A METHOD OF PRODUCING AN ARTICLE COMPRISING AN INTERPENETRATING POLYMER NETWORK (IPN) AND AN ARTICLE COMPRISING AN IPN

TECHNICAL FIELD

The present invention relates to a method of producing an article comprising an interpenetrating polymer network (IPN) as well as an article comprising an IPN optionally being produced according to the method of the invention.

BACKGROUND ART

IPNs have been known for more than 40 years. IPNs are defined as macromolecular assemblies comprising two or more polymers wherein at least one is in the form of a network, the polymers are at least partially interlaced on a molecular scale but not covalently bonded to each other.

Because there is no chemical bond between the networks (or polymer/network), each network may retain its individual properties independently of its individual proportion in the blend. As a result an improvement can be attained in properties such as mechanical strength, impact resistance, and toughness and other. There are two main types of

IPNs, viz semi-IPN where at least one component is not in network form, and full IPN where all species are in network form. The term "IPN" as used herein comprises both semi-IPNs and full IPNs.

US 2002/01222946 relates to a process of producing an IPN comprising: providing a liquid mixture comprising silicone oligomers and silsesquioxane oligomers; and curing the liquid mixture to form a composition of first and second polymers, the first polymer comprising the silsesquioxane oligomers cross-linked by siloxane bonds and the second polymer comprising a cross- linked silicone network formed in part from the silicone oligomers.

US 20030000028 provides a colorant for use in tinting contact lenses in which the binding polymer used is capable of forming an interpenetrating

polymer network with the lens material. When the colorants of the invention are applied to uncured lens material that is subsequently cured, the binding polymer forms an interpenetrating polymer network with the lens material embedding the colorant within the lens material, resulting in a stable, tinted lens.

Several other methods for producing IPNs are known. The methods e.g. include simultaneously forming and cross-linking the polymer networks in the presence of each other. Other methods include forming a first network and thereafter swelling this network with monomers, cross-linking agents and optionally initiator/catalyst with or without solvents where after this monomer may form a polymer and optionally a network, e.g. as disclosed in US 2002/0052448 and WO 98/40425 Even though some transparent IPN products have been obtained using these methods, it has heretofore not been possible to obtain an essentially transparent product i.e. a product which is essentially free of different domains of refractive indexes which result in deflections of light rays within the material.

Applicant's co-pending US 2006/0148985 relates to a method of producing an IPN by forming a first polymer substrate and thereafter swelling this substrate with monomers in the presence of CO ₂ in supercritical or liquid state. The monomers may be induced to form a polymer and optionally cross-linked to form a network.

SUMMARY OF INVENTION

The inventors of the present invention have surprisingly found a method of producing an IPN comprising article which is essentially transparent.

This new method thus provides the possibility of obtaining essentially transparent articles of new materials and combinations of materials. Heretofore articles made of IPN rubbers have had a very poor transparency due to difference between the refractive index of the substrate and the refractive index of the interpenetrating polymer.

As it will appear from the following description the method provides the possibility of producing new articles with desired properties which simultaneously are essentially transparent.

The method and the article of the invention are defined in the claims.

The method of the invention comprises

i) providing an essentially transparent rubber substrate having a refractive index n ₀ and being shaped to provide the desired shape of the article, and applying it in a reaction chamber,

ii) providing a least one first monomer having a refractive index ni in homopolymerized condition wherein ni is lower than no,

iii) providing a least one second monomer having a refractive index n ₂ in homopolymerized condition, wherein n ₂ is higher than n ₀ ,

iv) exposing said rubber substrate in said reaction chamber to said first and said second monomers to impregnate said rubber substrate with said monomers in the presence of an impregnation solvent comprising CO ₂ under conditions wherein said CO ₂ is in its liquid or supercritical state and

v) co-polymerizing said first and said second monomers to form an IPN,

wherein said at least one first monomer and said at least one second monomer are selected such that n and r ₂ independently of each other are 3 or less, where

n = (Qi/Q ₂ ) exp [-e1(e1-e2)] and

r ₂ = (Q2/Q1) exp [-e2(e2-e1 )] and

Qi= denotes the intrinsic reactivity of the first monomer,

Q ₂ = denotes the intrinsic reactivity of the second monomer, and e1= denotes the polarity of the first monomer, and e2= denotes the polarity of the second monomer.

The values Q and e for the various monomers can be found in reference books, such as Polymer Handbook, by Brandrup, J. and Immergut, E. H. and Grulke, E.A. Wiley-lnterscience, John Wiley and Sons, Fourth Edition, 1999 USA (ISBN 0-471-47936-5).

The interpenetrating copolymer may e.g. be cross-linked as explained further below.

The term essentially transparent means that visible light of at least one wavelength can pass through the material. The rubber substrate as well as the produced article may preferably be essentially transparent to visible light in the wavelengths from about 400 to about 700 nm. The article produced is preferably essentially free of internal refractive borderlines, i.e. borderlines with different refractive index on the respective sides of the borderline.

According to the invention it has been found that by providing an substrate with refractive index no, and an interpenetrating copolymer made from at least one first and at least one second monomer, wherein the at least one first monomer has a refractive index ni in homopolymerized condition, where ni is lower than n ₀ , and the least one second monomer has a refractive index n ₂ in homopolymerized condition, where n ₂ is higher than no, and wherein said first and second monomers will react with each other to form an interpenetrating copolymer, an essentially transparent IPN article can be provided.

The values n and r ₂ indicate to which degree the first and the second monomers are likely to react with each other. In case there are two or more first monomers, an ^ value is determined for each first monomer in relation to at least one second monomer, and each r^ value may preferably be within the value specified. In case there is to or more second monomers an r ₂ value

is determined for each second monomer in relation to at least one first monomer, and each r ₂ value may preferably be within the value specified.

In one embodiment wherein η and r ₂ may preferably independently of each other be 2.5 or less, preferably Ti and r ₂ independently of each other are 2 or less, more preferably ^^ and r ₂ independently of each other are 1.5 or less, even more preferably π and r ₂ independently of each other are 1 or less.

In general it can be said that the lower the η and r ₂ , the more the first and the second monomers will react with each other to form a copolymer.

When ri and r ₂ independently of each other are 1 or less, an alternating or random copolymer with a relatively homogenous structure will normally be produced.

In one embodiment wherein n and r ₂ independently of each other are 0.7 or less, preferably ri and r ₂ independently of each other are 0.5 or less, more preferably n and r ₂ independently of each other are 0.3 or less.

In one embodiment wherein η and r ₂ independently of each other are 0.1 or less, a true alternating copolymer will normally be produced.

In one embodiment at least one of the T ₁ and r ₂ is 1.3 or less, preferably at least one of the η and r ₂ is 1 or less, at least one of the π and r ₂ is 0.5 or less.

In one embodiment wherein n and r ₂ independently of each other are 0.7 or more and 1.3 or less, e.g. 1.0 or less, a random copolymer will normally be produced.

In one embodiment it is preferred that the absolute value of n - r ₂ is 1 or less, more preferably 0.5 or less, such as 0.2 or less. It has thus been found that when the difference between T ₁ and r ₂ is relatively small, the first and the second monomers are even more likely to react with each other.

The rubber substrate may preferably have a refractive index n ₀ between 1.33 and 1.75, such as between 1.335 and 1.65, such as between 1.4 and 1.5.

An interval stated using the term "between" e.g. between 1 and 2, means herein that the values in the upper and lower end of the interval - in this example 1 and 2 - are included in the interval.

In order to provide an article which is essentially transparent to the major part of visible light, each of the first and the second monomers should preferably in homopolymerized condition have a refractive index which is relatively close to the refractive index no of the rubber substrate.

Therefore in one embodiment the at least one first monomer in homopolymerized condition has a refractive index which is up to 0.3 lower than n ₀ , such as up to 0.2 lower than n ₀ , such as between 0.01 and 0.2 lower than n ₀ .

An interval stated using the term "up to an upper value" e.g. up to 0.3, means herein that the upper value - in this example 0.3 - is included in the interval.

In one embodiment the at least one second monomer in homopolymerized condition has a refractive index n ₂ which is up to 0.3 higher than no, such as up to 0.2 higher than n ₀ , such as between 0.01 and 0.2 higher than no.

The relative molar amount of the first and the second monomers also influences the transparency of the produced article. In order to further improve the transparency of the article the rubber substrate may preferably be exposed to the first and the second monomers in the reaction chamber, where the molar amount Mi of the at least one first monomer relative to the molar amount M ₂ of the at least one second monomer introduced into the reaction chamber prior to and/or during the impregnation is between 1 :100 and 100:1, such as between 1:50 and 50:1, such as between 1:10 and 10:1, such as 1:1.

In order to obtain a particular transparent article the rubber substrate may in one embodiment be exposed to the first and the second monomers in the reaction chamber, wherein the molar amount Mi of the at least one first monomer relative to the molar amount M ₂ of the at least one second monomer introduced into said reaction chamber is selected to fulfill the conditions

abs(n ₁ - N/n ₂ -N)=(M ₁ ZM ₂ ) * ((r ₁ *M ₁ )+M ₂ )/(M ₁ +(r ₂ *M ₂ ))

wherein n _o +O.5 > N > n ₀ -0.5

In one embodiment N is n _o +O.4 or less, such as n _o +O.3 or less, such as no+0.2 or less, such as n _o +O.1 or less, such as about no.

In one embodiment N is n _o -O.4 or more, such as n _o -O.3 or more, such as n ₀ - 0.2 or more, such as no-0.1 or more.

In a preferred embodiment n _o +O.2 > N > n ₀ -0.2, more preferably n _o +O.1 > N > no -0.1.

It has been found that the volume fractions φi and φ ₂ of the respective monomers can be used in determine the resulting refractive index n _p of the interpenetrating copolymer polymerized from said monomers according to the following:

Where Np is the refractive index of the resulting interpenetrating copolymer, ni is the refractive index of the first monomer in homopolymerized condition, n ₂ is the refractive index of the second monomer in homopolymerized condition, φi is the volume fraction of the first monomer, φ ₂ is the volume fraction of the second monomer, and

φi ⁺ φ2 = 1

Thereby the relative amount of monomers for obtaining an interpenetrating copolymer can be found in a very simple manner.

In one preferred embodiment the monomers and the fractions of the monomers are selected such that the refractive index n _p of the interpenetrating copolymer is

N ₀ -0.1 < n _p < n _o +0.1 , where n ₀ is the refractive index of the rubber substrate.

In an even more preferred embodiment no-0.05 < n _p < no+0.05.

In principle there is no upper limit to the amount of monomers introduced into the reaction chamber. The amount of monomer impregnated into the rubber substrate depends on several things, including the type of monomers, the impregnation conditions and time and the concentration of monomers in the reaction chamber. In one embodiment the total amount of monomers introduced to the reaction chamber is up to 500 % by weight of the rubber substrate, such as up to 200%, such as up to 100%, such as up to 10% by weight of the rubber substrate.

The rubber substrate may be any kind of transparent rubber substrate e.g. selected from the group consisting of silicone rubber, styrene-butadiene rubber (SBR), urethane rubber, latex and thermoplastic elastomers (TPE).

A useful styrene-butadiene rubber is of a material as described in US Patent 6849690.

In one embodiment the rubber substrate comprises at least 10 %, such as at least 20 %, such as at least 40 %, such as at least 60 % by weight of polymer having a backbone consisting of Si and O atoms or consisting of Si atoms, said rubber substrate preferably comprising one or more polymers selected from the group consisting of poly(dimethyl siloxane), poly(methylphenyl siloxane), fluorosilicone rubber, silicone esters,

polysiloxanes, polysilanes, chlorosilanes, alkoxysilanes, aminosilanes, polysilanes polydialkylsiloxanes, polysiloxanes containing phenyl substituents, said polymers of the rubber substrate optionally being vinyl- functionalized and/or optionally being partially or fully fluohnated.

In a preferred embodiment the rubber substrate is a silicone substrate. The silicone substrate may e.g. be a silicone copolymer, or a grafted silicone e.g. grafted with HEMA. By grafting a silicone the refractive index may be modified to thereby obtain a preferred refractive index.

The rubber substrate may preferably be at least partially vulcanized, such as up to a vulcanization degree (cross-linking degree) of at least 10 %, such as at least 50 %, such as at least 80 % or wholly, such as at least 96 %, such as at least 97 %, such as at least 98 %.

The degree of vulcanization may depend on the type of rubber used and the article produced. The skilled person will for a given rubber and a given article in aim, be able to select a useful vulcanization degree.

The rubber substrate may e.g. be of a composite material or e.g. be a substrate of two or more elements fixed to each other e.g. by gluing or other well known methods, wherein at least one of the elements is of rubber. The rubber substrate may be pre-coated if desired e.g. using plasma deposition or wet chemical application, provided that the monomer still can be impregnated into the rubber substrate. The rubber substrate may additionally be subjected to heat treatment and/or cold tempering (e.g. ad described in WO06045320).

In one embodiment the rubber substrate comprises low molecular weight residuals, and the method further comprises extracting at least a part of the low molecular weight residuals from the rubber substrate prior to subjecting the rubber substrate to the monomers. The extraction may preferably be performed by subjecting the rubber substrate to a CO2 containing extraction solvent under conditions wherein CO ₂ is in its liquid or its supercritical state.

Low molecular weight residuals are herein defined as residuals which are in liquid state at 1 atm. and 50 ⁰ C.

The rubber substrate may be shaped using any method e.g. by use of stamping, extrusion, injection molding, calendaring, casting, cutting, pressing or a combination thereof.

In one embodiment the shaping is performed prior to the vulcanization. In one embodiment the shaping is performed after the vulcanization. In one embodiment the shaping is performed simultaneously with the vulcanization.

The monomers used may in principle be any monomers which are reactable with each other and fulfill the condition with respect to refractive index.

In one embodiment the monomer(s) is/are free radical polymerizable monomer(s). The monomer(s) may thus preferably comprise at least one C=C double bond or triple bond. In one embodiment the monomers(s) are ring opening polymerizable (β-lactones), or anionic (Urethanes).

In one embodiment the at least one monomer comprises one or more of the monomers selected from the group consisting of silicone containing monomers, such as silanes, e.g. tetraethylorthosilicate or tetraethoxysilane (TEOS) or chloro- or alkoxy-functional silanes; olefins such as ethylene, propylene, n-vinyl pyrolidone (nVP), styrene; oxygen-, phenyl, amino and nitrogen-containing monomers, such as acrylic and methacrylic derivatives, e.g. acrylic esters, acrylic acids, methacrylic acid and -esters, alkyl and hydroxyalkyl acrylates and methacrylates; functionalized methacrylates such as 2-hydroxyethyl methacrylate (HEMA), glycerol monomethacrylate (GMMA), heptaflurobutyl acrylate (HFBA) ₁ 2-methacryloyloxyethyl phosphorylcholine (MPC) and [2-(methacryloyloxy)ethyl]-dimethyl-(3- sulfopropyl)-ammonium hydroxide (Betain); alkyl substituted acrylates and methacrylates such as methyl methacrylate (MMA), ethyl methacrylate (EMA), butyl methacrylate (BMA), dodecyl methacrylate (DMA); urethanes; mono- and di-functional alcohols; carboxylic acids; amines; isocyanates; epoxides; aromatic compounds such as aromatics carrying substituents such

as alky I groups and sulfonated aromatics, aromatic resins, imidazol and imidazol derivatives; pyrazoles; quaternary ammonium compounds; polyurethane prepolymers; epoxy resins; substituted β- and γ- lactones, lactic acid monomers; carbohydrides and fluorinated monomers.

In one embodiment the at least one monomer comprises one or more of the monomers selected from the group consisting of silicone containing monomers, such as silanes, e.g. tetraethylorthosilicate or tetraethoxysilane (TEOS) or chloro- or alkoxy-functional silanes; olefins such as ethylene, propylene, n-vinyl pyrolidone (nVP), styrene; oxygen-, phenyl, amino and nitrogen-containing monomers, such as acrylic and methacrylic derivatives, e.g. acrylic esters, acrylic acids, methacrylic acid and -esters, alkyl and hydroxyalkyl acrylates and methacrylates; functionalized methacrylates such as 2-hydroxyethyl methacrylate (HEMA), glycerol monomethacrylate (GMMA), heptaflurobutyl acrylate (HFBA), 2-methacryloyloxyethyl phosphorylcholine (MPC) and [2-(methacryloyloxy)ethyl]-dimethyl-(3- sulfopropyl)-ammonium hydroxide (Betain); alkyl substituted acrylates and methacrylates such as methyl methacrylate (MMA), ethyl methacrylate (EMA), butyl methacrylate (BMA), dodecyl methacrylate (DMA); urethanes; mono- and di-functional alcohols; carboxylic acids; amines; isocyanates; epoxides; aromatic compounds such as aromatics carrying substituents such as alkyl groups and sulfonated aromatics, aromatic resins, imidazol and imidazol derivatives; pyrazoles; quaternary ammonium compounds; polyurethane prepolymers; epoxy resins; substituted β- and γ- lactones, lactic acid monomers; carbohydrides and fluorinated monomers.

Functionalization of monomers e.g. of methacrylates may e.g. be performed prior or post to exposing the silicone rubber to the monomers.

In one embodiment the at least one first monomer is selected from the group of functionalized acrylates, preferably flouro-containing acrylates, such as heptaflourobutyl acrylate (HFBA).

In one embodiment the at least one second monomer is selected from the group of functionalized methacrylate, MPC, GMMA and Betain, preferably a

hydroxyalkyl methacrylate, more preferably 2-hydroxyethyl methacrylate (HEMA).

In a preferred embodiment the first and second monomers comprise heptaflourobutyl acrylate (HFBA) and 2-hydroxyethyl methacrylate (HEMA).

The first and second monomers may be introduced into the reaction chamber one-by-one, simultaneously, or partly overlapping with each other in time. The molar amount of the respective monomers may be equal or different from each other.

The introduction of said one or more monomers into the reaction chamber may take place before, during or after the CO2 and optional co-solvent is introduced.

In one embodiment at least one first monomer and said at least one second monomer are introduced one after the other.

The molar amount of the respective monomers may be equal or different from each other as explained above. The velocity of the feeding flow of the respective monomers may be equal or different. The velocity may e.g. vary during the feeding of the respective monomers.

The impregnation solvent may preferably comprise at least 10%, such as at least 30%, such as at least 50 %, such as at least 75 %, such as at least 90

% by weight of one or more of the components selected from the group consisting of CO2, and N ₂ O, and C1-C5 hydrocarbons. The impregnation solvent/polymerization solvent (meaning the impregnation solvent and the polymerization solvent independently of each other) may preferably comprise at least 50 %, such as at least 90 % of CO ₂ .

The impregnation solvent may further comprise a surfactant preferably selected from the group of anionic, cationic, non-ionic and amphoteric surfactants, said impregnation solvent preferably comprising up to 5 % by

weight, such as between 0.001-50 grams of surfactant per kg impregnation solvent.

The impregnation solvent may further comprise a co-solvent, preferably selected from water and the group consisting of organic solvents such as hexane, benzene, methanol, ethanol, chloroform, xylene, iso-butanol, propanol, acetone, ethylene glycol and mixtures thereof including mixtures of organic solvent(s) and water.

In one embodiment at least one radical starter (also called initiator) is incorporated into the rubber substrate, preferably by physical compounding, by swelling or impregnation in dissolved condition, or by co-impregnation with the monomers. The amount of radical starter should preferably be sufficient to initiate the polymerization and preferably be sufficient to ensure a sufficient molecular weight (Mw).

The molecular weight of the resulting interpenetrating copolymer can be adjusted by controlling the amount of added radical starter.

The skilled person will by a few experiments be able to select a useful amount of radical starter for a given polymerization process.

A large number of radical starters (often called free radical initiators) are available; they may be classified into four major types: 1) Peroxides and hydroperoxides, 2) azo compounds, 3) redox initiators, and 4) compounds that form radicals under the influence of light (photo initiators). Any of these types of radical starters may in principle be used.

In one embodiment the radical starter is selected from the group consisting of peroxides such as diethyl peroxydicarbonate (DEPDC), benzoyl peroxide (BPO) and dicumylperoxide; hydro-peroxide; azo-compounds such as azo- bis-iso-butyronitril (AIBN); redox initiators and photoinitiators such as benzoyl-based radical starters.

In one embodiment the radical starter is activated by heat, pressure, irradiation and/or chemical activation, the latter e.g. by providing an exotermic process.

If BPO is used as radical starter the polymerization should preferably be performed in the absence of CO ₂ because CO ₂ has been found to inhibit the decomposition of BPO and thereby inhibit the generation of free radical by the BPO.

In one embodiment at least one cross-linking agent is incorporated into the rubber substrate, preferably by physical compounding, by swelling or impregnation in dissolved condition, or by co-impregnation with the one or more monomers. A useful amount and type of cross-linking agent may easily be found by the skilled person. An example of cross-linking agent includes 1 ,3,5-Triallyl-1 ,3,5-triazine-2 ,4,6(1 H,3H,5H)-trione (TTT) and ethylene glycol dimethacrylate (EGDMA).

In general it is difficult to polymerize all of the impregnated monomers and most often the article will comprise non-polymerized monomers after termination of the polymerization. In one embodiment the method further comprises extracting at least a part of said non-polymerized monomers from the article after termination of polymerization: The extraction of non- polymerized monomers preferably is performed by subjecting the article to a CO ₂ containing extraction solvent under conditions wherein CO ₂ is in its liquid or its supercritical state e.g. as described in US WO06045320 and e.g. using an extraction solvent which independently of the composition of the impregnation solvent has a composition as described above for the impregnation solvent.

In one embodiment the polymerization of the at least one first monomer and the at least one second monomer is performed in a solvent, referred to as the polymerization solvent, wherein said monomers are partly or totally in dissolved state.

The polymerization solvent and the polymerization conditions may be as described in the co-pending patent applications filed simultaneously with the present patent application.

In one embodiment the polymerization solvent independently of the impregnation solvent used has a composition as described above for the impregnation solvent.

The polymerization of the monomers may be performed under conditions where a layer of polymer, preferably a copolymer is polymerized from said monomers onto at least one surface part of said rubber article. The layer of polymer may preferably be a copolymer essentially identical with the interpenetrating copolymer. In an alternative embodiment the layer of polymer is made from one or more monomers different from the combination of monomers providing the interpenetrating copolymer.

In one preferred embodiment the at least one first monomer and the at least one second monomer are polymerized to form an alternating copolymer.

In one preferred embodiment the at least one first monomer and the at least one second monomer are polymerized to form a random copolymer.

The depth of the interpenetrating copolymer into the rubber substrate depends largely on the type of monomers, the type and cross-linking degree of the rubber substrate and the impregnation condition, including the time of impregnation.

The rubber substrate may preferably be exposed to said monomers and said impregnation solvent for a sufficient time to impregnate a sufficient amount of said monomers into the rubber substrate for providing an interpenetrating copolymer from said monomers into a depth of at least 0.1 μm, preferably at least 1 μm of said rubber substrate upon polymerization of said monomers.

In one embodiment the rubber substrate is exposed to said monomers and said impregnation solvent under conditions where CO ₂ is in its liquid and/or

its supercritical state, and under conditions where polymerization of said at least monomers is not initiated and for a sufficient time to impregnate a sufficient amount of said monomers into said rubber substrate for providing an interpenetrating network from said monomers into a depth of at least 0.1 μm, preferably least 1 μm of said rubber substrate upon polymerization of said monomers.

The pressure and the temperature may be varied during the impregnation and/or during the polymerization.

Variation of the temperature and or pressure may e.g. be used to initiate the polymerization of the monomers.

In one embodiment the rubber substrate is exposed to the monomers and the impregnation solvent at a first pressure, followed by an increase in the pressure to thereby initiate polymerization of said monomers.

In one embodiment the rubber substrate is exposed to the monomers and the impregnation solvent at a first temperature, followed by an increase in the temperature to thereby initiate polymerization of said monomers.

In one embodiment the polymerization is initiated by heat e.g. in the presence of a polymerization solvent which may e.g. be in liquid and/or gas form.

In one embodiment the polymerization is initiated by irradiation e.g. using infrared irradiation (IR) or ultraviolet irradiation (UV). A laser may e.g. be used for performing the irradiation.

In one embodiment the rubber substrate is exposed to the monomers and the impregnation solvent where after the polymerization of said monomers is initiated using UV light.

In one embodiment the rubber substrate is exposed to the radical starter and the impregnation solvent (e.g. in the presence of monomers or preferably not

in the presence of monomers), where after the rubber substrate is exposed to monomers and said impregnation solvent while said radical starter is simultaneously being initiated using UV light.

In one embodiment the rubber substrate is exposed to the monomers and the impregnation solvent for a sufficient time to impregnate at least a part of the monomers, where after the impregnation solvent is removed and a polymerization solvent having another composition than the removed impregnation solvent is introduced and polymerization of said monomers is initiated. In this embodiment the polymerization solvent may likely be free of CO ₂ .

As mentioned above, the polymerization of said monomers may e.g. be performed under conditions where a layer of polymer/copolymer is polymerized from monomers onto at least one surface part of said polymer substrate. By polymerizing the monomers under conditions where at least a part of the monomer(s) is dissolved in the polymerizing solvent, such a layer of polymer/copolymer will be polymerized from said monomers onto at least one surface part of said polymer substrate.

The method may in principle be used to produce any type of rubber based article including implants, contact lens, medical articles, hearing aid elements, baby care articles and other elements for use in contact with humans and/or animals. Silicone rubber is accepted for use in close contact with the mammal body including contact with mammal mucous membranes. In particular when using silicone rubber as the rubber substrate, many new articles with desired properties may be produced.

The article of the method may accordingly comprise any rubber based article such as implants, contact lens, medical articles, hearing aid elements, baby care articles and other elements for use in contact with humans and/or animals.

In a preferred embodiment the article of the invention is a contact lens.

The article of the invention comprises a body formed of a rubber substrate and an interpenetrating copolymer. The article should preferably be essentially transparent. The interpenetrating copolymer may e.g. be a network of a non-rubber copolymer.

In one embodiment the interpenetrating copolymer is an alternating or a random copolymer from at least two monomers, preferably selected from the group consisting of silicone containing monomers, such as silanes, e.g. tetraethylorthosilicate or tetraethoxysilane (TEOS) or chloro- or alkoxy- functional silanes; olefins such as ethylene, propylene, n-vinyl pyrolidone (nVP), styrene; oxygen-, phenyl, amino and nitrogen-containing monomers, such as acrylic and methacrylic derivatives, e.g. acrylic esters, acrylic acids, methacrylic acid and -esters, alkyl and hydroxyalkyl acrylates and methacrylates; functionalized methacrylates such as 2-hydroxyethyl methacrylate (HEMA), glycerol monomethacrylate (GMMA), heptaflurobutyl acrylate (HFBA), 2-methacryloyloxyethyl phosphorylcholine (MPC) and [2- (methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide

(Betain); alkyl substituted acrylates and methacrylates such as methyl methacrylate (MMA), ethyl methacrylate (EMA), butyl methacrylate (BMA), dodecyl methacrylate (DMA); urethanes; mono- and di-functional alcohols; carboxylic acids; amines; isocyanates; epoxides; aromatic compounds such as aromatics carrying substituents such as alkyl groups and sulfonated aromatics, aromatic resins, imidazol and imidazol derivatives; pyrazoles; quaternary ammonium compounds; polyurethane prepolymers; epoxy resins; substituted β- and γ- lactones, lactic acid monomers; carbohydrides and fluorinated monomers.

In a preferred embodiment the interpenetrating copolymer is an alternating or a random copolymer from at least two monomers, preferably at least one first monomer selected from the group consisting of functionalized acrylates, preferably flour containing acrylates, such as heptaflourobutyl acrylate (HFBA) and at least one second monomer selected from the group consisting of functionalized methacrylate, , MPC, GMMA and Betain, preferably a hydroxyalkyl methacrylate, preferably 2-hydroxyethyl methacrylate (HEMA).

In one embodiment the body formed of a rubber substrate has a refractive index n ₀ as described above and said article has a refractive index n _A , wherein n ₀ - n _A is between -0.2 and 0.2, such as between -0.1 and 0.1, such as between -0.01 and 0.01.

In one embodiment the body formed of a rubber substrate has a refractive index n ₀ as described above and said interpenetrating copolymer has a refractive index n _P , wherein no - n _P is between -0.3 and 0.3, such as between -0.2 and 0.2, such as between -0.1 and 0.1, such as between -0.01 and 0.01.

The refractive index n _A of the article may preferably be between 1.33 and 1.75, such as between 1.335 and 1.65, such as between 1.4 and 1.5.

The interpenetrating copolymer is made from at least one first monomer and at least one second monomer, wherein the type and amounts of monomers are as described above.

Preferably the molar amount Mi of the at least one first monomer relative to the molar amount M2 of the at least one second monomer is such that

abs(n ₁ - N/n ₂ -N)=(M ₁ ZM ₂ ) ^* ((r ₁ ^* M ₁ )+M ₂ )/(M ₁ +(r ₂ ^* M ₂ ))

wherein n _o +O.5 > N > n ₀ -0.5, preferably n _o +O.2 > N > n ₀ -0.2.

The amount of interpenetrating copolymer relative to the amount of rubber substrate depends on the article produced and may e.g. comprise up to 200 % by weight.

In one embodiment the interpenetrating copolymer constitute up to about 80 % by weight of the total article, such as up to 50 % by weight, such as up to 10 % by weight.

The rubber substrate may preferably be as described above.

In one embodiment the article comprises a body formed of a rubber substrate and an interpenetrating copolymer and an outer surface layer on at least a part of its surface of a polymer, which preferably may be essentially identical with the interpenetrating polymer. Preferably the outer surface layer covers essentially the entire surface of said rubber substrate.

The outer surface layer may have any desired thickness, for example the outer surface layer has a thickness of at least 100 nm, such as at least 100 μm.

In one embodiment the interpenetrating copolymer and/or the surface layer has a more hydrophilic surface than an exposed surface of the rubber substrate.

An exposed surface of the rubber substrate means a surface of the rubber substrate within the article exposed by cutting through the article.

The invention also relates to a contact lens comprising a body formed of a silicone substrate and an interpenetrating copolymer, said contact lens being essentially transparent. The silicone substrate and the interpenetrating copolymer may be as described above.

EXAMPLES

Example 1

A silicone rubber substrate was provided and impregnated with monomer A and monomer B. The monomers A and B were polymerized.

Monomer A was selected to be 2-hydroxyethyl methacrylate.

Q, e and refractive index in homopolymerized condition for 2-hydroxyethyl methacrylate are as follows:

Refractive

Monomer A Q e index 2-hydroxyethyl methacrylate 1.78 -0 .39 1.5119

Monomer A was combined with monomers B

Q, e and refractive index in homopolymerized condition for monomers B is listed in table 1.

Monomer B Q e r1 r2 n

Heptafluorobutyl acrylate 0.96 1.34 0.053 0.944 1.367

2,3-dimethylbutadieπe 1.42 -0.43 0.784 1.273 1.525

2-bromoethyl methacrylate 1.18 0.74 0.287 0.971 1.5426

2-chloroethyl methacrylate 1.04 0.31 0.470 1.303 1.517

2-hydroxyethyl methacrylate 1.78 -0.39 1.000 1.000 1.5119

Acrolein 0.8 1.31 0.048 1.147 1.529

Acrylic acid 0.83 0.88 0.153 1.307 1.527

Acrylonitrile 0.48 1.23 0.037 1.971 1.52

Benzyl methacrylate 0.88 0.35 0.382 1.516 1.568

Butyl acrylate 0.38 0.85 0.074 2.888 1.4631

Ethyl acrylate 0.41 0.55 0.137 3.009 1.4685

Ethyl methacrylate 0.76 0.17 0.388 1.883 1.485 lsobutyl methacrylate 0.82 0.27 0.385 1.678 1.477 lsoprene 1.99 -0.55 1.024 0.952 1.521 lsopropyl methacrylate 0.97 0.1 0.519 1.516 1.4728

Methacrylonitrile 0.86 0.68 0.233 1.364 1.52

Methyl acrylate 0.45 0.64 0.131 2.647 1.472

Methyl methacrylate 0.78 0.4 0.319 1.677 1.4893 o-chlorostyrene 2.66 1.57 0.069 0.312 1.6098

Phenyl methacrylate 1.25 0.79 0.276 0.899 1.5706 p-methoxystyrene 1.53 -1.4 0.209 1.725 1.5967

Styrene 1 -0.8 0.405 2.089 1.59

Table 1

In comparative examples not according to the invention, monomer A was combined with monomer C.

Q, e and refractive index in homopolymerized condition for monomer C are listed in table 2.

Monomer C Q e r1 r2 n Tetrafluoroethylene 0.032 1.63 0.001 25.301 1.35 Diallyl phthalate 0.031 -0.26 0.018 54.581 1.572 Ethyl acrylate 0.41 0.55 0.137 3.009 1.4685 Ethyl methacrylate 0.76 0.17 0.388 1.883 1.485 Ethylene 0.016 0.05 0.009 93.708 1.51 Propylene 0.009 -1.69 0.001 328.371 1.4735 Vinyl acetate 0.026 -0.88 0.009 82.878 1.4665 Vinyl benzoate 0.03 -0.89 0.011 72.108 1.5775 Vinyl butyl ether 0.038 -1.5 0.004 72.218 1.4563 Vinyl chloride 0.056 0.16 0.029 25.649 1.54 Vinyl chloroacetate 0.039 -1.61 0.003 73.450 1.512 Vinyl dodecyl ether 0.041 -1.69 0.003 72.081 1.464 Vinyl ethyl ether 0.018 -1.8 0.001 171.382 1.454 Vinyl formate 0.043 -1.19 0.009 56.552 1.4757 Vinyl isobutyl ether 0.03 -1.27 0.006 83.627 1.4507 Vinyl octyl ether 0.02 -1.57 0.002 141.011 1.4613 Vinyl phenyl sulfide 0.33 -0.99 0.102 6.816 1.6568 Vinylidene chloride 0.31 0.34 0.136 4.319 1.6

Example 2

Rubber substrate:

Discs with a radius of 5.0 mm were punched out of a 1.00 mm thick sheet of Elastosil LR 3003/10 silicone rubber supplied by Wacker Silicones (Germany). The discs were used as substrate material for producing the interpenetrating polymer networks. All discs were extracted in SCCO2 to remove low molecular weight residuals, before they were used as substrate material.

Monomers:

98 % 2-hydroxyethyl methacrylate (HEMA) with 200 ppm monomethyl ether hydroquinone as inhibitor supplied by Acros Organics (MB, Belgium) was purified by distillation at reduced pressure, and the fraction at 67 ⁰ C and 3.5 mbar was collected and stored under an argon atmosphere at 5 ⁰ C. 97 % 1H,1H-heptafluorobutyl acrylate supplied by ABCR (Karlsruhe, Germany) was stored at 5 ⁰ C and used as received.

Radical starter:

Diethyl peroxydicarbonate (DEPDC) was synthesized from 98 % Ethyl chloroformat (supplied by Fluka Chemie (Buchs CH)) and 30 % H ₂ O ₂ and NaOH pellets (Supplied by Bie & Berntsen (Rødovre, DK) and stored in hexane (0.15 M) under an argon atmosphere at -18 ⁰ C. 98 %.

Cross linking agent:

1 ,3,5-triallyl-i ,3 _> 5-triazine-2,4,6- (1 H,3H,5H)-trione (TTT) supplied by Fluka Chemie (Germany) was used as received as cross-linking agent and stored under an argon atmosphere at 5 ⁰ C.

Solvent

CO ₂ N48 was supplied by Air Liquid Denmark A/S (Denmark) and used as received.

96% ethanol (EtOH) and 99.9% ethylene glycol were used as co-solvent.

A 16 ml stainless steel high-pressure reactor was used for the experiments. A Thar P-50 electrical driven pressure pump from That Design Inc. USA, was applied for ensuring the operation pressure. The pump was equipped with a heat exchanger and was supplied with cooling water at 5 ⁰ C.

In a typical experiment a number of extracted discs of silicone (m ~ 150 mg/disc), 200 μl TTT are placed in the reactor, with 1-2 ml co-solvent. Then the reactor is closed and pressurized to about 50 bars at 25°C. The monomer is injected into the reactor (0.64 ml_ HEMA and 0.64 ml_ HFBA). Then the reactor is heated to 75°C and CO ₂ is added to ensure a pressure of 200 bars. After an impregnation time of 2 hours 0.05 ml_ 0.2 M DEPDC in hexane mixture is injected together with CO ₂ to ensure a pressure of 300 bars. After the polymerization has ended the pressure is slowly released and the reactor is cooled. The produced IPN is cleaned in EtOH to remove excess polymer material.

The treated discs with monomer A and B will be transparent and very clear since the material will be essentially free of internal deflections of light rays.

The interpenetrating copolymer is a random or an alternating copolymer and has a refractive index which is very close to the refractive index of the rubber substrate.

The treated discs with monomer A and C will be transparent or translucent. However they will not be completely clear since they will have internal differences in refractive indexes which result in deflections of light rays. The interpenetrating polymer is a block copolymer or in the form of two or more homopolymers.