A plurality of microcapsules and use thereof in polymers

Abstract

A plurality of microcapsules and use thereof in polymers A plurality of microcapsules having a cross-linked polymeric shell encapsulating an active ingredient wherein said microcapsules have a mean diameter between 1 and 30 µm, preferably from 2 to 25 µm and said plurality displaying an average rupture stress determined by nanoindentation, of at least 80 MPa.

Description

A plurality of microcapsules and use thereof in polymers

[0001] The present invention concerns a plurality of microcapsules which is mechanically and thermally resistant and useful in particular for improving the processing and the properties of polymers. The invention also concerns the use of the plurality of microcapsules in polymer processing, premixes comprising a polymer and the plurality of microcapsules and polymer compositions comprising the plurality of microcapsules.

[0002] The encapsulation of active ingredients has been developed as a technical option to protect such active ingredients from undesired and premature interactions with other components of formulations or reaction mixtures. The encapsulation is useful in particular to provide formulations, e.g. cosmetic, pharmaceutical and agricultural formulations having an improved efficiency of use of the active ingredients and reaction mixtures, for example polymerization mixtures or polymer processing mixtures, which allows for improved processes and final products due to a better controlled use of active ingredients such as catalysts. WO-A-2018 / 172431 in the name of the applicant discloses a series of microcapsules having a polymeric shell with a pore size less than 1 nm which are generally suitable for such purpose.

[0003] EP-A-2360221 relates to a thermally expandable microcapsule, which comprises: a shell made of a polymer; and a volatile expansion agent as a core agent encapsulated in the shell, the storage elastic modulus (E') of the shell at a temperature of 200°C and a frequency of 10 Hz being 1 × 10 N / m or more, the storage elastic modulus (E') of the shell at a temperature of 250°C and a frequency of 10 Hz being 1 × 10 N / m or more, and a maximum displacement amount measured by thermomechanical analysis being 300 µm or more. The elastic modulus is not measured on the capsules but on a test piece having a thickness of 0.2 mm (200 µm) which is not a suitable wall thickness for microcapsules capable of delivering an active ingredient and even exceeds the diameter of certain microcapsules.

[0004] WO-A-2022 / 081958 discloses benefit agent delivery particles having a core and a shell encapsulating the core, the shell comprising certain multifunctional (meth)acrylate-based polymers. The delivery particle has a core to polymer wall ratio by weight from about 96:4 to about 99.5 to 0.5 and a volume-weighted particle size from about 30 to about 50 microns. The mechanical stability of the particles is low.

[0005] JP2009155443 A2 discloses benefit agent delivery particles having a core and a shell, in which the shell is composed of inorganic materials, specifically calcium carbonate. The mechanical stability of these particles is implicitly high, however not disclosed in the documents. Furthermore, the use of organic shell materials has certain advantages in terms of liberation of actives through diffusion processes.

[0006] References WO-A-2020 / 194910, WO-A-2016 / 100477, CN-A-15970604-and US-B-8119587 disclose the use of core-shell microcapsules in personal care and related applications. These applications require a low mechanical stability of the microcapsules.

[0007] G. Dou, Z. Lu, Y. Hu, Y. Sun, H. Jiang, G. Peng, J. Appl. Polym. Sci. 2023, 140(42), e54549.https: / doi.org / 10.1002 / app.54549 discloses TiO2 nanoparticle modified melamine formaldehyde capsules for encapsulation of PCM materials. These materials are not supposed to be released from the microcapsules.

[0008] The present invention now makes available still improved microcapsules which are particularly advantageous in terms of mechanical stability, enabling in particular their advantageous use in polymer processing processes which may involve high shear stress.

[0009] The invention consequently concerns, in a first aspect, a plurality of microcapsules having a cross-linked polymeric shell encapsulating an active ingredient wherein said microcapsules have a mean diameter between 1 and 30 µm, preferably from 2 to 25 µm and said plurality displaying an average rupture stress determined by nanoindentation, of at least 80 MPa. More particularly, the rupture stress is equal to or greater than 120MPa. In some aspects the rupture stress is equal to or greater than 200MPa or even equal to or greater than 350MPa. Often, the rupture stress is equal to or lower than 400MPa.

[0010] It has been found that the plurality of microcapsules according to the invention remains substantially intact under high mechanical stress conditions and is thereby particularly advantageous e.g ; for targeted release of active ingredients. The plurality of microcapsules according to the invention has also particularly advantageous storage and transportation properties as breakage of microcapsules and associated degradation of the plurality of microcapsules can be substantially avoided. A further advantage of said plurality of microcapsules is the ability to survive and thereby protect active ingredients over the course of industrial processing and forming of polymers, by techniques such as injection molding and / or extrusion molding. The microcapsules are then able to release any needed active ingredients upon a purposive exposure to a stimulus, such as a change in temperature and exposure to temperature for an extended time, without loss of the reactive component before said exposure.

[0011] According to the invention, the mechanical properties of the plurality of microcapsules are measured by nanoindentation.

[0012] For the purpose of the present invention, nano-indentation is a method by which an individual microcapsule is exposed to a compressive stress through the application of a flat-punch indenter. In the present invention, by way of example, the Anton Paar NHT3 nanoindenter can be employed. A suitable way of carrying out the measurement by nano-indentation can be described as follows:

[0013] An important aspect of this measurement method is the need for the formation of a monolayer of monodisperse capsules. A hard tip whose mechanical properties are known, frequently made of a very hard material like diamond, is pressed into a sample whose properties are unknown. The load placed on the indenter tip is increased as the tip penetrates further into the specimen until it reaches a user-defined value. At this point, the load may be held constant for a period or removed.   During the course of the instrumented indentation process, a record of the depth of penetration is made, and then the area of the indent is determined using the known geometry of the indentation tip. While indenting, parameters such as load and depth of penetration can be measured using the capacitive sensors. A record of these values can be plotted on a graph to create a load-displacement curve, which is then used to extract mechanical properties of the material.The area of the residual indentation in the sample is measured through an optical or scanning electron microscope that is a standard component of a nanoindentation system, and the hardness, H, is defined as the maximum load, Pmax, divided by the residual indentation area, A, as determined by an in-situ microscopic image analysis. The deformation and rupture strength can also be determined through the afore-mentioned load-displacement curve.

[0014] The rupture force, i.e. the force at which a large displacement of the indenter can be observed, is indicative of the force a capsule can withstand before rupture. Accordingly, another aspect of the present invention concerns a plurality of microcapsules having a mechanical resistance such that, the rupture force for said capsules is greater than 100 µN, preferably greater than 300 µN, but does generally not exceed 20000 µN. In certain instances, the rupture force does not exceed 15000 µN.

[0015] The rupture stress for the purposes of the present invention is calculated using the contact surface area between the surface of the indentor and the surface of the microcapsule. The contact area in the sense of the current invention can be determined using the principle of conservation of volume before rupture of the microcapsule. The microcapsules are observed under optical microscopy before being measured by nanoindentation. The diameter of the capsule is determined from the two dimensional images taken of the microcapsule to be investigated. The capsules are on average spherical before nanoindentation. Therefore the volume of the capsules in the plurality of microcapsules according to the invention is calculated as a sphere. The volume is conserved under compression, which induces a deformation into an ellipsoid. For the purpose of determining the rupture stress of the plurality of microcapsules according to the invention, the ellipsoid is considered as a rectangular cuboid whose volume is given by the formula V=z x A, wherein V is the volume, z is the height of the deformed capsule, determined as the difference between the undeformed capsules diameter d and the displacement h measured by the nanoindentor and A is the contact area. The volume of the rectangular cuboid is set as equal to the volume of the capsule prior to compression.

[0016] Therefore, the contact area A is simply the capsule volume divided by the capsule height z, given by the formula A=(4 / 3xπ x(d / 2)3) / z.

[0017] The contact area at rupture is determined based on the z value at the point of nonlinearity of the displacement curve of force versus the measured displacement.

[0018] Microscopy and nanoindentation measurements may take place simultaneously, with in-situ microscopy images being taken during application of force by a nanoindentor, as described, by way of example in Rzepiejewska-Malyska, K., Buerki, G., Michler, J., Major, R., Cyrankowski, E., Asif, S., & Warren, O. (2008). In situ mechanical observations during nanoindentation inside a high-resolution scanning electron microscope. Journal of Materials Research, 23(7), 1973-1979. doi:10.1557 / JMR.2008.0240. In this case, detection of rupture may also be performed by microscopy and correlated to the force and / or mechanical stress applied. Detection of rupture could be performed by optical or electronic microscopies after application of a force or a mechanical stress as post-mortem analysis.

[0019] For the purpose of the present invention, the term “mean diameter or average diameter of the microcapsules” means the size distribution of the microcapsules, and thus the mean diameter of the microcapsules, may be measured by methods well known to the skilled person in the art, e.g. by a light scattering technique such as a Mastersizer 3000 equipped with a hydro SV measuring cell, or by image analysis of optical microscopy pictures, or by image analysis of electronic microscopy pictures. Light scattering techniques such as e.g; used by Mastersizer 3000 provide as mean diameter the size distribution by volume D50Vol, whereby 50% of the microcapsules have a smaller diameter than the mean diameter.

[0020] For the purposes of the present invention, «monodisperse» is understood to denote with reference to a series of droplets or a series of capsules, that the standard deviation of the distribution of the diameter of said droplets or said capsules is less than 50%, in particular less than 25%, or less than 1 μm. For the purposes of the present invention, the diameter of said droplets or said capsules is determined by light scattering technique using a Mastersizer 3000 (Malvern Instruments) equipped with a Hydro SV measurement cell.

[0021] For the purpose of the present invention «plurality» refers to a significant number of microcapsules, for example a quantity of microcapsules obtained from a synthesis of microcapsules or a quantity of microcapsules suitable for application, in particular industrial application in the intended use of the microcapsules.

[0022] In the plurality of microcapsules according to the invention, the microcapsules generally have an average diameter of equal to or greater than 1 µm, preferably equal to or greater than 3 µm, more preferably equal to or greater than 5 µm. In the plurality of microcapsules according to the invention, the microcapsules generally have an average diameter of equal to or smaller than 30 µm, preferably equal to or smaller than 20 µm. In a particular aspect, the plurality of microcapsules according to the invention, the microcapsules have an average diameter from 2 µm to 25 µm.

[0023] In the plurality of microcapsules according to the invention, the microcapsules generally have a shell thickness of equal to or greater than 0.1 µm, preferably equal to or greater than 0.2 µm, more particularly equal to or greater than 0.5 µm. In the plurality of microcapsules according to the invention, the microcapsules generally have a shell thickness of equal to or smaller than 20 µm, preferably equal to or smaller than 8 µm more particularly equal to or smaller than 3 µm. A shell thickness of from 1 to 2 µm is more particularly preferred. Shell thickness can also be denoted as wall thickness and refers to the thickness of the, generally solid, envelope of cross-linked polymer which encloses the inner space of a microcapsule.

[0024] The plurality of microcapsules according to the invention is often monodisperse.

[0025] In a second particular aspect of the plurality of microcapsules according to the invention, the microcapsules have mean diameter between 1 μm and 30 μm, the thickness of the solid enveloping shell is between 0.2 μm and 8 μm and the standard deviation of the distribution of the diameter of microcapsules is less than 50%, or less than 10 μm. Preferably the microcapsules have a mean diameter of between 10 and 20 µm, with a standard deviation of 50%. More preferably the standard deviation is between 0 and 30%.

[0026] The plurality of microcapsules may have pores on the shell surface of the microcapsules which have an average diameter smaller than 1 nm, determined by BET surface analysis.

[0027] In a preferred aspect of the plurality of microcapsules according to the invention, the crosslinked polymeric shell may be suitably obtained by photopolymerization of a photopolymerizable composition having reactive groups. In this aspect, the conversion of reactive groups of the photopolymerizable composition is generally at least 80%, preferably at least 90%.

[0028] The conversion of reactive groups can be determined by the monitoring of the disappearance of one band representative of a functional group under FTIR, the absorption of IR bands being proportional to the amount of the functional group, therefore the reduction of peak height corresponds to the reduction of the amount of the functional group, further indicating successful polymerization. The standard method of doing this is comparison of the FTIR absorption of the polymer before and after cross-linking, in particular by photopolymerization. For the purpose of the present invention this can be done using the method disclosed in Barszczewska-Rybarek,Materials2019, 12(24), 4057. By way of example, the conversion of reactive acrylate groups over the course of radical polymerization can be observed as a function of the reduction in FTIR absorption of the signature spectrum thereof, for instance 1600 cm-1, 1407 cm-1or 810 cm-1.

[0029] The invention consequently also concerns a plurality of microcapsules having a cross-linked polymeric shell encapsulating an active ingredient, wherein the cross-linked polymeric shell has a conversion rate of cross-linkable precursor group of the cross-linking bond,determined by observation of the reduction of FTIR absorption of a characteristic FTIR absorption band of said precursor group equal to or greater than 90 mole % and less than 99 mole % relative to the initial molar amount of cross-linkable precursor group present in the cross-linked polymeric shell.

[0030] The invention consequently also concerns a plurality of microcapsules having a cross-linked polymeric shell encapsulating an active ingredient, wherein the cross-linked polymeric shell has a given cross-linking density, which is generally equal to or greater than 1.0 / mmole / g. The cross-linking density of the cross-linked polymeric shell is preferably higher than 2.0 mmole / g. The cross-linking density of the cross-linked polymeric shell often does not exceed 5.0 mmole / g.

[0031] The crosslinking density can be determined by dividing the functionality of oligomers or monomers by their average molar masses weighted by the conversion rate, of the reactive groups, including but not limited to cross-linkable precursor group of the cross-linking bond. Functionality is the number of reactive groups in the respective oligomers or monomers composing the shell.

[0032] Preferred crosslinkable groups useful in the present invention are selected from acrylate, methacrylate, and epoxy. Without wishing to be bound by any theory, it is believed that a high but not necessarily complete degree of cross-linking and a high cross-linking density confers advantages in terms of mechanical stability and retention capabilities of the microcapsules.

[0033] In the plurality of microcapsules according to the invention, the crosslinked polymeric shell often comprises or consists of at least one polymer selected from polyethers, polyesters, polyurethanes, polyureas, polyethylene glycols, polypropylene glycols, polyamides, polyacetals, polyimides, polyolefins, polysulfides, and polydimethylsiloxanes, said polymers bearing at least one reactive function selected from the group consisting of acrylate; methacrylate; vinyl ether; N-vinyl ether; mercaptoester; thiolene; siloxane; epoxy; oxetane; urethane; isocyanate; and peroxide.

[0034] The term “crosslinking agent” Is used to refer to a compound bearing at least two reactive functional groups that are capable of crosslinking a monomer or a polymer, or a mixture of monomers or polymers, during its polymerization.

[0035] Examples of specific polymers which can be used to produce the cross-linked shell include, but are not limited to, the following polymers: poly(2-(1-naphthyloxy)-ethyl acrylate), poly(2-(2-naphthyloxy)-ethyl acrylate), poly(2-(2-naphthyloxy)-ethyl methacrylate), polysorbitol dimethacrylate, polyacrylamide, poly((2-(1-naphthyloxy) ethanol), poly(2-(2-naphthyloxy) ethanol), poly(1-chloro-2),3-epoxypropane),poly(n-butyl isocyanate), poly(N-vinyl carbazole), poly(N-vinyl pyrrolidone), poly(p20benzamide), poly(p-chlorostyrene), poly(p-methyl styrene) poly(p-phenylene oxide), poly(p-phenylenesulfide), poly(N-(methacryloxyethyl)-succinimide), polybenzimidazole,polybutadiene, polybutylene terephthalate, polychloral, polychlorinated trifluoroethylene, polyether imide, polyether ketone, polyether sulfone, polyhydridosilsesquioxane, poly(m-phenyleneisophthalamide), poly(methyl-2-acrylamido-2-methoxyacetate), poly(2-acrylamido-25 2-methylpropanesulfonic acid), poly-mono-butyl maleate, polybutyl methacrylate, poly(N-tertbutylmethacrylamide),poly(N-butylmethacrylamide), polycyclohexylmethacrylamide, poly(N-xylene bisacrylamide-2,3-dimethyl-1,3-butadiene, N,N-dimethylmethacrylamide), poly(n-butylmethacrylate), poly(cyclohexyl methacrylate), polyisobutyl methacrylate, poly(4-cyclohexylstyrene), polycyclol acrylate, polycyclol methacrylate, polydiethyl30 ethoxymethylenemalonate, poly(2,2,2-trifluoroethyl methacrylate), poly(1,1,1-trimethylolpropane trimethacrylate) polymethacrylate, poly(N, N-dimethylaniline, dihydrazide),poly(isophthalic dihydrazine), isophthalic polyacid, polydimethyl benzilketal, epichlorohydrin,poly(ethyl-3,3-diethoxyacrylate), poly(ethyl-3,3-dimethylacrylate), poly(ethyl vinyl ketone),, poly(vinyl ethyl ketone), poly(penten-3-one), polyformaldehyde poly(diallyl acetal),polyfumaronitrile, polyglyceryl propoxy triacrylate, polyglyceryl trimethacrylate,polyglycidoxypropyltrimethoxysilane, polyglycidyl acrylate, poly(n-heptyl acrylate), poly(n-heptylacrylic acid ester), poly(n-heptyl methacrylate), poly(3-hydroxypropionitrile), poly(2-hydroxypropyl acrylate), poly(2-hydroxypropyl methacrylate) poly(N-(5 methacryloxyethyl)-phthalimide), poly(1,9-nonanediol diacrylate), poly(1,9-nonanediol dimethacrylate), poly(N-(n-propyl)acrylamide), poly(ortho-phthalic acid), poly(iso-phthalic acid), poly(1,4-benzenedicarboxylic acid), poly(1,3-benzenedicarboxylic acid), poly(phthalic acid),poly(mono-2-acryloxyethyl ester), terephthalic polyacid, phthalic polyanhydride polyethylene glycol diacrylate, polyethylene glycol methacrylate, polyethylene glycol dimethacrylate,polyisopropyl acrylate, polysorbitol pentaacrylate, polyvinyl bromoacetate, polychloroprene, poly(di-n-hexylsilylene), poly(di-n-propylsiloxane), polydimethylsilylene, polydiphenyl siloxane, polyvinyl propionate, polyvinyl triacetoxysilane, polyvinyl tris-tert-butoxysilane, polyvinylbutyral, polyvinyl alcohol, polyvinyl acetate, polyethylene co-vinyl acetate, poly(bisphenol-A15polysulfone), poly(1,3-dioxepane), poly(1,3-dioxolane), poly(1,4-phenylene vinylene),poly(2,6-dimethyl-1A-phenylene oxide), poly(4-hydroxybenzoic acid), poly(4-methyl pentene-1), poly(4-vinylpyridine), polymethylacrylonitrile, polymethylphenylsiloxane,polymethylsilmethylene, polymethylsilsesquioxane, poly(phenylsilsesquioxane),poly(pyromellitimide-1,4-diphenyl ether), polytetrahydrofuran, polythiophene, poly(trimethylene oxide), polyacrylonitrile, polyether sulfone, polyethylene-co-vinyl acetate, poly(perfluoroethylene propylene), poly(perfluoroalkoxyl alkane), or poly( styreneacrylonitrile).

[0036] Preferred examples of polymers which can be used to produce the cross-linked shell include aliphatic epoxidized poly acrylates, e.g. soy bean oil acrylates, bisphenol A based epoxy acrylates, glyceryl propoxy triacrylates, difunctional polyester acrylate oligomers, aliphatic polyester based urethane dimethacrylates or diacrylates and amine modified polyether acrylates. In that case the cross-linked shell comprises or consists of at least one of the aforesaid polymers.

[0037] The crosslinking agent may be selected from molecules bearing at least two functional groups selected from among the group constituted of the functions: acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate, and peroxide.

[0038] By way of example of crosslinking agent, mention may be made in particular of: diacrylates, such as 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, polyethylene glycol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,4-butanediol dimethacrylate, 2,2-bis(4-methacryloxyphenyl) propane, 1,3-butanediol dimethacrylate, 1,10-decanediol dimethacrylate, bis(2-methacryloxyethyl) N,N′-1,9-nonylene biscarbamate, 1,4-butanediol diacrylate, ethylene glycol diacrylate, 1,5-pentanediol dimethacrylate, 1,4-phenylene diacrylate, allyl methacrylate, N,N′-methylenebisacrylamide, 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy) phenyl]propane, tetraethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, polyethylene glycol diglycidyl ether, N,N-diallylacrylamide, 2,2-bis[4-(2-acryloxyethoxy) phenyl]propane, glycidyl methacrylate; multifunctional acrylates such as dipentaerythritol pentaacrylate, 1,1,1-trimethylolpropane triacrylate, 1,1,1-trimethylolpropane trimethacrylate, ethylenediamine tetramethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate; acrylates also having other reactive functional groups, such as propargyl methacrylate, 2-cyanoethyl acrylate, tricyclodecane dimethanol diacrylate, hydroxypropyl methacrylate, N-acryloxysuccinimide, N-(2-hydroxypropyl)methacrylamide, N-(3 aminopropyl)methacrylamide hydrochloride, N-(t-BOC-aminopropyl)methacrylamide, 2-aminoethyl methacrylate hydrochloride, monoacryloxyethyl phosphate, o-nitrobenzyl methacrylate, acrylic anhydride, 2-(tert-butylamino)ethyl methacrylate N,N-diallylacrylamide, glycidyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxybenzophenone, N-(Phthalimidomethyl)acrylamide, cinnamyl methacrylate.

[0039] In a preferred aspect, the crosslinked polymeric shell comprises or consists of rigid moieties and flexible moieties.

[0040] “Rigid moieties” are understood to denote functional groups comprising unsaturated groups. Typically these are organic molecules containing at least one double bond, triple bond, or ring . By way of example of rigid moieties, the following chemical groups may be listed: alkenes, alkynes, esters, urethanes, aromatic or aliphatic carbocycles, aromatic or aliphatic heterocycles, ester groups, amide groups, urethane groups, sulphoxide, or phosphate. Without wishing to be bound by any theory, it is believed that a rigid moiety by its structure resists elongation in case of application of mechanical stress. Particularly, the rigid moieties are selected from carbocycles, heterocycles, ester groups, amide groups, urethane groups, tetra substituted carbons, internal double bonds, internal triple bonds. In a particular aspect of the plurality of microcapsules according to the invention, wherein the molar quantity of aliphatic cycles is below 10% relative to the total molarity of the constituents of the cross-linked polymeric shell.

[0041] “Flexible moieties” are understood to denote saturated chains of aligned C, O or N. They can be in the main backbone of the polymer chain or in non-cross-linkable branches. A flexible moiety is understood to denote a group of atoms which by its structure is capable of elongation due to the degree of freedom in rotational movement of saturated atoms. Flexible moieties are selected in particular from carbon chains having concatenated atoms, said concatenated atoms being primarily carbon atoms which may be optionally partially replaced by oxygen or nitrogen. Examples of flexible moieties include but are not limited to alkyl chains in a polymer backbone chain, alkyl pendant chains, alkyl pendant groups, ether groups, in particular alkyl(poly)ether chains or amine groups, in particular alkyl(poly)amines. Typically, the chains of the flexible moieties comprise from 1 to 30 catenary atoms, particularly from 7 to 20 catenary atoms. The flexible moieties are often selected from carbon chains having at least 6 catenary atoms said catenary atoms optionally being partially replaced by oxygen and / or nitrogen. Often, the flexible moiety is incorporated into the shell through use of a monomer having 1 or 2 crosslinkable groups in particular selected from (meth)acrylate groups and epoxy groups. A particular example is 1,6-hexanediol diacrylate.

[0042] In the plurality of microcapsules according to the invention, the flexible moiety is often incorporated into the shell in a quantity of 20% molar relative to the total molarity of the constituents of the cross-linked polymeric shell. More particularly, the flexible moiety is incorporated into the shell in a quantity of between 40 % and 60 % of molar relative to the total molarity of the constituents of the cross-linked polymeric shell.

[0043] “Monomer” refers to a molecule which can undergo polymerization thereby contributing constitutional units to the essential structure of a macromolecule.

[0044] “Oligomer” refers to a macromolecule comprising a repetition of monomers, preferably a repetition of less than 10 monomers.

[0045] To calculate the number % of rigid and flexible moieties, respectively, the weight% of each oligomer and monomer present in the cross-linked polymer shell is converted in number % knowing the molar mass and the Avogadro number. Knowing the molar mass of the respective rigid or flexible moiety and the number of recurrences of each group in the monomers and oligomers and assuming they do not react during polymerization, the number % of respective rigid and flexible moieties can be determined. The ratio between rigid moieties and flexible moieties is then calculated.

[0046] It has been found that the presence of both rigid and flexible of moieties in the cross-linked polymeric shell allows to provide particularly good mechanical resistance, in particular through the selection of the ratio of rigid to flexible moieties. Without wishing to be bound by any theory, it is believed that a rigid moiety, by its structure, resists elongation in case of application of mechanical stress.

[0047] In a particular embodiment, rigid and flexible moieties are incorporated into the shell through use of a monomer selected from a polybutadiene, a urethane a polyester or an epoxy, or any combination thereof. In a further embodiment thereof, the monomer(s) may be an acrylate. It has been found that particularly good results concerning the mechanical stability may be achieved using monomers which contain both rigid and flexible moieties. Without wishing to be bound by any theory, it is believed that the locally inhomogeneous distribution of rigid and flexible moieties in the shell which can be achieved through the use of monomers containing both types of moieties is particularly advantageous to generate mechanically stable shells.

[0048] In a variant, rigid and flexible moieties are incorporated into the shell through the use of an oligomer containing both rigid and flexible moieties The oligomer containing both rigid and flexible moieties may be selected, for example from an epoxidized soy bean acrylate and polybutadiene urethane acrylates. In this preferred aspect, the plurality of microcapsules has generally a number ratio of rigid moieties to flexible moieties in the shell of between 0.3 and 2, preferably between 0.6 and 1.8 more preferably from 1.0 to 1.6.

[0049] In a still further preferred aspect, the aforesaid ratio of rigid moieties to flexible moieties, is combined with the cross-linking density of the copolymer network formed in the polymeric shell as described above.

[0050] The rigid moiety may suitably be incorporated into the shell through use of a monomer having at least 2, preferably 3, 4, 5 or 6 crosslinkable groups. (Meth)acrylate and epoxy groups are preferred.

[0051] In a particular aspect of the plurality of microcapsules according the invention, the rigid moiety is incorporated into the shell through use of an oligomer selected from (meth)-acrylated oligomers.

[0052] In a further advantageous embodiment of the plurality of microcapsules according to the invention, the number percentage of rotatable bonds constituting the polymeric shell is from 30 % to 75 %. A rotatable bond is defined as a single bond excluding (i) X-H bonds, wherein X is an atom different from hydrogen, and (ii) annular bonds and (iii) X-T bonds, wherein X is an atom different from hydrogen and T is a terminal atom different from hydrogen. This definition limits the rotatable bonds in particular to single bonds and to bonds which are not part of a ring, or bonds which are not C-N bonds of primary amides, or bonds which are not attached to a terminal, non-hydrogen atom. The calculation of the percentage of rotatable bonds is performed by determining the ratio of rotatable bonds to the total number of bonds in each oligomer and monomer constituting the polymeric shell. The ratio of the number of rotatable bonds to the total number of bonds is calculated for each oligomer and monomer. For the final copolymer network that forms the microcapsule shell, the percentage of rotatable bonds is calculated as the sum of each percentage weighted by the value previously calculated for each oligomer and monomer.

[0053] In another aspect of the plurality of microcapsules according to the invention, the number of donors and acceptors of hydrogen bonds in the cross-linked polymeric shell is between 0 and 10 and preferably between 0 and 9. A hydrogen bond is a specific weak interaction where a hydrogen is covalently linked to a highly electronegative atom (O, N), called a donor of said hydrogen bond, but also attracted by another highly electronegative atom (O, N, F) or an atom bearing a non-bonding doublet, called an acceptor of hydrogen bonds. Atoms classified as donors can generally also be classified as acceptors of hydrogen bonds. The number of acceptors of hydrogen bonds is counted for each oligomer and monomer used to produce the cross-linked polymeric shell, and then calculated by summing up of the acceptors of each oligomer and monomer weighted by the %number of each oligomer and monomer in the cross-linked polymeric shell. The number of donors of hydrogen bonds is counted for each oligomer and monomer used to produce the cross-linked polymeric shell by counting the number of H-N, H-F, and H-O bonds, and then calculated by summing up of the donors of each oligomer and monomer weighted by the %number of each oligomer and monomer in the cross-linked polymeric shell.

[0054] Without wishing to be bound by any theory, it is believed that the influence of acceptors and donors of hydrogen bonds on the mechanical resistance of the capsule can be explained as follows. Acceptors and donors of hydrogen bonds are polar groups. Such groups generate intermolecular interactions influencing -the mechanical properties of the polymer. Applicants have found that a cross-linked polymeric shell having a number of acceptors and donors of hydrogen bonds described above contributes to achieving good mechanical properties, in particular an adequate mechanical resistance of the shell of the plurality of microcapsules according to the invention.

[0055] In a particularly preferred embodiment, the cross-linked polymeric shell of the plurality of microcapsules according to the invention has the following characteristics in combination:• (a) The sum of acceptor and donor of hydrogen bond groups of the cross-linked polymeric shell is between 0 and 10 , preferably between 2 and 9 .and at least one of the following 2 conditions• (b) the percentage of rotatable bonds over the total number of bonds of the cross-linked polymeric shell is between 30 and 75%and / or• (c) the ratio of rigid to flexible bonds in the cross-linked polymeric shell is from 0,3 to 2 preferably from 0,6 to 1,8, most preferably from 1 to 1,6.

[0056] The plurality of microcapsules according to the invention generally has a core / shell (wt. / wt.) ratio of equal to or greater than 20 / 80, preferably equal to or greater than 30 / 70, more preferably equal to or greater than 40 / 60. Often this core / shell ratio is at most 70 / 30, preferably at most 50 / 50.

[0057] The invention also concerns, in a second aspect, a plurality of microcapsules having the characteristics of the cross-linked polymeric shell described above separately or in combination, especially regarding (a) the sum of acceptor and donor of hydrogen bond groups, (b) the percentage of rotatable bonds over the total number of bonds and (c) the ratio of rigid to flexible bonds.

[0058] It has been found, surprisingly, that the plurality of microcapsules according to the second aspect has particular advantages notably to protect curing agents of thermoset resins such as in particular latent accelerators for epoxy resins or catalysts for polyurethane manufacture while maintaining good if not identical mechanical properties of the premix comprising the microcapsules.

[0059] In a preferred aspect of the plurality of microcapsules according to the second aspect, the percentage of rotatable bonds over the total number of bonds of the cross-linked polymeric shell is between 30 and 75%. More particularly, this percentage is from 35 to 50%.

[0060] In this preferred aspect, the ratio of rigid to flexible bonds in the cross-linked polymeric shell is advantageously from greater than 2, particularly at least 2.1 to 3.

[0061] Save for the specific disclosure here before, the other characteristics and preferences described generally for the plurality of microcapsules according to the invention equally apply to the second aspect.

[0062] The chemical composition and structure of the microcapsules may be determined through structural analysis methods available and well-known to a person skilled in the art. The presence and the quantity of functional groups such as, e.g. ester groups, carboxyl groups or hydroxyl groups in the cross-linked polymeric shell, can be determined for instance through NMR or Raman Spectroscopy or Fourier Transform Infrared spectroscopy. By using a reference material, e.g; the monomer and / or oligomer mix before polymerization, the amount of said functional groups can be compared to the respective amount in reference material. The evolution of such functional groups during polymerization can be followed in similar manner as described above for reactive groups. Methods of analysis are well established and known to a person skilled in the art. By way of example and not wishing to be bound by any theory, the methods of analysis disclosed in the following texts are incorporated herein by reference:

[0063] Atsushi Udagawa, Fumio Sakurai, Tatsuo Takahashi, In situ study of photopolymerization by Fourier transform infrared spectroscopy, Journal of Applied Polymer Science 42 (7), 1991, pp. 1861 – 1867.

[0064] Wolter F. Jager, Adrien Lungu, D. Y. Chen, Douglas C. Neckers, Photopolymerization of polyfunctional acrylates and methacrylate mixtures: Characterization of polymeric networks by a combination of fluorescence spectroscopy and solid state nuclear magnetic resonance, Macromolecules, 30 (4), 1997, pp. 780 – 791.

[0065] M. Jöhnck, L. Müller, A. Neyer, J.W. Hofsraat, Quantitative determination of unsaturation in photocured halogenated acrylates and methacrylates by FT-IR and Raman spectroscopy and by thermal analysis, Polymer, 40, 1999, pp. 3631 – 3640.

[0066] In a particular aspect of the plurality of microcapsules according the invention, the crosslinked polymeric shell is essentially free of nitrile functional groups. «Essentially free of nitrile functional groups» is understood to denote in particular a content of nitrile functional groups lower than 1 weight%, preferably less than 0.5 weight % relative to the total weight of the cross-linked polymeric shell. Preferably, the cross-linked polymeric shell is free of nitrile functional groups. This is in particular the case when no nitriles have been used as monomers, polymers or cross-linking agents for the production of the cross-linked polymeric shell.

[0067] In the plurality of microcapsules according to the invention, the shell encapsulates an active ingredient. The active ingredient can be a solid at 25°C. The active ingredient can also be a liquid at 25°C and 1013,25 kPa pressure. The active ingredient may be a reactive agent, which may be released through a specific external stimulus, including but not limited to a change in pH, exposure to ultra-violet radiation, a change in temperature, and / or any combination thereof. In order to achieve said release by external stimulus, certain components of the shell may be selected, as disclosed in for instance EP 3548529.

[0068] In that aspect, the active ingredient is often selected from a catalyst, a UV absorber, a lubricant and a flame retardant, a pigment and a liquid crystal material. The procedure for the preparation of the double emulsion is disclosed in particular in EP 3548529, US-A-2020129948 and US-A-2021113984 in the name of the applicant, the contents of which are incorporated by reference into the present patent application.

[0069] In the plurality of microcapsules according to the invention the active ingredient can be suitably selected from, for example: a crosslinking agent, a hardener, an organic or metal catalyst (such as an organometallic or inorganometallic complex of platinum, palladium, titanium, molybdenum, copper, zinc) used for polymerising polymer-, elastomer-, rubber-, paint-, adhesive-, sealant-, mortar-, varnish-, or coating formulations;

[0070] a dye or pigment intended for elastomer-, paint-, coating-, adhesive-, sealant-, mortar-, or paper formulations

[0071] a fragrance (in accordance with the list of molecules established by the International Fragrance Association (IFRA) and available on the website www.ifraorg.org) intended for detersive products such as cleaning / washing products, home care products, cosmetic and personal care products, textiles, paints, coatings;

[0072] an aroma / flavouring agent, a vitamin, an amino acid, a protein, a lipid, a probiotic, an antioxidant, a pH corrector, a preservative for food compounds and animal feed;

[0073] a softener, a conditioning agent for detersive products, cleaning / washing products, cosmetics and personal care products. In this regard, the active agents that may be used are for example as listed in the US patents U.S. Pat. No. 6,335,315 and U.S. Pat. No. 5,877,145;

[0074] an anti-discolouration or anti-fading agent (such as an ammonium derivative), an antifoaming agent (such as an alcohol ethoxylate, an alkylbenzene sulfonate, a polyethylene ethoxylate, an alkylethoxysulfate or alkylsulfate) intended for detersive products and cleaning / washing products and home care products;

[0075] a brightening agent, also referred to as a colour activating agent (such as a stilbene derivative, a coumarin derivative, a pyrazoline derivative, a benzoxazole derivative, or a naphthalimide derivative) intended for detersive products, cleaning / washing products, cosmetics and personal care products;

[0076] a biologically active compound such as an enzyme, a vitamin, a protein, a plant extract, an emollient agent, a disinfecting agent, an antibacterial agent, an anti-UV agent, a medicament intended for cosmetic and personal care products, and textiles. Among these biologically active compounds the following may be mentioned: vitamins A, B, C, D and E, para-aminobenzoic acid, alpha hydroxy acids (such as glycolic acid, lactic acid, malic acid, tartaric acid, or citric acid), camphor, ceramides, polyphenols (such as flavonoids, phenolic acid, ellagic acid, tocopherol, ubiquinol), hydroquinone, hyaluronic acid, isopropyl isostearate, isopropyl palmitate, oxybenzone, panthenol, proline, retinol, retinyl palmitate, salicylic acid, sorbic acid, sorbitol, triclosan, tyrosine;

[0077] a disinfecting agent, an antibacterial agent, an anti-UV agent, intended for paints and coatings;

[0078] a fertiliser, a herbicide, an insecticide, a pesticide, a fungicide, a repellent, or a disinfecting agent intended for agrochemical products;

[0079] a fire resistant agent, also known as a flame retarding agent, (for example a brominated polyol such as tetrabromobisphenol A, a halogenated or non-halogenated organophosphorus compound, a chlorinated compound, an aluminum trihydrate, an antimony oxide, a zinc borate, a red phosphorus, a melamine, or a magnesium dihydroxide) intended for use in plastic materials, coatings, paints, and textiles;

[0080] a photonic crystal or a photochromophore intended for use in paints, coatings, and in polymer materials that form curved and flexible screens;

[0081] a product known to the person skilled in the art under the accepted nomenclature Phase Change Materials (PCMs) that is capable of absorbing or releasing so-called ‘latent’ heat when going through a change in a phase, intended for the storage of energy. Examples of PCMs and the applications thereof are described in “A review on phase change energy storage: materials and applications”, Farid et al., Energy Conversion and Management, 2004, 45(9-10), 1597-1615. By way of examples of PCMs, mention may be made of molten salts of aluminum phosphate, ammonium carbonate, ammonium chloride, cesium carbonate, cesium sulfate, calcium citrate, calcium chloride, calcium hydroxide, calcium oxide, calcium phosphate, calcium saccharate, calcium sulfate, cerium phosphate, iron phosphate, lithium carbonate, lithium sulfate, magnesium chloride, magnesium sulfate, manganese chloride, manganese nitrate, manganese sulfate, potassium acetate, potassium carbonate, potassium chloride, potassium phosphate, rubidium carbonate, rubidium sulfate, disodium tetraborate, sodium acetate, sodium bicarbonate, sodium bisulfate, sodium citrate, sodium chloride, sodium hydroxide, sodium nitrate, sodium percarbonate, sodium persulfate, sodium phosphate, sodium propionate, sodium selenite, sodium silicate, sodium sulfate, sodium tellurate, sodium thiosulfate, strontium hydrophosphate, zinc acetate, zinc chloride, sodium thiosulfate, paraffinic hydrocarbon waxes, polyethylene glycols.

[0082] In a preferred embodiment of the plurality of microcapsules according to the invention the active ingredient is selected from the group consisting of a catalyst, a curing agent, a latent accelerator of curing of an epoxy resin, and polyurethane catalysts.

[0083] Suitable latent accelerators may be selected, for example, from amine latent accelerators, in particular polyamine latent accelerators. Particular examples are selected from modified polyamines, e.g. Ancamine2014 FG.

[0084] Suitable polyurethane catalysts are selected, for example from amine polyurethane catalysts, for example aliphatic, alicyclic and bicyclic compounds having at least one tertiary amino group. Specific examples include but are not limited to diazabicycloundecene (DBU) 1,6-Bis-(N,N-dimethylamino)-n-hexane, (N,N-dimethylamino)cyclohexane, 2-(N,N-dimethylamino)ethanol, N-methylmorpholine, dimorpholinodiethylether, dimethylaminoethoxyethanol and triethylenediamine,

[0085] In one embodiment of the plurality of microcapsules according to the invention, the active ingredient does not consist of a foaming agent. In this embodiment, the active ingredient does often not comprise a foaming agent. Generally, the microcapsules in the plurality of microcapsules according to the invention of this embodiment are not expandable.

[0086] In a particular embodiment of the preferred aspect of the plurality of microcapsules according to the invention, the active ingredient is a lubricant. Examples of suitable lubricants include but are not limited to oils such as mineral oils, polyalphaolefins, polyglycols, synthetic esters, phosphate esters, triglyceride esters, polyol esters, fatty acids, vegetal oils, silicone oils, polyethers, perfluoropolyethers, as well as solid lubricants, such as notably amides, such as erucamide or ethylene bis(stearamide), and synthetic or natural waxes (paraffins).

[0087] It has been found that the plurality of microcapsules of this particular embodiment are particularly advantageous to enhance the wear resistance or the scratch or the water resistance of a polymeric surface.

[0088] The invention consequently also concerns the use of the plurality of microcapsules according to this particular embodiment to enhance the wear resistance or the scratch resistance of a polymeric surface and the use of the plurality of microcapsules according to this particular embodiment to enhance the water resistance of a polymeric surface. Such polymeric surfaces include for example an epoxy-resin surface or an acrylic resin surface. Such surfaces may further be applied to objects such as e.g coatings, textiles and gaskets.

[0089] The invention consequently also concerns the use of the plurality of microcapsules according to this particular embodiment for the self-lubrication of an elastomer. Preferably, the lubricant is a polyol ester.

[0090] It has been found that the composition of elastomer and plurality of microcapsules according to the invention keeps storage and processing advantage while adequately releasing the lubricant when exposed to high shear stress over a long duration.

[0091] The invention also concerns the use of the plurality of microcapsules according to the invention, for the supply of an active ingredient to a polymerization process or to a polymer processing process.

[0092] It has been found that the plurality of microcapsules according to the invention and in particular according preferred aspect is particularly advantageous to protect active ingredients such as catalysts under the, sometimes severe conditions of mechanical stress and temperature encountered. In the aspect wherein the microcapsules include air or a gas, the plurality of microcapsules allows for an efficient and stable reduction of the density of the produced polymer. The use according to the invention may be for example, for the production of a thermoset polymer. It may also be for the production of a molded, extruded or cast thermoplastic article or thermoset article. It may also be for the production of a compression molded or an injection molded thermoplastic article or thermoset article.

[0093] The invention also concerns a premix for manufacturing a thermoset polymer, comprising the plurality of microcapsules according to the invention. The premix according to the invention preferably comprises an epoxy resin which is combined with the plurality of microcapsules according to the invention containing an anionic or cationic catalyst as the active ingredient. Another embodiment may be a premix in the form of acrylic resins, vinyl resins and polyesters. which are combined with the plurality of microcapsules according to the invention. In that aspect the microcapsules suitably contain an unsaturated monomer diluent such as, e.g; acrylic acid, acrylamide, acryloyl chloride, and methyl methacrylate as the active ingredient.

[0094] In another embodiment the premix according to the invention comprises an isocyanate resin which is combined with the plurality of microcapsules according to the invention containing at least a polyol as the active ingredient.

[0095] The premix according to this other embodiment may comprise, for example, from 85 wt.% to 99.9 wt.% of isocyanate resin and from 0.1.wt.% to 15 wt.% of microcapsules, comprising or consisting of the plurality of microcapsules according to the invention, relative to the total weight of the premix. In another variant, the premix according to this particular aspect comprises from 75 wt.% to 89.9 wt.% of isocyanate resin, from 0.1.wt.% to 15 wt.% of microcapsules, comprising or consisting of the plurality of microcapsules according to the invention, and up to 10% of a polymer additive preferably selected from fillers, pigments and blowing agents relative to the total weight of the premix.

[0096] It has been found that the storage and process stability of the premix according to the invention is improved. The premix according to the invention is capable of surviving extreme conditions to which the premix may be exposed during standard processing conditions, such as extrusion and / or injection molding.

[0097] In a particular aspect, the premix according to the invention comprises an epoxy resin and the plurality of microcapsules according to the invention wherein the active ingredient is a latent accelerator of curing of the epoxy resin. Suitable latent accelerators may be selected, for example, from amine latent accelerators, in particular polyamine latent accelerators. Particular examples are selected from modified polyamines, e.g. Ancamine2014 FG.

[0098] The premix according to this particular aspect may comprise, for example, from 85 wt.% to 99.9 wt.% of epoxy resin and from 0.1.wt.% to 15 wt.% of microcapsules, comprising or consisting of the plurality of microcapsules according to the invention, relative to the total weight of the premix. In another variant, the premix according to this particular aspect comprises from 75 wt.% to 89.9 wt.% of epoxy resin, from 0.1.wt.% to 15 wt.% of microcapsules, comprising or consisting of the plurality of microcapsules according to the invention, and up to 10% of a polymer additive preferably selected from fillers, pigments and blowing agents relative to the total weight of the premix.

[0099] The invention also concerns a mixture comprising a thermoplastic polymer and the plurality of microcapsules according to the invention.

[0100] The invention also concerns a polymer composition comprising a plurality of microcapsules according to the invention.

[0101] The invention also concerns a polymer composite material comprising a plurality of microcapsules according to the invention. In a particular aspect, the polymer composite material according to the invention is a prepreg material. “Prepreg” is understood to denote in particular laminate composites of fiber sheets that are impregnated with polymer resins that have not been fully cured.

[0102] The invention also concerns an adhesive composition comprising a plurality of microcapsules according to the invention.

[0103] The content of plurality of microcapsules according to the first or second aspect of the invention in the premix according to the invention, the mixture comprising a thermoplastic polymer, the polymer composition according to the invention, the polymer composite material according to the invention and the adhesive composition according to the invention is generally 0.1-15 % by weight, preferably 1-10% by weight relative to the total weight of the composition of microcapsules.

[0104] The invention also concerns a microcapsule having a cross-linked polymeric shell encapsulating an active ingredient wherein the polymeric shell comprises elastomeric units. Such as e.g polyene units, in particular polybutadiene units.

[0105] The plurality of microcapsules according to this aspect are obtainable, for example by a, preferably continuous, process which comprises (a) providing a double emulsion comprising droplets of at least one active ingredient (C1) dispersed in a polymerizable composition C2, said droplets being dispersed in a composition C3, the compositions C2 and C3 being immiscible with each other; (b) inducing a controlled shear rate in said double emulsion to provide a mixed double emulsion (C4) ; and (c) irradiating the mixed double emulsion (C4) such that the degree of conversion of polymerizable groups is at least 90% to prepare the microcapsules.to prepare the microcapsules . In a particular aspect, said polymerizable composition C2 may be photopolymerizable and contain at least 1% wt. preferably equal to or greater than 5% by weight relative to the total weight of composition C2 of a photoinitiator.

[0106] To the extent that there would be a conflict or inconsistency between any document incorporated by reference and the present description, the present description shall take precedence.

[0107] The examples here after are intended to illustrate the invention without however limiting it.

[0108] EXAMPLES

[0109] Preparation of double emulsion

[0110] The composition C1 is silicon oil. The composition C2 is a mixture of oligomers and monomers and a photoinitiator, whose precise compositions are delineated in Table 1. The composition C3 is a solution of cellulose derivatives at 8 % by weight and a rheological modifier.

[0111] A mechanical stirrer (IKA 2000) equipped with a 3 cm diameter deflocculating stirring propeller is used to carry out all the emulsification steps.

[0112] Step a). the composition Cl is added dropwise to the composition C2 at a ratio C1:C2=40:60 by weight with stirring at 2000 rpm with a mechanical stirrer (IKA 2000) equipped with a stirring anchor for 5 min.

[0113] Step b): the emulsion (E1) obtained in the preceding step is added to the composition C3 at a ratio E I C3=10:90 by weight. with stirring

[0114] Step c): The emulsion (E2) thus obtained is stirred at 2000 rpm with mechanical stirrer (IKA 2000) with a 3 cm diameter deflocculating stirring propeller for 2 min.

[0115] Step d): the monodisperse emulsion (E3) thus obtained is irradiated for 2 minutes using a UV light source (Dymax LightBox ECE 2000) having a maximum light intensity at a 385 nm wavelength to allow cross-linking of the capsules. The plurality of microcapsules is then recovered and dried to powder form.

[0116] Determination of rupture stress

[0117] Preparation of the samples for nanoindentation: a diluted slurry of microcapsules is cast on a glass side, which is then left to evaporate to enable the adhesion of the microcapsules to the glass slide. The device is equipped with a microscope enabling to position the indentor relative to the microcapsule to study and to measure its size.

[0118] Nanoindentation was then performed on the microcapsule to determine the rupture stress. An Anton Paar NHT3 nanoindenter is used with a flat-punch having a larger diameter than the capsule to be examined, e.g; 50 µm. The load rate was of 2 mN.min-1 for a maximal load of 3 mN. The rupture force of a given microcapsule corresponds to the inflection point of the displacement curve. The rupture stress is then calculated by dividing the rupture force through the projected contact area with the flat punch.

[0119] For each sample, nanoindentation was performed on 40 microcapsules having a size between 2 µm to 25 µm. The average rupture stress is determined from a series of 40 microcapsules.

[0120] ExampleComposition C2Core / shell ratio(wt. / wt.)Cross-linking density (mmol / g)Ratio rigid / flexiblemoietiesNumber of donors and acceptors hydrogen bonds% of rotatable bondsRupture stress (MPa)175% Ebecryl 4859 + 20% Genomer 1121M (acrylic acid ester) + 5% Photoinitiator30 / 701,271,086,6341,14 %238270 % Sartomer CN2295 (epoxidised soya bean oil acrylate) + 25 % HDDA+ 5 % Photoinitiator30 / 704,721,478,3862,65 %369370 % Bomar BR643 Difunctional Aliphatic Polybutadiene Urethane Acrylate Oligomer + 25 % HDDA+ 5 % Photoinitiator40 / 604,11,504,4271,29 %306470 % Sartomer CN2295 (epoxidised soya bean oil acrylate,) + 25 % HDDA + 5 % Photoinitiator40 / 604,721,478,3862,65 %121(Comp)185 % Sartomer CN111 epoxidised soya bean oil acrylate + 10 % HDDA+ 5 % Photoinitiator40 / 603,60,9717,0477,91 %24(Comp) 298,5% Sartomer CN111 epoxidised soya bean oil acrylate + 1,5% Photoinitiator30 / 7030,6521,0078,82 %62(Comp) 375% Sartomer CN109 (modified epoxy acrylate) + 24% Genomer 1121M + 1% Photoinitiator30 / 700,992,236,6736,14 %71

[0121] Genomer 1121M contains 0.44% flexible moieties. HDDA contains 1.35% flexible moieties therefore the addition of HDDA as a monomer increases the flexibility of the cross-linked polymeric shell.

[0122] As counter examples, microcapsules having a composition C2 of CN111 or CN109 exhibited relatively weak resistance. It is believed that this is due to a high content of flexible moieties associated to a high crosslinking density and a short average molecular weight as CN111, giving them a soft behaviour or a too rigid structure but poorly crosslinked and with a short average molecular weight as CN109, thereby giving fragile microcapsules.

Claims

A plurality of microcapsules having a cross-linked polymeric shell encapsulating an active ingredient wherein said microcapsules have a mean diameter between 1 and 30 µm, preferably from 2 to 25 µm and said plurality displaying an average rupture stress determined by nanoindentation, of at least 80 MPa.The plurality of microcapsules according to claim 1 wherein the rupture force of individual microcapsules determined by submitting a number of microcapsules, preferably from 25 to 40 microcapsules to nanoindentation in a Anton Paar NHT3 nanoindenter used with a flat-punch having a larger diameter than the individual microcapsule which is submitted to nanoindentation, and the rupture stress of the individual microcapsule is calculated by dividing the rupture force through the contact area A between the surface of the flat punch and the surface of the microcapsule at rupture. said contact area A being given by the formula given by the formula A=(4 / 3xπ x(d / 2)3) / z wherein d is the microcapsule diameter and z is the microcapsule height at rupture,The plurality of microcapsules according to claim 1 or 2 wherein the mean diameter is determined using a Mastersizer 3000 equipped with a hydro SV measuring cell.The plurality of microcapsules according to any of the preceding claims wherein the mean diameter is the size distribution by volume D50Voldetermined by light scattering, whereby 50% of the microcapsules have a smaller diameter than the mean diameter.TThe plurality of microcapsules according to any of the preceding claims wherein the rupture stress is equal to or greater than 120MPa.The plurality of microcapsules according to any of the preceding claims wherein the rupture stress is equal to or greater than 350MPa.The plurality of microcapsules according to any of the preceding claims, wherein the cross-linked polymeric shell has a degree of cross-linking determined by observation of the reduction of FTIR absorption of a characteristic FTIR absorption band of a cross-linkable precursor group of the cross-linking bond equal to or greater than 90 mole % and less than 99 mole % relative to the initial molar amount of cross-linkable precursor group present in the cross-linked polymeric shell.The plurality of microcapsules according to any of the preceding claims, wherein the cross-linked polymeric shell has a cross-linking density higher than 1 mmole per g of cross-linked polymeric shell, preferably equal.to or greater than 2.0 mmole per g of cross-linked polymeric shell.The plurality of microcapsules according to any of the preceding claims, wherein the crosslinked polymeric shell comprises or consists of rigid moieties and flexible moieties.The plurality of microcapsules according to claim 9 wherein the flexible moieties are selected from an alkyl chain in a polymer backbone chain, alkyl pendant chains, alkyl pendant groups, ether groups, in particular alkyl(poly)ether chains and amine groups, in particular alkyl(poly)amines.The plurality of microcapsules according to claim 9 or 10 wherein the rigid moieties are selected from carbocycles, heterocycles, ester groups, amide groups, urethane groups, tetra substituted carbons, internal double bonds, internal triple bonds and carbon chains having at most 5 catenary atoms.The plurality of microcapsules according to any of the preceding claims wherein the number ratio of rigid moieties to flexible moieties in the crosslinked polymeric shell is from 0,3 to 2 preferably from 0,6 to 1,8, most preferably from 1 to 1,6.The plurality of microcapsules according any of the preceding claims wherein the sum of acceptor and donor hydrogen bond groups of the crosslinked polymeric shell is from 0 to 12, preferably from 2 to 9.The plurality of microcapsules according to any of the preceding claims wherein the % ratio of rotatable bonds over the total number of bonds of the crosslinked polymeric shell is between 30 and 75%.A plurality of microcapsules having a cross-linked polymeric shell encapsulating an active ingredient wherein(a) the sum of acceptor and donor of hydrogen bond groups of the cross-linked polymeric shell is between 0 and 10, preferably between 2 and 9.and / or•(b) the percentage of rotatable bonds over the total number of bonds of the cross-linked polymeric shell is between 30-75%and / or•(c) the ratio of rigid to flexible bonds in the cross-linked polymeric shell is from 0,3 to 2 preferably from 0,6 to 1,8, most preferably from 1 to 1,6.The plurality of microcapsules according to claim 15 wherein the percentage of rotatable bonds over the total number of bonds of the cross-linked polymeric shell is between 30 - 75%.The plurality of microcapsules according to claim 16 wherein the percentage of rotatable bonds over the total number of bonds of the cross-linked polymeric shell is from 35 to 50%.The plurality of microcapsules according to claim 15 or 16, wherein the ratio of rigid to flexible bonds in the cross-linked polymeric shell is from greater than 2 to 3, particularly from 2.1 to 3.The plurality of microcapsules according to any of the preceding claims, wherein rigid and flexible moieties are incorporated into the shell through the use of an oligomer containing both rigid and flexible moieties.The plurality of microcapsules according to claim 19 wherein the oligomer containing both rigid and flexible moieties is selected from an epoxidized soy bean acrylate and polybutadiene urethane acrylates.The plurality of microcapsules according to anyone of claims 9 to 20 wherein the rigid moieties are selected from carbocycles, heterocycles, ester groups, amide groups, urethane groups, tetra substituted carbons, internal double bonds, internal triple bonds and carbon chains having at most 5 catenary atoms.The plurality of microcapsules according to anyone of claims 9 to 21.wherein the rigid moiety is incorporated into the shell through use of a monomer having at least 3, preferably 3, 4, 5 or 6 crosslinkable groups preferably (meth)acrylate and epoxy groups.The plurality of microcapsules according to anyone of claims 9 to 22 wherein the rigid moiety is incorporated into the shell through use of a oligomer selected from (meth)-acrylated oligomers.The plurality of microcapsules according to anyone of claims 9 to 23, wherein the flexible moieties are selected from carbon chains having at least 6 catenary atoms said catenary atoms optionally being partially replaced by oxygen and nitrogen.The plurality of microcapsules according to according to anyone of claims 9 to 24 wherein the flexible moiety is incorporated into the shell through use of a monomer having 1 or 2 crosslinkable groups in particular selected from (meth)acrylate groups and epoxy groups.The plurality of microcapsules according to according to anyone of claims 9 to 25. wherein the flexible moiety is incorporated into the shell through use of an oligomer selected from 1,6-hexanediol diacrylate.The plurality of microcapsules according to anyone of claims 9 to 26 wherein the flexible moiety is incorporated into the shell in a quantity of 20% molar relative to the total molarity of the constituents of the cross-linked polymeric shell.The plurality of microcapsules according to anyone of claims 9 to 27 wherein the flexible moiety is incorporated into the shell in a quantity of between 40 % and 60 % of molar relative to the total molarity of the constituents of the cross-linked polymeric shell.The plurality of microcapsules according to anyone of claims 9 to 28 wherein the molar quantity of aliphatic cycles is below 10% relative to the total molarity of the constituents of the cross-linked polymeric shell.The plurality of microcapsules according to any of the preceding claims wherein the microcapsules have a mean diameter of from 5 to 20 micrometer and a wall thickness from 0.5 to 3 micrometer, preferably from 1 to 2 micrometer. The plurality of microcapsules according to any of the preceding claims which is monodisperse.The plurality of microcapsules according to any of the preceding claims, wherein the pores on the shell surface of the microcapsules have an average diameter smaller than 1nm, determined by BET surface analysis. The plurality of microcapsules according to any of the preceding claims, wherein the crosslinked polymeric shell comprises or consists of at least one polymer selected from polyethers, polyesters, polyurethanes, polyureas, polyethylene glycols, polypropylene glycols, polyamides, polyacetals, polyimides, polyolefins, polysulfides, and polydimethylsiloxanes, said polymers bearing at least one reactive function selected from the group consisting of acrylate; methacrylate; vinyl ether; N-vinyl ether; mercaptoester; thiolen; siloxane; epoxy; oxetane; urethane; isocyanate; and peroxide.The plurality of microcapsules according to claim 33, wherein the crosslinked polymeric shell comprises or consists of at least one polymer selected from aliphatic epoxidized poly acrylates, e.g. soy bean oil acrylates, bisphenol A based epoxy acrylates, glyceryl propoxy triacrylates, difunctional polyester acrylate oligomers, aliphatic polyester based urethane dimethacrylates or diacrylates and amine modified polyether acrylates.The plurality of microcapsules according to any of the preceding claims, which has a core / shell (wt. / wt.) ratio of equal to or greater than 20 / 80, preferably equal to or greater than 30 / 70, more preferably equal to or greater than 40 / 60.The plurality of microcapsules according to any of the preceding claims, wherein the crosslinked polymeric shell is essentially free of nitrile functional groups.The plurality of microcapsules according to any of the preceding claims, which further comprises a dispersant.The plurality of microcapsules according to any of the preceding claims, wherein the active ingredient is a solid at 25°C.The plurality of microcapsules according to any of the preceding claims, wherein the active ingredient is a liquid at 25°C at a pressure of 1013,25 kPa. The plurality of microcapsules according to any of the preceding claims, wherein the active ingredient is selected from a catalyst, a UV absorber, a lubricant and a flame retardant, a pigment, an agrochemical compound, and a liquid crystal material.The plurality of microcapsules according to any of the preceding claims, wherein the active ingredient is selected from the group consisting of a curing agent, a latent accelerator of curing of an epoxy resin, and polyurethane catalysts.The plurality of microcapsules according to claim 41, wherein the latent accelerator is selected from amine latent accelerators, in particular polyamine latent accelerators.The plurality of microcapsules according to claim 41, wherein the polyurethane catalyst is an amine polyurethane catalysts, for example aliphatic, alicyclic and bicyclic compounds having at least one tertiary amino group.The plurality of microcapsules according to claim 43, wherein the amine polyurethane catalyst is selected from diazabicycloundecene (DBU) 1,6-Bis-(N,N-dimethylamino)-n-hexane, (N,N-dimethylamino)cyclohexane, 2-(N,N-dimethylamino)ethanol, N-methylmorpholine, dimorpholinodiethylether, dimethylaminoethoxyethanol and triethylenediamine. The plurality of microcapsules according to any of the preceding claims, wherein the active ingredient does not consist of a foaming agent.The plurality of microcapsules according to any of the preceding claims, wherein the active ingredient is a lubricant.The plurality of microcapsules according to any of the preceding claims, which is obtainable by a process which comprises (a) providing a double emulsion comprising droplets of at least one active ingredient (C1) dispersed in a photopolymerizable composition C2, said droplets being dispersed in a composition C3, the compositions C2 and C3 being immiscible with each other; (b) inducing a controlled shear rate in said double emulsion to provide a mixed double emulsion (C4) ; and (c) irradiating the mixed double emulsion (C4) , such that the degree of conversion of photopolymerizable groups is at least 90% to prepare the microcapsules.The plurality of microcapsules according to claim 47, wherein said photopolymerizable composition contains at least 4% wt. preferably equal to or greater than 5% by weight relative to the total weight of composition C2 of a photoinitiator.The plurality of microcapsules according to claim 48, wherein said photoinitiator contains at least two radicals.A polymer composition comprising the plurality of microcapsules according to any of the preceding claims.A microcapsule having a cross-linked polymeric shell encapsulating an active ingredient wherein the polymeric shell comprises elastomeric units preferably polyene units, in particular polybutadiene units.Use of the plurality of microcapsules according to any of claims 1 to 49 or of the microcapsules according to claim 51, for the supply of an active ingredient to a polymerization process or to a polymer processing process.Use according to claim 52, for the production of a thermoset polymer.Use according to claim 49, for the production of a molded, extruded or cast thermoplastic article.Use according to claim 52, for the production of a compression molded or an injection molded thermoplastic article.A premix for manufacturing a thermoset polymer, comprising the plurality of microcapsules according to anyone of claims 1 to 49.A premix according to claim 56, which comprises an epoxy resin.The premix according to claim 57, wherein the active ingredient is a latent accelerator of curing of the epoxy resin.The premix according to claim 57 or 58, which comprises from 85 wt.% to 99.9 wt.% of epoxy resin and from 0.1.wt.% to 15 wt.% of microcapsules.The premix according to claim 57 or 58, which comprises from 75 wt.% to 89.9 wt.% of epoxy resin and from 0.1.wt.% to 15 wt.% of microcapsules and up to 10% of a polymer additive preferably selected from fillers, pigments and blowing agents.The premix according to claim 56, which comprises an isocyanate resin.The premix according to claim 61, which comprises from 85 wt.% to 99.9 wt.% of isocyanate resin and from 0.1.wt.% to 15 wt.% of microcapsules.The premix according to claim 61, which comprises from 75 wt.% to 89.9 wt.% of isocyanate and from 0.1.wt.% to 15 wt.% of microcapsules and up to 10% of a polymer additive preferably selected from fillers, pigments and blowing agents.The premix according to anyone of claims 61 to 63, wherein the active ingredient is a polyurethane catalyst, preferably in accordance with claim 43 or 44.A mixture comprising a thermoplastic polymer and the plurality of microcapsules according to anyone of claims 1 to 49. A polymer composite material comprising the plurality of microcapsules according to anyone of claims 1 to 49. The polymer composite material according to claim 66, which is a prepreg material.An adhesive composition comprising the plurality of microcapsules according to anyone of claims 1 to 49. Use of the plurality of microcapsules according to claim 46, to enhance the wear resistance or the scratch resistance of a polymeric surface.Use of the plurality of microcapsules according to claim 46, to enhance the water resistance of a polymeric surface.Use of the plurality of microcapsules according to claim 46, for the self-lubrication of an elastomer.Use according to claim 46, wherein the lubricant is a polyol ester.