ES2957982A1 - Hydrolyzable crosslinkers and products derived from them (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Hydrolyzable crosslinkers and products derived from them. The present invention refers to a hydrolyzable crosslinker of formula I: {IMAGE-01} resins obtained with this type of crosslinker, as well as polymerized products derived from these materials and their use in industry, for example in additive manufacturing, such as 3D printing. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

Hydrolyzable crosslinkers and products derived from them

Technical field of the invention

The present invention refers to the field of materials that can be used in different industries, such as tissue engineering, regenerative medicine but also to obtain high resolution products for the sound industry, jewelry, among others.

Background

SLA/DLP (Stereolithography/Digital Light Processing) -Stereolithography/Digital Light Processing- and also inkjet technologies such as Polyjet and additive manufacturing (AM) technologies based on the use of photopolymerizable resins. These methodologies require the exposure of a liquid resin to ultraviolet light to photopolymerize and therefore create a solid network of polymers.

On the one hand, the high resolution of these techniques compared to other additive manufacturing approaches has made them the most used for high-precision applications such as jewelry, hearing aids, in the dental sector but also for the preparation of molds and equipment.

Furthermore, technologies such as bioprinting often benefit from the use of photocross-linkable materials to obtain hydrogels for biotechnology-related purposes.

There is a wide variety of resins with variable properties ranging from elastic/flexible to resistant or stable at high temperatures (https://formlabs.com/store/materials/; https://envisiontec.com/3d-printing-materials/ ). There are also commercially available biocompatible resins that are currently being used to make dental splints or surgical guides. However, all of these resins are typically formulated with large amounts of multifunctional cross-linkers to form stable, non-swellable structures, that is, covalently linked networks that remain unchanged for the life of the 3D printed part.

In this text the term 'cross-linker' will be understood to refer to a polymerizable compound with at least two polymerizable functionalities.

Taking into account both the high resolution of SLA (stereolithography) and the wide use of this AM technology for the preparation of 3D printed molds, it would be desirable to have:

1) Resins that can be used for the manufacture of high-resolution parts (such as molds) and that can be easily removed after use for the desired purpose.

This type of sacrificial materials already has counterparts in FDM (Fused deposition modeling) (for example, limonene-soluble HIPS (high impact polystyrene) and water-soluble PVA (polyvinyl alcohol)) for the manufacture of supports and also molds. However, the poor x-y resolution of FDM produces low-quality molds. It is worth mentioning that the molds currently used made with SLA do not allow the manufacture of intricate structures due to the need to be completely removed once the part has been manufactured. In this sense, soluble molds will significantly improve the complexity of the structures that can be manufactured. This could be achieved by using labile structures such as those provided by the present invention as cross-linking agents. The preferable solvent in terms of non-toxicity and accessibility for any type of use would be water, which carries the usp of hydrolyzable cross-linkers.

2) Hydrogels with interest in applications related to biotechnology.

The materials currently used for SLA and DLP in particular, but also for inkjet purposes lead to cross-linked solid materials. In the case of SLA and DLP, the printer configuration with the part being manufactured in an inverted position on a solid support introduces important limitations. In particular, the manufacture of materials with low cross-linking density (as is the case of hydrogels) is avoided. The reason is that the part during the manufacturing process is capable of swelling in contact with the polymerizable resin. As a result, the part/platform adhesion decreases and finally the part falls onto the resin tank. A solution to this problem is the manufacture of highly cross-linked pieces (capable of remaining adhered to the support) that, in a second step, can be partially hydrolyzed.

3) 3D printed reprocessable cross-linked materials.

A major limitation of the cross-linked materials currently used is the possibility of recycling them after use. These materials are typically sent directly to landfill or used for combustion, and only a small percentage of these materials are included as an additive in new plastics. The present invention provides the use of these hydrolyzable cross-linking agents in reversibly cross-linked formulations, also known as "vitrimers".

Several documents refer to compounds similar to the hydrolyzable cross-linkers of the invention:

CN109851572 relates to the field of synthesis of polymeric materials, in particular to a methacrylate monomer for dental restorative materials and a method of preparation

CN109651296 discloses a water-soluble methacrylate monomer, the purpose of which is to solve the problem that an existing light-curing coating does not have water resistance. The monomer has the advantages that the molecular structure contains the quaternary ammonium salt structure, so that the monomer has good water solubility and can serve as a water-based photocuring system or photocuring hydrogel.

In particular, embodiments of the present invention, such as those in which R3 in formula I is different from a hydrocarbon chain, are more hydrophilic than the structures described by CN109851572 and CN109651296. As a result, the hydrolyzable cross-linkers of the present invention interact more favorably with water and will result in products with better properties.

JACS, 2009, 131, 14795-14803, describes some polyester dendrimer structures that are useful for in vivo delivery of bioactive molecules due to their biodegradability, but their synthesis generally requires multi-step reactions with intensive purifications.

The article titled “Synthetic clay nanocomposite-based coatings prepared by UV curing photopolymerization” by B. S. Shemper, J.-F. Morizur, M. Alirol, A. Domenech, V. Hulin, L. J. Mathias; First published: May 4, 2004;Journal of Applied Polymer Science,vol. 93, 1252-1263 (2004) refers to the effect of synthetic clay on the photopolymerization kinetics and coating properties of methyl alpha-hydroxymethylacrylate (MHMA) systems in the presence of hydroxylated dimethacrylate crosslinkers. To increase the compatibility between the clay and the polymer matrix, Jeffamines are used as polymer/clay compatibilizers.

Description of the invention

The present invention relates to a hydrolyzable crosslinker of formula I:

in which:

- X can be the same or different in the two positions and means oxygen or nitrogen - R1 and R1' can be the same or different, and can be:

- an alkylene group of 1 to 20 carbon atoms, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from:

- heteroatoms, so that said heteroatom can be one or more halogen atoms,

- functional groups such that said functional group can be: one or more alkoxy groups having 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl, carbamoyl groups and combinations of these substituents, and - alkyl groups,

and such that in the alkylene group there may be heteroatoms that replace one or more carbon atoms, said heteroatoms being selected from O, N-substituted, S,

- oligomers or polymers of the polyether type (such as polyethylene glycol) or polyester (such as those derived from polycaprolactone)

- R2 and R4 can be the same or different, and can be:

- H, alkyl of 1 to 20 carbon atoms, which can be linear or branched, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from heteroatoms, functional groups or alkyl groups, such that said heteroatom can be one or more halogen atoms, so that said functional group can be one or more alkoxy groups of 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more oxo groups, one or more oxy groups, one or more carboxyl groups, oxycarbonyl groups, carbamoyl groups and combinations of these substituents,

and such that in the alkyl group there may be heteroatoms substituting one or more carbon atoms, said heteroatoms being selected from O, N-substituted, S,

- or R2 and R4 can be linked, giving rise, together with R3, to a cyclic structure of 5 or more members, which can be a saturated or unsaturated structure, in which the carbon atoms of the cyclic structure can be substituted by heteroatoms, and in which said carbon atoms may also have substituents,

- and optionally R2 and R4 can be linked, giving rise together with R3 to a cyclic structure of 5 or more members, with a saturated or unsaturated structure, so that R2 and R4, together, have the same meaning as R3, so that the cyclic structure is symmetrical,

- R3 can be:

- a hydrocarbon chain of 1 to 20 carbon atoms, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from heteroatoms, functional groups or alkyl groups, so that said heteroatom can be one or more halogen atoms, so that said functional group can be one or more alkoxy groups of 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl groups and combinations of these substituents,

and in which there may be heteroatoms that replace one or more carbon atoms, said heteroatoms being selected from O, N, S

- an oligomer or polymer of the polyether, or polyester type (such as those derived from polycaprolactone),

with the condition of:

1) when:

- X is identical in the two positions, and is oxygen,

- R1 and R1' are identical and are 2-hydroxy-propane-1,3-diyl, or ethane-1,2-diyl

- R2, R3 and R4 form a cycle, then the cycle is not a piperazine-1,4-diyl residue,

2) when

- X is identical in the two positions, and is oxygen,

- R2 and R4 are both a methyl group,

then: R3 is not -(C H 2)n -, where n=2-4 or R2 and R4 with R3 do not form a piperazine-1,4-diyl moiety,

3) when

- X is identical in the two positions, and is oxygen, and

- Ri and Ri' are identical and are 2-hydroxy-propane-1,3-diyl,

- R2 and R4 are H

then: R3 is different from

-CH(CH3)-CH2-O-CH(CH3)-CH2-(O-CH2-CH2-)x-O-CH2-CH(CH3)-O-CH2-CH(CH3)- where x = 14.

In the definition of formula I above, "N-substituted" means "a tertiary amino group."

In the definition of formula I above, a “polyether type” oligomer or polymer is meant to comprise ethylene glycol or propylene glycol groups, or mixtures of ethylene glycol and propylene glycol groups.

The crosslinkers of the invention are hydrolyzable and also transesterifiable.

The term "transesterifiable" means herein that these compounds comprise ester groups, which can be transesterified by molecules with structures containing OH groups.

According to particular realizations:

- X is identical in both positions, and is oxygen or nitrogen

- R1 and R1' are identical

- R2, R3 and R4 have the meaning given above.

According to additional particular embodiments:

- X is identical in both positions, and is oxygen or nitrogen

- Ri and R i' are identical and are an alkylene group of 1 to 10 carbon atoms, where one or more hydrogen atoms are substituted with hydroxyl groups (-OH)

- R2, R3 and R4 have the meaning given above.

According to additional particular embodiments:

- X is identical in both positions, and is oxygen or nitrogen

- Ri and R i' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, R3 and R4 form an al cycle minus 5 members, where the non-N members are methylene groups.

According to additional particular embodiments:

- X is identical in both positions, and is oxygen

- R1 and R1' are identical and are an alkylene group of 3 carbon atoms, where one or more hydrogen atoms are substituted with hydroxyl groups (-OH), more preferably, R1 and R1' are 2-hydroxy-propane-1 ,3-diyl

- R2, R3 and R4 form a cycle of at least 5 members, where the members other than N are methylene groups.

According to additional particular embodiments:

- X is identical in both positions, and is oxygen

- R1 and R1' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, and R4 are identical and are H or a alkyl group of 1 to 5 carbon atoms - R3 is a hydrocarbon chain, comprising oxygen atoms replacing one or more carbon atoms, and such that in the chain there is at least one group of each of the following structures:

-CH(CH3)-CH2--(O-CH2-CH(CH3))x--(O-CH2-CH2V

-(O-CH2-CH(CH3))zwhere x, y, z, have values, independently of each other, between 1 and 12.

In a preferred embodiment:

- X is identical in both positions, and is oxygen

- R1 and R1' are identical and are 2-hydroxy-propane-1,3-diyl

- R2 and R4 are identical, and are H,

- R3 is a hydrocarbon chain, formed by oxygen atoms replacing one or more carbon atoms, and such that in the chain there is at least one group of each of the following structures, in the order specified below:

-CH(CH3)-CH2--(O-CH2-CH(CH3))x--(O-CH2-CH2V

-(O-CH2-CH(CH3))zwhere x, y, z, have values, independently of each other, between 1 and 3.

According to additional particular embodiments:

- X is identical in both positions, and is oxygen

- R1 and R1' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, and R4 are identical and are H or a alkyl group of 1 to 5 carbon atoms - R3 is a hydrocarbon chain, comprising oxygen atoms that replace one or more carbon atoms.

In a preferred embodiment:

- X is identical in both positions, and is oxygen

- R1 and R1' are identical and are 2-hydroxy-propane-1,3-diyl

- R2, and R4 are identical and are H

- R3 is an alkylene group, comprising oxygen atoms substituting one or more carbon atoms, with the structure: -(CH2)3-O-(CH3))2-O-(CH3))2-O-( CH2)3-. A particular case of this preferred embodiment is the following compound:

The hydrolyzable crosslinkers of the invention can be obtained by conventional synthesis methods. For example, they can be obtained by carrying out a Michael reaction between an acrylate or acrylamide with the amino groups of the corresponding diamine, under conditions well known to a person skilled in the art.

Another object of the invention is a resin that comprises:

- a hydrolyzable crosslinker of formula II:

in which:

- X can be the same or different in the two positions and means oxygen or nitrogen - R1 and R1' can be the same or different, and can be:

- an alkylene group of 1 to 20 carbon atoms, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from:

- heteroatoms, so that said heteroatom can be one or more halogen atoms,

- functional groups such that said functional group can be: one or more alkoxy groups having 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl groups, carbamoyl groups and combinations of these substituents, and

- alkyl groups,

and such that in the alkylene group there may be heteroatoms that substitute one or more carbon atoms, said heteroatoms being selected from O, N-substituted, S,

- oligomers or polymers of the polyether type (such as polyethylene glycol) or polyester (such as those derived from polycaprolactone)

- R2 and R4 can be the same or different, and can be:

- H, alkyl of 1 to 20 carbon atoms, which can be linear or branched, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from heteroatoms, functional groups or groups alkyl, so that said heteroatom can be one or more halogen atoms, so that said functional group can be one or more alkoxy groups of 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or several cyano groups, one or more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl groups, carbamoyl groups and combinations of these substituents,

and such that in the alkyl group there may be heteroatoms substituting one or more carbon atoms, said heteroatoms being selected from O, N-substituted, S,

- or R2 and R4 can be linked, giving rise, together with R3, to a cyclic structure of 5 or more members, which can be a saturated or unsaturated structure, in which the carbon atoms of the cyclic structure can be substituted by heteroatoms, and in which said carbon atoms can also have substituents,

- and optionally R2 and R4 can be linked, giving rise together with R3 to a cyclic structure of 5 or more members, with a saturated or unsaturated structure, so that R2 and R4 together have the same meaning as R3, so that the structure cyclic is symmetrical,

- R3 can be:

- a hydrocarbon chain of 1 to 20 carbon atoms, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from heteroatoms, functional groups or alkyl groups, so that said heteroatom can be one or more halogen atoms, so that said functional group can be one or more alkoxy groups of 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl groups and combinations of these substituents,

and in which there may be heteroatoms that replace one or more carbon atoms, said heteroatoms being selected from O, N, S

- an oligomer or polymer of the polyether type, or polyester (such as those derived from polycaprolactone),

- at least one starter

- optionally, at least one monofunctional monomer,

- optionally, at least one stable cross-linker

- optionally, a light absorber.

- optionally, one or more solvents.

The term "resin" according to the present invention should be understood as a mixture comprising the components mentioned in the previous definition, in which at least one hydrolyzable cross-linker and at least one initiator are present for any embodiment of the resin, while the rest components are optional.

The resin defined above comprises polymerizable components which are the hydrolyzable cross-linkers and the monofunctional monomers (if present). The rest of the components (initiator, absorbent, solvent) have a different function, that is, they are not included by polymerization in the resulting polymer chain.

According to particular embodiments, the resin of the invention has a composition such that it comprises a hydrolyzable cross-linker of formula I.

According to particular embodiments, the resin of the invention has a composition corresponding to any of the particular embodiments previously defined for the previous hydrolyzable crosslinkers.

In the definition of formula II above, "N-substituted" means "a tertiary amino group."

In the definition of formula II above, a "polyether type" oligomer or polymer is meant to comprise ethylene glycol or propylene glycol groups, or mixtures of ethylene glycol and propylene glycol groups.

According to particular embodiments of the resin, in formula II:

- X is identical in both positions and is oxygen or nitrogen

- Ri and R i' are identical

- R2, R3 and R4 have the meaning given above.

According to additional particular embodiments of the resin, in formula II:

- X is identical in both positions and is oxygen or nitrogen

- R1 and R1' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, R3 and R4 have the meaning given above.

According to additional particular embodiments of the resin, in formula II:

- X is identical in both positions and is oxygen or nitrogen

- Ri and R i' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, R3 and R4 form an al cycle minus 5 members, where the non-N members are methylene groups.

According to additional particular embodiments of the resin, in formula II:

- X is identical in both positions and is oxygen or nitrogen

- R1 and R1' are identical and are an alkylene group of 3 carbon atoms, where one or more hydrogen atoms are substituted with hydroxyl groups (-OH), more preferably, R1 and R1' are 2-hydroxy-propane-1 ,3-diyl

- R2, R3 and R4 form a cycle of at least 5 members, where the members other than N are methylene groups.

According to additional particular embodiments of the resin, in formula II:

- X is identical in both positions, and is oxygen

- R1 and R1' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, and R4 are identical and are H or a alkyl group of 1 to 5 carbon atoms - R3 is a hydrocarbon chain, comprising oxygen atoms replacing one or more carbon atoms, and such that in the chain there is at least one group of each of the following structures:

-CH(CH3)-CH2--(O-CH2-CH(CH3))x--(O-CH2-CH2V

-(O-CH2-CH(CH3))zwhere x, y, z, have values, independently of each other, between 1 and 12.

In a preferred embodiment of the resin, in formula II:

- X is identical in both positions, and is oxygen

- R1 and R1' are identical and are 2-hydroxy-propane-1,3-diyl

- R2 and R4 are identical, and are H,

- R3 is a hydrocarbon chain, formed by oxygen atoms replacing one or more carbon atoms, and such that in the chain there is at least one group of each of the following structures, in the order specified below:

-CH(CH3)-CH2--(O-CH2-CH(CH3))x--(O-CH2-CH2V

-(O-CH2-CH(CH3))zwhere x, y, z, have values, independently of each other, between 1 and 3.

According to additional particular embodiments of the resin, in formula II:

- X is identical in both positions, and is oxygen or nitrogen

- R1 and R1' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, and R4 are identical and are H or a alkyl group of 1 to 5 carbon atoms - R3 is a hydrocarbon chain, comprising oxygen atoms that replace one or more carbon atoms.

In a preferred embodiment of the resin, in formula II:

- X is identical in both positions, and is oxygen

- R1 and R1' are identical and are 2-hydroxy-propane-1,3-diyl

- R2 and R4 are identical, and are H,

- R3 is an alkylene group, comprising oxygen atoms substituting one or more carbon atoms, with the structure: -(CH2)3-O-(CH3))2-O-(CH3))2-O-( CH2)3-.

The resin has a composition in which the weight ratio HCL/I (hydrolyzable crosslinker/Initiator) is greater than 1. According to particular embodiments, the resin has a composition in which the weight ratio HCL/I (hydrolyzable crosslinker/Initiator) ) is greater than 10.

Sacrificial materials or vitrimers can be obtained using radical polymerization of the resin. The sacrificial character in aqueous media or the reversibility of the vitrimer is based in both cases on the use of HCL.

According to particular embodiments, the resin of the invention comprises a cross-linker of formula II, at least one initiator and at least one stable cross-linker. Resettable networks can be obtained using this resin comprising at least one stable crosslinker.

According to particular embodiments, the resin comprises a cross-linker of formula II, at least one initiator, and at least one stable cross-linker, where the weight ratio (HCL+ stable cross-linker)/I is greater than 10, and the weight ratio HCL/( stable cross-linking) is less than 1000 and greater than 0.1.

According to additional particular embodiments, resettable networks can be obtained using the resin comprising a cross-linker of formula II, at least one initiator, and at least one stable cross-linker, where the weight ratio (HCL+ stable cross-linker)/I is greater than 10, and the weight ratio HCL/(stable cross-linker) is less than 1000 and greater than 0.1, by radical polymerization; and after hydrolysis.

The stable cross-linking agent may be a commercially available stable cross-linking agent. It can also be selected from any of the crosslinkers with alkenic (meth)acrylic structures (a,pinsaturated structures) or divinylbenzene, described in application WO2019193236.

In a preferred embodiment, the stable cross-linker is selected from ethylene glycol methacrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, bisphenol A di(meth)acrylate, di(meth)acrylate. bisphenol A meth)acrylate, bisphenol A di(meth)acrylate (meth)acrylate, pentaerythritol tri- and tetra(meth)acrylate, tetramethylenedi(meth)acrylate, N,N'-methylenebisacrylamide, divinylbenzene, polysiloxanylbisalkyl(meth) acrylate, diurethane dimethacrylate, polyethylene glycol di(meth)acrylate, or combinations of the above.

In a more preferred embodiment, the stable cross-linker is ethylene glycol dimethacrylate.

According to preferred embodiments, the resin comprises one or more monofunctional monomers M1, M2...Mn. These monofunctional monomers can be, for example, any of the monofunctional monomers described in application WO2019193236.

The amount of monofunctional monomer(s) in the resin may be, for example, in a weight ratio (M1+M2+...Mn)/HCL equal to or less than 9.

In a more preferred embodiment, the monofunctional monomer is selected from the following hydrophilic (meth)acrylic structures: hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate, polyethylene glycol methyl ether acrylate (PEGMEA), polyethylene glycol acrylate, methyl ether methacrylate polyethylene glycol, polyethylene glycol methacrylate, dimethylacrylamide (DMA), methacrylic acid (MAA), acrylic acid, carboxyethyl acrylate (CEA).

In a more preferred embodiment, HEA and PEGMEA are selected as monofunctional monomers. The HEA/PEGMEA weight ratio may be, for example, between 1/100 and 100/1.

In a further more preferred embodiment, DMA and PEGMEA are selected as monofunctional monomers. The DMA/PEGMEA weight ratio may be, for example, between 1/100 and 100/1.

In a further more preferred embodiment, HEA and DMA are selected as monofunctional monomers. The HEA/DMA weight ratio may be, for example, between 1/100 and 100/1.

In a further more preferred embodiment, MAA and HEA are selected as monofunctional monomers. The MAA/HEA weight ratio may be, for example, between 1/100 and 100/1.

In a further more preferred embodiment, CEA and HEA are selected as monofunctional monomers. The CEA/HEA weight ratio may be, for example, between 1/100 and 100/1.

In a further more preferred embodiment, the monofunctional monomer is selected from the following hydroxylated (meth)acrylic structures: 2-hydroxyethylacrylamide, 2-hydroxypropylacrylate, 4-hydroxybutylacrylate, hydroxypropylmethacrylate, 2-hydroxyethylmethacrylate, 3-phenoxy 2-hydroxypropylmethacrylate, glycerol monomethacrylate, N -(2-hydroxypropyl)methacrylamide, 2-hydroxy-3-phenoxypropyl acrylate (HPPA). Hydroxylated monofunctional monomers can be used to facilitate reprocessability as vitrimers.

In a further more preferred embodiment, HPPA is selected as a monofunctional monomer.

In a further preferred embodiment, the monofunctional monomer is a styrenic structure, this is a monomer that comprises a styrene group, of chemical formula C6H5CH=CH-, or derivatives thereof.

In a more preferred embodiment, the styrenic structure is selected from styrene, chlorostyrene, bromostyrene, vinylaniline, vinylnaphthalene, vinylbenzoate or vinylanisole.

In a further preferred embodiment, the monofunctional monomer is a monomer with a vinyl structure, that is, comprising a vinyl group. For example, it may contain a vinyl group attached to a heteroatom.

In a more preferred embodiment, the vinyl structure monomer containing a vinyl attached to a heteroatom is selected from N-vinylacetamide, vinylpyrrolidone, vinylcarbazole, vinylpyridine, vinylimidazole, vinyl acetate, vinylformamide, vinylphosphonic acid, sodium vinylsulfonate or vinyltrimethylsilane.

Optionally, the resin comprises one or more solvents. The solvents that can be used are selected, for example, from acetonitrile, nitromethane, THF, dioxane, DMF or DMSO or a combination of the above.

The initiator may be a photoinitiator, a thermal initiator or a redox polymerization initiator.

Photoinitiators that can be used, for example, 1-hydroxycyclohexyl-phenyl ketone, trimethylbenzoyl-diphenylphosphine oxide or any other photoinitiators mentioned in The Photoinitiators Used in Resin Based Dental Composite—A Review and Future Perspectives, Polymers (Basel). February 2021; 13(3): 470, https://doi.org/10.3390/polym13030470, or in the

Aldrich Paper: https://www.sigmaaldrich.eom/US/en/deepweb/assets/sigmaaldrich/marketing/global/d ocuments/233/907/photoinitiators

In a preferred embodiment, the initiator is a thermal initiator.

Thermal initiators that can be used are, for example, benzoyl peroxide, potassium persulfate, ammonium persulfate, azoinitiators such as azo-bis-isobutyronitrile, 4,4'-azobis(4-cyanovaleric acid), 2,2-dihydrochloride '-azobis(2-(2-imidazolin-2-yl)propane), 2,2-azobis(2-methylpropionamidine) dihydrochloride, 2,2-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis ( 2-methylbutyronitrile), dimethyl 2,2'-azobis(2-methylpropionate), or any other initiator mentioned in the document:

https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/marketing/global/documen ts/411/888/thermal_initiators.pdf.

In a preferred mode, the initiator is a redox initiator.

The redox initiators can be any oxidizing/reducing agent pair, for example, as oxidants benzoyl peroxide, persulfates, peroxides or hydroperoxides and as reducing agents ascorbic acid, dimethyl-p-toluidine, dimethylaniline, formaldehyde sulfoxylate (SFS), tetramethyl ethylenediamine ( TMEDA), Bruggolit 6 and 7 (FF6 and FF7), sodium metabisulfites.

In a preferred embodiment, benzoyl peroxide and dimethylaniline are used as redox initiators.

The UV absorbers that can be used are of the diazo type - that is, they comprise at least one diazo group - or based on benzophenone, benzotriazole or triazines.

In a more preferred embodiment, the UV absorber is Sudan I.

Another aspect of the invention relates to a process for polymerizing the resin of the invention.

The resin polymerization procedure includes at least the following steps:

a) A mixture of:

- one or more hydrolyzable/transesterifiable crosslinkers of formula II,

- starter,

- UV absorber, if present,

- one or more stable cross-linkers, if present,

- one or more monofunctional monomers, if present,

- solvent, if present,

b) optionally, bubble the mixture from step (a) with a gas,

c) transfer of the product obtained in step b) to a container where the polymerization will take place, such as a vial, a flask, a reactor, a mold, a tank for 3D printing

d) polymerization, and

e) recovery of the resulting polymerized material.

An additional object of the present invention is a polymerized material resulting from step e) of the procedure defined above.

According to particular embodiments, in the procedure defined above, the mixture in step a) comprises:

- one or more hydrolyzable/transesterifiable crosslinkers of formula II, - initiator,

- UV absorber, if present,

- one or more monofunctional monomers, if present,

- solvent, if present,

and the procedure also includes:

f) hydrolyze or transesterify at least part of the cross-linking bonds of the hydrolyzable cross-linkers of the mixture from step a).

An additional object of the present invention is a polymerized product resulting from the procedure defined in the previous paragraph. The polymerized product is optionally subjected to one or more operations, such as washing, heating, cooling.

According to particular embodiments, in the process defined above, the mixture in step a) comprises:

- one or more hydrolyzable/transesterifiable crosslinkers of formula II, - initiator,

- one or more stable crosslinkers

- UV absorber, optionally,

- one or more monofunctional monomers, if present,

- solvent, optionally,

and the procedure also includes:

f) hydrolyze or transesterify at least part of the cross-linking bonds of the hydrolyzable cross-linkers of the mixture from step a).

An additional object of the present invention is a polymerized product resulting from the procedure defined in the previous paragraph. The polymerized product is optionally subjected to one or more operations, such as washing, heating, cooling.

An additional object of the present invention is a polymerized product resulting from the procedure defined in any of claims 18 or 19.

According to particular additional embodiments, the polymerized product is selected from:

- a sacrificial piece,

- a resettable network or

- a reprocessable or vitrimeric material.

The way of carrying out the polymerization procedure defined above is well known to a person skilled in the art.

A radical polymerization can be differentiated in the mode of initiation: it can be photoinitiated, thermally initiated, or initiated through the use of a redox couple, or by other methods. At another level, the type of radical polymerization can also be distinguished in terms of components: solution polymerization if there is a solvent, or bulk polymerization if there is no solvent. At another level, photopolymerization can be carried out in a curing chamber or in a layer-by-layer procedure (Additive Manufacturing, also known as 3D printing) for example using SLA/DLP or even Polyjet(R), injection-based 3D. from ink. Printers or material extrusion 3D printers.

In a preferred embodiment, the polymerization is carried out in a photocuring chamber and the UV radiation is maintained between 0.01 and 60 minutes.

In a preferred embodiment, the polymerization is carried out in a layer-by-layer process comprising the deposition of a photosensitive material and a curing step. This approach can be carried out, for example, using SLA/DLP 3D printers, Polyjet technology or material extrusion.

In a preferred embodiment, the polymerization is carried out without addition of solvent (step a). That is, mass polymerization.

In a preferred embodiment, the polymerization is carried out by thermal initiation at a temperature between 30°C and 120°C for a time between 0.1 and 24 hours.

Another object of the invention is the use of the resins of the invention for additive manufacturing and, in particular, for stereolithographic 3D printing.

The terms "curing" and polymerization are used interchangeably herein.

The resins of the invention have the following advantageous characteristics: Ability to be printed on standard commercial DLP/SLA 3D printers. Potentially also for Polyjet technology.

1. Once cured (e.g. light cured), the polymerized material resists temperature so that it can be used, for example, for mold making.

2. The polymerized material carries hydrolyzable/transesterifiable cross-linking agents that can be cleaved using non-toxic solvents, such as water, or using hydroxyl groups present in the network structure. In particular, non-permanent or hydrolyzable cross-linkers will be hydrolyzable in basic aqueous media.

3. As will be explained later, depending on the relative amount of hydrolyzable cross-linkers versus the total amount of cross-linkers and the type of monomers used in the formulation, the final 3D printed part will be able to:

- Be able to dissolve completely in the appropriate solvent. The crosslinkers of this resin will be designed exclusively with hydrolyzable crosslinkers.

- swell, but will retain the general structure (behavior similar to that of a hydrogel). To do this, a mixture of stable and hydrolyzable crosslinkers will be used as crosslinkers in the resin.

- Be used to produce reprocessable cross-linked materials. This means that the material can be, for example, reprocessed by heating it into the desired shape but still be cross-linked at room temperature ("vitrimer" material). Furthermore, these materials can be hydrolyzed at the end of their use, giving rise to linear chains that can be recycled.

Another object of the invention is a polymerized product derived from the polymerized product resulting from step e) in the procedure defined above. The polymerized product can be, for example:

- a sacrificial piece,

- a resettable network or

- a reprocessable or vitrimeric material.

A sacrificial piece is a type of polymerized product, to obtain which only hydrolyzable crosslinkers of the invention are used as crosslinkers, but not stable crosslinkers.

A resettable network according to the invention is a type of polymerized product, to obtain which hydrolyzable crosslinkers of the invention, as well as stable crosslinkers, are used. In a first stage, the network comprises a number of cross-links coming from the hydrolyzable and stable cross-linkers, but in a second stage (after hydrolysis), the cross-links coming from the hydrolyzable cross-linkers are broken and it only comprises the cross-links formed by the cross-links. stable.

A reprocessable material or vitrimer, according to the invention, is a type of polymerized product, to obtain which only hydrolyzable crosslinkers of the invention are used as crosslinkers, but not stable crosslinkers. In a first stage, the network comprises several cross-links coming from the hydrolyzable cross-links, and in a second stage (after transesterification), at least some of the cross-links are exchanged with different cross-links. That is, some crosslinks are broken and some new crosslinks are created.

Another object of the invention is the use of the polymerized material defined above for additive manufacturing.

Another object of the invention is the use of the polymerized product in the previously defined industry, preferably in medicine, automotive or jewelry.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1: Strategy for preparing water sacrificial materials from resins containing hydrolyzable HCL cross-linkers (HCL1, HCL2, HCL3 or combinations of the above; they are represented with a 3 in the figure), as described in example 2. Other monofunctional monomers are included as polymerizable components in this example, specifically, combinations of PEGMEA (2 in the Figure) and HEA or DMA (both represented as 1 in the Figure). After polymerization, which in this case is produced by 3D printing, a polymer network is obtained. This network is sacrificed in basic water because the cross-linking bridges are broken, giving rise to soluble linear chains.

Figure 2: Example of a 3D printed mold with elastic properties, as described in Example 2, section 2.1. This template can be dissolved in water after hydrolysis of the cross-linkers.

Figure 3. Example of a 3D printed mold with rigid properties, as described in Example 2, section 2.2. This mold can be dissolved in water after hydrolysis of the cross-linkers (a) Obtained after 3D printing and (b) obtained after washing and post-curing.

Figure 4. Digital mold designs for 3D printing two types of screws with the photocurable resin used to print materials with elastic properties, as described in Example 2, section 2.3. The difference between the two molds is based on the thread pitch.

Figure 5. Silicon pieces obtained by thermal cross-linking of Sylgard 184 inside the 3D printed resin mold, as described in Example 2, section 2.3.1. (a) Silicone screw obtained using Mold 1 in Figure 4 and (b) Silicone screw obtained using Mold 2 in Figure 4, in both cases after dissolving the molds in basic water.

Figure 6. Left: 3D printed mold with fused PCL in the central part, as described in Example 2, section 2.3.2. Right: Images of the PCL screws obtained after dissolving the molds in basic water.

Figure 7. Left: 3D printed mold with photocurable liquid formulation in the central part, as described in Example 2, section 2.3.2. Right: Polymer network screws obtained after dissolving the molds in basic water; These networks are capable of swelling in water, behaving like thermosensitive hydrogels.

Figure 8. Strategy to prepare resettable networks after hydrolysis, from resins containing both crosslinker. hydrolyzable HCL2 (1 in Figure) as stable cross-linkers (PEGDMA, 2 in Figure), as described in Example 3. Other monofunctional monomers are included as polymerizable components in this example, specifically, PEGMEA (4 in Figure) and HEA (3 in the Figure). After printing (and polymerization), a polymer network is obtained. This network is partially hydrolyzed in basic water because the PEGDMA cross-linking bridges remain stable while those of HCL2 are broken, giving rise to resettable networks capable of swelling in water, behaving as a hydrogel.

Figure 9. Swelling of series 1 hydrogels prepared as described in example 3, after all treatment: DLP printing and immersion in basic water.

Figure 10. Left: 3D printed part obtained directly after printing, as described in example 3. Right: Image of the refitted network after partial hydrolysis in basic water and swelling.

Figure 11. Schematic representation of the behavior of a "vitrimer" observed upon heating, as described in Example 4. The material has been obtained by photopolymerization of a resin containing a transesterifiable HCL cross-linker (HCL1, HCL2, HCL3 or combinations of the above; are represented by 3 in the Figure) and monofunctional and hydroxyl-containing HPPA monomer. After polymerization, a polymeric network rich in OH with transesterifiable crosslinks has been obtained. In the Figure, the beta-amino ester of the hydrolyzable cross-linker in the printed material, activated for transesterification, is represented as 1. Upon heating, an -OH from the environment attacks the ester 2, producing a new beta-amino ester 3. In the Figure, 2 represents the void related to the original ester 1.

Figure 12. Illustrative images of: a) liquid resin after mixing, as described in example 4, b) film obtained after photocuring in a chamber, c) film cut into small pieces and d) film reprocessed by heating to 220° C / 100 bar for 10 minutes.

EXAMPLES

MATERIALS

Sylgard 184, vinylcaprolactam, ethylene glycol dimethacrylate, hydroxycyclophenyl ketone, polycaprolactone, poly(ethylene glycol) dimethacrylate (PEGDMA Mn= 550 g/mol), poly(ethylene glycol) methyl ether acrylate (PEGMEA, Mn= 480 g/mol), N, N-dimethylacrylamide (DMA), 2-hydroxyethyl acrylate (HEA), methacrylic acid (MAA), carboxyethyl acrylate (CEA), 2-hydroxy-3-phenoxypropyl acrylate (HPAA), Sudan I, tin (II) 2 -ethylhexanoate and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) were supplied by Aldrich.

N,N-divinylimidazoline was supplied by BASH.

EXAMPLE 1

PREPARATION OF THE HYDROLIZABLE/TRANSESTERIFYABLE CROSS-CROSSLER

The synthesis of some examples of hydrolyzable/transesterifiable cross-linkers is depicted in Scheme 1. The acryloyloxy group of 3-(acryloyloxy)-2-hydroxypropyl methacrylate (also called 1-(acryloyloxy)-3-(methacryloyloxy)-2-propanol ) reacts with the amino groups of, for example:

a) piperazine to produce the cross-linker HCL1, or

b) jeffamine, to produce the cross-linker HCL2, or

c) 4,7,10-trioxa-1,13-tridecanediamine to produce the cross-linker HCL3 in a molar ratio of 2:1, thus giving rise to a dimethacrylate. This reaction is carried out overnight at 37°C in the presence of a catalytic amount of acetic acid (0.25% by weight). 1H NMR spectroscopy was used to follow the disappearance of the vinyl acrylate peaks. The compounds were used without further purification.

Scheme 1

Compound HCL1 (procedure is not included as it is a compound described above):

1H NMR (400 MHz, CDCl3) d: 6.11 (m, 2H, 1-H), 5.58 (m, 2H, 1-H), 4.37-3.45 (m, 16H, 4-6-H OH+ H-b), 2.80 -2.37 (m, 12H, 1'-H 2'-H H-a), 1.87 (m, 6H, Me) ppm.

HRMS (High Resolution Mass Spectrometry) (ESI+, M H+) HCL1: 515.2582 calculated for C24H38N2O10, 515.2599 found.

Procedure for the preparation of HCL2: 60.00 g (0.28 mol) of 3-(acryloyl)-2-hydroxypropyl methacrylate were mixed with 84.02 g (0.14 mol) of jeffamine as in Scheme 1, where x+z=3.6 and y=9, and the reaction was allowed to stir overnight at 37 °C in the presence of 0.33 mL of acetic acid. The product was used without further purification. The product was not characterized by mass spectroscopy because jeffamine is a mixture of oligomers.

1H NMR (400 MHz, CDCl3) d: 6.10 (m, 2H, 1-H), 5.56 (m, 2H, 1-H), 4.18 (m, 4H 4-H), 3.92 (m, 2H, 5- H), 3.80-3.17 (m, OH 6-H Hjeff), 3.03-2.69 (m, H-b CHjeff), 2.50 (m, H-a CH2O), 1.92 (m, 6H, Me), 1.11 (m, Me-jeff ), 1.0 (m, Me-jeff) ppm.

Procedure for the preparation of HCL3: 60.00 g (0.28 mol) of 3-(acryloyl)-2-hydroxypropyl methacrylate were mixed with 30.85 g (0.14 mol) of 4,7,10-trioxa-1,13 -tridecanediamine and were allowed to react overnight with stirring at 37 °C in the presence of 0.21 mL of acetic acid. The product was used without further purification.

<1>H NMR (400 MHz, CDCl3) d: 6.07 (m, 2H, 1-H), 5.53 (m, 2H, 1-H), 4.30-4.05 (m, 10H,4-6-H), 3.72-3.23 (m, 12H, 3'-5'-H), 2.91-2.32 (m, 14H, H-b H-a 1'-H OH), 1.88 (m, 6H, Me), 1.77-1.63 (m, 6H , 2'-H) ppm.

HRMS (ESI+, M H+) HCL3: 649.3526 calculated for C30H52N2O 13, 649.3542 found.

EXAMPLE 2

PREPARATION AND USE OF 3D PRINTED SACRIFICE MOLDS

Sacrificial molds are an example of sacrificial pieces.

This example describes the use of the hydrolyzable cross-linkers of Example 1, HCL, for resins. These resins can be printed by SLA/DLP, by photopolymerization, to obtain elastic or rigid cross-linked pieces of a sacrificial nature, that is, soluble in aqueous media after hydrolysis of HCL (Figure 1). Hydrolyzable cross-linkers are based on p-amino esters that can be hydrolyzed in neutral to basic aqueous media [1] ([1] :Y. Al Thaher, S. Latanza, S. Perni, P.J.J.o.c. Prokopovich,i. science, Role of poly -beta-amino-esters hydrolysis and electrostatic attraction in gentamicin release from layer-by-layer coatings,526 (2018) 35-42). As a result of hydrolysis, the cross-linked structure is transformed into linear soluble polymer chains.

In addition to HCL, the resin includes monofunctional monomers, as indicated below (for example, a linear monomer such as HEA (2-hydroxyethyl acrylate) or DMA (dimethylacrylamide) (could be another hydrophilic monomer)), as well as an appropriate photoinitiator (absorbing at the wavelength of the ultraviolet light from the 3D printer) to photopolymerize the mixture using a DLP 3D printer. A UV absorber is also included to improve definition. As a result of photopolymerization, a cross-linked structure is obtained.

2.1 Sacrificial molds with elastic properties

In this case, the polymerizable components of the resin are a hydrolyzable cross-linker (HCL1, HCL2 or HCL3) and different combinations of PEGMEA (polyethylene glycol methyl ether acrylate), HEA (hydroxyethyl ether acrylate) and DMA (dimethylacrylamide) as monofunctional monomers. In addition to the monomers, the following components were added to the photocurable formulation: TPO photoinitiator (phenylbis(2,4,6-trimethylbenzoyl)phosphine) oxide in a range of 0.35-1% by weight (with respect to the total weight of the polymerizable components [HCL (difunctional) and monofunctional monomers] and a UV absorber (Sudan I) at 0.2% by weight (with respect to the total weight of the polymerizable components).

Table 1 summarizes the 8 different series of resins prepared. Each series (each column) refers to a set of formulations in the ranges indicated in the Table. Thus, taking series 1 and 2, PEGMEA is used as a monofunctional monomer and HCL1 or HCL2 respectively as a hydrolyzable cross-linker. These series include formulations with different HCL(1 or 2)/PEGMEA weight ratios in intervals of 5. Specifically, 10 formulations have been prepared in which the HCL(1 or 2)/PEGMEA weight ratios have been 15/85. , 20/80, .... 55/45 and 60/40. For series 3 to 8, a weight percentage of HCL (1, 2 or 3) of 15% has been kept fixed (with respect to the total crosslinker plus monofunctional monomers), and combinations of two monofunctional monomers have been tested in the indicated ranges. In the table. Thus, taking series 3 as an example, in this series the 13 formulations prepared contain HCL1 and a combination of PEGMEA and HEA as monofunctional monomers in HCL/PEGMEA/HEA weight ratios of 15/85/0, 15/80/5. 15/30/55 and 15/25/60.

Table 1. Compositions of the prepared resins. All amounts are in weight % with respect to the total weight of the cross-linker plus the monofunctional monomers.

Example for the preparation of impression parts for 20 g of a photocurable resin containing HCL2, PEGMEA and HEA in a weight ratio of 15/25/60: First 3 g of HCL2 is added to a vial, then 5 g and 12 g of PEGMEA and HEA. After this, 2.67 mg of Sudan I is added and the vial is covered with aluminum foil. Then, 0.2 g of photoinitiator is added (in this case using 1% by weight) and the mixture is stirred for 5-10 minutes until the mixture is completely homogeneous. The resin is then ready to be tested on the printer. The resin is added to the tank and after choosing the printing parameters: layer 100 |j,m, raft height 1 mm, raft displacement 4 mm, layer exposure time 20 s, exposure time off 5 s, exposure time of the bottom layer 60 s, bottom layers 5 pcs, bottom speed of the platform 100 mm/m and lifting speed of the platform 100 mm/m. The printers used are the Zortrax Inkspire and the Creality LD-002H, using Chitubox for Creality and Z-Suite for Zortrax as design programs, respectively. After printing, a washing step is carried out in isopropanol for 5 minutes and a post-curing process of 30 minutes at room temperature in a photocuring chamber.

The process described above was carried out for all 108 formulations cited in Table 1. Printability was tested by manufacturing 2 cm x 2 cm x 2 mm pieces. All formulations can be printed normally.

In order to mechanically characterize the materials, specimens were printed for compression and tensile tests. The size of the compression specimens (always 5 specimens per test) was 29 cm in diameter and 12.5 cm in height. The size of the tensile specimens (always 5 specimens for each test) was test type V, i.e., W (Narrow section width) = 3.18 ± 0.03 mm (0.125 ± 0.001 in.), L ( Narrow Section Length) = 9.53 ± 0.08 mm (0.375 ± 0.003 in.), G (Gauge Length) = 7.62 ± 0.02 mm (0.300 ± 0.001 in.) and R (Sheet Radius ) = 12.7 ± 0.08 mm (0.500 ± 0.003 in.). The measurements were carried out in a "Universal testing machine", INSTRON brand, with load cells of 1-5kN, according to need, tensile test speed: 100 mm/min and test speed compression: 10 mm/min.

The ranges of mechanical properties of the obtained printing parts (specifically prepared to perform these measurements) are listed below, along with some examples for given printed materials.

Range of mechanical properties of printed parts:

Tensile strength test: 1.68-17.45 Mpa

Compression stress: 0.09-1.00 MPa (10%), 0.32-3.27 MPa (20%)

Tensile strength test results of selected examples:

Weight ratio of crosslinker and monofunctional monomers in the photocurable formulation: HCL2/PEGMEA/DMA = 15/25/60. Modulus of the printed part: 2.148 ± 0.049 MPa.

Weight ratio of crosslinker and monofunctional monomers in the photocurable formulation: HCL2/PEGMEA/HEA = 15/25/60. Modulus of the printed part: 2.245 ± 0.025 MPa.

Weight ratio of crosslinker and monofunctional monomer in the photocurable formulation: HCL1/PEGMEA = 30/70. Modulus of the printed part: 9.230 ± 0.290 MPa.

Weight ratio of crosslinker and monofunctional monomer in the photocurable formulation: HCL2/PEGMEA = 30/70. Modulus of the printed part: 4.384 ± 0.060 MPa.

Compression test results of selected examples:

Weight ratio of crosslinker and monofunctional monomers in the photocurable formulation: HCL2/PEGMEA/DMA = 15/25/60. Compression Modulus at 20%: 0.560 ± 0.050MPa.

Weight ratio of crosslinker and monofunctional monomers in the photocurable formulation: HCL2/PEGMEA/HEA = 15/25/60. Compression Modulus at 20%: 20%: 0.565 ± 0.037MPa.

Weight ratio of crosslinker and monofunctional monomer in the photocurable formulation: HCL1/PEGMEA = 30/70. Compression Modulus at 20%: 3.272 ± 0.573 MPa.

Weight ratio of crosslinker and monofunctional monomer in the photocurable formulation: HCL2/PEGMEA = 30/70. Compression Modulus at 20%: 0.789 ± 0.122 MPa.

Figure 2 shows a piece obtained from a soluble resin prepared according to this section.

2.2 Sacrificial pieces with rigid properties

To improve the mechanical resistance of the printed materials, a modification of the formulation was made by replacing PEGMEA with acidic components that will increase the rigidity, such as methacrylic acid (MAA) or 2-carboxyethyl acrylate (CEA). These resins made it possible to manufacture parts with improved modulus up to 88 MPa.

Thus, in this case, the polymerizable components of the resin are the hydrolyzable cross-linker HCL2 and different combinations of HEA, MAA and CEA as monofunctional monomers. In addition to the cross-linker and monofunctional monomers, the photoinitiator TPO (phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide) in the range of 0.35 1 wt % (relative to the total weight) and 0.2 % was added. by weight (relative to the total weight) a UV absorber (Sudan I) to the photocurable formulation.

Table 2 summarizes the 3 different series of resins prepared. Each series (each column) refers to a set of formulations in the ranges indicated in the Table. In the case of series 1, CEA (carboxyethyl acrylate) is used as a monofunctional monomer and HCL2 as a hydrolyzable cross-linker. The series includes formulations with different HCL2/CEA weight ratios. Specifically, 4 formulations have been prepared in which the HCL2/CEA weight ratios have been 15/85, 20/80, 25/75 and 30/70. For series 3 and 4, a percentage by weight of HCL2 of 15% has been kept fixed (relative to the total crosslinker plus monofunctional monomers), and combinations of two monofunctional monomers have been tested in the ranges indicated in the table. Thus, for series 2, 3 formulations containing HCL2 and a combination of HEA and CEA as monofunctional monomers were prepared in HCL/HEA/CEA weight ratios of 10/15/75, 15/40/45 and 15/75. /10. For series 4, 6 formulations containing HCL2 and a combination of HEA and MAA as monofunctional monomers were prepared in HCL/HEA/MAA weight ratios of 15/77.5/7.5, 15/70/15, 15 /60/35, 15/50/35, 15/42.5/42.5 and 15/0/85,. In the case of series 2, a single formulation was prepared containing HCL2 and MAA as monofunctional monomer in HCL/MAA weight ratios of 30/70.

Table 2 shows the composition of the resins obtained. All amounts are in weight % with respect to the total weight of cross-linker plus monofunctional monomers.

Example of preparation of print parts using 20 g of a photocurable resin containing HCL2, HEA and MAA in a weight ratio of 15/42.5/42.5: First 3 g of HCL2 is added to a vial, followed by 8.5 g of both monomers. After this, 2.67 mg of Sudan I is added and the vial is covered with aluminum foil. Then, 0.2 g of photoinitiator is added (in this case using 1% by weight) and the mixture is stirred for 5-10 minutes until the mixture is completely homogeneous. The resin is then ready to be tested on the printer. The resin is added to the tank and the printing parameters are chosen: layer 100 p.m, raft height 1 mm, raft displacement 4 mm, layer exposure time 20 s, exposure off time 5 s , exposure time of the lower layer 60 s, lower layers 5 pcs, lower speed of the platform 100 mm/m and lifting speed of the platform 100 mm/m. The printers used are the Zortrax Inkspire and the Creality LD-002H, using Chitubox for Creality and Z-Suite for Zortrax as design programs, respectively. After printing, a wash is carried out in isopropanol for 5' and a post-curing of 30' at room temperature in a photopolymerization chamber.

The process described above was carried out for the 14 formulations cited in Table 2. Printability was tested by manufacturing 2 cm x 2 cm x 2 mm pieces. All formulations allowed correct printing capacity.

In order to mechanically characterize some selected materials, specimens were printed for compression and tensile tests. The size of the compression specimens (5 test pieces for each test) was 29 cm in diameter and 12.5 cm in height. The size of the tensile test pieces (5 test pieces for each test) was test type V, i.e. W (Width of narrow section) = 3.18 ± 0.03 mm (0.125 ± 0.001 in.), L (Narrow Section Length) = 9.53 ± 0.08 mm (0.375 ± 0.003 in.), G (Gauged Length) = 7.62 ± 0.02 mm (0.300 ± 0.001 in.) and R (Sheet Radius) = 12.7 ± 0.08 mm (0.500 ± 0.003 in.). The measurements were carried out in a "Universal testing machine", INSTRON brand, with load cells of 1-5kN, according to need, tensile test speed: 100 mm/min and test speed compression: 10 mm/min.

The mechanical properties of the selected examples are listed below.

Mechanical property range:

Tensile strength test results of selected examples:

Weight ratio of crosslinker and monofunctional monomers in the photocurable formulation: HCL2/HEA/MAA = 15/42.5/42.5. Printed part module: 88.27 ± 6.85

Compression test results of selected examples:

Weight ratio of crosslinker and monofunctional monomers in the photocurable formulation: HCL2/HEA/MAA = 15/42.5/42.5. With a 5kN load cell, it did not exceed 2.6% deformation at maximum load.

Figure 3 shows a piece obtained according to this section. (a) Obtained after 3D printing and (b) obtained after washing and post-curing.

2.3 Use of sacrificial molds with elastic properties

In order to demonstrate the resistance and capacity of the materials obtained in section 2.1 for the production of high-resolution and sacrificial molds, three different use examples have been explored. To carry out these proofs of concept, the digital designs shown in figure 4 have been printed, being molds for the preparation of screws. For these tests, the HCL2/PEGMEA/HEA 15/25/60 formulation (weight ratios) was selected.

Thus, in the following paragraphs these sacrificial molds with elastic properties obtained by 3D printing of the photocurable resin described in section 2.1 with HCL2/PEGMEA/HEA weight ratios of 15/25/60 will be identified as printed molds.

The three examples are:

A) use the mold for the preparation of solid elastic silicone materials from liquid components; After curing at 60 °C and 15 hours, a solid elastic silicone piece is obtained with the shape given by the mold.

B) use the mold to contain molten polymer, specifically polycaprolactone; After cooling, a rigid PCL piece is obtained with the shape given by the mold.

C) use the mold to house a photocurable liquid resin, which after photocuring gives rise to a solid polymeric network with hydrogel characteristics and with the shape given by the mold.

In all three cases, the final part is recovered by sacrificing (solubilizing) the mold in basic water. In what follows, basic water refers to a treatment in water with 2% NaOH by weight for 20 hours and at room temperature.

2.3.1 Use of sacrificial molds with elastic properties to obtain 3D silicone structures

Silicones are deformable cross-linked polydimethylsiloxanes. We use Sylgard 184, a silicone-based elastomeric kit that is a two-component liquid system:

1) a polymer (called base)

2) and a curing agent that cross-links with the base.

Both components 1) and 2) are mixed in a weight ratio of 10 (base):1 (curing agent). The mixture was stirred manually and left under vacuum for 15' to inhibit oxygen. After this, the mixture was added to the printed sacrificial molds mentioned above and placed in the oven at 60°C for 15 hours. After this, the construct (mold with the Sylgard 184) is immersed in basic water, the printed sacrificial mold is solubilized and the silicone part is recovered with the shape and definition provided by the printed sacrificial mold.

We test the thermal resistance of the sacrificial mold to produce such materials. The Tga analysis showed that the mold is capable of resisting 140-150°C for a few hours, which expands its potential uses.

Figure 5 shows silicone parts obtained by thermal polymerization of Sylgard 184 inside the 3D printed resin mold. (a) Silicone screw obtained with Mold 1 and (b) Silicone screw obtained with Mold 2.

2.3.2 Use of sacrificial molds with elastic properties to accommodate molten PCL and obtain 3D structures after cooling

This example illustrates the use of printed sacrificial molds in the manufacture of parts (for example to be used as molds) made of a thermoplastic polymer capable of melting and flowing in the mold, so that the polymer takes the shape of the printed mold. . We selected poly(s-caprolactone) (PCL) as a thermoplastic polymer. PCL is a crystalline, biocompatible polymer, approved by the FDA and widely used for biomedical applications. The PCL granules were placed in the printed mold and this material was melted at a temperature close to 100°C. After cooling, the printed mold was dissolved in basic water and the PCL part was recovered with the shape and definition provided by the printed mold. Figure 6 shows (Left) a mold printed with molten PCL in the central part; (right) images of the PCL parts without the external printed molds (1 and 2), which were dissolved.

2.3.3 Use of sacrificial molds with elastic properties to house liquid photocurable resin and obtain 3D structures after photocuring

This example illustrates the use of printed molds in the manufacture of parts obtained by photocuring a photopolymerizable liquid formulation, so that the material obtained after polymerization takes the shape of the printed mold.

To fill the mold, a photocurable formulation based on vinylcaprolactam has been used, which gives rise to thermosensitive hydrogels. Specifically, the formulation is composed of vinylcaprolactam (2.355 g), N,N-divinylimidazoline (11.6 mg), ethylene glycol dimethacrylate (EGDMA) (31 μL9 and hydroxycyclophenyl ketone (9.1 mg). The photopolymerization of this construction ( mold filled with photocurable formulation) was carried out for 40 min under UV radiation (<á>= 365 nm) in a UV chamber (model CL-1000L, 230 V). After photocuring, the printed mold was dissolved in basic water. and the photocured part was recovered with the shape and definition provided by the printed mold. Figure 7 shows (Left) a printed mold with liquid photocuring formulation in the central part, (right) images of the photocured solid parts without the printed molds. external (1 and 2), which were dissolved.

EXAMPLE 3

PREPARATION OF RETURNABLE NETWORKS AFTER HYDROLYSIS

(HYDROGELS)

This example describes the use of the hydrolyzable cross-linkers of the invention to print resettable networks that, by hydrolysis of the beta-amino esters of HCL, are capable of swelling in water, behaving like hydrogels (Figure 8).

In this case, hydrolyzable cross-linkers are used to obtain hydrogels in a single step.

To obtain the resettable networks, monofunctional monomers (such as HEA or PEMEA) or a mixture of them are combined with a mixture of a permanent or stable cross-linker (such as poly(ethylene glycol) dimethacrylate (PEGDMA - PCL1) and hydrolyzable cross-linkers according to the invention (such as HCL1 or HCL2). Using a photoinitiator and a UV absorber, the mixture can obtain the desired structure by 3D printing. The resulting 3D printed structure can be immersed in a basic aqueous solution. partially hydrolyzes (due to the hydrolyzable cross-linking agents according to the invention) and, therefore, the final cross-linking density decreases. As a result, the generated printed structure is able to accommodate a greater amount of water and behave like a hydrogel.

An example of a resettable network is obtained as follows: the polymerizable components of the resin (1, 2, 3 and 4 shown in Figure 8) are:

A) different weight proportions of the hydrolyzable cross-linker HCL2 and a stable cross-linker (polyethylene glycol dimethacrylate, PEGDMA) and

B) different weight proportions of PEGMEA and HEA as monofunctional monomers.

A) and B) form a photocurable formulation

The sum of the amounts of monomers (monofunctional) and cross-links is 100% of the weight to which the weight ratios refer: HCL2 PEGMEA HEA+ PEGMDA = 100 (hereinafter referred to as "total weight").

In addition to the cross-linkers and monofunctional monomers, the TPO photoinitiator in a range of 0.35-1% by weight (relative to the total weight) and a UV absorber (Sudan I) at 0.2% by weight (relative to the total weight) were added to the photocurable formulation. This mixture (A+B+ TPO Sudan I) was used to 3D print the desired adjustable network. As the resulting 3D printed resizable network contains stable and hydrolyzable cross-links (see Figure 8), when the structure is immersed in a basic aqueous solution, the cross-links are partially hydrolyzed (due to the presence of HCL2) and therefore the final cross-link density decreases. As a result, the generated resizable network: is able to accommodate a greater amount of water and behave like a hydrogel (see Figure 8).

Figure 8 shows an example of how the hydrogel is obtained using the crosslinkers of the invention.

Table 3 summarizes the 2 different series of resins prepared. Each series (each column) refers to a set of formulations in the ranges indicated in the Table. For all formulations, the weight ratio (HCL2+PEGDMA)/(PEGMEA+HEA) is 15/85.

In case of series 1, the weight percentage of PEGMEA and HEA, compared to the total weight of the polymeric components (crosslinkers and monofunctional monomers) remains constant at values of 25 and 60, respectively. This series 1 includes formulations with different HCL2/PEGDMA weight ratios. Specifically, 6 formulations have been prepared in which the HCL2/PEGDMA weight ratios have been 0/15, 3/12, 5/10, 7.5/7.5, 10/5 and 13/2.

In the case of series 2, the weight percentage of HCL2 and PEGDMA, with respect to the total weight of the polymeric components (crosslinkers and monofunctional monomers) remains constant at values of 7.5 and 7.5. This series 2 includes formulations with different PEGMEA/HEA weight ratios. Specifically, 5 formulations have been prepared in which the PEGMEA/HEA weight ratios have been 85/0, 60/25, 40/45, 20/65 and 0/85.

Table 3. Compositions of the prepared resins. All amounts are in weight % with respect to the total weight of the cross-linker plus the monofunctional monomers.

Example for the preparation of 20 g impression parts of a photocurable resin containing HCL2, PEGDMA, PEGMEA and HEA in a weight ratio of 7.5/7.5/25/60:

First, 1.5 g of HCL2, 1.5 g of PEGDMA, 5 g of PEGMEA and 12 g of HEA are added to a vial. After this, 2.67 mg of Sudan I is added and the vial is covered with aluminum foil. Next, 0.2 g of photoinitiator is added (in this case using 1% by weight with respect to the total weight) and the mixture is stirred for 5-10 minutes until the mixture is completely homogeneous. The resin is then ready to be tested on the printer. The resin is added to the tank and the printing parameters are chosen: layer 100 |j,m, raft height 1 mm, raft displacement 4 mm, layer exposure time 20 s, exposure off time 5 s , exposure time of the lower layer 60 s, lower layers 5 pcs, lower speed of the platform 100 mm/m and lifting speed of the platform 100 mm/m. The printers used are the Zortrax Inkspire and the Creality LD-002H, using Chitubox for Creality and Z-Suite for Zortrax as design programs, respectively. After printing, a 5-minute washing step in isopropanol and a 30-minute post-curing process at room temperature in a photocuring chamber are carried out.

The process described above was carried out for the 11 formulations cited in Table 3. Printability was tested by manufacturing 2 cm x 2 cm x 2 mm pieces. All formulations can be printed normally.

The printed parts were immersed in basic water (2 wt% NaOH in water, for 20 hours at RT (15-30 °C) to hydrolyze HCL2 and obtain swollen hydrogels, and then gravimetrically characterize the swollen hydrogels in swollen and dry state. The swelling was determined from 100(WS-WD)/WD, with WS and WD being the weight in the hydrated state and in the dry state. Figure 9 shows the swelling of the hydrogels of series 1, as an example, after. the entire treatment (DLP printing and immersion in basic water). The greater the relative amount of PEGDMA (with respect to the sum of cross-linkers), the lower the swelling capacity of the final hydrogels, which is consistent with the indicated mechanism. in Figure 8, since more stable crossovers are maintained in the systems

Figure 10. Left: 3D printed parts obtained directly after DLP printing. Right: Pieces after treatment in basic water.

EXAMPLE 4

MANUFACTURE OF 3D PRINTED REPROCESSABLE CROSS-CROSSBOW MATERIALS.

In this case, the hydrolyzable crosslinkers of the invention are used to obtain vitrimers - reprocessable crosslinked materials. (Figure 11). The reprocessing capacity is based on the sensitivity of HCL beta-aminoesters (1, 2 or 3) leading to transesterification reactions in a -OH-rich environment. The cross-linking points in this case behave as so-called dynamic covalent bonds (DCBs) that impart reprocessability to the printed structure.

This example is based on a literature example (Nature Communications(2018) 9:1831) that describes a typical vitrimeric formulation based on transesterification. This literature example uses as polymerizable components a cross-linker containing non-activated esters and 2-hydroxy-3-phenoxypropyl acrylate (HPPA) as a monofunctional monomer containing -OH, in a weight ratio of 1:9. A catalyst for transesterification (zinc acetylacetone hydrate, Zn(acac)2)) should be included according to this article.

According to the present invention, the cross-linker of the bibliographic example has been replaced by any of the HCL (1, 2 or 3) of the invention. Thus, as these HCL cross-linkers contain activated esters, transesterification can take place without the need for a catalyst (although a catalyst can be used). Thus, the polymerizable components of the resin of this example of the invention are: a transesterifiable crosslinker (HCL1, HCL2 or HCL3) and HPPA in a HCL/HPPA weight ratio of 1/9. In addition to the monomers, the TPO photoinitiator was added at 2% by weight (relative to the total weight) and a UV absorber (Sudan I, just print the formulation) at 0.2% by weight (relative to the total weight) to the photocurable formulation.

Particular example of preparation of reprocessable cross-linked material (vitrimer): The polymerizations described below have been carried out with or without tin (II) 2-ethylhexanoate as catalyst (3 g, 5 mol% with respect to OH groups) to transesterification. Since the pieces obtained without catalyst behave like vitrimers, only the procedure without catalyst is described below. 45 g of HPPA was added in a 100 ml flask with 5 g of HCL2 as cross-linker. The components were mixed at about 60 °C. TPO (1.0 g) was added as an initiator at room temperature. In the case of photocuring in a curing chamber, the reaction mixture (Figure 12a) was injected into appropriate molds, prepared with polypropylene films separated with 0.5 mm thick silicone spacers. Photopolymerization was carried out for 40 minutes under UV radiation (<á>=365 nm) in a UVP ultraviolet lamp (model CL-1000L, 230V). After photopolymerization, the networks were recovered from the molds (Figure 12b). In the case of 3D printing, Sudan I (0.02% by weight with respect to the total weight) was added as a photosorbent. The resins were stored in amber laboratory bottles at 5 °C. The resins are stable for more than 4 months without gelation or precipitation, and can be used directly for 3D printing. For the printing process, the resin is added to the tank and the printing parameters are chosen: layer 50 .^m, exposure time of the layer 15 sec, exposure time of the bottom layer 30 sec, descent speed of the platform 150 mm/m and platform lifting speed 65 mm/meter. The printer used is the Creality LD-002H, using Chitubox for Creality as design programs. After printing, a 5-minute wash in isopropanol and a 30-minute post-cure at 60°C in a curing chamber using photopolymerization is carried out.

To test the vitrimeric behavior, both types of pieces, those obtained by photopolymerization in a UV chamber or those prepared in a 2D printer (2cmx2cm2mm), were cut into small pieces (Figure 12-c) and pressed with heat (180°C for HCL3 and 50 bars of pressure) for 5 min (for HCL3) again obtaining a homogeneous film (Figure 12-d). Upon heating, bond exchange can occur due to transesterification reactions between the hydroxyl and beta-aminoester groups (Figure 11). At this temperature, the cross-linking points are dynamic covalent bonds (DCBs) that confer reprocessability to the printed structure. The pristine printed material only contains the original beta-amino esters of HCL (1, in Figure 11). When heated, and thanks to the fact that this ester is labile and therefore activated towards transesterification, these bonds are broken giving rise to new beta-amino esters (3, in Figure 11). Label 2 in Figure 11 indicates the original ester. This operation is called "reprocessing," which means that the polymer chains can be rearranged by heating the cross-linked structure, allowing processability.

More interestingly, the material can be transformed into a linear thermoplastic chain by hydrolysis of the cross-linking agents HCL. Specifically, the photopolymerized parts obtained by 3D printing described in the previous section become soluble after immersion for 20 hours in a mixture of basic water/THF (tetrahydrofuran) or basic water/ethanol. Organic solvents are necessary due to the hydrophobicity of the network structure.

Claims (25)

CLAIMS 1. A hydrolyzable cross-linker of formula I: in which: - X can be the same or different in the two positions and means oxygen or nitrogen - R1 and R1' can be the same or different, and can be: - an alkylene group of 1 to 20 carbon atoms, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from: - heteroatoms, so that said heteroatom can be one or more halogen atoms, - functional groups such that said functional group can be: one or more alkoxy groups having 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl, carbamoyl groups and combinations of these substituents, and - alkyl groups, and such that in the alkylene group there may be heteroatoms that replace one or more carbon atoms, said heteroatoms being selected from O, N-substituted, S, - oligomers or polymers of the polyether type (such as polyethylene glycol) or polyester (such as those derived from polycaprolactone) - R2 and R4 can be the same or different, and can be: - H, alkyl of 1 to 20 carbon atoms, which can be linear or branched, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from heteroatoms, functional groups or alkyl groups, such that said heteroatom may be one or more halogen atoms, so that said functional group may be one or more alkoxy groups of 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more oxo groups, one or more oxy groups, one or more carboxyl groups, oxycarbonyl groups, carbamoyl groups and combinations of these substituents, and such that in the alkyl group there may be heteroatoms substituting one or more carbon atoms, said heteroatoms being selected from O, N-substituted, S, - or R2 and R4 can be linked, giving rise, together with R3, to a cyclic structure of 5 or more members, which can be a saturated or unsaturated structure, in which the carbon atoms of the cyclic structure can be substituted by heteroatoms, and in which said carbon atoms may also have substituents, - and optionally R2 and R4 can be linked, giving rise together with R3 to a cyclic structure of 5 or more members, with a saturated or unsaturated structure, so that R2 and R4, together, have the same meaning as R3, so that the cyclic structure is symmetrical, - R3 can be: - a hydrocarbon chain of 1 to 20 carbon atoms, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from heteroatoms, functional groups or alkyl groups, so that said heteroatom can be one or more halogen atoms, so that said functional group can be one or more alkoxy groups of 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl groups and combinations of these substituents, and in which there may be heteroatoms that replace one or more carbon atoms, said heteroatoms being selected from O, N, S, - an oligomer or polymer of the polyether, or polyester type (such as those derived from polycaprolactone), with the condition of: 1) when: - X is identical in the two positions, and is oxygen, - R1 and R1' are identical and are 2-hydroxy-propane-1,3-diyl, or ethane-1,2-diyl - R2, R3 and R4 form a cycle, so the cycle is not a piperazine-1 residue ,4-diyl, 2) when - X is identical in the two positions, and is oxygen, - R2 and R4 are both a methyl group, then: R3 is not -(C H 2)n -, where n=2-4 or R2 and R4 with R3 do not form a piperazine-1,4-diyl moiety, 3) when - X is identical in the two positions, and is oxygen, and - Ri and Ri' are identical and are 2-hydroxy-propane-1,3-diyl, - R2 and R4 are H then: R3 is different from -CH(CH3)-CH2-O-CH(CH3)-CH2-(O-CH2-CH2-)x-O-CH2-CH(CH3)-O-CH2-CH(CH3)- where x = 14. 2. A hydrolyzable cross-linker according to claim 1, wherein: - X is identical in both positions, and is oxygen or nitrogen - Ri and R i are identical - R2, R3 and R4 have the meaning given above in claim 1. 3. A hydrolyzable cross-linker according to claim 1, wherein: - X is identical in both positions, and is oxygen or nitrogen - R1 and R1' are identical and are an alkylene group of 1 to 10 carbon atoms, where one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, R3 and R4 have the meaning given above in claim 1. 4. A hydrolyzable cross-linker according to claim 1, wherein: - X is identical in both positions, and is oxygen or nitrogen - R1 and R1' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, R3 and R4 form a cycle of at least 5 members, where the non-N members are methylene groups. 5. A hydrolyzable cross-linker according to claim 1, wherein: - X is identical in both positions, and is oxygen - Ri and R i' are identical and are an alkylene group of 3 carbon atoms, where one or more hydrogen atoms are substituted with hydroxyl groups (-OH), more preferably, Ri and R i' are 2-hydroxy-propane -1,3-diyl - R2, R3 and R4 form a cycle of at least 5 members, where the members other than N are methylene groups. 6. A hydrolyzable cross-linker according to claim 1, wherein: - X is identical in both positions, and is oxygen - R1 and R1' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, and R4 are identical and are H or a alkyl group of 1 to 5 carbon atoms - R3 is a hydrocarbon chain, comprising oxygen atoms replacing one or more carbon atoms, and such that in the chain there is at least one group of each of the following structures: -CH(CH3)-CH2--(O-CH2-CH(CH3))x--(O-CH2-CH2V -(O-CH2-CH(CH3))zwhere x, y, z, have values, independently of each other, between 1 and 12. 7. A hydrolyzable cross-linker according to claim 1, wherein: - X is identical in both positions, and is oxygen - R1 and R1' are identical and are 2-hydroxy-propane-1,3-diyl - R2 and R4 are identical, and are H, - R3 is a hydrocarbon chain, formed by oxygen atoms replacing one or more carbon atoms, and such that in the chain there is at least one group of each of the following structures, in the order specified below: -CH(CH3)-CH2--(O-CH2-CH(CH3))x--(O-CH2-CH2V -(O-CH2-CH(CH3))zwhere x, y, z, have values, independently of each other, between 1 and 3. 8. A hydrolyzable cross-linker according to claim 1, wherein: - X is identical in both positions, and is oxygen or nitrogen - R1 and R1' are identical and are an alkylene group of 1 to 10 carbon atoms, in which one or more hydrogen atoms are substituted with hydroxyl groups (-OH) - R2, and R4 are identical and are H or a alkyl group of 1 to 5 carbon atoms - R3 is a hydrocarbon chain, comprising oxygen atoms that replace one or more carbon atoms. 9. A hydrolyzable cross-linker according to claim 1, wherein: - X is identical in both positions, and is oxygen - R1 and R1' are identical and are 2-hydroxy-propane-1,3-diyl - R2, and R4 are identical and are H - R3 is an alkylene group, comprising oxygen atoms substituting one or more carbon atoms, with the structure: -(CH2)3-O-(CH3))2-O-(CH3))2-O-( CH2)3-. 10. A resin comprising: - a hydrolyzable crosslinker of formula II. in which: - X can be the same or different in the two positions and means oxygen or nitrogen - R1 and R1' can be the same or different, and can be: - an alkylene group of 1 to 20 carbon atoms, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from: - heteroatoms, so that said heteroatom can be one or more halogen atoms, - functional groups such that said functional group can be: one or more alkoxy groups having 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl groups, carbamoyl groups and combinations of these substituents, and - alkyl groups, and such that in the alkylene group there may be heteroatoms that substitute one or more carbon atoms, said heteroatoms being selected from O, N-substituted, S, - oligomers or polymers of the polyether type (such as polyethylene glycol) or polyester (such as those derived from polycaprolactone) - R2 and R4 can be the same or different, and can be: - H, alkyl of 1 to 20 carbon atoms, which can be linear or branched, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from heteroatoms, functional groups or groups alkyl, so that said heteroatom can be one or more halogen atoms, so that said functional group can be one or more alkoxy groups of 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or several cyano groups, one or more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl groups, carbamoyl groups and combinations of these substituents, and such that in the alkyl group there may be heteroatoms substituting one or more carbon atoms, said heteroatoms being selected from O, N-substituted, S, - or R2 and R4 can be linked, giving rise, together with R3, to a cyclic structure of 5 or more members, which can be a saturated or unsaturated structure, in which the carbon atoms of the cyclic structure can be substituted by heteroatoms, and in which said carbon atoms can also have substituents, - and optionally R2 and R4 can be linked, giving rise together with R3 to a cyclic structure of 5 or more members, with a saturated or unsaturated structure, so that R2 and R4 together have the same meaning as R3, so that the structure cyclic is symmetrical, - R3 is selected between: - a hydrocarbon chain of 1 to 20 carbon atoms, which can be saturated or unsaturated, and in which the hydrogen atoms can, optionally, be substituted with substituents selected from heteroatoms, functional groups or alkyl groups, so that said heteroatom can be one or more halogen atoms, so that said functional group can be one or more alkoxy groups of 1 to 8 carbon atoms, one or more hydroxyl groups, one or more nitro groups, one or more cyano groups, one or more more oxo groups, one or more oxy groups, one or more carboxy groups, oxycarbonyl groups and combinations of these substituents, and in which there may be heteroatoms that replace one or more carbon atoms, said heteroatoms being selected from O, N, S - an oligomer or polymer of the polyether type, or polyester (such as those derived from polycaprolactone), - at least one starter - optionally, at least one monofunctional monomer, - optionally, at least one stable cross-linker - optionally, a light absorber, - optionally, one or more solvents. 11. The resin according to claim 10, wherein the weight ratio of hydrolyzable crosslinker/initiator is greater than 10 and less than 10,000. 12. The resin according to claim 10 or 11, comprising: - a hydrolyzable crosslinker of formula II, - at least one starter - at least one monofunctional monomer, - optionally, at least one stable cross-linker - optionally, a light absorber, - optionally, one or more solvents. 13. The resin according to claim 10 or 11, comprising: - a hydrolyzable crosslinker of formula II, - at least one starter - at least one monofunctional monomer, - at least one stable cross-linker, in which the weight ratio (hydrolyzable cross-linker stable cross-linker)/I is greater than 10, and the weight ratio hydrolyzable cross-linker/(stable cross-linker) is less than 1000 and greater than 0.1, - optionally, a light absorber, - optionally, one or more solvents. 14. The resin according to one of claims 10 to 13, comprising one or more monofunctional monomers selected from the following hydrophilic (meth)acrylic structures: hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate, polyethylene glycol methyl ether acrylate (PEGMEA). ), polyethylene glycol acrylate, polyethylene glycol methyl ether methacrylate, polyethylene glycol methacrylate, dimethylacrylamide (DMA), methacrylic acid (MAA), acrylic acid, carboxyethyl acrylate (CEA), preferably selected from the following hydroxylated (meth)acrylic structures: 2-hydroxyethylacrylamide, 2-hydroxypropylacrylate, 4-hydroxybutylacrylate, hydroxypropylmethacrylate, 2-hydroxyethylmethacrylate, 3-phenoxy-2-hydroxypropylmethacrylate, glycerol monomethacrylate, N-(2-hydroxypropyl)methacrylamide, 2-hydroxy-3-phenoxypropyl acrylate (HPPA ). 15. The resin according to one of claims 10 to 13, comprising at least one monofunctional monomer with a styrenic structure, preferably selected from styrene, chlorostyrene, bromostyrene, vinylaniline, vinylnaphthalene, vinylbenzoate or vinylanisole. 16. The resin according to one of claims 10 to 13, comprising at least one monofunctional monomer with a vinyl structure, preferably with a vinyl vinyl structure containing a vinyl linked to a heteroatom, and more preferably, selected from N-vinylacetamide, vinylpyrrolidone, vinylcarbazole, vinylpyridine, vinylimidazole, vinyl acetate, vinylformamide, vinylphosphonic acid, sodium vinylsulfonate or vinyltrimethylsilane. 17. A resin polymerization procedure defined in any one of claims 10 to 16, comprising at least the following steps: a) a mixture of: - one or more hydrolyzable/transesterifiable crosslinkers of formula II, - starter, - UV absorber, if present, - one or more stable cross-linkers, if present, - one or more monofunctional monomers, if present, - solvent, if present, b) optionally, bubble the mixture from step (a) with a gas, c) transfer of the product obtained in step b) to a container where the polymerization will take place, such as a vial, a flask, a reactor, a mold, a tank for 3D printing d) polymerization, and e) recovery of the polymerized material resulting from step d). 18. A procedure according to claim 17, wherein the mixture of step a) comprises: - one or more hydrolyzable/transesterifiable crosslinkers of formula II, - starter, - UV absorber, if present, - one or more stable cross-linkers, if present, - one or more monofunctional monomers, if present, - solvent, if present, and the procedure also includes: f) hydrolyze or transesterify at least part of the cross-linking bonds of the hydrolyzable cross-linkers of the mixture from step a). 19. A procedure according to claim 17, wherein the mixture of step a) comprises: - one or more hydrolyzable/transesterifiable crosslinkers of formula II, - starter, - one or more stable crosslinkers, - UV absorber, optionally, - one or more monofunctional monomers, optionally, - solvent, optionally, and the procedure also includes: f) hydrolyze or transesterify at least part of the cross-linking bonds of the hydrolyzable cross-linkers of the mixture from step a). 20. A polymerized material resulting from step e) in the procedure defined in claim 17. 21. A polymerized product resulting from the procedure defined in any one of claims 18 or 19. 22. A polymerized product according to claim 21, selected from: - a sacrificial piece, - a resettable network or - a reprocessable or vitrimeric material. 23. Use of the resins defined in any one of claims 10 to 16 for additive manufacturing, preferably for 3D stereolithographic printing. 24. Use of the polymerized material defined in claim 20 for additive manufacturing. 25. Use of the polymerized product defined in claim 21 or 22 in industry, preferably in medicine, automotive or jewelry industry.