WO1984000968A1

WO1984000968A1 - Prostheses contact lenses and polymers therefor

Info

Publication number: WO1984000968A1
Application number: PCT/GB1983/000212
Authority: WO
Inventors: Maurice John Whitford
Original assignee: Contact Lens Mfg Ltd
Priority date: 1982-08-27
Filing date: 1983-08-30
Publication date: 1984-03-15
Also published as: IT8322671A0; EP0116611A1; AU1940883A; IT1194381B; DK214084D0; DK214084A

Abstract

A polymer for making a prosthesis or contact lens, which polymer is prepared by polymerizing a vinyl siloxane of general formula (I), 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, which may be same as or different from each other, represents a C1-C5 alkyl group, a phenyl group, or -CH = CH2, with one or more comonomers, preferably a compound of the general formula (II), wherein each B, which may be the same as or different from each other, represents -OR1, R1 being a C1-C5 alkyl group or phenyl, s has a value of from 1 to 5, t has a value of from 1 to 5 and R2 is C1-C5 alkyl, hydrogen or another organo siloxy group as defined in the general formula (II). The invention also includes prostheses and contact lens made from such polymers.

Description

PROSTHESES CONTACT LENSES AND POLYMERS THEREFOR

This invention relates to prostheses, contact lenses, to polymer compositions for such prostheses and lenses and to methods for preparation of these compositions. U.S. Patent No. 3,808,178 discloses copolymer compositions for contact lenses which are prepared by copolymerizing particular polysiloxanylalkyl 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 need for oxygen-permeable polymer compositions with the potential of low surface wetting angle and which can be formulated to be hard and soft, eye-compatible and workable by conventional techniques.

Polysiloxanes containing vinyl groups in chain or terminally, have not been favoured for conventional 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 of the vinyl group is increased when adjoining a substituted silicon atom directly, so favouring an ionic over free radical reaction mechanism. Indeed, it has been thought that vinyl methyl siloxane cannot be homopolymerised under normal free radical polymerisation conditions. However activating groups separating the vinyl group and

0 silicon atom retain the normal free radical reactivity as with the siloxy acrylates, which are known as copolymers in the preparation of contact lenses. For this reason, the polymerisation of polysiloxanes containing vinyl-Si bonds has 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 (150°C) curing (U.S. Patents Nos. 2793223, 3819772 and 3969290), 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. 2865885), gums and elastomers (U.S.

Patent Nos. 3228741, 3341490, 3996187 and 3996189). 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 of the 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 of the present invention are of the general formula (I):

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, which may be same as or different from each other , represents a C₁ - C₅ alkyl group, a phenyl group, or - CH = CH₂.

It is to be understood that the repeating siloxane units of this prepolymer can repeat in a regular or irregular manner and that the order of the respective units may likewise be irregular.

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

-

Vinyl methyl siloxane prepolymer

although 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 copolymers with useful and controllable levels of oxygen permeability, hardness, transparency refractive index and wettability.

This is in direct contrast to the teaching of the prior art. For example in U.S. Patent No. 3203919, surface coatings for fibrous 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 repellent finish.

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

The polymer composition of the 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 such 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 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 acryiamlde hydroxy ethyl or propyl methacrylate and acrylate diethylene glycol 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 (II):

(

_L _. _ . wherein: each B, which may be the same as or different from each other, represents -OR₁, R₁ being a C₁ - C₅ alkyl group or phenyl, s has a value of from 1 to 5, t has a value of from 1 to 5 and R₂ is C₁ - C₅- alkyl, hydrogen or another organo siloxy group as defined in the general formula II. The monomer of the foregoing general formula II is preferably gamma methacryloxypropyl trimethoxy silane of the formula

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 of the vinyl siloxane, up to 60 parts by weight of a monomer of general formula II and the balance being a said monomer derived from acrylic or methacrylic acid although, to increase the rigidity of the polymerized composition, a cross-linking agent may be incorporated in amounts which may be as high as 20 or 30 parts by weight of the total composition. The cross-linking agent may be selected from one or more of 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. Δ-irradiation, electron beam irradiation etc. In the case of chemical polymerization a free radical initiator or catalyst is generally added and the mixture subjected to controlled heat, preferably in a stepwise manner to ensure orderly and efficient incorporation of the monomers into the polymer. The temperatures selected are preferably from 40-90° C, the polymerization being effected preferably for not less than 3 days. Conventional free radical polymerization initiators may be employed such as azobis buty-ronitrile. benzoyl peroxide, tertiarybutyl peroxypivalate chlorobenzyl peroxide, etc. The polymer can be cast into discs, rods or sheets for subsequent 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

X-irradiation, any suitable source may be employed, such as a Cobalt-60 source. The

-irradiation dosage is suitably from 2 to 5 Mega Rads.

Embodiments of the present invention will now be described by way 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 ingredients were 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 be 7 DK x 10^-11 at 20ºC where D^k has the following units:

(cm²/sec) (m10₂/ml x mmHg). Wetting angle was 62.3°.

EXAMPLE 2

VS 27.0 parts by weight

MEMOS 18 parts by weight cross-linking agent (Allylmethacrylate)

10 parts by weight MMA 45 parts by weight

The ingredients were thoroughly mixed and polymerization was effected, using 0.1% AZBN, in the same 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 D^k x 10^-11 at 34°C. The wetting angle was 66.5°. EXAMPLE 3

VS 20 parts by weight

MMA 50 parts by weight MEMOS 30 parts by weight

The ingredients were thoroughly mixed and polymerization effected by α-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^-11at 20ºC. Wetting angle was 64.5°. EXAMPLE 4

VS 20 parts by weight MEMOS 25 parts by weight

Cross-linking agent* 6 parts by weight MMA 49 parts by weight *The cross-linking agent was an 88: 12parts by weight mixture of allyl methacrylate and ethylene glycol dimethacrylate.

Polymerization was effected using a small percentage of AZBN, 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^-11 at 34°C.

EXAMPLE 5

VS 17.5 parts by weight MEMOS 22.5 parts by weight MMA 40 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 MMA 40 parts by weight

Cross-linking agent (allyl methacrylate) 10 parts by weight AZBN 0.1 part by weight. The resultant polymer was opaque, had a oxygen permeability of DK 31.5 and a water uptake of.1.2%.

EXAMPLE 7

A polymer was prepared according to the procedures of Example 1 employing a mixture as follows VS 27 parts by weight MMA 45 parts by weight Vinyl pyrrolidone 13 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 weight of AZBN and 10 parts by weight of allyl methacrylate as cross-linking agent. The resultant polymer was transparent with a refractive index of 1.45. I thad a hardness of 80.46 (shore D) and a water uptake of 0.672%. Wetting angle was 62° and DK 12.4.

EXAMPLE 9

A polymer was prepared exactly as in Example 8 but using ethyl methacrylate instead of methyl methacrylate and MEMOS instead of gamma methacryloxypropyl triethoxy silane. The resultant polymer was transparent, 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 polymer was prepared as in Example 1 using 7 parts by weight vinyl methyl siloxane, 18 parts of gamma methacryloxypropyl trimethoxy silane, 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%. DK was 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 bacteriologi cally inert, scratch resistant, machinable and polishable, hard or soft, transparent or opaque, wettable or not. Preferred polymers are hard and transparent with low wetting 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 permeability by virtue of 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 is finally to be noted that colouring matter can be introduced into the monomer mixtures in order that tinted contact lenses can be produced.

Claims

CLAIMS:

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

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, which may be same as or different from each other, represents a C₁ - C₅ alkyl group, a phenyl group, or -CH = CH₂, with one or more comonomers.

2. A polymer according to claim 1, wherein the vinyl siloxane comprises vinyl methyl siloxane.

3. A polymer according to claim 1, which is the result of polymerizing vinyl methyl siloxane with a derivative of an acrylic or methacrylic acid, or with 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 methacrylic comonomer and a silane of the following general formula II:

wherein: each B, which may be the same as or different from each other, represents -OR₁, R₁ being aC₁ - C₅ alkyl group or phenyl, s has a value of from 1 to 5,t has a value of from 1 to 5 and R₂ is C₁ - C₅ alkyl, hydrogen or another organo siloxy group as defined in the general formula II.

5. A polymer according to claim 3 or 4,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 methecrylate bυtyl acrylate and methacrylate amyl acrylate and methacrylate hexyl acrylate and methacrylate heptyl acrylate and methacrylate octyl acrylate and methacrylate

2-rethylhexyl 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 polymar according to claim 5, wherein the silane of general formula II comprises gamma methacryloxypropyl trimethoxy or triethoxy silane.

7. A polymer according to claim 5 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 II, the balance being essentially a said acrylic or methacrylic acid derivative, a cross-linking agent optionally being present.

8. A polymer according to claim 7, wherein a cross-linking agent is present, selected from one or more of divinyl tetramethyl disiloxane ethylene glycol dimethacrylate allyl methacrylate and pentaerylthritol tetraacrylate polyethylene glycol dimethacrylate triethoxy glycol dimethacrylate tetraacrylate glycol dimethacrylate divinyl benzene

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

10. A polymer according to claim 9, wherein free radical polymerization initiators comprises azobis butyronitrile, benzoyl peroxide, tertiarybutyl peroxypivalate or chlorobenzyl peroxide.

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

12. A polymer according to Claim 1 and substantially as hereinbefore described with reference to any one of the foregoing individual Examples 1 to 11.

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

14. A prosthesis composed of a polymer as claimed in any one of the preceding Claims.

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

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, which may be same as or different from each other, represents a C₁ - C₅ alkyl group or a phenyl group, with one or more comonomers.

16. A contact lens according to claim 15, composed of a polymer made 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 II, the balance being essentially a said acrylic or methacrylic acid derivative, a cross-linking agent optionally being present.