FR3149011A1 - Copolymers containing polydimethylsiloxane (PDMS) moieties - Google Patents

Abstract

Copolymers containing polydimethylsiloxane (PDMS) parts The present invention relates to a method for synthesizing a triblock copolymer comprising the following steps: (1) reaction between (A) a polydimethylsiloxane (PDMS) comprising at least two amine end groups, i.e. primary amine (-NH2) and/or secondary amine (-NH(alkyl)) groups, and (B) a molar excess, relative to all molecules of type (A), of a molecule comprising at least two isocyanate groups (-N=C=O), in order to obtain a prepolymer terminated by isocyanate groups; (2) reaction between the prepolymer obtained in step (1) and a polyamide comprising an amine end group (-NH2), the number of moles of polyamide comprising an amine end group (-NH2) being at least equivalent to the number of moles of isocyanate groups (-N=C=O) in the prepolymer obtained in step (1). The present invention also relates to a triblock copolymer thus obtained and the use thereof in dressings.

Description

Copolymers containing polydimethylsiloxane (PDMS) moieties

The present invention relates to novel copolymers containing polydimethylsiloxane (PDMS) moieties, the use of such copolymers in adhesive products intended to be applied to the skin, wounds, appendages and/or mucous membranes, and dressings comprising an elastomeric matrix obtained from such copolymers.

Silicone elastomers are used in many fields (automotive, medical devices, childcare, optics, cosmetics, etc.). In the field of adhesives, silicone elastomers are particularly interesting in a medical context, particularly in their application to the skin, wounds, appendages or mucous membranes. They are "soft" adhesives, which are not aggressive on the skin in the sense that they are well tolerated, while having good resistance over time. They are also repositionable, atraumatic when removed and therefore well tolerated by the skin, in particular fragile skin such as peri-wound skin. These adhesives can be applied, removed and then reapplied, without leaving any residue or causing redness. Silicones can be used at the edge of a dressing or in direct contact with the wound to be treated.

However, the manufacturing processes for silicone elastomers are quite complex: whether they are obtained by hot or cold vulcanization, their manufacturing process must respect very precise temperature and humidity conditions. In addition, due to the nature of the components entering into their composition and their production process, silicone elastomers are expensive.

In the general context of adhesive copolymers containing polydimethylsiloxane (PDMS) moieties, not limited to medical-type adhesive applications such as in dressings, prior technologies using polysiloxanes linked to other polymer segments via isocyanate or amide groups include:
- US applications 2006/194937 and US 2006/036055 which describe polydimethylsiloxane (PDMS) terminated by amino (bisaminomethyl) groups, reacted with diisocyanates;
- applications US 2013/225768 and US 2007/148475 which describe a technology comprising the reaction of a PDMS diamine with diethyl oxalate, the product resulting from this reaction being able to then be reacted with diamines such as ethylene diamine.
- US patent 6,090,902 which describes poly(ethylene-butylene) with terminal groups carrying an isocyanate residue, obtained with methacryloyl isocyanate, the resulting polymer then being reacted with a PDMS carrying a methacryl group, in the presence of 2-ethylhexyl acrylate;
- application US 2021/0009880 which describes polyolefin-polydiorganosiloxane copolymers, the synthesis route used involving the preparation of polyethylene with –SiMe ₂ H groups in the terminal position, capable of reacting with Si-OH groups carried in the terminal position by PDMS;

- application WO 2014/123775 which describes polysiloxane-polyamide copolymers whose bond is produced by polymerization of diacids and diamines (such as hexamethylenediamine (HDMA) and adipic acid for Nylon 6,6) with the incorporation at the end of the reaction of undecylenic acid (UDA), introducing a C=C double bond which can react with a –SiH group of a siloxane;
- application CN109384930 which describes a polyamide block copolymer based on a linear aliphatic chain (abbreviated in English) and polysiloxane;
- application KR20170032726 which describes a polyamideimide-polydimethylsiloxane-polyamideimide (PAI-PDMS-PAI) triblock copolymer:

- application KR20160146250) which describes polymers as follows:

The present invention aims to develop specific copolymers whose manufacturing process is simple and inexpensive. The compatibility of the precursors is a relevant element for an efficient synthesis of the polymers. As for the copolymer product obtained, together with a melting temperature that allows use in practical "hot melt" conditions with an appropriate solid-liquid transition temperature, it is appropriate to have copolymers whose melting temperature is fully reversible and whose mechanical properties are stable over time, instability in these properties generally being indicative of reactions such as additional crosslinks that occur after the initial synthesis of the copolymer.

The present invention relates not only to specific copolymers but also to an elastomeric matrix obtained from such copolymers. Finally, the present invention relates to a dressing comprising such an elastomeric matrix.

<Statement of the invention>

Thus, according to a first aspect, the present invention therefore relates to a method for synthesizing a triblock copolymer comprising the following steps:
(1) reaction between (A) a polydimethylsiloxane (PDMS) comprising at least two amine terminal groups, either primary amine (-NH ₂ ) and/or secondary amine (-NH(alkyl)) groups, and (B) a molar excess, relative to all molecules of type (A), of a molecule comprising at least two isocyanate groups (-N=C=O), in order to obtain a prepolymer terminated by isocyanate groups;
(2) reaction between the prepolymer obtained in step (1) and a polyamide comprising an amine terminal group (-NH ₂ ), the number of moles of polyamide comprising an amine terminal group (-NH ₂ ) being at least equivalent to the number of moles of isocyanate groups (-N=C=O) in the prepolymer obtained in step (1).

According to a particular characteristic of the invention, step (2) is carried out at a minimum temperature Tf of at least 100°C, preferably at least 130°C.

According to a particular characteristic of the invention, in the process for synthesizing a triblock copolymer:
- in step (1), a reaction is carried out, preferably at a temperature of at least 25°C and at most 50°C, between at least one polydimethylsiloxane of formula (A)
[Chem. 1]

(HAS)
and at least one diisocyanate of formula (B):
[Chem. 2]

(B)
with a molar ratio (B)/(A) > 1, to obtain a prepolymer terminated by isocyanate groups of formula (C):
[Chem. 3]

(C)
in which
- x represents an integer greater than or equal to 10;
- n represents an integer greater than or equal to 1;
- R ₁ and R ₂ represent saturated, linear or branched hydrocarbon groups; and
- L ₁ represents a saturated, linear or branched, cyclic or acyclic hydrocarbon group, or an unsaturated, linear or branched hydrocarbon group, comprising at least one double bond and/or at least one aromatic cycle;
and in step (2), a reaction is carried out between the prepolymer (C) obtained in step (1) and a semi-crystalline polyamide with a melting temperature T _f and comprising an amine terminal group (-NH ₂ ), of formula (D):
[Chem. 4]

(D)
with a molar ratio (D) / (C) of more than 0 and less than 4, preferably (D) / (C) being approximately or equal to 2, at a reaction temperature T > Tf, to obtain the triblock copolymer of formula (E):
[Chem. 5]
(E)
in which
- y and z represent numbers between 0 and 100;
- T _f represents a temperature greater than or equal to 100 °C.

Preferably in carrying out a synthesis method according to the invention, a polydimethylsiloxane (PDMS) used in step (1) comprises at least two primary amine end groups (-NH ₂ ), and preferably comprises –(CH ₂ ) ₃ NH ₂ and/or –(CH ₂ )—(CH)CH ₃ -(CH ₂ )NH ₂ end groups, and/or R1 may be chosen from the following groups, the symbol * indicating a branch point:
(R1-1) [Chem. 6]
(R1-2) [Chem. 7]

Preferably in carrying out a synthesis method according to the invention, the polydimethylsiloxane (PDMS) used in step (1) comprises at least two secondary amine end groups, preferably –NH(ethyl) or –NH(methyl) groups and/or R2 can be chosen from the following groups, the symbol * indicating a branch point:
(R2-1 [Chem. 8])
(R2-2) [Chem. 9]
(R2-3) [Chem. 10]

Preferably in the execution of a synthesis method according to the invention, the polydimethylsiloxane (PDMS) used comprises at least two amine terminal groups, has a number-average molecular mass (Mn) of at least 500 g.mol ^-1 and at most 150,000 g.mol ^-1 , preferably at least
800 g.mol ^-1 and at most 50000 g.mol ^-1 , and/or the number of units x is at least 10 and at most 900.

Preferably in the execution of a synthesis process according to the invention, the molecule comprising at least two isocyanate groups (-N=C=O) is chosen from alkyl diisocyanates, aromatic diisocyanates or alicyclic diisocyanates.

Preferably in the execution of a synthesis method according to the invention, L1 is a hydrocarbon structure such that at least 4 and at most 12 carbon atoms separate the two branch points by the shortest route, and preferably L1 is chosen from the following groups, the symbol * indicating a carbon atom forming part of the structure L1 and also being a branch point:
(L1-1) [Chem. 11]
(L1-2) [Chem. 12]
(L1-3) [Chem. 13]
(L1-4) [Chem. 14]
(L1-5) [Chem. 15]

Preferably in the execution of a synthesis method according to the invention, the molecule comprising at least two isocyanate groups
(-N=C=O) is an alkyl diisocyanate with the isocyanate groups in the terminal position, and preferably hexamethylene diisocyanate.

Preferably in the execution of a synthesis method according to the invention, in step (1), the quantity used of the molecule comprising at least two isocyanate groups (-N=C=O) corresponds to a value (n+1) in number of moles, n being the number of moles of polydimethylsiloxane (PDMS) comprising at least two amine terminal groups (-NH ₂ ).

Preferably in the execution of a synthesis process according to the invention, the polyamide comprising an amine terminal group (-NH ₂ ) used in step (2) is chosen from: a copolymer polyamide containing units of 6 and 11 carbon atoms, preferably a copolymer between the acid
6-aminohexanoic acid and 11-aminoundecanoic acid and/or between caprolactam and 11-aminoundecanoic acid.

According to a second aspect, the present invention relates to a triblock copolymer obtained according to the process of the invention. A copolymer according to the present invention may also be a triblock copolymer having the following structure:
[Chem. 16]
in which:
- each group (LDI ¹ -LDI ² ) corresponds to an alkyl, aromatic or alicyclic group, and preferably is a hydrocarbon structure such that at least 4 and at most 12 carbon atoms separate the two branch points by the shortest route, and preferably chosen from groups (L1-1) to (L1-5);
- each group R ¹ corresponds to H, Me or Et;
- polydimethylsiloxane (PDMS) is connected to –NR ¹ - groups by reaction of a terminal –(CH ₂ ) ₃ NH ₂ and/or –(CH ₂ )—(CH)CH ₃ -(CH ₂ )NH ₂ bond of a starting PDMS;
- PA denotes a polyamide.

According to a third aspect, the present invention relates to the use of a triblock copolymer according to the present invention in adhesive products intended to be applied to the skin, wounds, appendages and/or mucous membranes.

According to a third aspect, the present invention relates to a dressing comprising an elastomeric matrix obtained from the triblock copolymer according to the present invention. Preferably, in a dressing according to the present invention, the elastomeric matrix has through holes. In preferred dressings according to the present invention, the elastomeric matrix further contains one or more active ingredients for treating a wound, the active ingredients being selected from the group consisting of: antibacterials, antiseptics, painkillers, anti-inflammatories, healing-promoting active ingredients, and anesthetics. In preferred dressings according to the present invention, the elastomeric matrix obtained from the triblock copolymer is present in the form of an adhesive border allowing the dressing to be fixed to the skin surrounding a wound to be treated. In preferred dressings according to the present invention, the elastomeric matrix obtained from the triblock copolymer is present in the form of a film having a thickness of at least 20 μm and at most 50 μm.

<Brief description of the drawings>

There represents a triblock synthesis scheme
SC-b-PDMS _urea -b-SC according to the present invention.
There represents the structure (A) and the DSC analysis (B) of the polyamide used.
There represents the structures and DSC analyses of the polyethylenes used: PE _NH2 (A), PE _NH-hexyl (B) and PE _I (C).
There represents thermograms of urea prepolymers: cooling (A) and heating (B) cycles.
There represents a study of the rheological properties of the urea prepolymer 1 as a function of temperature.
There represents the rheological properties of urea prepolymers during a heating cycle.
There represents the thermograms of PE _NH2 , urea prepolymer and PE-b-PDMS _urea -b-PE triblock system: cooling (A) and heating (B) cycles.
There represents the rheological properties of the system
PE-b-PDMS _urea -b-PE before (A) and after addition of PE (B) during a heating cycle.

There represents the thermograms of the PA_NH2, urea prepolymer and PA-b-PDMS triblock system_urea-b-PA: cooling (A) and heating (B) cycles.
There represents the rheological properties of the system
PA-b-PDMS_urea-b-PA before (A) and after addition of PA (B) during a heating cycle.
There represents a reaction scheme of the polyaddition of PDMS_{end NH2}on the HDI.
There represents a reaction scheme of the polyaddition of PA6-11 on PDMS prepolymer_urea.
There represents a DSC thermogram of the PDMS prepolymer_urea
There represents a DSC thermogram of the triblock
PA-b-PDMS_urea-b-PA.
There represents the G' and G'' modules of PA-b-PDMS_urea-b-PA as a function of temperature during a heating cycle.
There represents the stress curve as a function of the elongation of the PA-b-PDMS system_urea-b-PA.
There represents a reaction scheme of the two-step synthesis of PA-b-PDMS_{urea eth}.-b-PA.
There represents a DSC thermogram of a triblock
PA-b-PDMS_{urea eth}.-b-PA.
There represents the rheological properties of the system
PA-b-PDMS_{urea eth}.-b-PA during the second heating cycle.
There represents a reaction scheme of the two-step synthesis of PA-b-PDMS_{urea/urea eth}.-b-PA.
There represents the storage moduli of urea/ethyl urea prepolymers as a function of the urea fraction at room temperature.
There represents the evolution of G' as a function of the urea fraction at 25 °C (A); sol/liq transition temperature as a function of the urea fraction (B).
There represents a stress curve as a function of strain (A), maximum elongation (B) and elastic moduli as a function of the % of urea group (C) of the PA-b-PDMS systems_{urea/urea eth}.-b-PA.

<Description of embodiments>

The triblock copolymers according to the present invention comprise a polydimethylsiloxane (PDMS), linked by isocyanate-derived regions to a polyamide. In the context of the present invention, for the preparation of such copolymers, the compatibility of the PDMS and polyamide precursors is a relevant element for an efficient synthesis of the polymers. The polyamide part can strongly influence the final mechanical properties of the material (high elastic modulus, very low strain deformation). Along with the issue of the final mechanical properties, it should be noted that an aim is also to prepare copolymers containing a polysiloxane block (such as PDMS) and semi-crystalline blocks, so that the semi-crystalline nodules are physical crosslinking nodes, which can be reversibly formed and destroyed by applying suitable temperature ramps, thus allowing a reversible transition from an “elastic solid” state to a “viscous liquid” state. Preferably, the semi-crystalline blocks will have a melting temperature that is within the target temperature range of at least 100°C and at most 140°C. In this context, it has been observed by the inventors that certain products obtained from PDMS precursors having hydroxyl groups along the chain and terminal epoxide groups, transformed into a copolymer by reaction with a secondary diamine such as N-N-dimethyl-1,6-hexanediamine, are not satisfactory in an industrial context because the liquid-solid transition of the materials is not reversible. It seems that a parasitic reaction leads to the chemical (i.e. irreversible) crosslinking of the materials. Thus, after a storage period of a few weeks, the materials can no longer be melted in the form of a viscous liquid. They can no longer be easily solubilized in a solvent either. The inventors postulate that the pendant hydroxyl groups are involved in a parasitic reaction leading to the crosslinking of the PDMS phase, in particular with residual epoxy groups, or even with the terminal ester functions of the polyamide (PA).

According to the present invention, a PDMS terminated by amine functions is first reacted with a diisocyanate spacer, a preferred example of diisocyanate being hexamethylene diisocyanate. The ratio between reactants is chosen so that the PDMS _urea prepolymers are terminated by isocyanate functions. The second synthesis step then consists in adding the monofunctional semi-crystalline polymer, terminated by an NH ₂ function, which will be able to react with the terminal isocyanate functions of PDMS prepolymers, to lead to the formation of SC-b-PDMS _urea -b-SC triblock copolymers,
where SC = semi-crystalline. The approach is described in the .

The potential benefits of this approach are considered to be multiple:
1. Urea functions are known to develop strong hydrogen bonds (N–H O). Their presence along the PDMS chain should allow the development of intra-chain physical interactions within the PDMS phase, which should in turn make it more cohesive. This should improve the mechanical properties of the material, in particular its strain rates at break.
2. The urea functions are polar and should therefore allow to observe a good reactive compatibilization between the PDMS _urea prepolymers and the polyamide, PA.

In a particularly preferred embodiment of the present invention, the polyamide (PA) part used in the preparation of the copolymer of the invention is a PA _6/11 copolymer containing mixed 6-carbon and 11-carbon units. A polymer of this type is commercially available, supplied by ARKEMA under the trade name APOLYA, with proportions of PA ₆ and PA ₁₁ of approximately 0.3 and 0.7 respectively (by mass) with a molar mass M _n = 2500 g.mol ^-1 , terminated at one end by a primary amine function and at the other by a methyl ester function (see , part A).

According to one aspect, the present invention relates to a triblock copolymer having the following structure:
(PA)-(NH-CO-NH)-(LDI1)-[(PDMS urea) _n (PDMS urea alkyl) _m ]-(LDI1)-(NH-CO-NH)-(PA)
in which:
PA represents a polyamide block;
NH-CO-NH represents a urea bond;
LDI1 represents a linker group that can be derived from a portion of a diisocyanate chain;
the part -[(PDMS urea) _n (PDMS urea alkyl) _m ]- represents an entity comprising n PDMS groups integrated into the copolymer by urea groups and m PDMS groups integrated into the copolymer by urea alkyl groups, n and m being integers and the PDMS urea and PDMS urea alkyl groups being present in separate blocks or mixing in the chain constituting the part
-[(PDMS urea) _n (PDMS urea alkyl) _m ]- ;
elements (PDMS urea) having repeating units represented by the formula
-[(LDI2)-(NH-CO-NH)-(LSX1)-(PDMS)-(LSX1)-(NH-CO-NH)-(LDI2)]-
in which:
LDI2 represents a linker that can be derived from a portion of a diisocyanate chain;
NH-CO-NH represents a urea bond;
LSX1 represents a linker between the urea group and the silicon atom at the end of the poly(dimethyl)siloxane (PDMS) chain;
the elements [(PDMS urea alkyl) having repeating units represented by the formula
-[(LDI2)-(NH-CO-NR)-(LSX2)-(PDMS)-(LSX2)-(NH-CO-NR)-(LDI2)]-
in which:
LDI2 represents a linker that can be derived from a portion of a diisocyanate chain;
NH-CO-NR represents an alkyl urea bond, R being an alkyl group of at least 2 carbon atoms, preferably ethyl;
LSX2 represents a linker between the urea group and the silicon atom at the end of the poly(dimethyl)siloxane (PDMS) chain.

According to the aspect of the invention cited above, preferably the combined linker elements LDI1-LDI2, LSX1 and LSX2 each correspond to an alkyl, aromatic or alicyclic group, and preferably to a hydrocarbon structure such that at least 4 and at most 12 carbon atoms separate the two branching points by the shortest route, and preferably the linkers LDI1-LDI2, LSX1 and LSX2 correspond to a group L1 chosen from the following groups, the symbol * indicating a carbon atom forming part of the structure L1 and also a branching point:
(L1-1) [Chem. 17]
(L1-2) [Chem. 18]
(L1-3) [Chem. 19]
(L1-4) [Chem. 20]
(L1-5) [Chem. 21]
According to this aspect, the polydimethylsiloxane(s) (PDMS) present, at one or more units in the overall structure of the copolymer, have for each PDMS unit (used during the synthesis) a number-average molecular mass (Mn) of at least 500 g.mol ^-1 and at most 150,000 g.mol ^-1 , preferably of at least 800 g.mol ^-1 and at most 50,000 g.mol ^-1 , and/or the number of units x is at least 10 and at most 900.

<Elastomeric matrix>

According to one aspect, the present invention relates to an elastomeric matrix obtained from the triblock copolymers according to the invention as described above. In particular, the elastomeric matrix can be obtained by hot physical transformation according to methods well known to those skilled in the art.

The elastomeric matrices thus obtained can be implemented in various devices, such as for example dressings. In order to produce dressings, the matrix according to the invention will preferably be formed in a thin layer.

According to a preferred embodiment of the invention, the matrix has through holes. The through holes can be made by perforation or punching of the matrix previously formed in a thin layer.

Alternatively, the dies according to the invention can be manufactured by hot casting a polymer composition as described above onto a plate etched with the chosen pattern to form through holes, followed by a cooling step and finally a demolding step.

The production of adhesive dressings generally meets a complex specification in order to reconcile contradictory characteristics. The main criteria to check for such a dressing are essentially to have good breathability while avoiding the risk of leaks, and to be impermeable to liquids and bacteria while being breathable (i.e. permeable to water vapor). Preferably, the dressing will maintain its cohesion when it is removed once loaded with exudates, and will preferably be easy to manufacture. The dressing must also be easy to apply and remain in place for as long as possible without altering the peri-wound skin. Preferably, it will not alter the healing of the wound when it is removed. Finally, the dressing must fit the patient's morphology.

The elastomeric matrix is preferably thin, so as to better fit the shapes of the body and follow movements without risking detachment. The adhesive support is advantageously conformable. Generally speaking, the elastomeric matrices in accordance with the invention have a thickness of between 15 µm and 2 mm.

The elastomeric matrix will preferably be impermeable to external fluids and pathogenic microorganisms while ensuring permeability to water vapor, so as to avoid both contact of the wound with external liquids and bacteria and maceration of the wound.

The elastomeric matrix is preferably adhesive so as to hold the dressing in place.

The matrix may contain active ingredients having a favorable role in the treatment of the wound. Among the substances likely to be used in the context of the present invention as active ingredients, we can, by way of examples, cite:
- antibacterials such as silver derivatives such as silver or other metal salts (e.g. silver sulfate, chloride or nitrate and silver sulfadiazine), silver or other metal complexes (e.g. silver zeolites such as alphasan, or ceramics), metrodinazole, neomycin, Polymyxin B, penicillins (Amoxycillin), clavulanic acid, tetracyclines, Minocycline, chlortetracycline, aminoglycosides, Amikacin, Gentamicin or probiotics;
- antiseptics such as chlorhexidine, triclosan, biguanide, hexamidine, thymol, Lugol, Povidone iodine, Benzalkonium and Benzethonium Chloride;
- painkillers such as Paracetamol, Codeine, Dextropropoxyphene, Tramadol, Morphine and its derivatives, Corticosteroids and derivatives;
- anti-inflammatory drugs such as glucocorticoids, non-steroidal anti-inflammatory drugs, aspirin, ibuprofen, ketoprofen, flurbiprofen, diclofenac, aceclofenac, ketorolac, meloxicam, piroxicam, tenoxicam, naproxen, indomethacin, naproxcinod, nimesulide, celecoxib, etoricoxib, parecoxib, rofecoxib, valdecoxib, phenylbutazone, niflumic acid, mefenamic acid;
- active ingredients that promote healing such as Retinol, Vitamin A,
Vitamin E, N-acetyl-hydroxyproline, Centella Asiatica extracts, papain, essential oils of thyme, niaouli, rosemary and sage, hyaluronic acid, polysulfated oligosaccharides and their salts (in particular synthetic sulfated oligosaccharides having 1 to 4 sugar units such as the potassium salt of octasulfated sucrose or the silver salt of octasulfated sucrose), sucralfate, Allantoin, urea, metformin, enzymes (e.g. proteolytics such as streptokinase, trypsin or collagenase), peptides or protease inhibitors;
- anesthetics such as benzocaine, lidocaine, dibucaine, pramoxine hydrochloride, bupivacaine, mepivacaine, prilocaine, or etidocaine.

In the context of the present invention, it is possible to envisage matrices which are easy to handle, repositionable, allow painless removal when applied to the skin, mucous membranes or appendages, and have satisfactory durability over time.

<Bandages>

The present invention also relates to a dressing comprising the elastomeric matrix obtained from triblock copolymers according to the invention.

According to a preferred embodiment of the invention, the present application aims to cover an absorbent dressing comprising an elastomeric matrix in the form of an adhesive border that can take the form of a "sidewalk", and allowing the dressing to be fixed to the skin surrounding the wound. These dressings, in particular when used for the treatment of particularly painful chronic wounds, are advantageously conformable and thin in order to limit the tensions that the dressing can generate on the surface of the skin. According to a preferred embodiment of the invention, the adhesive absorbent dressing comprises the assembly of an absorbent layer and the elastomeric matrix forming the sidewalk of the absorbent dressing, which is respectful of the fragile and sensitive peri-wound skin.

According to a preferred embodiment of the invention, the present application aims to cover an absorbent dressing comprising an absorbent layer coated with an elastomeric matrix in the form of a perforated coating. The through holes allow the passage of exudates towards the absorbent layer. The elastomeric matrix is present over the entire surface of the dressing in contact with the skin. Advantageously, this type of dressing does not adhere to moist wounds but adheres to the peri-wound skin, thus allowing removal without trauma or pain. Among the known dressings of this type, the products marketed by the company Mölnlycke under the brand name Mepilex®, can be cited.

According to a preferred embodiment of the invention, the present application aims to cover a self-supporting interface dressing comprising an elastomeric matrix in the form of a thin layer having through holes to allow exudates to pass through. The thickness of such a dressing is preferably between 0.4 and 2 mm. In order to protect the matrix from the external environment, the interface dressing may be covered, preferably on each of its faces, by a temporary protective film which will be removed before use by the user. Among the known dressings of this type, the products marketed by URGO Laboratories under the UrgoTul® brand may be cited.

According to a preferred embodiment of the invention, the present invention aims to cover a dressing composed of an elastomeric matrix in the form of a thin transparent adhesive film. The thickness of such a dressing is preferably between 20 and 50 µm. The transparency allows visual inspection of the area to be treated. These films are semi-permeable, they are permeable to gas exchanges, and are impermeable to liquids and bacteria. They provide mechanical protection against friction, friction and shearing phenomena. Among the known dressings of this type, the products marketed by the company Smith & Nephew under the brand name Opsite®, or by the company 3M under the brand name Tegaderm® or by Laboratoires URGO under the brand name Optiskin®, can be cited.

According to a preferred embodiment of the invention, the present invention aims to cover a dressing composed of an elastomeric matrix in the form of a flexible gel plate having through holes. These dressings, in particular when used in the treatment of hypertrophic or keloid scars, are advantageously self-adhesive and conformable in order to adapt to each scar. Among the known dressings of this type, the products marketed by the company Smith & Nephew under the brand name Cica-care®, can be cited.

In the present invention, the term “dressing” means any medical device of the dressing type comprising at least one elastomeric matrix. In particular, the invention applies to dressings used for the treatment of wounds, the treatment of scars and cosmetic patches.

<Examples>

<Reagents>

All raw materials used are commercially available. The characteristics of all products are set out in Table 1 below.

<a) Semi-crystalline polymers>

Two semi-crystalline polymers were used, a polyamide and a polyethylene. These polymers differ in many aspects. For example, polyethylene has an inert structure while polyamide has many amide functions on its chain. Being semi-crystalline and each having melting temperatures between 100 and 130 °C, they are potentially promising candidates for the preparation of thermoplastic elastomers.

Regarding the issue of possible incompatibility between polymer components, polyethylene does not show strong incompatibility with PDMS, polyethylene having a lower solubility parameter than polyamide with a value δ _PE = 16 MPa ^1/2 .

<Polyamide>

The PA _6/11 copolymer is supplied by ARKEMA under the trade name APOLYA. The proportions of PA ₆ and PA ₁₁ were determined by analysis
¹ H NMR and are respectively 21% by weight and 79% by weight. This low molar mass copolymer (M _n = 2500 g.mol ^-1 ) is terminated at one end by a primary amine function and at the other by a methyl ester function ( , part A). It exhibits melting temperatures, T _f ~130°C, and crystallization temperatures, T _f ~105°C, which were measured by DSC ( , part B).

<Polyethylene>

Polyethylene is obtained from Activation. More precisely, these are three types of monofunctional polyethylenes with low molar masses that differ in their terminal functions. The first is an iodinated terminated polyethylene (PE _I ) with a molar mass defined by SEC (M _w = 1039 g.mol ^-1 ). This polyethylene is the precursor for obtaining the other two primary amine terminated polyethylenes (PE _NH2 ) and secondary amine (PE _NH-hexyl ) with molar masses, defined from the PE _I substrate, of 929 and 1013 g.mol ^{- 1} respectively.

In DSC, these polyethylenes exhibit bimodal melting peaks as shown in . For low molar masses, the presence of bimodal peaks seems to be linked to two crystal sizes due to a fraction of non-functional polyethylene (C. Soulié-Ziakovic, Macromolecules, 2015, 48, pp. 3257-3268).

<b) PDMS>

The PDMS used were supplied by Gelest, Genesee Polymers and ABCR. The exact molar masses were systematically calculated from ¹ H NMR data using trichlorobenzene as an internal standard. These products were used without further treatment.

<PDMS pendant primary amines>

These PDMS will be denoted PDMS _{graft NH2} . Their chemical formula is shown below. A polymer with a molar mass of M _n ~50000 g.mol ^-1 with 6 to 7% of aminopropylmethylsiloxane unit (trade name AMS-163 at Gelest) was used.
[Chem. 22]

<PDMS terminated primary amines>

These PDMS will be denoted PDMS _{end NH2} . Their chemical formula (PDMS terminated at each end by an aminopropyl group) is shown below. A polymer with a molar mass of M _n ~5000 g.mol ^-1 was used (trade name DMS-A21 at Gelest and AB109371 at ABCR).
[Chem. 23]

<PDMS terminated secondary amines>

These PDMS will be noted PDMS _{end NH} . Their chemical formula (PDMS terminated at each end by an N-ethylaminoisobutyl group) is represented
hereinafter. A polymer having a molar mass of M _n ~2500 g.mol ^-1 at
3500 g.mol ^-1 was used (trade name DMS-A214 at Gelest).
[Chem. 24]

<Analysis and characterization techniques>

<a) Nuclear magnetic resonance (NMR)>

• Blocs de PDMS:
  RMN¹H sur spectromètre Bruker Avance 400 dans du chloroforme deutéré à 25°C.
• Produits contenant du polyamide:
  RMN¹H sur spectromètre Bruker Avance 400 dans un mélange de chloroforme deutéré et d’acide trifluoroacétique anhydre à 25°C (6:1).
• Produits contenant du polyéthylène :
  RMN¹H sur spectromètre Bruker Ascend 400 Prodigy dans du chloroforme deutéré à 70°C.

Due to different solubilization conditions, NMR analysis parameters are separated according to the products concerned.

• PDMS blocks:
  ¹ H NMR on Bruker Avance 400 spectrometer in deuterated chloroform at 25°C.
• Products containing polyamide:
  ¹ H NMR on Bruker Avance 400 spectrometer in a mixture of deuterated chloroform and anhydrous trifluoroacetic acid at 25°C (6:1).
• Products containing polyethylene:
  ¹ H NMR on Bruker Ascend 400 Prodigy spectrometer in deuterated chloroform at 70°C.

The spectra are processed and analyzed on the Topspin software provided by Bruker.

<b) Differential scanning calorimetry (DSC)>

Thermograms of the samples are obtained using the DSC Q100 device marketed by TA ^® instruments, equipped with a liquid nitrogen refrigeration system. Samples with masses between 5 and 10 mg are introduced into sealed aluminum capsules and then analyzed using the following procedure:
- Equilibrium at -150°C
- ^1st heating up to 150°C with a ramp of 10°C/min
- Isothermal 1 min at 150°C
- Temperature drop to -150°C at 10°C/min
- Isothermal 1 min at -150°C
- ^2nd heating up to 200°C with a ramp of 10°C/min
The glass transition, crystallization and melting temperatures are determined after erasing the thermal history of the materials during the ^first heating.

<c) Rheology>

Rheological measurements were performed on the MCR rheometer from Anton Paar. The measurements were made with a 8 mm diameter plane-plane geometry for solid or particularly viscous samples. For the less viscous samples, a 25 mm diameter cone-plane geometry was preferred. Two types of measurements were performed:
- A frequency sweep: measurement of the elastic modulus (G') and the loss modulus (G'') as a function of the shear rate at constant angular frequency at 25°C
- A temperature scan: measurement of G' and G'' as a function of temperature (ramp of 3.6 °C/min) at a constant shear rate and an angular frequency of 10 rad/s. During these measurements, the sample was placed on the low geometry at 150 °C. The first analysis is carried out during cooling from 150 to 25 °C. The second analysis corresponds to heating the sample from 25 to 150 °C.

<d) Tensile test>

Tensile tests were performed on an MTS QTest 25 at room temperature. Measurements were made on dogbone-shaped samples approximately 40 mm long, 4 mm wide and 1 mm thick. Deformations were applied at a rate of 5 mm/min.

<e) X-ray diffraction and scattering (XRD)>

The DRX material analyses were carried out in a partner laboratory, the CRPP, on a Xeuss 2.0 device marketed by Xenocs. This device delivers a beam with an energy of 8 keV. The data are collected on a DECTRIS PILATUS-300k detector placed at different distances from the sample, thus providing access to the angle range 0.03° to 50°.
(0.025 nm ^-1 to 34.5 nm ^-1 ).

Table 1 below summarizes the commercially available semi-crystalline polymers and PDMS polymers experimentally explored by the present inventors in the preparation of polymers according to the present invention and comparative polymers.

Names Denominations Names
Commercials
(Supplier) Molar masses (g.mol ^-1 )
(Supplier data) Polyamide 6-11 PA _6-11 APOLYA
(Arkema) 2500 Mono-terminated polyethylene iodine PE _I PE-I
(Activation) 1039 Mono-terminated amine polyethylene PE _NH2 PE-NH ₂
(Activation) 929 N-hexyl mono-terminated polyethylene PE _NH-hexyl PE-NH-hexyl
(Activation) 1013 Epoxypropoxypropyl terminated polydimethylsiloxane PDMS _{end epoxy 1000} DMS-E12
(Frost) 1000-1400 PDMS _{end epoxy 5000} DMS-E21
(Frost)
GP504
(Genesee Polymers) 4500-5500 Mono-terminated epoxypropoxypropyl polydimethylsiloxane PDMS _{end mono epoxy} MCR-E11
(Frost) 5000 Copolymer (6-7% aminopropylmethylsiloxane)-dimethylsiloxane PDMS _{graft NH2} AMS-163
(Frost) 50000 Aminopropyl terminated polydimethylsiloxane PDMS _{end NH2} DMS-A21
(Frost)
AB109371
(Frost) 5000 N-ethylaminoisobutyl terminated polydimethylsiloxane PDMS _{end NH} DMS-A214
(Frost) 2500-3000

Table 1 presents a summary of data regarding the commercial products used.

<Reactors>

The various reactions were conducted in glass reactors consisting of a glass tube or flask and a glass or Teflon mechanical stirrer under nitrogen flow. A Radleys 6 Plus carousel was also used in order to launch up to 6 reactions in parallel.

<Isocyanate-amine chemistry>

<SC-b-PDMS _urea -b-SC triblock systems>

The synthesis of these triblock copolymers is carried out in two stages ( ) :
1. Prepolymer synthesis: reaction between PDMS _{end NH2} and hexamethylene diisocyanate with excess diisocyanate to obtain isocyanate-terminated prepolymers.
2. Addition of the semi-crystalline polymer terminated by a primary amine.

<i) PDMS _urea prepolymer >

The primary objective in the synthesis of this type of prepolymer was to observe the reactivity between the isocyanate and the primary amine located at the end of a PDMS chain. Several materials with a molecular weight gradient were prepared to observe the influence of chain length on thermal and rheological properties.

<Summary>

To do this, three materials were synthesized in order to obtain amine-terminated prepolymers. These materials differ in the ratio
r = [isocyanate] / [NH ₂ ], thus the quantities of material introduced are stated in Table 2 below. For these syntheses, a PDMS _{end NH2} supplied by ABCR (AB109371) and having a molar mass of 5800 g.mol ^-1 was used. The reactions were carried out in the carousel at room temperature under mechanical stirring.

Sample m _HDI g m _{PDMSend NH2} g r ^has DPn ^b M _n ^c theoretical
k g.mol ^-1 NH Conversion ₂ ^d
% (NMR) 1 0.066 2.42 0.95 39 120 90 2 0.048 1.83 0.90 19 60 86 3 0.050 2.05 0.85 12.3 40 83

Table 2 presents data on the synthesis of primary amine terminated _urea PDMS prepolymers.
[Math. 1]

As soon as the two precursors come into contact by mechanical stirring, a significant increase in viscosity can be observed. Thus, due to an almost instantaneous reaction, kinetic monitoring could not be carried out. The products obtained are transparent elastic solids that can be shaped.

¹ H NMR analysis allowed the measurement of the conversion rate of the amine functions. According to the results obtained by analyzing the evolution of the intensity of the peak corresponding to the alpha protons of the NH ₂ group, we can conclude that there is a total reaction between the isocyanates and the primary amines (NH ₂ conversion ~100 xr). The remaining amines in the systems correspond to the chain ends of the synthesized prepolymers.

As expected, the reactive compatibility between the two precursors allows a complete conversion with reaction conditions of time and temperature perfectly compatible with a reactive extrusion process. Therefore, it is possible to imagine the synthesis of urea prepolymers with primary amine or isocyanate terminations and presenting various concentrations in urea function using PDMS _{end NH2} of various molar masses.

Urea prepolymer synthesis tests were carried out with a lower molecular weight PDMS _{end NH2} precursor (AB109370 with
Mn = 3200 g.mol ^-1 ). This change of precursor leads to an increase in the concentration of functional groups. The high reactivity then leads to the production of solid materials in a liquid PDMS phase.

<Characterization>

<DSC>

The thermal phase transitions of the materials presented in Table 2 were analyzed by DSC. These materials were obtained from the same precursors introduced in varying proportions in order to obtain three distinct molar masses.

Thermal cycles are described in the experimental part. , part B, represents the ^2nd heating cycles of the three samples. In all cases, a first inflection point is observed, around -120 °C, characteristic of the glass transition of PDMS (T _g PDMS). Only sample 3 presents an exothermic peak and an endothermic peak, between -80 and -40 °C, corresponding to the crystallization and melting of PDMS. While the prepolymers obtained by the epoxy-amine route did not present any other thermal transition than that mentioned above, the DSC analyses of the urea prepolymers systematically present an endothermic peak around 20 °C. This peak can then be attributed to a melting in a phase constituted by the stacking of the urea groups. The inflection points relating to the T _g as well as the crystallization of the urea phase are observable during cooling ( , part A).

The values of T _g (PDMS), T _f (urea) and ΔH _f (urea) are reported in Table 3 for all samples. For clarity, the fusion enthalpies of the urea groups have been reduced to one mole of urea and expressed in kJ.mol ^-1 .

Sample r = [ isocyanate ] / [amine] T _g
PDMS
°C T _f
Urea
°C Δ H _f
Urea
J.g ^-1 Δ H _f
Urea
kJ.mol ^-1 1 0.95 -123.55 20.15 0.85 5.36 2 0.90 -123.29 19.64 0.82 5.44 3 0.85 -123.64 19.25 0.76 5.35 PDMS _{end NH2} / -123.36 / / /

Table 3 presents characteristics of the thermal phase transitions of urea prepolymers and the PDMS precursor _{end NH2} measured by DSC.

The glass transition temperatures of the PDMS obtained are identical and of a value of -123.5 °C for all the synthesized prepolymers. This value is equal to that of the PDMS precursor _{end NH2} . Thus, the introduction of urea groups by reaction of the isocyanate HDI on the PDMS _{end NH2} does not influence the glass transition temperature of the PDMS phase. Similarly, the T _g of the PDMS is not impacted by the chain length of the “decorated” PDMS with identical values for the three synthesized materials.

Finally, the fusion enthalpies, ΔH _f , of the urea phases were measured. Samples 1 (r = 0.95), 2 (r = 0.90) and 3 (r = 0.85) have melting temperatures of 20.15; 19.64 and 19.25 °C respectively. A slight decrease in T _f is observed with decreasing concentration in urea function. Consistently, the fusion enthalpy values change from 0.85 to 0.76 Jg ^-1 between samples 1 and 3. When reduced to enthalpy values in kJ.mol ^-1 , all samples have identical values of 5.4 kJ.mol ^-1 .

<Rheological properties>

As a preliminary step, the linearity domain of urea prepolymers was measured by performing a shear rate scan at constant temperature and angular frequency. Thus, all the mechanical properties presented here were obtained in plane-plane mode (8 mm diameter geometry) with a shear rate, γ = 5% and an angular frequency, ω = 10 rad.s ^-1 . G' and G'' were analyzed during a cooling cycle from 150 to 25 °C and heating from 25 to 150 °C (1.3 °C/min).

There represents the storage (G') and loss (G'') moduli of sample 1. The sample was placed on the geometry at 150 °C, at this temperature the material is a viscous liquid. The mechanical properties are first measured during cooling, we can then observe a transition from a liquid state (G'<G'') to a solid state (G'>G'') at a temperature of 69 °C (G' = G''). During heating, this transition temperature is measured at 89 °C. This hysteresis between the heating cycle and the cooling cycle is consistent with the difference between the crystallization temperature and the melting temperature of the urea domains measured in DSC. A slight increase in the G' modulus is observed around 80 °C, this can reflect an incomplete conversion during the reaction or a sliding of the sample in the geometry.

The drastic drop in modulus G’ observed during heating to a temperature of about 110 °C cannot be fully explained. It only reflects a significant drop in viscosity in this temperature range. At these modulus values, of the order of Pa, the analysis comes up against the limits of the apparatus. This phenomenon is also present during cooling with a drastic increase in G’ at about 80 °C.

At 25 °C, sample 1 behaves like an elastic solid with modulus values G’ = 230 kPa and G’’ = 62 kPa. These values are relatively low and are consistent with the macroscopic appearance (“soft” materials).

The comparison of the mechanical properties of the three urea prepolymers of variable molar mass is presented in the . Only heating cycles are shown. The hysteresis phenomenon described for sample 1, between heating and cooling, was observed for all materials studied.

The three synthesized urea prepolymers exhibit similar behavior: soft elastic solid at room temperature and viscous liquid at a temperature above the transition temperature (T _sol/liq ). However, these phase change temperatures are a function of the chain length. Sample 1 ( _{theoretical M n} = 120 kg.mol ^-1 ) exhibits a transition at 89 °C, sample 2 at 56 °C ( _{theoretical M n} = 60 kg.mol ^-1 ) and sample 3 at 47 °C
(M _{n theoretical} = 40 kg.mol ^-1 ). Similarly, the values of G' and G'' vary according to the molar mass. All the data obtained are summarized in Table 4.

Sample M _{n theoretical}
kg.mol ^-1 T _{ground / liquid}
cooling
°C T _{ground / liquid}
heated
°C G’
T = 35 °C
kPa G’’
T = 35 °C
kPa 1 120 69 89 160 38 2 60 42 56 69 35 3 40 37 47 21 13

Table 4 presents a summary of the rheological properties of urea prepolymers.

Increasing the molar mass of the synthesized urea prepolymers, from 40 to 120 kg.mol ^-1 , results in two effects on the rheological properties. The first is an increase in the storage modulus (21 to 160 kPa at 35 °C) and loss modulus (13 to 38 kPa at 35 °C). The second is an increase in the solid/liquid transition temperature (47 to 89 °C during heating). Increasing the chain length results in an increase in entanglement and in the concentration of urea groups as seen in thermal analysis (DSC). Thus, the length of the prepolymer can strongly influence the intra- and inter-chain interactions and therefore the mechanical properties.

<Conclusion>

These first attempts at the synthesis of urea prepolymers are of great interest due to their synthesis conditions (short time and room temperature) and their mechanical properties. The materials obtained are flexible and reprocessable. However, the sol/liq transition temperatures are relatively close to room temperature. Thus, the addition of a crystalline polymer to these urea “decorated” PDMS systems appears to be an appropriate solution for obtaining thermally stable, reprocessable flexible materials.

<ii) PE-b-PDMS _urea -b-PE triblocks (PE Comparative Examples)>

The production of PE-b-PDMS _urea -b-PE (PE = polyethylene) triblock systems is made possible by the presence of functional groups at each end of the PDMS _urea prepolymer.

<Summary>

In order to facilitate the comparison between the PE-b-PDMS _urea -b-PE and PA-b-PDMS _urea -b-PA systems, the prepolymer used is identical and has the characteristics set out in Table 5 below. The molar mass of the PDMS _{end NH2} used is 5827 g.mol ^-1 .

Prepolymer urea ( PDMS _urea ) Termination Isocyanate r = [amine] / [ isocyanate ] 0.95 M _{n theoretical} [kg.mol ^-1 ] 120

Table 5 presents characteristics of the PDMS _urea prepolymer used for the synthesis of SC-b-PDMS _urea -b-SC triblocks.

The addition of a semi-crystalline polymer to the prepolymer is described in the ^2nd step of the synthesis scheme of the . The prepolymer being terminated at each end by an isocyanate function, it can therefore react directly with a polyethylene mono-functionalized by a primary amine. The quantity of polyethylene to be reacted with the prepolymer is calculated by considering a 100% conversion of the primary amines during the synthesis of the isocyanate terminated prepolymer. The polyethylene is then added in a ratio [1:1] with the isocyanate functions present at each end of the PDMS _urea prepolymer according to the following equation (1):
[Math. 2]

Experimentally, the prepolymer is preheated in a flask to 150 °C to be in a molten state. Polyethylene, which has a melting temperature of about 100 °C, is then added to the reaction medium. The quantities of material introduced for the synthesis of the PE-b-PDMS _urea -b-PE system are presented in Table 6:

Sample PDMS _urea PE _NH2 mass
g M _{n theoretical}
kg.mol ^-1 mass
g M _n % by weight PE-b-PDMS _urea -b-PE 2,288 120 0.032 929 1.4

Table 6 presents experimental data from the system synthesis
PE-b-PDMS _urea -b-PE

As with the synthesis of the urea prepolymer, the kinetics of this reaction could not be studied. Thus, the reaction time was determined from visual observations. First, the polyethylene melts in the PDMS phase. A two-phase system is then initially observed with a transparent low-viscosity phase on the edges of the flask (PDMS _urea ) and a more viscous and opaque phase around the mechanical stirring blade. Within a few minutes, the system homogenizes with a single opaque and more viscous phase. The material obtained after one hour at 150 °C (overestimation of the reaction time) is a slightly translucent white "soft" elastic solid. This can be shaped and reshaped by placing it in an oven at 150 °C in a silicone mold.

Confirmation of the formation of a covalent bond between the prepolymer and polyethylene could not be performed due to the superposition of peaks during NMR analysis. Similarly, the difference in molar masses between the prepolymer and the triblocks was not observed in size exclusion chromatography due to a small mass difference of the order of one percent. Nevertheless, visual observations during the synthesis as well as dispersion tests of non-functionalized polyethylene in the urea prepolymer seem to indicate the obtaining of the PE-b-PDMS _urea -b-PE triblock system.

For this reaction, it is necessary to note the low mass proportion of polyethylene. With the available precursors, the increase in this mass fraction can only be done by decreasing the molar mass of the prepolymer (increase in the number of chain ends for a given mass).

<Characterization>

<DSC>

The phase transitions of the PE-b-PDMS _urea -b-PE system were analyzed by DSC. For clarity, the obtained thermogram is compared with those of the urea prepolymer and PE _NH2 on the .

The T _g values of PDMS can be identified during the heating cycle on the , part B. These glass transition temperatures are thus not influenced by the addition of polyethylene with values of -123.4 °C for the urea prepolymer and -123.3 °C for the triblocks. On the contrary, the melting temperatures of the urea and polyethylene domains are modified. Indeed, when PE is added, T _f (urea) decreases and goes from 20 to 14 °C and T _f (PE) increases from 97 to 114 °C. The fusion enthalpy of polyethylene, ΔH _{f PE} = 1.03 J/g ^-1 , allows access to the crystallinity rate of the polyethylene phase, χ _PE = 36 %. This value is much lower than that of PE _NH2 alone, which is 80 %. All of these results seem to indicate the presence of a phase where the urea groups and the polyethylene coexist. X-ray diffraction analysis is one technique that can help confirm this conclusion.

<Rheological properties>

To facilitate comparison between the different systems, the measurement conditions of the G' and G'' moduli of the triblock systems with urea prepolymers are identical to the conditions set for the urea prepolymers. That is, a shear rate, γ = 5% and an angular frequency, ω = 10 rad.s ^-1 with a cooling and heating ramp of 1.3 °C.min ^-1 .

There presents the storage (G') and loss (G'') moduli during a heating cycle of the PE-b-PDMS _urea -b-PE triblock system before (urea prepolymer) and after addition of polyethylene.

With the addition of polyethylene at each end of the prepolymer, the sol/liq transition temperature increases from 53 to 58 °C. Similarly, the G’ modulus increases from 73 to 90 kPa. Thus, the mechanical and thermal properties of the material are only slightly improved by the presence of the semi-crystalline polyethylene polymer. This result is explained by the low mass proportion of PE in the system (1.4%) and by the melting temperature of PE close to 100 °C.

<Conclusion>

The synthesis of PE-b-PDMS _urea -b-PE triblocks shows interest due to the problem of having synthesis conditions suitable for industrial processes. The materials obtained are flexible and reprocessable. However, the low thermal stability of the system is a barrier to its use.

<iii) Triblocks PA-b-PDMS _urea -b-PA>

The polyamide 6/11 used here has a molar mass of 2500 g.mol ^-1 while polyethylene has a molar mass of less than 1000 g.mol ^-1 . Thus, for the use of the same prepolymer, the mass fraction of semi-crystalline polymer is multiplied by approximately 2.5 in the case of the polyamide supplied by Arkema. In addition, the melting temperature of this polyamide is much higher than that of polyethylene with a T _f = 130 °C.

<Summary>

For the synthesis of the PA-b-PDMS _urea -b-PA triblock system, the urea prepolymer used is identical to that used during the synthesis of
PE-b-PDMS _urea -b-PE. Its characteristics are given in Table 7. The addition of polyamide to PDMS _urea is carried out in the same way as for polyethylene and corresponds to the second step presented in the . The prepolymer is heated to 150 °C with mechanical stirring, the polyamide is then added through the neck of the flask and the reaction is continued until a homogeneous mass is obtained. The material obtained is an opaque elastic solid with a non-adherent surface, it can be shaped into a bar or film in an oven at 150 °C.

As a reminder, the quantity of polyamide to be reacted with the prepolymer is calculated by considering a 100% conversion of primary amines during the synthesis of the finished isocyanate prepolymer. The quantities of material used in this synthesis are given in Table 7. The mass proportion of semi-crystalline polymer is here 4.1%.

Sample PDMS _urea PA _NH2 mass
g M _{n theoretical}
kg.mol ^-1 mass
g M _n % by weight PA-b-PDMS _urea -b-PA 2,312 120 0.098 2500 4.1

Table 7 presents experimental data from the system synthesis
PA-b-PDMS _urea -b-PA

As previously for systems containing urea groups, the reaction kinetics could not be studied due to the superposition of the urea and isocyanate peaks with those of the polyamide in NMR analysis. The reaction was monitored using visual observation such as the transition from a two-phase system with a dense and opaque phase around the stirring blade and a transparent phase to a homogeneous system. The creation of a covalent bond between the prepolymer and the polyamide could be observed during a DOSY experiment. This experiment showed a difference in diffusion index between the prepolymer and the PA-b-PDMS _urea -b-PA triblocks.

<Characterization>

<DSC>

The phase transitions of the PA-b-PDMS _urea -b-PA system were analyzed by DSC. For clarity, the obtained thermogram is compared with those of the urea prepolymer and PA _6-11 on the .

As shown by the thermograms of the , part B, obtained during the second heating cycle, the glass transition temperature is unchanged upon addition of the polyamide, with values of -123.4 °C for the prepolymer and -123.9 °C for the PA-b-PDMS _urea -b-PA triblocks. Unlike the prepolymer and the system containing polyethylene, the system with polyamide no longer exhibits an endothermic peak around 15-20 °C (urea domains). This can be explained by a greater interaction between the amide groups of the polyamide and the ureas contained in the PDMS chain.

Finally, thermal analysis by DSC allows to observe the presence of an endothermic peak corresponding to the melting of the crystalline phase of the polyamide. This temperature is 130 °C for the polyamide alone and 131 °C for the triblock system. The fusion enthalpy of the polyamide, ΔH _{f PA} = 1.23 J/g ^-1 , allows access to the crystallinity rate of the polyethylene phase, χ _PA = 10.5%. This value is lower than that of PA _NH2 alone, which is 19%. Again, these results seem to indicate the presence of a phase where the urea groups and the polyamide coexist.

<Rheological properties>

The conservation (G') and loss (G'') modules of the system
PA-b-PDMS _urea -b-PA, over a temperature range of 25 to 150 °C, are presented on the , part B and compared to those of the urea prepolymer ( , part A).

The rheological analysis first allows the observation of a significant increase in the sol/liq transition temperature between the prepolymer and the triblock system with respective values of 53 and 82 °C. The G' modulus also increases significantly with the addition of polyamide, going from 70 kPa for the urea prepolymer to a value of 330 kPa. This increase was expected with the addition of a greater mass proportion than with the addition of polyethylene (4.1% and 1.4%). These semi-crystalline polymers creating "hard" nodules within the final material naturally increase the elastic moduli. Finally, the PA-b-PDMS _urea -b- PA triblock material exhibits good thermal resistance with a slight decrease in mechanical properties up to a temperature close to 80 °C.

<Conclusion>

Compared to the use of polyethylene with respect to the prepolymer, the impact of polyamide is very promising. Indeed, its use combined with a PDMS “decorated” with urea functions allows the obtaining of reprocessable elastic solid materials with properties better corresponding to those sought in the context of the present invention. Indeed, these materials are both flexible, elastic and meltable at a relatively high temperature.

<iv) Scale-up of the Triblocs PA-b-PDMS _urea -b-PA system>

So far, the synthesis of the materials has been carried out from a quantity of precursors of the order of 2 to 5 grams. The aim here is to verify the potential for scaling up the synthesis of the PA-b-PDMS _urea -b-PA system. To do this, the synthesis was carried out from 50 g of PDMS _{end NH2} .

<Summary>

As seen previously, the synthesis of this type of triblocks is carried out in two steps. First, a prepolymer containing urea groups is synthesized. This is terminated at each end by an isocyanate function in order to be able to react in the second step with the mono-functionalized polyamide with a primary amine.

< ^1st step: synthesis of PDMS _urea prepolymer>

The prepolymer synthesis is carried out from hexamethylene diisocyanate (HDI) and a PDMS terminated at each end by a primary amine function. This PDMS _{end NH2} is not identical to that used in the synthesis of the systems presented in sub-parts i, ii and iii. This is a new batch ordered from ABCR (AB109371) which has a molar mass of
47200 g.mol ^-1 (analyzed by NMR). The difference in molar mass with the previous batch leads to a change in the concentration of urea groups, here, it is an increase with the decrease in molar mass
(5800 to 4700 g.mol ^-1 ). This difference explains the gap between the properties of the PA-b-PDMS _urea -b-PA system presented in subsection III and those presented below.

For the synthesis of PDMS _urea prepolymer ( ), the ratio [NH ₂ ]/[NCO] is 0.95. Thus, the theoretical molar mass of the prepolymer is 93,000 g.mol ^-1 .

Experimentally, 50 g of PDMS _{end NH2} were placed in a 100 mL three-necked flask under nitrogen flow at room temperature. The addition of the diisocyanate is done directly into the PDMS using a syringe under vigorous mechanical stirring. During some scale-up tests, non-homogeneous products with viscosity gradients were observed. Considering that this is likely due to the significant reactivity between primary amines and isocyanates, a small volume of THF was added to the diisocyanate, in order to reduce this reactivity, this volume representing no more than 5% by mass of precursors. Thus, a gradual addition of the THF/HDI solution (~50/50 by volume) allows a "controlled" reaction. The solidification is of the order of a minute and mechanical stirring is then no longer efficient. The medium is then placed at a temperature of 150°C to melt, lower the viscosity of the product and ensure maximum conversion.

The conversion of primary amines to urea is finally monitored by ¹ H NMR. This analysis allows the elimination of the THF introduced earlier to be observed.

< ^2nd step: Addition of polyamide>

Since the reaction mixture was already placed at a temperature higher than the T _f of the polyamide used (T _f = 130 °C), the addition of the PA could be done directly with stirring. The medium became opaque and whitened in a few minutes. The product could then be shaped to obtain films of approximately 0.5 and 1 mm thickness. This shaping was carried out in a silicone mold by allowing the product to flow at a temperature of 150 °C.

<Conclusion>

When switching from a synthesis of 2 to 50 g of the copolymer
PA-b-PDMS _urea -b-PA, the high reactivity of the system causes a sudden solidification that was controlled with the use of a small amount of solvent (less than 5% by weight). However, this solvent disappears very quickly (confirmation by NMR). The reaction times, of the order of a minute to ten minutes, are short. A protocol for monitoring the ^2nd step of the reaction will have to be developed to obtain a more precise reaction time. This experiment confirms that scaling up is easy and could be considered in particular in reactive extrusion.

<Characterization>

The mechanical properties of the material were studied by rheology and tensile testing, the thermal properties by DSC.

<DSC>

The measurements presented were carried out between -75 and 150°C. The thermograms presented correspond to the second heating of the material.

DSC analysis of isocyanate terminated PDMS prepolymer is presented in . We can observe the characteristic melting temperature of the urea groups of the prepolymer, around 25 °C.

After the ^2nd synthesis step, the addition of polyamide, the melting temperature of PA can be observed at 130 °C ( ).

<Rheological properties>

For rheology analyses, the material is placed at room temperature and directly melted at 150 °C to adapt to the 8 mm plane-plane geometry. After analysis of the moduli during cooling, the storage and loss moduli are measured during heating from 25 to 150 °C with a ramp of 1.3 °C.min ^-1 (γ = 5% and ω = 10 rad.s ^-1 ) and presented on the .

The sol/liq phase transition temperature is measured at about 116 °C. At 25 °C, the storage modulus has a value of 412 kPa. These two results are as expected higher than those obtained during syntheses with a PDMS _{end NH2} precursor of higher molar mass. Indeed, the increase in the concentration of urea group leads to an increase in inter and intramolecular hydrogen interactions and therefore an increase in the moduli and thermal stability.

The absence of an increase in modulus at high temperature suggests a complete reaction during the balloon synthesis. This result is also in agreement with the macroscopic appearance of the material, which does not have a “sticky” appearance.

<Pull test>

The measurements of the modulus of elasticity (E') and the elongation at break were carried out by tensile testing. To do this, a constant speed deformation was applied to 6 samples cut with a die in the shape of a "dogbone". The results obtained are reproducible and only the measurement with the highest elongation at break is shown on the .

The tensile analysis of the PA-b-PDMS _urea -b-PA system shows a typical behavior of an elastic solid at low deformation. It is therefore possible to determine a value of the modulus of elasticity, E' = 108 kPa, from the linear domain. The material exhibits an elongation at break of 44%.

<v) PA-b-PDMS _{urea eth.} -b-PA triblock systems>

PA-b-PDMS _urea -b-PA systems show strong potential, but nevertheless it is still possible to try to improve the mechanical properties of the designed systems by playing on the nature of the bonds created between the PDMS and the spacer. The replacement of the PDMS _{end NH2} by a PDMS _{end NH} thus makes it possible to obtain ethylated urea groups and to reduce inter and intramolecular interactions by bulkiness of the group.

<Summary>

In the following, polyamide 6-11 is used as a semi-crystalline polymer. The reaction scheme of the two-step synthesis of
PA-b-PDMS _{urea eth.} -b-PA is shown in the .

The PDMS _{end NH} used here is supplied by Gelest (DMS-A214) and has a molar mass of 1900 g.mol ^-1 .

The experimental conditions for the synthesis of this type of triblocks are identical to those presented during the synthesis of the systems
PA-b-PDMS _urea -b-PA. The total quantities of material used are stated in Table 8.

Sample r = (n _NH /n _NCO ) m _HDI
g m _{PDMSend NH} g m _PA6-11
g % by weight PA _6-11 PA-b-PDMS_{urea eth .}-b-PA 0.95 0.3371 3,5924 0.5737 12.7

Table 8 presents experimental data from the system synthesis
PA-b-PDMS _{urea eth.} -b-PA

The ^first synthesis step consists of synthesizing an ethyl urea prepolymer terminated at each end by an isocyanate function. ¹ H NMR analysis allows the total conversion of primary amines to be observed and the presence of isocyanates at the end of the chains to be controlled. When the product obtained has solidified and is homogeneous, the reaction is considered complete and the product is then heated to 150 °C to be able to introduce the polyamide.

The polyamide is added directly to the reaction medium with stirring. The medium quickly becomes opaque and whitens. The white material obtained exhibits mechanical behavior at the boundary between liquid and solid and particularly strong adhesion to glass or metal. It should be noted that there is a significant polyamide mass fraction of 12.7% by weight. This difference is due to the low molar mass of the PDMS _{end NH} precursor.

<Characterization>

<DSC>

DSC thermal analysis of PA-b-PDMS _{urea eth.} -b-PA material is shown in . This figure shows the cooling cycle followed by the second heating cycle.

In this thermogram, the glass transition temperature of PDMS can be observed at a temperature of -120 °C. This temperature is close to the reference value of the PDMS used in this study (-123.5 °C). An analysis of the PDMS _{end NH} precursor will allow us to conclude on the difference in T _g values.

The endothermic melting peak and the exothermic crystallization peak of polyamide are present at temperatures of 129 (T_{f PA}) and 108°C (T_{c PA}). These values are consistent with the expected and already observed values. From the fusion enthalpy value, ΔH_{f PA}= 3.71 J.g^-1, it is possible to access the crystallinity rate of the polyamide phase, χ_PA= 12.2 %. This rate is higher than that obtained on PA-b-PDMS systems_urea-b-PA (χ_PA= 10.5%) and therefore closer to the crystallinity of PA alone (χ_PA= 19.0%) . This result indicates a more marked phase separation with the use of ethyl urea group.

Unlike systems containing urea groups, no melting peak is observed around 15-20 °C. However, the presence of a weak inflection point between 0 and 50 °C may provide information on a state transition of the ethylated urea phase.

<Rheological properties>

The storage (G') and loss (G'') moduli, during the second heating cycle, of the PA-b-PDMS _{urea eth.} -b-PA system, over a temperature range from 25 to 150 °C, are shown in the .

At a temperature of 25 °C, the storage and loss moduli have respective values of 84 and 77 kPa. These two values are particularly close and explain the behavior observed at the end of the synthesis. Although G’ is greater than G’’, the material does not exhibit the behavior of a classic solid. At low stress frequency, the material appears close to a viscous liquid (partial flow in the pillbox), whereas at high stress frequency, the material behaves like a solid.

The sol/liq transition temperature here is 107°C but does not in any way reflect a change of state with a very small delta between G’ and G’ over the entire temperature range studied.

<Conclusion>

The introduction of ethyl urea-type bonds has allowed to obtain materials with strong adhesion properties. In addition, these bonds can reduce the interactions between the “decorated” PDMS chains compared to urea bonds.

<vi) PA-b-PDMS _{urea/urea eth.} -b-PA triblock systems>

According to the results obtained on the PA-b-PDMS _urea -b-PA and
PA-b-PDMS _{urea eth.} -b-PA and due to similar reaction conditions, it is quite possible to imagine synthesizing materials with intermediate properties with a mixture of urea and ethyl urea groups. In these materials, cohesion can be ensured by the urea bonds and adhesion properties by the ethyl urea bonds.

<Summary>

For this part on PA-b-PDMS _{urea/urea eth.} -b-PA triblock copolymers, four materials were synthesized with variable urea/urea ethyl ratios. The precursors used for these syntheses are a PDMS _{end NH2} with a molar mass of 4728 g.mol ^-1 , a PDMS _{end NH} with a molar mass of 1887 g.mol ^-1 and hexamethylene diisocyanate (HDI). The reaction scheme of this type of reaction allowing the production of PA-b-PDMS _{urea/urea eth.} -b-PA systems is presented in . The experimental parameters for these syntheses are given in Table 9. Sample 1 (100 wt. % urea) corresponds to the sample presented in the scale-up part of the PA-b-PDMS _urea -b-PA system. For all syntheses, the ratio
r = (n _amines / n _isocyanates ) = 0.95.

Sample m _HDI
g m _{PDMSend NH} g m _{PDMSend NH2} g % in weight ^has _{PDMSend NH} % in weight ^b _{PDMSend NH2} M _{n theoretical}
kg.mol ^-1 % by weight PA _6-11 1 1,885 0 50,351 0 100 93 5.8 2 0.155 0.747 2,259 25 75 80 7.7 3 0.180 1,203 1,801 40 60 72 8.5 4 0.219 1,698 1,670 50 50 66 9.3

Table 9 presents data relating to the system synthesis.
PA-b-PDMS _{urea/urea eth.} -b-PA

^has% by weight _{PDMS NH} = m _{PDMS NH}
,^b% by weight _{PDMS NH2} = m _{PDMS NH2}
m _{PDMS NH2} + m _{PDMS NH}
m _{PDMS NH2} + m _{PDMS NH}

The two synthesis steps proceed in a similar manner to those presented so far in the section on isocyanate-amine chemistry.

Once formed into a film by flow in an oven at 150 °C, the materials exhibit strong macroscopic differences ( ). While samples 1 and 2 are white in color, sample 3 is slightly translucent. Sample 4 is relatively close to transparency. These observations provide information on the dimensions of the polyamide nodules within the material.

The second difference concerns the adhesion properties of the materials. Adhesion is greatly increased with increasing ethyl urea group fraction.

<Characterization>

<DSC>

Sample % urea M _{n theoretical}
kg.mol ^-1 T _g
PDMS
°C T _f
PA _6-11
°C ΔH _f
PA _6-11
J.g ^-1 % by weight PA _6-11
% 1 100 93 -123.4 127.9 1.91 5.8 14 2 75 80 -122.98 128.9 2.01 7.7 11 3 60 72 -122.65 129.1 2.69 8.5 13 4 50 66 -122.3 127.6 3.10 9.3 14

Table 10 presents characteristics of thermal phase transitions of PA-b-PDMS _{urea/urea eth.} -b-PA systems measured by DSC.

The PDMS glass transition temperatures measured for the 4 materials are very close with values ranging from -123.4 °C for the sample with 100% urea group and -122.3 °C for 50% urea. Generally, a slight increase is observed with increasing ethylated urea fraction. Analysis of the PDMS precursor_{end NH}will allow us to conclude on the difference in values of T_g.

The melting temperatures of polyamide are very close and contained between 127.6 and 129.1 °C. These values depending on the analysis of the thermograms will be considered identical. Finally, the melting enthalpy values of the crystalline phase of the polyamide allow the calculation of the crystallinity rate. These rates are between 11 and 14% but it is impossible to conclude on the differences without analyzing the dimensions and the separation of the phases by a technique such as DRX.

<Rheological properties>

The storage (G’) and loss (G’’) moduli of the 4 materials as well as their 4 associated prepolymers were obtained by rheological analyses.

First, the behavior of the prepolymers should be noted. Surprisingly, the prepolymers corresponding to materials 1 and 4 appear as solids (G'>G'') at room temperature, while prepolymers 2 and 3 are liquids (G'<G''). The G' values for all prepolymers are shown in and summarized in Table 11.

After addition of polyamide, these four elastic solid materials show a decrease in the storage moduli with the increase in the fraction of ethyl urea group ( , part A). Indeed, G' goes from 410 kPa for 100% urea to a value of 74 kPa for 50% urea. This is explained by the decrease in inter and intramolecular hydrogen interactions.

For the same reason, a decrease in the sol/liq transition temperature is observed, from 117 to 83 °C, with the decrease in the urea fraction ( ).

Sample %
urea Prepolymer PDMS _{urea /urea eth .} PA -b- PDMS _{urea /urea eth .} - b- PA G’ 25°C
kPa G’’ 25°C
kPa G’ 25°C
kPa G’’ 25°C
kPa T _{ground / liquid
°C} 1 100 73 40 410 94 117 2 75 0.2 2 321 75 115 3 60 2 6.5 283 92 135 4 50 23 24 74 47 83

Table 11 summarizes the rheological properties of PDMS _{urea/urea eth.} prepolymers and PA-b-PDMS _{urea/urea eth.} -b-PA systems.

<Pull test>

The measurements of the modulus of elasticity (E') and the elongation at break of the 4 materials were obtained by tensile test. For each material, 6 dogbone-shaped specimens were analyzed. The stress-strain curves were obtained during a deformation at constant speed (5 mm/min). The results obtained are reproducible and presented on the .

The tensile analysis of PA-b-PDMS _{urea/urea eth.} -b-PA systems shows a typical behavior of elastic solid at low deformation. It is therefore possible to determine the elastic modulus values from the linear domains. It can be observed, on the , part C, a linear relationship between the modulus of elasticity and the rate of urea groups. By going from 100% urea to 50%, the modulus E' changes from a value of 108 to 7 kPa. The introduction of 50% ethylated urea makes it possible to reduce the modulus of elasticity by a factor greater than 10. Similarly, the , part B, shows the relationship between λ _max and the urea content. Thus, the maximum elongation at break increases from 44 to 95% between 100 and 50% urea (factor 2). These two results are consistent with the modification of hydrogen interactions induced by the presence of hindered urea groups. The summary of the results is given in Table 12.

Sample % urea E'
kPa λ max
% 1 100 108 44 2 75 80 53 3 60 30 62 4 50 7 95

Table 12 provides a summary of the mechanical properties of the systems.
PA-b-PDMS _{urea/urea eth.} -b-PA

<Conclusion>

The synthesis of PA-b-PDMS _{urea/urea eth.} -b-PA systems did not show any difference with the synthesis of PA-b-PDMS _urea -b-PA systems. Reaction times remain of the order of one minute to ten minutes at temperature and pressure conditions compatible with industrial processes.

The partial replacement of the PDMS _{end NH2} precursor by a PDMS _{end NH} precursor allows the production of flexible and reprocessable materials with a wide range of properties. Indeed, the introduction of this new precursor leads to the creation of hindered urea groups within the final material. Thus, the reduction of intra and intermolecular interactions allows a reduction of the storage moduli E' and G' in parallel with an increase in the elongation at break.

Finally, these materials exhibit interesting adhesion properties, the presence of ethyl urea group leading to an increase in these properties.

Claims (19)

Process for the synthesis of a triblock copolymer comprising the following steps:
(1) reaction between (A) a polydimethylsiloxane (PDMS) comprising at least two amine terminal groups, i.e. primary amine groups
(-NH ₂ ) and/or secondary amine (-NH(alkyl)), and (B) a molar excess, relative to all molecules of type (A), of a molecule comprising at least two isocyanate groups (-N=C=O), in order to obtain a prepolymer terminated by isocyanate groups;
(2) reaction between the prepolymer obtained in step (1) and a polyamide comprising an amine terminal group (-NH ₂ ), the number of moles of polyamide comprising an amine terminal group (-NH ₂ ) being at least equivalent to the number of moles of isocyanate groups (-N=C=O) in the prepolymer obtained in step (1). Process for the synthesis of a triblock copolymer according to claim 1, step (2) being carried out at a minimum temperature Tf of at least 100°C, preferably at least 130°C. Process for the synthesis of a triblock copolymer according to claim 1 or 2 in which:
- in step (1), a reaction is carried out, preferably at a temperature of at least 25°C and at most 50°C, between at least one polydimethylsiloxane of formula (A)
[Chem. 1]

(HAS)
and at least one diisocyanate of formula (B):
[Chem. 2]

(B)
with a molar ratio (B)/(A) > 1, to obtain a prepolymer terminated by isocyanate groups of formula (C):
[Chem. 3]
(C)
in which
- x represents an integer greater than or equal to 10;
- n represents an integer greater than or equal to 1;
- R ₁ and R ₂ represent saturated, linear or branched hydrocarbon groups; and
- L ₁ represents a saturated, linear or branched, cyclic or acyclic hydrocarbon group, or an unsaturated, linear or branched hydrocarbon group, comprising at least one double bond and/or at least one aromatic cycle;
and in step (2), a reaction is carried out between the prepolymer (C) obtained in step (1) and a semi-crystalline polyamide with a melting temperature T _f and comprising an amine terminal group (-NH ₂ ), of formula (D):
[Chem. 4]

(D)
with a molar ratio (D) / (C) of more than 0 and less than 4, preferably (D) / (C) being approximately or equal to 2, at a reaction temperature T > Tf, to obtain the triblock copolymer of formula (E):
[Chem. 5]
(E)
in which
- y and z represent numbers between 0 and 100;
- T _f represents a temperature greater than or equal to 100 °C. A synthesis process according to any one of claims 1 to 3 wherein a polydimethylsiloxane (PDMS) used in step (1) comprises at least two primary amine end groups (-NH ₂ ), and preferably comprises –(CH ₂ ) ₃ NH ₂ and/or –(CH ₂ )—(CH)CH ₃ -(CH ₂ )NH ₂ end groups, and/or R1 may be selected from the following groups, the symbol * indicating a branch point:
(R1-1) [Chem. 6]
(R1-2) [Chem. 7] A synthesis process according to any one of claims 1 to 3 wherein a polydimethylsiloxane (PDMS) used in step (1) comprises at least two secondary amine end groups, preferably –NH(ethyl) or –NH(methyl) groups and/or R2 may be selected from the following groups, the symbol * indicating a branch point:
(R2-1 [Chem. 8])
(R2-2) [Chem. 9]
(R2-3) [Chem. 10] Synthesis process according to any one of claims 1 to 3, wherein the polydimethylsiloxane (PDMS) used, comprising at least two amine end groups, has a number-average molecular weight (Mn) of at least 500 g.mol ^-1 and at most 150,000 g.mol ^-1 , preferably at least 800 g.mol ^-1 and at most 50,000 g.mol ^-1 , and/or the number of units x is at least 10 and at most 900. Synthesis process according to any one of claims 1 to 6, in which the molecule comprising at least two isocyanate groups (-N=C=O) is chosen from alkyl diisocyanates, aromatic diisocyanates or alicyclic diisocyanates. Preparation process according to any one of claims 3 to 7, according to which L1 is a hydrocarbon structure such that at least 4 and at most 12 carbon atoms separate the two branch points by the shortest route, and preferably L1 is chosen from the following groups, the symbol * indicating a carbon atom forming part of the structure L1 and also being a branch point:
(L1-1) [Chem. 11]
(L1-2) [Chem. 12]
(L1-3) [Chem. 13]
(L1-4) [Chem. 14]
(L1-5) [Chem. 15] Synthesis process according to claim 7, in which the molecule comprises at least two isocyanate groups
(-N=C=O) is an alkyl diisocyanate with the isocyanate groups in the terminal position, and preferably hexamethylene diisocyanate. Synthesis process according to any one of claims 1 to 9, wherein, in step (1), the quantity used of the molecule comprising at least two isocyanate groups (-N=C=O) corresponds to a value (n+1) in number of moles, n being the number of moles of polydimethylsiloxane (PDMS) comprising at least two amine terminal groups (-NH ₂ ). Synthesis process according to claim 1 or 2, in which the polyamide comprising an amine terminal group (-NH ₂ ) used in step (2) is chosen from: a copolymer polyamide containing units of 6 and 11 carbon atoms, preferably a copolymer between 6-aminohexanoic acid and 11-aminoundecanoic acid and/or between caprolactam and 11-aminoundecanoic acid. Triblock copolymer obtained according to the process of any one of claims 1 to 11. Triblock copolymer having the following structure:
[Chem. 16]
in which:
- each group (LDI ¹ -LDI ² ) corresponds to an alkyl, aromatic or alicyclic group, and preferably to a group as defined in claim 8;
- each group R ¹ corresponds to H, Me or Et;
- polydimethylsiloxane (PDMS) is connected to –NR ¹ - groups by reaction of a terminal –(CH ₂ ) ₃ NH ₂ and/or –(CH ₂ )—(CH)CH ₃ -(CH ₂ )NH ₂ bond of a starting PDMS;
- PA denotes a polyamide. Use of a triblock copolymer according to one of claims 12 or 13 in adhesive products intended to be applied to the skin, wounds, appendages and/or mucous membranes. Dressing comprising an elastomeric matrix obtained from the triblock copolymer according to one of claims 12 or 13. A dressing according to claim 15, wherein the elastomeric matrix has through holes. A dressing according to claim 15 or 16, wherein the elastomeric matrix further contains one or more active ingredients for treating a wound, the active ingredients being selected from the group consisting of: antibacterials, antiseptics, painkillers, anti-inflammatories, active ingredients promoting healing, and anesthetics. A dressing according to any one of claims 15 to 17, wherein the elastomeric matrix obtained from the triblock copolymer is present in the form of an adhesive border allowing the dressing to be fixed to the skin surrounding a wound to be treated. A dressing according to any one of claims 15 to 18, wherein the elastomeric matrix obtained from the triblock copolymer is present in the form of a film having a thickness of at least 20 μm and at most 50 μm.