GB2127421A - Prostheses contact lenses and polymers therefor - Google Patents

Abstract

A polymer for making a prosthesis or contact lens, is prepared by co- polymerizing (A) a vinyl siloxane of the following general formula I: <IMAGE> wherein: m has a value of from 1 to 6, n can be from 0 to an integer preferably less than or equal to 6 and each A represents a C1-C5 alkyl group, a phenyl group, or -CH=CH2, with (B) one or more comonomers. Monomer (A) is suitably a vinyl methyl siloxane prepolymer and numerous comonomers (B) are exemplified.

Description

SPECIFICATION Prostheses contact lenses and polymers therefor This invention relates to prostheses, contact lenses, to polymer com positions for such prostheses and lenses and to methods for preparation ofthese compositions.

U.S. Patent No. 3,808,178 discloses copolymer compositions for contact lenses which are prepared by copolymerizing particularpolysiloxanylalkyl esters of acrylic or methacrylic acid with alkanol esters of acrylic or methacrylic acid. It is asserted that the polymers so prepared are suitable for contact lenses and that some of the polymers are inherently wettable by human tears although it may be necessary to improve their wettability by surface treatments of various sorts. There remains however a needforoxygen-permeable polymercompostions with the potential of low surface wetting angle and which can be fomulated to be hard and soft, eye-compatible and workable by conventional techniques.

Polysiloxanes containing vinyl groups in chain or terminally, have not been favouredforconventional free radical polymerisation through the double bond, and the prior art specifically remarks upon this when advocating the use of activated unsaturated groups.

This is because the polarity of the double bond ofthe vinyl group is increased when adjoining a substituted silicon atom directly, so favouring an ionic over free radical reaction mechanism. Indeed, it has been thoughtthatvinyl methyl siloxane cannot be homopolymerised under normal free radical polymerisation conditions. However activating groups

separating the vinyl group and silicon atom retain the normal free radical reactivity as with the siloxy acrylates, which are known as copolymers in the preparation of contact lenses. Forthis reason, the polymerisation of polysiloxanes containing vinyl-Si bonds as hitherto employed different catalyst types (e.g. chloroplatinic acid) which may enable other polymerisation modes to occur-- e.g. addition of silicon hydrides to vinyl siloxanes.

Other known methods of vinyl siloxane polymerisation entail high temperature (1 50"C) cur- ing (U.S. Patents Nos. 2 793 223,3 819 772 and 3969 290), which would not be suitable for organic co-monomers in the present invention.

Vinyl polysiloxanes have been used in the manufacture of silicone fluids as lubricants (U.S. Patent No.

2 865 885), gums and elastomers (U.S. Patent Nos.

3 228 741,3 341 490,3996 187 and 3 996 189).

Although such elastomers have been fabricated as contact lenses and biomedical devices, their lack of adequate strength and rigidity, combined with high hydrophobicity (poor wetting) are major disadvantages in a contact lens.

According to a first aspect ofthe present invention there is provided a prosthesis or contact lens which is composed of a polymer prepared by the polymerisation of a vinyl or aryl siloxane, with a co-monomer.

The present invention also embraces such a polymer for use in the preparation of a contact lens or prosthesis.

The vinyl alkyl/aryl siloxanes ofthe present invention are ofthe general formula (I):

wherein: m hasa valueoffrom 1 to 6, ncan be from 0 to an integer preferably less than or equal to 6 and each A, which may be same as or differentfrom each other, represents a C1-C5 alkyl group, a phenyl group, or-CH=CH2.

It isto be understood that the repeating siloxane units ofthis prepolymer can repeat in a regular our irregular manner and that the order of the respective units may likewise be irregular.

The preferred vinyl alkyl siloxane is vinyl methyl siloxane prepolymerwhich may be considered to have the following formula:

Vinyl methyl siloxane prepolymeralthough as supplied commercially it probably also contains other prepolymers including cyclics. The Applicants have employed vinyl methyl siloxane as commercially available.

Surprisingly, in the present invention, vinyl siloxanes can be co-polymerised with common and other organic (or semi-organic) monomers using moderate free radical polymerisation conditions (with preferred reaction time-temperatures stages) to yield copolymerswith useful and controllable levels of oxygen permeability, hardness, transparency refractive index and wettability.

This is in direct contrastto the teaching ofthe prior art. For example in U.S. Patent No.3203 919, surface coatingsforfibrous sheet fabrics, suedes and fabrics composed of copolymers of vinyl siloxanes with acrylic and other monomers are applied to the article as a liquid before curing to a water repellentfinish.

U.S. Patent No.3763081 discloses vinyl siloxane copolymers buttheir polymers also essentially contain imidestructures and are applied to the manufacture of composite (filled) materials and mouldings.

The polymer composition ofthe present invention may be a copolymer of such a vinyl alkyl siloxane of two or more different siloxanes such as vinyl alkyl siloxanes. Alternatively the composition may be a copolymer of a vinyl alkyl siloxane with one or more monomers derived from substituted or unsubstituted acrylic or methacrylic acid as esters or amides of these acids.

Examples of such monomers are: methyl acrylate and methacrylate ethyl acrylate and methacrylate propyl acrylate and methacrylate isopropyl acrylate and methacrylate butyl acrylate and methacrylate amyl acrylate and methacrylate hexyl acrylate and methacrylate heptyl acrylate and methacrylate . octal acrylate and methacrylate 2-ethylhexyl acrylate and methacrylate nonyl acrylate and methacrylate decyl acrylateand methacrylate undecyl acrylate and methacrylate lauryl acrylate and methacrylate cetyl acrylate and methacrylate octadecyl acrylate and methacrylate diacetone acrylamide hydroxy ethyl or propyl methacrylate and acrylate diethyleneglycol monomethacrylate phenyl acrylate and methacrylate The vinyl siloxanes employed in the present invention may also be copolymerized, in the presence or absence of acrylic or methacrylic monomers, with other monomers such as N-vinyl pyrrolidone or styrene and/or monomers having the following general formula (ll):

wherein:: each B, which may be the same as ordifferentfrom each other, represents-OR1, R1 being a C1-C5alkyl group orphenyl,shasavalue offrom 1 to 5, thasa value offrom 1 to 5 and R2 is C1-C5 alkyl, hydrogen or another organo siloxy group as defined in the general formula 11. The monomer oftheforegoing general formula II is preferably gamma methacryloxypropyl trimethoxysilane oftheformula

or gamma methacryloxypropyl triethoxy silane.

Preferred compositions are copolymers of such monomers with methyl methacrylate and vinyl methyl siloxane prepolymer.

Preferred monomer mixtures contain up to 30 parts by weight ofthe vinyl siloxane, up to 60 parts by weight of a monomer of general formu la 11 and the balance being a said monomer derived from acrylic or methacrylic acid although, to increase the rigidity ofthe polymerized composition, a cross-linking agent may be incorporated in amounts which may be as high as 20 or30 parts byweight ofthetotal composition.

The cross-linking agent may be selected from one ormoreof divinyl tetramethyl disiloxane ethylene glycol dimethacrylate allyl methacrylate and pentaerythritol tetraacrylate polyethylene glycol dimethacrylate triethoxy glycol dimethacrylate tetraacrylate glycol dimethacrylate divinyl benzene although any suitable cross-linking agent can be employed.

The compositions may be chemically polymerized or polymerized by electromagnetic irradiation, e.g.

y-irradiation, electron beam irradiation etc. In the case of chemical polymerization a free radical in itiator or catalyst is generally added and the mixture subjected to controlled heat, preferably in a stepwise mannerto ensure orderly and efficient incorporation of the monomers into the polymer. The temperatures selected are preferably from 40-90 C,the polymeriza tion being effected preferably for not less than 3 days.

Conventional free radical polymerization initiators may be employed such as azobis butyronitrile, benzoyl peroxide, tertiarybutyl peroxypivalatechlor- obenzyl peroxide, etc. The polymer can be cast into discs, rods orsheets forsubsequent machining or directly into a lens shaped configuration. When polishing lenses prepared from such formulations it is generally advisable to use a water based polish.

In the case of y-irradiation, any suitable source may be employed, such as a Cobalt-gO source. The y-irradiation dosage is suitablyfrom 2 to 5 Mega Rads.

Embodiments of the present invention will now be described byway of example only be reference to the following Examples. Wetting angle is measured by the sessile drop method, advancing.

EXAMPLE 1 Vinylmethylsiloxane prepolymer (VS): 15 parts by weight Methyl methacrylate (MMA): 60 parts by weight Gamma methacryloxypropyl trimethoxy silane (MEMOS): 25 parts by weight The above ingredientswere weighed, thoroughly mixed in the proportions stated and then filtered and degassed at room temperature. Up to 1 part by weight azobisbutyronitrile (AZBN) was added as a polymerization initiator and polymerization was effected at above ambient temperature with gentle stepwise heating to form a rod of polymer which was hard,transparent, had good wettability and a water uptake of approximately 1 part by weight. The oxygen permeability was ascertained by a polarographic electrode technique to be7 DK x 10-11 at 20"C where Dk has the following units: (cm2/sec) (m1 02/ml x mmHg). Wetting angle was 62.3 .

EXAMPLE2 VS 27.0 parts by weight MEMOS 18 parts by weight cross-linking agent (Allylmethacrylate) 10 parts by weight M MA45 parts by weight The ingredients were thoroughly mixed and polymerization was effected, using 0.1% AZBN, in the same save manner as in Example 1 to produce a rod of polymer which was transparent and machinable, had a water uptake of less than 1 part by weight and an oxygen permeability measured as in Example 1 of 24 DkX 10-11 at 340C. The wetting angle was 66.5 .

EXAMPLE 3 VS 20 parts by weight MMA 50 parts by weight MEMOS 30 parts by weight The ingredientswere thoroughly mixed and polymerization effected by y-irradiation using a Cobalt 60 source to provide a dose of 2-5 MegaRads.

A rod of polymer was formed which was hard, reasonably transparent and had an uptake of water of 1.75 parts by weight. The oxygen permeability, measured as hitherto, was 6.5 Dk x 10-11 at 20"C.

Wetting angle was 64.5 .

EXAMPLE 4 VS 20 parts by weight MEMOS 25 parts by weight Cross-linking agent* 6 parts byweight MMA49 parts by weight *The cross-linking agent was an 88:12 parts by weight mixture of allyl methacrylate and ethylene glycol dimethacrylate.

Polymerization was effected using a small percentage ofAZBN, in the manner of Example 1,to produce a rod of polymer which was fairly transparent, machinable, had a low water uptake and an oxygen permeability, measured as hitherto, of 15 Kd x 10-" at 34"C.

EXAMPLES VS 17.5 parts by weight MEMOS 22.5 parts by weight MMA40 parts by weight Divinyltetramethyl siloxane (cross-linking agent) 20 parts by weight The mixture was polymerized in the presence of AZBN, in the manner of Example 1, to produce a rod of opaque, soft polymer (hardness 60.4: shore D) and high oxygen permeability (DK, 21.6).

EXAMPLE 6 A polymer was prepared according to the procedures of Example 1 employing a mixture as follows VS 50 parts by weight MMA40 parts by weight Cross-linking agent(allyl methacrylate) 10 parts by weight AZBN0.1 partbyweight The resultant polymer was opaque, had a oxygen permeability of DK 31.5 and a water uptake of 1.2%.

EXAMPLE 7 Apolymerwas prepared according to the procedures of Example 1 employing a mixture as follows VS 27 parts by weight MMA45 parts by weight Vinyl pyrrolidone 18 parts by weight Allyl methacrylate 10 parts by weight AZBN 0.1 parts by weight The resultant polymer was translucent, machinable, had an oxygen permeability of DK 9.4 and a water uptake of 0.9%.Wetting angle was 76.5 .

EXAMPLE 8 Following the procedure of Example 1 a polymer was prepared from a mixture of 17.5 parts by weight of vinyl methyl siloxane, 54 parts by weight methyl methacrylate,22.5 parts by weight of gamma methacryloxypropyl triethoxy silane, 0.1 parts by weightofAZBN and 10 parts byweightofallyl methacrylate as cross-linking agent. The resultant polymer was transparent with a refractive index of 1.45. 1 thad a hardness of 80.46 (shore D) and a water uptake of 0.672%. Wetting angle was 62 and DK 12.4.

EXAMPLE9 A polymerwas prepared exactly as in Example 8 but using ethyl methacrylate instead of methyl methacrylate and MEMOS instead of gamma methacryloxypropyl triethoxy silane. The resultant polymerwastransparent, machinable, had a water uptake of 0.92% and an oxygen permeability of 20.1 DK.

EXAMPLE 10 A polymer was prepared exactly as in Example 8 but using 24 and 30 parts by weight respectively of ethyl and methyl methacrylates instead of methyl methacrylate alone. The resultant polymer was transparent, machinable had a water uptake of 1.1 and a DK of 13.2.

EXAMPLE 11 A polymerwas prepared as in Example 1 using 7 parts by weight vinyl methyl siloxane, 18 parts of gamma methacryloxypropyltrimethoxysilane, 15 parts by weight hexyl methacrylate, 30 parts by weight methyl methacrylate, 10 parts by weight allyl methacrylate and 0.1 part by weight AZBN. The resultant polymer was transparent, machinable and had a water uptake of 1.34%. DKwas 8.7 and the wetting angle was 70 .

It will be appreciated that the present invention provides a polymer whose characteristics such as transparency, hardness (or softness), wettability and oxygen permeability can be tailored to meet a particular requirement. Specifically the present invention provides polymers for contact lenses which can be eye-compatible, relatively bacteriologically inert, scratch resistant, machinable and polishable, hard or soft, transparent or opaque, wettable or not.

Preferred polymers are hard and transparent with lowwetting angles and high oxygen permeability.

In the preferred polymers of the present invention it is believed that the vinyl alkyl siloxane monomer contributes to the oxygen permeabilitybyvirtueof the high flexibility of the Si-O bond and low hindrance siloxy group rotation that the acrylic or methacrylic monomer, if present, contributes to the optical and cutting qualities and that the monomer of general formula II, if present, contributes to monomer solution/polymerization compatibility,to oxygen permeability and to lens wettability (and hence to wearer comfort).

It isfinallyto be noted that colouring matter can be introduced into the monomer mixtures in orderthat tinted contact lenses can be produced.

Claims (16)

1. A polymer for making a prosthesis or contact lens, which polymer is prepared by polymerizing a vinyl siloxane ofthefollowing general formula I:

wherein: m hasa value of from 1 to 6, n can befrom 0 to an integer preferably less than or equal to 6 and each A, which may be same as or differentfrom each other, represents a C1-C5 alkyl group, a phenyl group, or-CH=CH2, with one or more comonomers.

2. Apolymeraccordingto claim 1,whereinthe vinyl siloxane comprises vinyl methyl siloxane.

3. Apolymeraccording to claim 1, which is the resultofpolymerizing vinyl methyl siloxanewith a derivative of an acrylic or methacrylic acid, orwith N-vinyl pyrrolidone or with styrene.

4. A polymer according to claim 3, which is the result of polymerizing with the vinyl siloxane a derivative of acrylic or methacryliccomonomer and a silaneofthefollowing general formula ll:

wherein: each B, which may bethe same as or different from each other, represents-OR1, R1 being a -C1-C5 alkyl group or phenyl, s has a value of from I to 5, thas a value of from 1 to Sand 5 is C1-C5 alkyl, hydrogen or another organo siloxy group as defined in the general formula li.

5. A polymer according to claim 3 or4, wherein the acrylic or methacrylic acid derivative is selected from the group consisting of: methyl acrylate and methacrylate ethyl acrylate and methacrylate propyl acrylate and methacrylate isopropyl acrylate and methacrylate butyl acrylate and methacrylate amyl acrylate and methacrylate hexyl acrylate and methacrylate heptyl acrylate and methacrylate octyl acrylate and methacrylate 2-ethylhexyl acrylate and methacrylate nonyl acrylate and methacrylate decyl acrylate and methacrylate undecyl acrylate and methacrylate lauryl acrylate and methacrylate cetyl acrylate and methacrylate octadecyl acrylate and methacrylate diacetone acrylamide hydroxy ethyl or propyl methacrylate and acrylate diethylene glycol monomethacrylate phenylacrylate and methacrylate.

6. A polymer according to claim 5, wherein the silane of general formula comprises gamma metharyloxypropyl trimethoxy or triethoxy silane.

7. A polymer according to claim or 6, which is produced by polymerizing up to 30 parts by weight of the vinyl siloxane and up to 60 parts by weight of the monomer of general formula 11, the balance being essentially a said acrylic or methacrylic acid derivative, a cross-linking agent optionally being present.

8. Apolymeraccording to claim 7, wherein a cross-linking agent is present, selected from one or moreof divinyl tetramethyl disiloxane ethylene glycol dimethacrylate allyl methacrylate and pentaerylthritol tetraacrylate polyethlene glycol dimethacrylate triethoxy glycol dimethacrylate tetraacrylate glycol dimethacrylate divinyl benzene

9. A polymer according to any preceding claim, which has been chemically polymerized bya free radical polymerization initiator.

10. A polymer according to claimS, wherein free radical polymerization initiators comprises azobis butyronitrile, benzoyl peroxide, tertirybutyl peroxypivalate orchlorobenzyl peroxide.

11. A polymer according to any of Claims 1 to 8, which has been polymerized by y-irradiation.

12. Apolymeraccording to Claim 1 andsubstan- tially as hereinbefore described with reference to any oneoftheforegoing individual Examples 1 toll.

13. A contact lens composed of a polymer as claimed in any one of the preceding Claims.

14. Aprosthesiscomposedofa polymeras claimed in any one ofthe preceding Claims.

15. A contact lens composed of a polymer made by polymerizing a vinyl siloxane of the following general formula l:

wherein: m has a value of from 1 to 6, n can be from 0 to an integerpreferably lessthan orequal tossand each A, which may be same as ordifferentfrom each other, represents a C15 alkyl group ora phenyl group, with one or more comonomers.

16. A contact lens according to claim 15, composed of a polymer made by polymerizing upto 30 parts by weight ofthe vinyl siloxane and up to 60 parts by weight ofthe monomer of general formula II, the balance being essentially a said acrylic or methacrylic acid derivative, a cross-linking agent optionally being present.