplary embodiments are provided purely for illustrative purposes of the present invention and must not be construed as limiting the scope of protection defined by the attached claims.

Example 1

A first polymerizable polyurethane composition according to the present invention was prepared having the following composition (percentages by weight referred to the weight of the dry polyurethane polymer):

The polyol, the chain extender and a part of the isocyanate were mixed in dimethylformamide at a temperature of 40 ° C (+/- 2 ° C) and kept under stirring until the total dissolution of the components, forming a solution of dimethylformamide from 25% to 55% by weight of dry part.

The temperature of the mixture was increased to 75 ° C (+/- 2 ° C). At this temperature, the remaining isocyanate was gradually added to the mixture for the stifling phase.

The synthesis was carried out in an anhydrous environment, under constant nitrogen flow (flow = 0.8-1.2 1 / min).

The composition was spread by replicating the application conditions of an industrial plant in the laboratory. A layer of polymer (Polyurethane A) with a thickness of 50 μπι was thus obtained. The following performance characteristics evaluation tests were performed on this layer:

- elastic modulus at 100% (according to ASTM D638, ISO 527),

- percentage elongation (according to ASTM D638, ISO 527),

- resistance to hydrolysis,

- resistance to solvents.

Resistance to hydrolysis was evaluated by keeping the sample immersed in water at 95 ° C for 8 hours. This test is similar to that required by the UNI 4818-19 standard. The degree of resistance to hydrolysis was assessed visually.

Resistance to solvents was evaluated by keeping the sample immersed in the typical solvents for the evaluation of synthetic leather articles (acetone, methyl-ethyl-ketone (MEK), denatured ethyl alcohol and trichlorethylene) at room temperature for 30 sec.

This test is similar to that required by the UNI 4818-28 standard. The degree of resistance to solvents was assessed visually.

The results of the evaluation tests performed on the Polyurethane A layer are shown in the following Table 1.

Table 1 - Polyurethane A

Example 2

A second polymerizable polyurethane composition was prepared having the following composition (percentages by weight based on the weight of the dry polyurethane polymer):

The mixing of the different components was carried out in the same solvent and under the same operating conditions of Example 1.

With this second composition, a second polymer layer (Polyurethane B) with a thickness of 50 μπi was prepared using the process described in Example 1, under the same spreading and drying conditions.

The same tests for evaluating the performance characteristics of Example 1 were carried out on the polyurethane layer B.

The results of the evaluation tests performed on the polyurethane layer B are shown in the following Table 2.

Table 2 - Polyurethane B

The polyurethanes A and B of examples 1 and 2 were coupled to a textile support, using the polyurethane layer A as adhesive and the polyurethane layer B as the external layer (so-called skin or pre-skin). The synthetic leather thus obtained was suitable for use in the production of furniture and leather goods, such as shoes, bags, suitcases and belts.

Examples 1 and 2 show that the polymerizable polyurethane compositions of the present invention (and the related polyurethane polymers obtainable therefrom), containing polyol compounds derived from renewable vegetable raw materials are suitable to be used for the preparation of synthetic leathers.

Claims (5)

CLAIMS 1) Polymerizable polyurethane composition to prepare synthetic leathers comprising the following components: i) 50-80% by weight, preferably 55-75% by weight, based on the weight of the dry polyurethane polymer, of one or more polyols, ii) 10-40% by weight, preferably 15-35% by weight, based on the weight of the dry polyurethane polymer, of one or more isocyanates or polyisocyanates, iii) 0-10% by weight, based on the weight of the dry polyurethane polymer, of one or more additives, iv) a solvent, characterized in that said component i) consists of one or more polyols obtained from renewable raw materials of vegetable origin, said one or more polyols having a nominal functionality of isocyanate-reactive groups in the range 1.99-2.01, preferably equal at 2.0, and a number average molecular weight comprised in the range of 200-4000 UMA, preferably between 500 and 2000 UMA. 2) Composition according to claim 1, characterized in that said one or more polyols are polyols obtained from a vegetable oil selected from the group consisting of: castor oil, soybean oil, rapeseed oil, olive oil, walnut oil coconut, linseed oil, cottonseed oil, peanut oil, almond oil, cashew oil, preferably from castor oil. 3) Composition according to claim 1 or 2, characterized in that said isocyanator-reactive groups are of the proton type, preferably OH groups and / or SH groups and / or primary amino groups and / or secondary amino groups. 4) Composition according to any one of the preceding claims, characterized in that said polyols are selected from the group consisting of polyester polyols, polyether polyols or polycarbonate polyols; preferably they are polyester polyols. 5) Composition according to any one of the preceding claims, characterized in that said component ii) is selected from the group consisting of methyldiphenyl-2,4 '-diisocyanate (2,4'-MDI), methyldiphenyl-4,4' -diisocyanate ( 4,4'-MDI), toluene-2,4-diisocyanate (2,4-TDI), toluene-2,6-diisocyanate (2,6-TDI), naphthalen-1,5-diisocyanate (NDI), isophorondisocyanate (IPDI), hexamethylene-1,6-diisocyanate (HDI), tetramethylen-1,4-diisocyanate, 3,3'-dimethyl-4,4 '-diphenyl-diisocyanate, triisocyanates, MDI polyisocyanates (pMDI) and their blends; preferably it is MDI. 6) Composition according to any one of the preceding claims, characterized in that said component ii) is a mixture of polyisocyanates having on average from 1.8 to 2.2 NCO groups for each polyisocyanate molecule. 7) Composition according to any one of the preceding claims, characterized in that said component iii) is selected from the group consisting of catalysts, chain extenders and cross-linking agents; it is preferably selected from the group consisting of chain extenders and crosslinking agents. 8) Composition according to the preceding claim, characterized in that said chain extenders and said cross-linking agents have an equivalent weight of the isocyanate-reactive group variable in the range 30-400 and are selected from the group consisting of: hydroxyl-terminated compounds, amines primary, secondary amines. 9) Composition according to any one of the preceding claims, characterized in that said component iv) is a solvent selected from the group consisting of dimethylformamide (DMF), ethyl acetate, toluene. 10) Multilayer product comprising a paper support such as release paper coupled with one or more layers, the same or different, of a polyurethane obtained by polymerization of the aforesaid polymerizable polyurethane composition. 11) Multilayer product according to the preceding claim, characterized in that each of said one or more polyurethane layers has: - elastic modulus at 100% variable in the range from 0. 5 MPa to 35.0 MPa, - percentage elongation up to 900%. 12) Synthetic leather comprising one or more layers of a polyurethane obtained by polymerization of a polymerizable polyurethane composition according to any one of claims 1 to 9. 13) Use of the synthetic leather according to claim 12 to produce coverings for furniture and leather goods, such as shoes, bags, suitcases and belts.