Vitrimer, method for preparing the same, article and method for reprocessing the vitrimer

Abstract

The present invention relates to a vitrimer and to a method for preparing the same. The present invention also relates to an article made of the aforementioned vitrimer and to a method for reprocessing said vitrimer. In particular, the Applicant has surprisingly found that permanently and covalently attaching an amine catalyst to the polymer network of a vitrimer, in particular a PTU vitrimer, allows to form internal catalytic moieties that enable indefinite reprocessability, simultaneously reducing the reaction rate of the initial thiol-isocyanate reaction.

Description

[0001] VITRIMER, METHOD FOR PREPARING THE SAME, ARTICLE AND

[0002] METHOD FOR REPROCESSING THE VITRIMER

[0003] Field of the invention

[0004] The present invention relates to a vitrimer and to a method for preparing the same.

[0005] The present invention also relates to an article obtainable by molding, cross-linking and hardening said vitrimer, in particular an article for optical application .

[0006] Furthermore, the present invention relates to a method for reprocessing said vitrimer.

[0007] Background of the invention

[0008] Shape memory polymers (SMPs) exhibit the capability to deform into a temporary shape, and retain it below a certain transition temperature, but recover the original (factory-set) shape upon exposure to appropriate stimuli, such as heat, electricity, light, or magnetic field. SMPs have been proposed for a range of applications, including biomedical devices, electronic devices, sensors, and deployable structures. The vast majority of current SMPs are made of elastomers, hydrogels, or thermoplastic polymers, which often lack adequate mechanical strength and toughness that are necessary for engineering applications. High-performance thermoset polymers such as epoxies, polyurethanes, polythiouerthanes , acrylates, are ideal SMP materials for engineering applications due to their mechanical strength and their thermal and chemical stability. High- performance thermoset SMPs must undergo permanent crosslinking to achieve excellent thermal stability, high mechanical strength, and good chemical resistance . This cross-linking defines the natural ( factory-set ) shape . However, a permanently cross-linked network renders reprocessability and recycling impossible . Therefore , high-performance thermosets crosslinked with dynamic networks have been utilized to address the reprocessability and recycling challenges , whi le maintaining their mechanical integrity alongside the shape-memory performance .

[0009] The emergence of a new class of polymeric materials crosslinked with Covalent Adaptable Networks ( CANs ) enables traditional thermoset polymers to undergo postpolymeri zation processing and recycling . Two distinct types of bond-exchange reactions can occur within a CAN network to make it dynamic : a dissociative bond exchange ( e . g . Diels-Alder reaction) when the bonds are made to break and then re- form in a di f ferent topology, or an associative bond exchange ( e . g . , transesteri f ication) when the bonds can only break when the new bond configuration is already available and established, thus never changing the total number of covalent bonds in the material . Both pathways occurring simultaneously is also possible .

[0010] The term "vitrimer" strictly refers to a polymer that shows solely associative reaction mechanism .

[0011] Vitrimers are polymeric materials which bridge the gap between thermoplastics and thermosets , as they are permanently crosslinked polymer networks , insoluble in solvents , but unlike thermosets they can be made to plastically flow at high temperatures due to the bond exchange , allowing for their reprocessing and making a multi-use plastic . The elastic-plastic transition occurs due to the dynamic exchange of covalent bonds in such networks , which is fundamentally di f ferent from thermoplastics that are viscous fluids above the melting transition temperature .

[0012] A catalyst i s required for the dynamic exchange o f covalent bonds to occur in most vitrimers . It is known, dispersing organometallic catalyst or organic catalysts into the polymeric matrix . Since organic catalysts are usually low molecular weight compounds with a low boiling point , they can either be lost by evaporation or thermally degrade during the heating step of the reprocessing phase . Loss of the catalyst can be detrimental for the vitrimeric behavior since it can be di f ficult for the covalent bonds to really break and reform at a suf ficient rate upon subsequent cooling . This is even more critical i f the reprocessing of the material is designed to be repeated several times .

[0013] Chemically crosslinked polythiourethane ( PTU) thermosets have been around for a long time and used in applications that require high heat and chemical resistance . PTUs exhibit mechanical properties akin to traditional polyurethane ( PU) materials due to their similar chemical structure , with the substitution of sul fur for some oxygen atoms . This similarity enables the formation of hydrogen bonds in a similar manner to PU . However, PTUs of fer several advantages . The formation of PTUs from isocyanates and thiols i s characteri zed as a click-type reaction, which mitigates side reactions typically observed in PU synthesis . Additionally, PTU thermosets possess a higher refractive index due to the presence of sul fur, rendering them promising candidates for optical applications . Currently, reprocessabil ity of casted eyewear frames is not known in state-of-the-art .

[0014] Recently, Torkelson, Bowman, and Serra research groups , at the same time , have investigated the bondexchange mechanisms acting in thio-urethanes polymer networks . The dynamic bond of thio-urethane linkages can be triggered by organometallic, or amine catalysts , or a combination of both . Amine catalysts of fer several advantages over organometallic catalysts . They ef ficiently catalyze the initial click-reaction between thiol and isocyanate and the reaction during the bondexchange between thio-urethane l inkages , resulting in a more homogeneous network formation without the formation of unexpected moieties .

[0015] Additionally, it is known that amine catalysts are less toxic compared to organometallic catalysts .

[0016] All current methods for preparing dynamically crosslinked PTU rely on adding amine catalysts to the monomer mixture of thiol and isocyanate . However, this often results in a rapid and uncontrollable reaction, leading to immediate gelation within a few seconds . It is critical to note that amine catalysts are more susceptible to evaporation and degradation at high temperatures compared to organometallic catalysts , making them less desirable for producing recyclable materials . Alternatively, the addition of toxic organometallics , such as dibutyltin di laurate , has been explored, but these compounds may easily leak from the network or degrade after a few reprocessing cycles .

[0017] Therefore , the need is felt to obtain vitrimers which overcomes the drawbacks of the prior art .

[0018] Summary of the invention

[0019] Facing this problem, the Applicant has surprisingly found that permanently and covalently attaching an amine catalyst to the polymer network of a vitrimer, in particular a PTU vitrimer, allows to form internal catalytic moieties that enable indefinite reprocessability, simultaneously reducing the reaction rate of the initial thiol-isocyanate reaction .

[0020] Indeed, as reported below, the Applicant has covalently reacted an amine catalyst , with a multifunctional isocyanate to form stable chemical moieties containing urea linkages . These chemical moieties containing urea linkages subsequently and mildly catalyze the reaction between the remaining isocyanates groups and the thiol groups of poly-thiols subsequently added and, during the reprocessability, activate the dynamic bond-exchange of thio-urethane .

[0021] The same principle ( covalently binding the amine catalyst to the polymer ) can be applied also to polymer di f ferent from polythiolurethane , such us polyurethanes .

[0022] The vitrimer of the invention of fers the following advantages : - amine catalysts are less toxic than organometallic catalysts ,

[0023] - homogeneous network formation without the formation of unexpected moieties ,

[0024] - the catalyst covalently bonded do not evaporate during the reprocessing of the article made o f such vitrimer,

[0025] - in the case of a polythiolurethane vitrimer, the rapid and uncontrollable reaction, leading to immediate gelation within a few seconds i s avoided,

[0026] - the articles made of vitrimers according to the invention are indefinitely reprocessable .

[0027] In accordance with a first aspect , therefore , the present invention concerns a vitrimer comprising :

[0028] - a polyisocyanate moiety,

[0029] - a polythiol moiety and / or a polyol moiety, wherein an amine catalyst is covalently bond to the polyisocyanate moiety .

[0030] In accordance to a second aspect , the present invention concerns a method for preparing the aforementioned vitrimer, said method comprising the following steps : a ) reacting an amine catalyst with a polyisocyanate monomer ; b ) reacting a second monomer selected from a polythiol compound and / or a polyol compound with the product of step a ) to obtain a cured vitrimer .

[0031] In accordance with a third aspect , the invention concerns an article made of the aforementioned vitrimer, obtainable by molding, cross-linking and hardening said vitrimer . Preferably, the article is an eyewear frame , more preferably made of a polythiourethane vitrimer .

[0032] In accordance with a fourth aspect , the invention concerns a method for reprocessing said article .

[0033] In the present description and in the claims that follow, the definitions of the numerical intervals include the individual values within the interval and its extremes , unless otherwise speci fied .

[0034] In the present description and in the claims that follow, the term "comprising" also includes the terms "essentially consisting of" or "consisting of" .

[0035] Further characteristics and advantages of the present invention will appear from the following detailed description .

[0036] Brief description of the drawings

[0037] Figures 1A and IB show respectively the first and the second step of the method for preparing a polythiolurethane ( PTU) vitrimer according to the invention .

[0038] Figure 1C shows the reprocessing of an article made of a PTU vitrimer according to the invention wherein the dynamic bond-exchange of thio-urethane is activated in the presence of the catalyst .

[0039] Figure 2A shows the shape memory ef fect in the PTU vitrimer of the invention, wherein deformation is recovered upon heating above the glass transition temperature ( Tg) . Figure 2B is a graph Storage modulus (MPa) / Temperature (°C) / Tan delta.

[0040] Figure 3A shows the DMA plot of Storage modulus (MPa) and tan delta as a function of temperature for different formulations. The plot illustrates that both the glass transition temperature (Tg) and the rubber modulus increase with the amount of the thiol crosslinker (Thiocure 360) .

[0041] Figure 3B is a plot of stress (MPa) versus strain (%) for different formulations. The plot illustrates that the ultimate stress increases with an increase in the amount of Thiocure 360, while the strain to failure increases with a decrease in the amount of Thiocure 360.

[0042] Figure 4A shows the reprocessability of the vitrimer by hot-pressing

[0043] Figure 4B is a graph Strain (%) / Temperature ( °C) wherein the stress applied is 50KPa. This graph shows the deformability of the material as a function of temperature and gives information regarding the reprocessing temperature of the material.

[0044] Figure 5 shows some sample of vitrimers according to the invention reduced to uniform-sized powder by means of a food grinder.

[0045] Figure 6 shows the polydispersity of the vitrimer powder .

[0046] Figure 7 shows a uniform recycled sample obtained from the hot-pressing at 80°C for overnight of a mixture comprising 75% of vitrimer powder and 25% of uncured vitrimer . Detailed description of the invention

[0047] The present invention relates to a vitrimer comprising :

[0048] - a polyisocyanate moiety,

[0049] - a polythiol moiety and / or a polyol moiety, wherein an amine catalyst is covalently bond to the polyisocyanate moiety.

[0050] The polyisocyanate monomer can be aromatic or aliphatic. It can be selected from compounds having two, three or four isocyanate groups, or mixture thereof, preferably three.

[0051] According to one embodiment, the polyisocyanate moiety derives from a monomer selected from: compound of formula (I) wherein n, m and o are integers, independently from each other, selected from 1 to 10, preferably from 4 to 8, more preferably 6, or mixture thereof;

[0052] - compound of formula (II)

[0053] OCN- (CH2) n-NCO (II) wherein n is an integer comprised from 1 to 20, preferably from 2 to 10, more preferably from 3 to 8, more preferably n is equal to 6, or mixture thereof; poly (hexamethylene diisocyanate) , methylene diphenyl diisocyanate, 2 , 4 , 6-trioxtriazine-

[0054] 1,3,5 (2H, 4H, 6H) -triyl) tris (hexamethylene) isocyanate, imidodicarbonicdiamide, N,N',2-tris (6- isocyanatohexyl ) , 4,4' diphenylmethanediisocyanate, or mixture thereof; or mixture thereof, preferably it derives from the monomer of formula (I) wherein n is equal to 6 (1,3,5— tris ( 6-isocyanatohexyl ) -1, 3, 5-triazine-

[0055] 2 , 4 , 6 ( 1H, 3H, 5H) -trione (HDI-Trimer) (CAS no. : 3779-63- 3) ) .

[0056] Preferably, said polythiol moiety and / or polyol moiety derives from a monomer selected from: a polythiol selected from 1 , 6-hexanedithiol , 1,5- pentanedithiol , poly ( ethyleneglycol ) dithiol with a number of ethylene glycol unit ranging from 1 to 10, dipentaerythritol hexakis ( 3-mercaptopropionate ) , 2, 2'- ( ethylenedioxy ) diethiol , pentaerythritol tetrakis (3- mercaptopropionate ) , or mixture thereof; a polyol selected from hexane-1, 6-diol, dipentaerythritol, or mixture thereof; or mixture thereof.

[0057] A preferred polythiol monomer has from two to eight thiol groups, or it is a mixture thereof.

[0058] More preferably, in the vitrimer according to the invention, said polythiol moiety and / or polyol moiety derives from a mixture of polythiols, preferably from a mixture of dipentaerythritol hexakis (3- mercaptopropionate ) and 2, 2 '- ( ethylenedioxy ) diethiol , more preferably wherein the molar ratio between dipentaerythritol hexakis ( 3-mercaptopropionate ) and 2, 2 '- ( ethylenedioxy ) diethiol ranges from 2 to 4, preferably from 2.8 to 3.2.

[0059] The amine catalyst can be aliphatic or aromatic.

[0060] In a preferred embodiment, the amine catalyst is selected from: a primary amine selected from ispropylamine, butylamine, benzylamine, N, N-diethylethylenediamine, N, N-dimethyltrimethylenediamin, 2- aminoethyl (ethyl) amine, N, N-diethyl-p-phenylenediamine, aminoethylpiperazine, or mixture thereof; - a secondary amine selected from N, N, N ' -Trimethyl-1 , 3- propanediamine, dimethylamine, diethylamine, dipropylamine, N-Ethylisopropylamine, dibutylamine, dipentyl amine, l,5,7-triazabicyclo[4.4.0] dec-5-ene, N, N-dimethyl-N ' -pyridin-2 -ylmethyl-e thane- 1 , 2 -di amine,

[0061] N,N'-BIS- (2, 4 -dimethyl -phenyl ) -ethane- 1 , 2 -di amine, N ' -

[0062] Cyclohexyl-N, N-dime thyl-e thane- 1 , 2 -di amine, N, N- dimethyl aminopropyl amine N-methylhexan-3-amine, ethylphenylamine, N, N ' -Dimethyl-1 , 3-propanediamine, lH,2H,3H-[l,3]diazolo[l,2-a] imidazole, 3- azabicyclo [ 3.2.1 ] octane, dicyclohexylamine, N,N- dimethyl dipropylene triamine, or mixture thereof; or mixture thereof, preferably it is dipropylamine.

[0063] According to a preferred embodiment, the molar ratio between the amine catalyst and the polyisocyanate moiety ranges from 0.003 to 0.2, preferably from 0.02 to

[0064] O.08, more preferably it is 0.045.

[0065] According to another preferred embodiment, the molar ratio between the polythiol and / or polyol moiety and the polyisocyanate moiety ranges from 0.2 to 1, preferably from 0.4 to 0.8, preferably it is 0.6.

[0066] The present invention also relates to a method for preparing a vitrimer, said method comprising the following steps: a) reacting an amine catalyst with a polyisocyanate monomer; b) reacting a second monomer selected from a polythiol monomer and / or a polyol monomer with the product of step a) to obtain a cured vitrimer.

[0067] The amine catalyst must be a primary and / or secondary amine, not tertiary. The amine catalyst can be aliphatic or aromatic . Pref erred primary amine catalysts are isopropylamine, butylamine, benzylamine, N,N- diethylethylenediamine, N, N-dimethyltrimethylenediamin, 2-aminoethyl (ethyl) amine, N, N-diethyl-p- phenylenediamine, aminoethylpiperazine, or mixture thereof .

[0068] Preferred secondary amine catalysts are N,N,N'- trimethyl-1, 3-propanediamine, dimethylamine, diethylamine, dipropylamine, N-ethylisopropylamine, dibutylamine, dipentylamine, 1,5,7- triazabicyclo[4.4.0] dec-5-ene, N, N-dimethyl-N ' -pyridin- 2-ylmethyl-ethane-l , 2 -di amine, N,N'-BIS- (2, 4 -dime thy 1- phenyl ) -ethane- 1 , 2 -di amine, N ' -cyclohexyl-N, N- dime thy 1- ethane-1 , 2-diamine, N, N-dimethylaminopropylamine N- methylhexan-3-amine, ethylphenylamine, N, N ' -dimethyl- 1 , 3-propanediamine, lH,2H,3H-[l,3]diazolo[l,2- a] imidazole, 3-azabicyclo[3.2.1] octane, dicyclohexylamine, N,N-dimethyl dipropylene triamine, or mixture thereof. Preferably, the amine catalyst is not solid due to the need of solvent, arising bubble formation issues during the curing step.

[0069] The polyisocyanate monomer can be aromatic or aliphatic. It can be selected from compounds having two, three or four isocyanate groups, or mixture thereof, preferably three.

[0070] The polyisocyanate monomer is preferably selected from the following compounds:

[0071] - compound of formula (I)

[0072] (I) wherein n, m and o are integers, independently from each other, selected from 1 to 10, preferably from 4 to 8, more preferably 6 ( 1 , 3 , 5-tris ( 6- isocyanatohexyl ) -1, 3, 5-triazine-2 , 4, 6 (1H, 3H, 5H) - trione (HDI-Trimer) (CAS no. : 3779-63-3) ) ;

[0073] - compound of formula (II)

[0074] OCN- (CH2) n-NCO (II) wherein n is an integer comprised from 1 to 20, preferably from 2 to 10, more preferably from 3 to 8, more preferably n is equal to 6 (hexamethylene di-isocyanate (HDI) (CAS no : : 822-06-0) ;

[0075] - poly (hexamethylene diisocyanate) (poly HDI) (CAS no. : 28182-81-2) , methylene diphenyl diisocyanate (MDI) , 2 , 4 , 6- trioxtriazine-

[0076] 1,3,5 (2H, 4H, 6H) -triyl) tris (hexamethylene) isocyanate (CAS no. : 3779-63-3) , imidodicarbonicdiamide, N,N',2-tris (6- isocyanatohexyl ) (CAS no. : 4035-89-6) , 4,4' diphenylmethanediisocyanate (CAS no. : 9016-87- 9) .

[0077] More preferably, the polyisocyanate monomer is 1, 3, 5-tris ( 6-isocyanatohexyl ) -1, 3, 5-triazine- 2, 4, 6 (1H, 3H, 5H) -trione (HDI-trimer) .

[0078] In one embodiment, in step a) the equivalent ratio between said amine catalyst and said polyisocyanate monomer ranges from 0.005:1 to 0.5:1.

[0079] In one embodiment, in step a) from 0.01 to 0.2 moles of the amine catalyst, preferably from 0.05 to 0.15, react with from 1 to 3 moles of polyisocyanate monomer, preferably from 1.8 to 2.2.

[0080] Preferably the molar ratio between said amine catalyst and said polyisocyanate monomer ranges from 0.003 to 0.2, preferably from 0.02 to 0.08, more preferably it is 0.045.

[0081] As for step b) , the second monomer can be aliphatic or aromatic.

[0082] It can be selected from a polythiol, a polyol or mixture thereof.

[0083] Preferred polythiol monomer has from two to eight thiol groups, or it is a mixture thereof. For example, the polythiol monomer can be a mixture of dipentaerythritol hexakis ( 3-mercaptopropionate ) (Thiocure 360) and 2, 2 '- ( ethylenedioxy ) diethiol , preferably wherein the molar ratio between dipentaerythritol hexakis ( 3-mercaptopropionate ) and 2, 2 '- ( ethylenedioxy ) dithiol ranges from 2 to 4, preferably from 2.8 to 3.2. This preferred embodiment allows to obtain a vitrimer with thermomechanical properties suitable for eyewear industry: optimal balance between felxibility and glass transition, no smell and low volatility .

[0084] Other useful polythiol monomers according to the invention can be 1 , 6-hexanedithiol , 1 , 5-pentanedithiol , poly ( ethyleneglycol ) dithiol with a number of ethylene glycol unit ranging from 1 to 10, dipentaerythritol hexakis ( 3-mercaptopropionate ) (Thiocure 360) , 2, 2'- ( ethylenedioxy ) diethiol , pentaerythritol tetrakis (3- mercaptopropionate ) or mixture thereof. Preferred polyol monomers according to the invention can be hexane-1, 6-diol, dipentaerythritol.

[0085] Preferably, the equivalent ratio between the polyisocyanate monomer and the polythiol monomer and / or a polyol monomer is 1:1. In one embodiment, in step b) , from 0.8 to 1.6 moles of said second monomer, preferably from 1 to 1.4 moles, react with the product of step a) . Preferably, the molar ratio between the second monomer and the polyisocyanate monomer ranges from 0.2 to 1, preferably from 0.4 to 0.8, preferably it is 0.6.

[0086] In the method according to the invention, step b) is preferably carried out at a temperature ranging from 25°C to 100°C, for a time ranging from 5 minutes to 3 days. In one embodiment, step b) is carried by means of an initial polymerization carried out at room temperature for 7-15 hours, preferably 12 hours, followed by a subsequent polymerization at 50-90 °C, preferably 60°C, for further 4-14 hours, preferably 12 hours. In another preferred embodiment, the subsequent polymerization is carried out at 80°C for just 6 hours.

[0087] The vitrimer thus obtained is useful to be indefinitly reprocessed.

[0088] The vitrimer according to the invention has preferably the following formula (III) :

[0089] (III) •

[0090] The present invention also refers to an article made of the vitrimer of the invention, wherein said article is obtainable by carrying out step b) in a mold .

[0091] Preferably, the article is made of the vitrimer having formula (III) .

[0092] In one embodiment, said article is an eyewear frame, preferably made of a PTU vitrimer, more preferably made of the vitrimer of formula III. The article according to the invention has shape-memory properties at 80-300 °C, preferably at 80-120 °C.

[0093] The present invention also relates to a method for reprocessing the vitrimer of the invention, or an article made of said vitrimer, for example waste products from eyewear. This method comprises: chopping the vitrimer or the article in parts, preferably having a particle size of 5-50 micrometers,

[0094] - mixing the chopped parts with 0-90%, preferably 25- 75%, of the uncured vitrimer,

[0095] - hot pressing in a mold at a temperature ranging from 80-300 °C, preferably 80-220°C.

[0096] By "uncured vitrimer" is meant a vitrimer composed by the monomers and the catalyst described above in the invention in the molar ratios described above.

[0097] Preferably the catalyst in the uncured vitrimer in present at a concentration of 0.5% by weight with respect to the total composition of the vitrimer.

[0098] Example 1 : Method for preparing a PTU vitrimer Materials :

[0099] - Tris-iso (HDI) , ( 2 , 4 , 6-trioxtriazine-

[0100] 1,3,5 (2H, 4H, 6H) -triyl) tris (hexamethylene) isocyanate (HDI trimer) ,

[0101] - dipropylamine (DPA) ,

[0102] - Thiocure 360,

[0103] 2, 2 '- ( ethylenedioxy ) diethiol (EDDT) . Method

[0104] In a plastic container, 9 g of DPA were mixed with 1000 g of HDI trimer using a mixer for the necessary time to produce stable chemical moieties containing urea linkages (see fig. 1A) .

[0105] A vacuum mixer was used to avoid introducing bubbles into the mixture during the mixing phase. During the mixing stage, the exothermic reaction between the isocyanate and dipropyl amine caused a slight heating of the solution. Subsequently, 699 g of Thiocure 360 and 54 g of EDDT (EDDT was added after Thiocure 360, due to its lower viscosity) were incorporate into the solution, for about 10 minutes, always avoiding to introduce bubbles during mixing. These chemical moieties containing urea linkages catalyze the reaction between the remaining isocyanates and poly-functional thiols (Fig. IB) .

[0106] Then the mixture was transferred into a mold for the crosslinking / hardening phase.

[0107] An initial polymerization was carried out at room temperature for 12 hours, followed by a subsequent polymerization at 60°C for a further 12 hours. If there is the need to reduce the subsequent polymerization, the post-cure step can be run at 80°C for just 6 hours. Both methods give the same results. A molded article made of PTU vitrimer was obtained.

[0108] Example 2: Method for reprocessing the vitrimer

[0109] Vitrimer samples are cut and chopped (Figure 5) and then milled into powder with a size of 25 micrometres (Figure 6) . 25% by weight of uncured vitrimer with respect to the total weight of the composition (vitrimer milled into powder + uncured vitrimer) is mixed with the vitrimer powder and the mixture is placed in a mold. The mold is then filled with the necessary quantity of powder (Figure 7) . 20 tons pressure are applied at 200°C for 1 hour .

[0110] The dynamic bond-exchange of thio-urethane is activated under said reprocessing conditions. Reference :

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Claims

CLAIMS1) Vitrimer comprising:- a polyisocyanate moiety,- a polythiol moiety and / or a polyol moiety, wherein an amine catalyst is covalently bonded to the polyisocyanate moiety.2) Vitrimer according to claim 1 wherein said polyisocyanate moiety derives from a monomer selected from: compound of formula (I)(I) wherein n, m and o are integers, independently from each other, selected from 1 to 10, preferably from 4 to 8, more preferably 6;- compound of formula (II)OCN- (CH2) n-NCO (II) wherein n is an integer comprised from 1 to 20, preferably from 2 to 10, more preferably from 3 to 8, more preferably n is equal to 6; poly (hexamethylene diisocyanate) , methylene diphenyl diisocyanate, 2 , 4 , 6-trioxtriazine-1,3,5 (2H, 4H, 6H) -triyl) tris (hexamethylene)isocyanate, imidodicarbonicdiamide, N,N',2-tris (6- isocyanatohexyl ) , 4,4' diphenylmethanediisocyanate; or mixture thereof, preferably it derives from the monomer of formula (I) wherein n is equal to 6.3) Vitrimer according to claim 1 or 2 wherein said polythiol moiety and / or polyol moiety derives from a monomer selected from: a polythiol selected from 1 , 6-hexanedithiol , 1,5- pentanedithiol , poly ( ethyleneglycol ) dithiol with a number of ethylene glycol unit ranging from 1 to 10, dipentaerythritol hexakis ( 3-mercaptopropionate ) , 2, 2'- ( ethylenedioxy ) diethiol , pentaerythritol tetrakis (3- mercaptopropionate ) , or mixture thereof; a polyol selected from hexane-1, 6-diol, dipentaerythritol, or mixture thereof; or mixture thereof.4) Vitrimer according to claim 3 wherein said polythiol moiety and / or polyol moiety derives from a mixture of polythiols, preferably from a mixture of dipentaerythritol hexakis ( 3-mercaptopropionate ) and 2, 2 '- ( ethylenedioxy ) diethiol , more preferably wherein the molar ratio between dipentaerythritol hexakis (3- mercaptopropionate ) and 2, 2 '- ( ethylenedioxy ) diethiol ranges from 2 to 4, preferably from 2.8 to 3.2.5) Vitrimer according to any one of the preceding claims, wherein said amine catalyst is selected from:- a primary amine selected from propylamine, butylamine,benzylamine, N, N-diethylethylenediamine, N,N- dimethyltrimethylenediamin, 2-aminoethyl (ethyl) amine, N, N-diethyl-p-phenylenediamine, aminoethylpiperazine, or mixture thereof;- a secondary amine selected from N, N, N ' -trimethyl-1 , 3- propanediamine, dimethylamine, diethylamine, dipropylamine, N-ethylisopropylamine, dibutylamine, dipentyl amine, l,5,7-triazabicyclo[4.4.0] dec-5-ene, N, N-dimethyl-N ' -pyridin-2 -ylmethyl-e thane- 1 , 2 -di amine,N,N'-BIS- (2, 4 -dimethyl -phenyl ) -ethane- 1 , 2 -di amine, N ' - cyclohexyl-N, N-dime thyl-e thane- 1 , 2 -di amine, N, N- dimethyl aminopropyl amine N-methylhexan-3-amine, ethylphenylamine, N, N ' -dimethyl-1 , 3-propanediamine, lH,2H,3H-[l,3]diazolo[l,2-a] imidazole, 3- azabicyclo [ 3.2.1 ] octane, dicyclohexylamine, N,N- dimethyl dipropylene triamine, or mixture thereof; or mixture thereof, preferably it is dipropylamine.6) Vitrimer according to any one of the preceding claims wherein the molar ratio between the amine catalyst and the polyisocyanate moiety ranges from 0.003 to 0.2, preferably from 0.02 to 0.08, more preferably it isO.045.7) Vitrimer according to any one of the preceding claims wherein the molar ratio between the polythiol and / or polyol moiety and the polyisocyanate moiety ranges from 0.2 to 1, preferably from 0.4 to 0.8, preferably it is 0.6.8) A method for preparing a vitrimer, said method comprising the following steps: a) reacting an amine catalyst with a polyisocyanate monomer; b) reacting a second monomer selected from a polythiol compound and / or a polyol compound with the product of step a) to obtain a cured vitrimer.9) Method according to claim 8, wherein the amine catalyst is selected from:- a primary amine selected from propylamine, butylamine, benzylamine, N, N-diethylethylenediamine, N,N- dimethyltrimethylenediamin, 2-aminoethyl (ethyl) amine, N, N-diethyl-p-phenylenediamine, aminoethylpiperazine, or mixture thereof;- a secondary amine selected from N, N, N ' -trimethyl-1 , 3- propanediamine, dimethylamine, diethylamine, dipropylamine, N-ethylisopropylamine, dibutylamine, dipentyl amine, l,5,7-triazabicyclo[4.4.0] dec-5-ene, N, N-dimethyl-N ' -pyridin-2 -ylmethyl-e thane- 1 , 2 -di amine, N,N'-BIS- (2, 4 -dimethyl -phenyl ) -ethane- 1 , 2 -di amine, N ' - cyclohexyl-N, N-dime thyl-e thane- 1 , 2 -di amine, N, N- dimethyl aminopropyl amine N-methylhexan-3-amine, ethylphenylamine, N, N ' -dimethyl-1 , 3-propanediamine, lH,2H,3H-[l,3]diazolo[l,2-a] imidazole, 3- azabicyclo [ 3.2.1 ] octane, dicyclohexylamine, N,N- dimethyl dipropylene triamine, or mixture thereof; or mixture thereof, preferably it is dipropylamine.

10. Method according to claim 8 or 9, wherein saidpolyisocyanate monomer is selected from: a compound of formula (I)i(i) wherein n, m and o are integers, independently from each other, selected from 1 to 10, preferably from 4 to 8, more preferably 6;- a compound of formula (II)OCN- (CH2) n-NCO (II) wherein n is an integer comprised from 1 to 20, preferably from 2 to 10, more preferably from 3 to 8, more preferably n is equal to 6; poly (hexamethylene diisocyanate) , methylene diphenyl diisocyanate, 2 , 4 , 6-trioxtriazine-1,3,5 (2H, 4H, 6H) -triyl) tris (hexamethylene) isocyanate, imidodicarbonicdiamide, N,N',2-tris (6- isocyanatohexyl ) , 4,4' diphenylmethanediisocyanate; or mixture thereof, preferably it is a compound of formula (I) wherein n is equal to 6.11) Method according to any one of claims 8 to 10, wherein said second monomer is selected from: a polythiol selected from 1 , 6-hexanedithiol , 1,5- pentanedithiol , poly ( ethyleneglycol ) dithiol with a number of ethylene glycol unit ranging from 1 to 10,dipentaerythritol hexakis ( 3-mercaptopropionate ) , 2, 2'- ( ethylenedioxy ) diethiol , pentaerythritol tetrakis (3- mercaptopropionate ) , or mixture thereof; a polyol selected from hexane-1, 6-diol, dipentaerythritol, or mixture thereof; or mixture thereof.12) Method according to claim 11, wherein said second monomer is selected from polythiols, preferably it is a mixture of dipentaerythritol hexakis (3- mercaptopropionate ) and 2, 2 '- ( ethylenedioxy ) diethiol , more preferably wherein the molar ratio between dipentaerythritol hexakis ( 3-mercaptopropionate ) and 2, 2 '- ( ethylenedioxy ) diethiol ranges from 2 to 4, preferably from 2.8 to 3.2.13) Method according to any one of the preceding claims 8 to 12, wherein said step b is carried out at a temperature ranging from 25°C to 100°C, for a time ranging from 5 minutes to 3 days.14) Article made of a vitrimer comprising- a polyisocyanate moiety,- a polythiol moiety and / or a polyol moiety, wherein an amine catalyst is covalently bonded to the polyisocyanate moiety.15) Article according to claims 14) , said article being an eyewear frame, preferably made of a polythiolurethane vitrimer .16) Article according to claim 14 or 15, said article having shape-memory properties at 80-120 °C.17) Method for reprocessing a cured vitrimer comprising- a polyisocyanate moiety,- a polythiol moiety and / or a polyol moiety, wherein an amine catalyst is covalently bonded to the polyisocyanate moiety, said method comprising:- chopping the cured vitrimer in parts, preferably having a particle size of 5-50 micrometers,- mixing the chopped parts with 0-90%, preferably 25- 75%, of the uncured vetrimer,- hot pressing in a mold at a temperature ranging from 80-300 °C, preferably 80-220°C.

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