Abstract:
According to the invention contact lenses are formed of unsaturated, multifunctional, organosiloxanes alone or mixed with monofunctional organosilanes and in some cases a hardening agent such as methyl methacrylate, hydrophilic monomer wetting agents, and itaconate hydrophilic and hardening agents. In the preferred embodiment, an additional hydrophilic cross-linking agent is used and the multifunctional organosiloxane is less than 50% of the organosiloxane used. The multifunctional organosiloxane adds higher impact strength and reduces brittleness, probably due to greater cross-linking density in the final product and retains the desirable properties of silicone-containing materials for use in contact lenses.

Description:
RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 06/583,151 filed Feb. 24, 1984, now abandoned, which is a continuation-in-part of application Ser. No. 501,293, filed June 3, 1983, now U.S. Pat. No. 4,604,479, which is a divisional of application Ser. No. 327,279, filed 12/4/81, now U.S. Pat. No. 4,424,328, issued Jan. 3, 1984. 
    
    
     BACKGROUND OF THE INVENTION 
     Soft contact lenses can be divided into two basic types, water absorptive and non-water absorptive. The water absorptive lenses, commonly referred to as &#34;hydrogel lenses&#34;, are generally prepared from 2-hydroxyethyl methacrylate (HEMA) or copolymers with HEMA as the major component. High water content lenses have also been produced from vinylpyrrolidone. Non-water absorptive soft contact lenses are produced from silicone rubber or like materials. Such soft contact lenses can have one or more of the following disadvantages: poor durability, less visual acuity than hard lenses, poor oxygen permeability, and/or ease of bacterial contamination. 
     Hard contact lenses produced from polymethyl methacrylate (PMMA) have been known in the art for many years and offer the advantages of optical clarity, dimensional stability and durability. Although PMMA has been the standard of the hard contact lens industry, it has at least two drawbacks. Because PMMA is marginally hydrophilic a lens wearer may experience discomfort as a result of a foreign body reaction. Secondly, oxygen gas transport through PMMA contact lenses is extremely low which dictates that the lenses cannot be worn continuously for an extended period of time. Since the cornea receives its oxygen directly from the atmosphere the PMMA lens wearer often experiences corneal swelling and irritation due to prolonged oxygen deprivation. 
     Within the past ten years commercial cellulose acetate butyrate (CAB) has been utilized in an attempt to provide a hard contact lens that will transport oxygen. Although CAB exhibits modest oxygen permeability it lacks other essential qualities necessary for a contact lens material. The scratch or mar resistance of CAB contact lenses is poor which may be a reflection of the relative softness of CAB when compared to PMMA. Additionally, CAB lenses are often dimensionally unstable. 
     More recently, siloxane containing copolymers have been introduced as oxygen gas permeable hard contact lens materials. These polymeric compositions are generally prepared by copolymerizing methyl methacrylate with a siloxanyl alkyl ester of methacrylic acid. Contact lenses containing substantial amounts of organosiloxane groups tend to be hydrophobic. Attempts to impart hydrophilic properties to such systems include the incorporation of a wetting agent and treatment of the lens surfaces. Incorporation of a wetting agent can improve the wettability of the lens but may also render the lens translucent when used in excessive amounts. Contact lenses containing such wetting agents can be tolerated by the wearer but tend to accumulate proteinaceous matter from the tear fluid. This results in decreased transparency of the lens and wearer discomfort. Surface treatment of the lens affords a wettable surface but can lack permanence. Any scratches or adjustments made on such lenses exposes the hydrophobic bulk material. Repeated surface treatment is then necessary which can be inconvenient. 
     The contact lens field has long known the advantages of silicone polymers for use in contact lenses. Poly(dimethylsiloxane) polymers are transparent and highly permeable to oxygen, although use of these polymers in contact lenses can present difficulties in the fabrication and finishing of lenses because of the rubbery nature of the polymers. Contact lenses produced from poly(dimethylsiloxane) are often inherently hydrophobic and often must be surface treated to render the surfaces wettable by tears. 
     It&#39;s known that the use of a methacrylate monomer containing a silicone moiety can be copolymerized with the standard monomer utilized in conventional hard contact lenses, i.e., methyl methacrylate, to obtain a copolymer of varying hardness values depending upon the ratio of hard and soft monomers employed. Thus, some attempts have been made in the art to produce hard oxygen-permeable contact lenses. For example, U.S. Pat. No. 3,808,178 discloses a copolymer of methyl methacrylate with a siloxanyl alkyl ester of methacrylic acid. The use of special wetting agents and cross-linking agents are also taught in U.S. Pat. No. 3,808,178. 
     In U.S. Pat. No. 4,152,508 the use of an itaconate ester copolymerized with a siloxanyl alkyl ester of methacrylic acid is disclosed. The siloxanyl alkyl ester provides for high permeability and the itaconate ester gives increased rigidity, hardness and some degree of wettability. In addition, specific cross-linking agents and hydrophilic monomers are incorporated which provide dimensional stability and wettability to contact lenses generated therefrom. 
     The compositions disclosed in U.S. Pat. Nos. 4,216,303 and 4,242,483 are branched siloxanyl alkyl esters of methacrylic acid essentially as suggested by the prior patents. 
     U.S. Pat. Nos. 4,153,641 and 4,189,546 teach the use of monomeric polysiloxanes end capped with activated, unsaturated groups. By varying the type and amount of comonomer as well as the moiety both hard and soft polymeric compositions are said to be possible. α,ωBis (4-methacryloxybutyl) polydimethylsiloxane is disclosed in which the poly(organosiloxane) moiety varies from about 0 to 800 units in length. For a hard contact lens the poly(organosiloxane) moiety should be of a rather short length, perhaps 0 to 10 units long, to avoid incompatibility in the final composition due to phase separation. Therefore, when comparing the monomeric polysiloxanes disclosed in both U.S. Pat. Nos. 4,153,641 and 4,189,546 with siloxanyl alkyl esters of methacrylic acid disclosed in U.S. Pat. Nos. 3,808,178 and 4,152,508, on the basis of utility in gas permeable hard contact lens compositions, similarities are noted. Whereas the siloxanyl alkyl esters of methacrylic acid disclosed in U.S. Pat. Nos. 3,808,178 and 4,152,508 are monomers, that is, contain one polymerizable unsaturated group, the monomeric polysiloxanes disclosed in U.S. Pat. Nos. 4,153,641 and 4,189,546 contain two such polymerizable unsaturated groups. 
     U.S. Pat. Nos. 4,306,042 and 4,414,375 disclose oxygen permeable contact lens materials comprising copolymers of multifunctional siloxanyl alkyl esters. These patents do not in any way recognize significant advantages to be obtained by the use of multifunctional organosiloxanes in combination with monofunctional siloxanes combined with the use of hydrophilic cross-linkers to form contact lens materials having outstanding properties when formed into contact lenses. U.S. Pat. No. 4,306,042 does not disclose a significant amount of multifunctional organosiloxane while U.S. Pat. No. 4,414,375 does not suggest the combination of organosiloxanes wherein the advantageous properties of the multifunctional material can be combined with the monofunctional material along with suitable cross-linking agents outside of the siloxane groupings. 
     SUMMARY OF THE INVENTION 
     It is an important object of this invention to provide novel unsaturated, multifunctional organosiloxane materials useful in forming contact lenses alone or in combination with other organic materials. 
     Another object of this invention is to provide unsaturated, multifunctional organosiloxanes in the form of contact lenses which siloxanes can be used alone or in combination with other organic materials. 
     A further object of this invention is to provide unsaturated, multifunctional organosiloxanes for use in combination with monofunctional organosiloxanes with or without other organic materials to form novel and improved contact lenses. 
     An important object of this invention is to provide an improved contact lens material utilizing a monofunctional organosiloxane in combination with unsaturated, multifunctional organosiloxanes and an additional non-siloxane, hydrophilic cross-linking agent. 
     An additional object of this invention is to provide contact lenses in accordance with this invention which are oxygen-permeable, dimensionally stable, hydrophilic and of good optical transparency. 
     Still another object of this invention is to provide contact lenses in accordance with the preceding objects wherein outstanding hard oxygen-permeable lenses are formed having good impact strength with reduced brittleness as compared to prior art organosiloxane-containing contact lenses. 
     According to the invention a contact lens is formed of an unsaturated multifunctional organosilane having the formula ##STR1## WHEREIN: Y&#39; is an unsaturated polymerizable group, 
     X&#39; is a divalent hydrocarbon having from 0 to 10 carbons, 
     Y is an unsaturated polymerizable group or hydrogen, 
     X is a divalent hydrocarbon having from 1 to 10 carbon atoms, or phenylene, 
     A is selected from the class consisting of straight chain, branched chain, or cyclic alkyl groups having 1 to 5 carbon atoms, phenyl groups and &#34;Z&#34; groups, 
     Z is a group selected from the following: 
     trimethyl siloxy 
     pentamethyl disiloxanyl 
     heptamethyl trisiloxanyl 
     nonamethyl tetrasiloxanyl 
     bis(trimethylsiloxy)methyl siloxanyl 
     Tris(trimethylsiloxy) siloxanyl 
     &#34;a&#34; is an integer from 0 to 10. The total of &#34;a&#34; values is at least 2, 
     &#34;n&#34; is an integer from 0 to about 10, and each of said X, X&#39;, Y, Y&#39;, a, A and Z groups being the same or different. 
     Preferably the organosiloxane is selected from the class consisting of 1,3-Bis(γ-methacryloxy propyl)-1,1,3,3 tetra(trimethylsiloxy)disiloxane, 1,3-Bis(γ-methacryloxypropyl)-1,1,3,3 tetra[Bis(trimethylsiloxy)methyl siloxanyl]disiloxane, 1,3-Bis(γ-methacryloxy propyl)-1,1,3,3 tetra(pentamethyldisiloxanyl) disiloxane, 1,7-Bis(γ-methacryloxypropyl)-1,1,3,3,5,5,7,7-octa(trimethylsiloxy)tetrasiloxane, 1,3-Bis(γ-methacryloxymethyl)-1,1,3,3 tetra(trimethylsiloxy)disiloxane, tetra [γ-methacryloxypropyl dimethylsiloxy]silane, 1,7-Bis(γ-methacryloxypropyl)-1,1,7,7-tetra(pentamethyl disiloxanyl)-3,3,5,5,-tetra(trimethyl siloxy)tetrasiloxane, Tris(γ-methacryloxypropyl tetramethyl disiloxanyl)methyl silane. 
     The following new compositions which are multifunctional organosilanes having properties particularly useful as contact lenses have been provided by the present invention: 
     1,7-Bis(γ-methacryloxypropyl)-1,1,3,3,5,5,7,7-octa(trimethylsiloxy) tetrasiloxane 
     1,7-Bis(γ-methacryloxypropyl)-1,1,7,7-tetra(pentamethyl disiloxanyl)-3,3,5,5,-tetra(trimethylsiloxy)tetrasiloxane 
     Preferably the material used for forming the contact lens if not a multifunctional unsaturated organosiloxane substantially alone can be a combination of such organosiloxane as described above with a contact lens significant amount of monofunctional organosiloxane having the formula: ##STR2## WHEREIN: R is selected from the class consisting of methyl groups and hydrogen, 
     &#34;a&#34; is an integer from 1 to 4, 
     A is selected from the class consisting of straight chain, branched chain, or alkyl groups of from 1 to 5 carbon atoms, cyclohexyl groups, phenyl groups and Z groups, 
     Z is a group selected from trimethyl siloxy, pentamethyl disiloxanyl, heptamethyl trisiloxanyl, nonamethyl tetrasiloxanyl, bis(trimethylsiloxy) methyl siloxanyl, tris(trimethylsiloxy) siloxanyl, 
     &#34;b&#34; is an integer from 0 to 10, each &#34;b&#34;, &#34;A&#34; and Z may be the same or different, and the total of &#34;b&#34; values being at least 1. 
     Preferably contact lens compositions can comprise a multifunctional organosiloxane alone or mixed with a monofunctional monomer or mixtures thereof. Difunctional organosiloxanes are preferred. The mixture can have incorporated therein a wetting agent such as a hydrophilic monomer. Preferably a hardening agent such as methyl methacrylate is also incorporated and in the preferred embodiment, hydrophilic hardening agents such as itaconates are also incorporated. 
     Most preferably contact lens compositions have a multifunctional organosiloxane which is preferably difunctional organosiloxane in admixture with a monofunctional organosiloxane and with the mixture having incorporated therein wetting agents such as hydrophilic monomers, hardening agents such as methyl methacrylate and dimethyl itaconate and a non-siloxane hydrophilic cross-linker such as the polyethylene glycol dimethacrylates or diacrylates. Contact lens compositions made from such materials have particularly desirable properties including good oxygen permeability, dimensional stability, optical transparency and have desirable hydrophilic properties and strength without excessive brittleness. 
     It has now been found that often when prior art lenses of the type fabricated in accordance with U.S. Pat. 4,152,508 are formed, a small amount of multifunctional organosiloxane is mixed with the original monofunctional organosiloxane monomer. This mixture has been an unwanted result of ordinary manufacture of the monomer. It has now been found that higher amounts of multifunctional organosiloxane to monofunctional siloxane than previously present are highly desirable to increase impact resistance and hardness while still retaining other desirable contact lens properties. Preferably the multifunctional component is in the range of from 20% to 50% by weight of a mixture of multifunctional and monofunctional organosiloxanes combined with a hardening agent, a wetting agent and a hydrophilic cross-linking agent. 
     It is a feature of this invention that contact lenses made from the materials of this invention are preferably hard, but can be semi-hard or soft, oxygen-permeable contact lenses having good dimensional stability and high transparency. When multifunctional organosiloxanes are used along with monofunctional organosiloxanes in combination with hydrophilic cross-linking agents, they have particularly good impact and fracture strength, i.e., reduced brittleness. It is believed that a greater degree of cross-linking occurs when polymerizing multifunctional organosiloxanes along with monofunctional organosiloxanes in combination with a hydrophilic cross-linker, so that the final products have greater cross-link density than would be the case with monofunctional organosiloxanes alone. This increased impact strength with increased cross-link density is surprising. The contact lenses of this invention are easily fabricated and finished by conventional means, have excellent dimensional stability, are inherently wettable with suitable refractive index and have good light transmission properties. Such lenses are durable, have high oxygen gas permeability, are biocompatible with the eye, substantially non-hydrating, are chemically stable and have resistance to proteinaceous accumulation with reasonable scratch resistance. They can be worn safely and comfortably by users for extended periods of time while providing the wearer with good vision. This minimizes handling of the lenses and greatly improves anticipated life. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Contact lenses which derive their oxygen permeability from poly(organosiloxane) moieties require a substantial content of poly(organosiloxane) to provide sufficient oxygen transport to the cornea. 
     In general poly(organosiloxane) molecules tend to be incompatible in many compositions which include other monomers. For example, dissolving poly(dimethylsiloxane) in methyl methacrylate and polymerizing said solution will result in an opaque material unsuitable for contact lens use. 
     Prior art has demonstrated that short organosiloxane units chemically bonded to an unsaturated, polymerizable group provides a means of copolymerizing such organosiloxane monomers with other monomers to achieve a compatible, therefore, transparent material. 
     On the other hand, organosiloxane units containing only one unsaturated, polymerizable group often times will not provide a random copolymer when copolymerized with other monomers, particularly hydrophilic monomers. This situation leads to phase separation and therefore an opaque material. In certain cases the phase separation is not detectable visually but is evidenced in the physical properties of the material. This condition can provide a material that exhibits brittle behavior and a propensity to fracture. 
     The physical properties of highly cross-linked polymer prepared from dimethyl siloxane diacrylate oligomers has been known in the art. In general, microphase separation is suppressed as the amount of dimethylsiloxane groups in the prepolymer increases. This phenomenon is attributed to the absence of long organic sequences. Overall, the work of Katz J. Polym. Sci. Chem. Ed. 16(3) 597 (1978) teaches against the copolymerization of such reactive organosiloxane monomers since organic sequences form leading to phase separation. However, in a contact lens material it has been found desirable to include one or more comonomers to provide a proper balance of physical properties. 
     For contact lens applications it is therefore desirable to provide a random copolymer that contains a substantial amount of compatibilized organosiloxane units. The novel method disclosed herein utilizes branched organosiloxane structures containing multiple unsaturated, polymerizable groups. These materials, when copolymerized with other monomers provide compositions which are transparent, highly oxygen-permeable and durable. The random nature of the polymerization process is enhanced by the presence of multiple, unsaturated polymerizable groups. The compatibilization of the organosiloxane monomers disclosed is improved through the use of highly branched organosiloxane moieties. 
     This invention also demonstrates the effectiveness of balancing the cross-link density, in the final composition, through the use of a combination of an organosiloxane containing one unsaturated polymerizable group with an organosiloxane containing multiple unsaturated, polymerizable groups. Compositions of this type exhibit a combination of desirable contact lens properties not found in systems where only one of the organosiloxane monomers is present. Furthermore, the use of hydrophilic cross-linking agent in conjunction with the combination of an organosiloxane containing one unsaturated polymerizable group and an organosiloxane containing multiple unsaturated, polymerizable groups produces contact lenses with an unxpected balance of properties which includes hardness, fracture resistance and dimensional stability. Balancing of the mono and multi organosixolanes and use of hydrophilic cross-linking agents act to provide an outstanding contact lens which has the properties desired as set forth above. 
     Physical properties of the compositions disclosed in this invention can be varied through structural changes in the multifunctional organosiloxane component and/or by varying the type and percent of comonomer. 
     In one embodiment of this invention is provided oxygen transporting, transparent, inherently wettable contact lenses comprising a polymer made from an organosiloxane containing multiple, unsaturated polymerizable groups. 
     In another embodiment of this invention are provided polymeric compositions comprising an organosiloxane containing multiple, unsaturated polymerizable groups copolymerized with one or more monomers from the class of lower esters of acrylic, methacrylic and itaconic acid as well as styryl, allyl or vinyl monomers. These copolymers are permeable, transparent and durable which allows them to be usefully employed in bulk or shaped forms such as contact lenses. 
     The polymeric compositions of this invention are preferably prepared by means of conventional free radical polymerization techniques. The free radical initiator is incorporated in amounts of from 0.01 to 2.0% by weight of the entire composition, at reaction temperatures of from 25° C. to 125° C., to initiate and complete the polymerization. Conventional bulk polymerization procedures can be used to produce castings which can be machined and polished by conventional procedures to produce contact lenses. Alternatively, the polymerization may be carried out directly in a contact lens mold. 
     It is a feature of this invention that the multifunctional organosiloxane provides for high oxygen permeability while strength and biocompatibility are provided by other portions of the copolymer. The use of methacrylate or acrylate esters provide for strength and hardness (or resiliency). Incorporation of a hydrophilic monomer greatly increases the wettability of the material to achieve biocompatibility. 
     The novel compositions disclosed in this invention are prepared from an organosiloxane containing multiple, unsaturated polymerizable groups. Optical contact lenses are fabricated from polymerizates of these monomers preferably incorporating other comonomers to provide the proper balance of physical and chemical properties desired in a contact lens. Typically, the organosiloxane multifunctional monomers useful in this invention which can be formed into contact lenses alone or copolymerized with other organic components, have the following formula: ##STR3## WHEREIN: Y&#39; is an unsaturated polymerizable group, 
     X&#39; is a divalent hydrocarbon having from 0 to 10 carbons, 
     Y is an unsaturated polymerizable group or hydrogen, 
     X is a divalent hydrocarbon having from 1 to 10 carbon atoms, or phenylene, 
     A is selected from the class consisting of straight chain, branched chain, or cyclic alkyl groups having 1 to 5 carbon atoms, phenyl groups and &#34;Z&#34; groups, 
     Z is a group selected from the following: 
     trimethyl siloxy 
     pentamethyl disiloxanyl 
     heptamethyl trisiloxanyl 
     nonamethyl tetrasiloxanyl 
     bis(trimethylsiloxy)methyl siloxanyl 
     Tris(trimethylsiloxy) siloxanyl 
     It is understood that the examples given above should not limit the invention to methylsubstituted siloxanes since phenyl (substituted and unsubstituted), cyclohexyl and other groups are useful in this invention either alone or in combinations. In some cases, the hydrocarbon groups can be substituted with other atoms such as halogens if desired optical and physical properties are not impaired. Each &#34;X&#34;, &#34;X&#39;&#34;, &#34;Y&#34;, &#34;Y&#39;&#34;, &#34;A&#34; and &#34;Z&#34; group shown in the general structure may be the same or different. 
     &#34;a&#34; is an integer from 0 to 10. The total of &#34;a&#34; values is at least 2, 
     &#34;n&#34; is an integer from 0 to about 10. 
     Preferably, the unsaturated polymerizable group of Y and Y&#39; chosen from among 
     vinyl 
     methacryloxy 
     acryloxy 
     methacrylamido 
     acrylamido 
     styryl 
     allyl 
     Preferably the alkylene radical group of X and X&#39; is chosen from among: 
     methylene 
     ethylene 
     propylene 
     butylene 
     Preferbly &#34;A&#34; is chosen from the class of alkyl, cycloalkyl, aryl, aralkyl, alkaryl, haloaryl and halo substituted lower alkyl radicals. Representative examples include: 
     methyl 
     ethyl 
     propyl 
     butyl 
     cyclohexyl 
     phenyl 
     benzyl 
     phenethyl 
     tolyl 
     xylyl 
     chlorophenyl 
     fluorophenyl 
     fluoromethyl 
     fluoropropyl 
     trifluoropropyl 
     The &#34;A&#34; group can also be a &#34;Z&#34; group which, preferably, is chosen from among: 
     trimethyl siloxy 
     pentamethyl disiloxanyl 
     heptamethyl trisiloxanyl 
     nonamethyl tetra siloxanyl 
     bis(trimethylsiloxy)methyl siloxanyl 
     tris(trimethylsiloxy)siloxanyl 
     phenyl dimethyl siloxy 
     methyl diphenyl siloxy 
     phenyl tetra methyl disiloxanyl 
     The multifunctional organosiloxane monomers employed in this invention are prepared utilizing techniques widely known in the art. 
     Representative multifunctional organosiloxane monomers which could be utilized in this invention include: ##STR4## 
     It is another object of this invention to provide polymerizates of monomers which are multifunctional organosiloxanes copolymerized with other monomers. 
     The comonomers used along with the multifunctional organosiloxanes in lens compositions of this invention, can be any polymerizable monomer which is capable of undergoing free radical polymerization and enhances a desirable property such as machinability, durability and biocompatibility. A combination of such comonomers can be used. 
     Illustration of comonomers which can be usefully employed in accordance with this invention are given below. 
     Preferably the comonomers can be hardening or softening agents such as an ester of a C 1  -C 21  monohydric or polyhydric alkanol or phenol and an acid selected from the class consisting essentially of acrylic and methacrylic acid. A hydrophilic hardening agent such as an itaconate mono- or di- ester is preferably used in addition. 
     The derivatives of acrylic, methacrylic and itaconic acid such as 
     methyl 
     ethyl 
     propyl 
     n-butyl 
     isopropyl 
     hexyl 
     hepyl 
     cyclohexyl 
     2-ethylhexyl 
     ethoxyethyl 
     butoxyethyl 
     2-hydroxyethyl 
     2- or 3-hydroxypropyl 
     3-methoxy-2-hydroxypropyl 
     tetrahydrofurfuryl 
     aryl 
     allyl 
     glycidoxy 
     are useful. 
     Other comonomers may include N-vinylcarbazole, N-vinylpyrrolidone, hydroxy naphthyl methacrylate, styryls, such as styrene, methylstyrene, methoxy styrene and acetoxy styrene. 
     Allylic monomers, such as diallyl diglycol dicarbonate, diallyl phthalate, diallyl carbonate and triallyl cyanurate are also useful comonomers. 
     The wettability of the compositions disclosed in this invention may be enhanced by the inclusion of hydrophilic neutral monomers, hydrophilic cationic monomers and hydrophilic anionic monomers and mixtures of these. The classes of these compounds are hydrophilic arylates and methacrylates, acrylamides, methacrylamides and vinyl-lactams. 
     Representative hydrophilic neutral monomers which impart hydrophilic properties to the surface of contact lens materials of this invention include: 
     N-vinylpyrrolidone 
     acrylamide 
     methacrylamide 
     N,N-dimethylacrylamide 
     2-hydroxyethyl acrylate or methacrylate 
     2- or 3-hydroxypropyl acrylate or methacrylate 
     glyceryl acrylate or methacrylate 
     glycidyl acrylate or methacrylate 
     3-methoxy-2-hydroxypropyl acrylate or methacrylate 
     mono esters of acrylic and methacrylic acid with polyethers of the general formula: 
     
         HO(C.sub.n H.sub.2n O).sub.x H 
    
     Wherein &#34;n&#34; is a number from 1 to about 4 and &#34;x&#34; is a number from 2 to about 10. 
     The cationic hydrophilic monomers either can be initially in their charged form or are subsequently converted to their charged form after formation of the contact lens. The classes of these compounds are derived from basic or cationic acrylates, methacrylates, acrylamides, methacrylamides, vinylpyridines, vinylimidazoles, and diallyldialkylammonium polymerizable groups. Such monomers are represented by: 
     N,N-dimethylaminoethyl acrylate and methacrylate 
     2-methacryloyloxyethyltrimethylammonium chloride 
     and methylsulfate 
     2-,4-, and 2-methyl-5-vinylpyridine 
     2-,4-, and 2-methyl-5-vinylpyridinium chloride 
     and methylsufate 
     N-(3-methacrylamidopropyl)-N,N-dimethylamine 
     N-(3-methacrylamidopropyl)-N,N,N-trimethylammonium chloride 
     N-(3-methacryloyloxy-2-hydroxylpropyl)-N,N,N-trime 
     thylammonium chloride 
     diallyldimethylammonium chloride and 
     methylsulfate 
     The anionic hydrophilic monomers either are in their neutral form initially or are subsequently converted to their anionic form. These classes of compounds include polymerizable monomers which contain carboxy, sulfonate, and phosphate or phosphate groups. Such monomers are represented by: 
     acrylic acid 
     methacrylic acid 
     sodium acrylate and methacrylate 
     vinylsulfonic acid 
     sodium vinylsulfonate 
     p-styrenesulfonic acid 
     sodium p-styrenesulfonate 
     2-methacryloyloxyethylsulfonic acid 
     3-methacryloyloxy-2-hydroxypropylsulfonic acid 
     2-acrylamido-2-methylpropanesulfonic acid 
     allylsulfonic acid 
     2-phosphatoethyl methacrylate 
     The copolymers described in this invention are prepared by radical polymerization through the incorporation of a free radical initiator. The initiator is chosen from those commonly utilized to polymerize vinyl type monomers and would include the following representative initiators: 
     2,2&#39;-azo-bis-isobutyronitrile 
     4,4&#39;-azo-bis-(4-cyanopentanoic acid) 
     t-butyl peroctoate 
     benzoyl peroxide 
     lauroyl peroxide 
     methyl ethyl ketone peroxide 
     diisopropyl peroxycarbonate 
     Representative preferred hydrophilic cross-linking agents which are useful in combination with multifunctional organosiloxanes alone or admixed with monofunctional organosiloxanes include: 
     ethylene glycol diacrylate 
     diethylene glycol diacrylate 
     tri-ethylene glycol diacrylate 
     tetraethylene glycol diacrylate 
     polyethylene glycol diacrylate 
     ethylene glycol dimethacrylate 
     diethylene glycol dimethacrylate 
     tri-ethylene glycol dimethacrylate 
     tetraethylene glycol dimethacrylate 
     polyethylene glycol dimethacrylate 
     The free radical initiator is normally used in amounts of from 0.01 to 2% by weight of the entire compound. 
     The materials of this invention can be polymerized directly in a suitable mold to form contact lenses. The materials are all thermosetting and thus various methods of fabrication can be used. It is preferable to polymerize into sheet or rod stock from which contact lenses may be machined. 
     It is preferred to use the conventional approach when forming contact lenses such as used for polymethyl methacrylate (PMMA). In this approach, the formulations are polymerized directly into a sheet or rod and the contact lenses are cut as buttons, discs or other preformed shapes which are then machined to obtain the lens surfaces. The resulting polymeric stock of buttons possesses the optical qualities necessary to produce aberration-free oxygen-permeable, hard contact lenses in accordance with this invention. 
     The multifunctional organosiloxane monomers of this invention provide many advantages when utilized as the basis for contact lens materials. The disclosed monomers are substantially organosiloxane but contain multiple functional groups which allows for rapid incorporation into a copolymer system by free radical polymerization. Furthermore, because of the presence of the multifunctional, polymerizable groups the organosiloxane portion is compatibilized in the copolymer structure. 
     The oxygen demand of the human cornea has been well established and contact lenses made from the polymers and copolymers of this invention can meet and easily exceed this requirement. 
     Because of the unique properties of the compositions, the contact lenses formed thereof have high oxygen permeability while maintaining other essential properties such as clarity, wettability and durability. 
    
    
     The following Examples are given to illustrate the invention and not meant to be limiting: 
     EXAMPLE 1 
     Synthesis of 1,3-Bis(γ-methacryloxypropyl)-1,1,3,3 tetra(trimethylsiloxy)disiloxane 
     A catalyst solution is prepared by adding, with stirring, 52 ml of concentrated sulfuric acid to a cooled mixture of 59 ml absolute ethanol and 66 ml of distilled water. 
     A 2000 ml round bottom flask, equipped with a magnetic stirring bar, is placed in a suitable size container which will function as a water bath. To the flask is added 300 ml (1.26 moles) of γ-methacryloxypropyltrimethoxysilane and 375 ml (2.54 moles) of trimethylacetoxysilane. The bath vessel is filled with water at a temperature of between 20° and 30° C. While stirring, 60 ml of catalyst solution (prepared earlier) is added dropwise from a dropping funnel into the flask. After the catalyst addition is complete, the reaction mixture is stirred at room temperature for 72 hours. The upper oily layer is separated and washed with two volumes of distilled water. The organic layer is then isolated and stripped of low boiling contaminants by vacuum distillation at a temperature of between 50° and 60° C. The monomer is then decolored with activated carbon yielding approximately 275 ml of 1,3-Bis(γ-methacryloxy propyl)-1,1,3,3 tetra(trimethylsiloxy)disiloxane. This material is designated SM-6. 
     EXAMPLE 2 
     Synthesis of 1,7-Bis(γ-methacryloxypropyl)-1,1,3,3,5,5,7,7-octa(trimethylsiloxy)tetrasiloxane 
     This monomer was prepared in a manner similar to that described in Example 1. The reactants were γ-methacryloxypropyltrimethoxysilane (2 moles) 1,3, Bis acetoxy-1,1,3,3 tetra(trimethylsiloxy) disiloxane (1 mole) and Trimethylacetoxysilane (4 moles). This material is designated SM-12. 
     EXAMPLE 3 
     Synthesis of 1,3-Bis(γ-methacryloxaypropyl)-1,1,3,3 Tetra(pentamethyldisiloxanyl)disiloxane 
     This monomer was prepared in a manner similar to that described in Example 1. The reactants were γ-methacryloxypropyltrimethoxysilane (2 moles) and acetoxypentamethyldisiloxane (4 moles). This material is designated SM-10. 
     EXAMPLE 4 
     Synthesis of 1,7-Bis(γ-methacryloxypropyl)1,1,7,7-TETRA (Pentamethyldisiloxanyl)-3,3,5,5-TETRA (Trimethylsiloxy)Tetrasiloxane 
     This monomer was prepared in a manner similar to that described in Example 1. The reactants were γ-methacryloxypropyltrimethoxysilane (2 moles), 1,3-Bis(acetoxy)-1,1,3,3-TETRA(trimethylsiloxy)disilox ane (1 mole) and acetoxypentamethyldisiloxane (4 moles). This material is designated SM-16. 
     EXAMPLE 5 
     Hard, oxygen-permeable lenses are made from a comonomer mixture of methyl methacrylate (MMA), 1,3-Bis(γ-methacryloxypropyl)-1,1,3,3 tetra(trimethylsiloxy)disiloxane (SM-6) and methacrylic acid (MA) using the free radical initiator 2,2&#39;-azobisisobutyronitrile (AIBN). The formulation components (shown in Table I in parts by weight) are thoroughly mixed, transferred to test tubes which are purged with nitrogen then sealed with serum caps. The test tubes are then placed in a water bath at 40° C. and allowed to polymerize for three days. The tubes are then placed in a 65° C. oven for an additional time period of three days, after which the polymerized rods are removed from the tubes. The hard, transparent rods are then subjected to conditioning for approximately twenty-four (24) hours at 100° C. under vacuum to complete polymerization process and relieve any mechanical stresses present. The conditioned rods are then machined to contact lens blanks (a disc 1/2 inch in diameter by 3/16 inch thick). 
     Oxygen permeability values of the contact lenses were generated by a procedure as described in ASTM D1434 except that plano contact lenses are used instead of large flat discs of material. The permeability apparatus was constructed in such a manner as to accept actual contact lenses and calibrated with other polymeric oxygen permeability data reported in Table I, polymethyl methacrylate, polycarbonate, and polystyrene have oxygen permeabilities of 1, 22, and 35 cm 3  mm/cm 2  sec cm Hg×10 -10 , respectively. The formulations of Table I illustrate the change in oxygen permeability with a change in MMA and SM-6 concentrations. 
     
                       TABLE I______________________________________Composition (wt. percent reagent)                  OxygenMMA      SM-6    MA        AIBN  Permeability*______________________________________57.1     38.0    4.7       0.2    3652.3     42.8    4.7       0.2    6647.5     47.6    4.7       0.2   10742.8     52.3    4.7       0.2   148______________________________________ *Value in cm.sup.3 mm/cm.sup.2 sec cm Hg (×10.sup.10) 
    
     EXAMPLE 6 
     Utilizing the experimental procedures of Example 3 this Example illustrates the preparation and properties of materials suitable for semi-rigid and flexible contact lenses. 
     
         ______________________________________Composition (wt. percent reagent)EEA*     SM-6    MA         AIBN  Properties______________________________________57.0     38.0    4.8        0.2   T, F35.0     60.0    4.8        0.2   T, SR______________________________________ *Ethoxyethylacrylate T = Transparent F = Flexible SR = Semirigid 
    
     EXAMPLE 7 
     Utilizing the Experimental Procedures of Example 3 this Example illustrates the preparation and properties of materials suitable for producing hard contact lenses. 
     
         ______________________________________Composition (Net percent reagent)MMA      SM-12   MA         AIBN  Properties______________________________________69.9     29.9    --         0.2   T, H66.5     28.5    4.8        0.2   T, H59.9     19.9    --         0.2   T, H57.0     38.0    4.8        0.2   NT, H49.9     49.9    --         0.2   T, H47.5     47.5    4.8        0.2   NT, H______________________________________ T = Transparent H = Hard NT = Hazy 
    
     EXAMPLE 8 
     Utilizing the experimental procedures of Example 5 this Example illustrates the preparation and properties of materials suitable for hard contact lenses. 
     
         ______________________________________Composition (wt. percent reagent)               PropertiesMMA   SM-10    MA      AIBN   Appearance                                  Hardness*______________________________________59.8  40.0     --      0.2    H, T     11657.0  38.0     4.8     0.2    H, T     11747.5  47.5     4.8     0.2    H, T     113______________________________________ H = Hard T = Transparent *Rockwell R 
    
     EXAMPLE 9 
     Utilizing the experimental procedures of Example 5 this Example illustrates the preparation and properties of materials suitable for hard contact lenses. 
     
         ______________________________________Composition (wt. percent reagent)               PropertiesMMA   SM-16    MA      AIBN   Appearance                                  Hardness*______________________________________69.8  30.0     --      0.2    H, T     11859.8  40.0     --      0.2    H, T     11466.5  28.5     4.8     0.2    H, T     11857.0  38.0     4.8     0.2    H, T     115______________________________________ H = Hard T = Transparent *Rockwell R 
    
     EXAMPLE 10 
     The following Example illustrates the use of a multifunctional, unsaturated organosiloxane in conjunction with a monofunctional unsaturated organosiloxane to provide an oxygen permeable contact lens material with improved impact strength. 
     The procedures described in Example 5 were utilized in preparing the copolymers. 
     Impact behavior was determined by dropping a steel ball (11/32 inch diameter, 2.75 gms) down a plastic tube onto the convex surface of a contact lens. The lens was positioned on a flat steel table so that the ball impacted the center of the lens. 
     
         ______________________________________Base Curve       7.80 mm to 7.90 mmPower            -6.75 to -7.25 dioptersthickness        0.10 mm to 0.12 mm______________________________________ 
    
     A number of lenses were tested and the height at which 50% of the samples failed (crack, hole or shatter) was called out as the drop impact resistance. 
     
         __________________________________________________________________________Composition        Properties(wt. percent reagent)              Rockwell R                     Oxygen**                            Drop***MMA SM-6   TRIS*       MA AIBN              Hardness                     Permeability                            Impact__________________________________________________________________________47.5    --  47.5       4.8          0.2 119    179    1247.5    19.0   28.5       4.8          0.2 119    161    1647.5    28.5   19.0       4.8          0.2 118    143    1847.5    38.0    9.5       4.8          0.2 118    130    19__________________________________________________________________________ *Methacryloxypropyl tris (trimethylsilyl)siloxane **Value in cm.sup.3 mm/cm.sup.2 sec cm Hg × 10.sup.-10 ***Height in inches 
    
     EXAMPLE 11 
     The following example illusstrates the use of a multifunctional, unsaturated organosiloxane with a monofunctional unsaturated organosiloxane and in combination with a hydrophilic dimethacrylate cross-linking agent to provide oxygen permeable contact lens materials with improved resistance to fracture. 
     The procedures described in Example 5 were utilized in preparing the copolymers. 
     The crude polymerized rods, of at least 4 inches length, were centerless ground to 0.500 inch diameter. A circular (circumferential notch) 0.050 inch deep by 0.020 inch width, was then cut at the approximate mid-point of the rod. 
     The fracture resistance of the test samples was determined utilizing a modified flexural strength procedure (ASTM D790 method I). The rod was supported at both eds with the load applied at the notch creating three point bending. A Tinius-Olsen testing machine was used under the following conditions. 
     
         ______________________________________Span                3 inchesCrosshead Speed     0.05 inches/minLoad Range          120 lbs.Temperature         230° C.______________________________________ 
    
     This test method compares the fracture properties of various materials relative to one another. In this case, polymethylmethacrylate was chosen as the standard for comparison to the compositions of this invention. 
     
         __________________________________________________________________________                           PropertyComposition (wt. percent reagent)                           Fracture ValueDMI.sup.1    MMA SM-6       TRIS.sup.2           MA VP.sup.3                 TEGDM.sup.4                       AIBN                           (lbs. at break).sup.5__________________________________________________________________________10.0    25.0   11.0       43.8           5.0              5.0                 --    0.2 259.0 25.0   11.0       43.8           5.0              5.0                 1.0   0.2 337.5 25.0   11.0       43.8           5.0              5.0                 2.5   0.2 385.0 25.0   11.0       43.8           5.0              5.0                 5.0   0.2 48__________________________________________________________________________ .sup.1 Dimethyl Itaconate .sup.2 Methacryloxypropyltris (trimethylsilyl) siloxane .sup.3 N--vinyl2-pyrrolidone .sup.4 Tetraethylene glycol dimethacrylate .sup.5 Fracture Value of PMMA control equals 62 lbs. 
    
     EXAMPLE 12 
     The following example illustrates the use of a multifunctional, unsaturated organosiloxane with a monofunctional unsaturated organosiloxane and in combination with a hydrophilic diacrylate cross-linking agent to provide oxygen permeable contact lens materials with improved resistance to fracture. 
     The procedures described in Example 5 were utilized in preparing the copolymers. 
     The testing methodology described in Example 11 was followed to generate fracture data. 
     
         __________________________________________________________________________                          PropertyComposition (wt. percent reagent)                          Fracture ValueDMI   MMA SM-6      TRIS          MA VP TEGDA*                      AIBN                          (lbs. at break)**__________________________________________________________________________10.0   14.0  16.5      38.3          5.0             5.0                1.0   0.2 4710.0   12.5  16.5      38.3          5.0             5.0                2.5   0.2 5110.0   10.0  16.5      38.3          5.0             5.0                5.0   0.2 53__________________________________________________________________________ *Tetraethylene glycol diacrylate **Fracture Value of PMMA control equals 62 lbs. 
    
     The following table illustrates the general combinations of materials as preferred for use in the present invention to form polymerized organosiloxane materials in a form suitable for machining or casting as contact lenses: 
     
         ______________________________________           Formula-                  Formula- Formula-           tion I tion II  tion III______________________________________oxygen   multifunctional                 80-99%   55-98% 35-87%permeable    unsaturatedmaterial organosiloxane    or mixture thereof    -30 to 100% by    weight monofunc-    tional unsaturated    organosiloxane    70-0% by weight    of    organosiloxanehardening    ester of a C.sub.1 -C.sub.20                 0        1-45%  1-45%or       monohydric orsoftening    polyhydricagent    alkanol or    phenol and    acid selected    from the class    consisting    essentially of    acrylic and    methacrylic    acidWetting  Hydrophilic  1-20%    1-20%  1-20%Agent    monomer or    mixture    thereofHydrophilic    Itaconate    0        0      1-20%hardening    or mixturesagent    thereof______________________________________ 
    
     In a more preferred range of materials, contact lens materials most preferred for use to form polymerized organosiloxane materials in a form suitable for machining or casting as contact lenses are shown in the following table: 
     
         ______________________________________              Formula-                      Formula-              tion I  tion V______________________________________oxygen   multifunctional 35-75%    35-75%permeable    unsaturatedmaterial organosiloxane or    mixture thereof    -20 to 50% by    weight monofunctional    unsaturated    organosiloxane    80-50% by weight    of organosiloxanehardening    ester of a C.sub.1 -C.sub.20                    1-45%     1-45%or       monohydric orsoftening    polyhydric alkanolagent    or phenol and    acid selected    from the class    consisting    essentially of    acrylic and    methacrylic acidWetting  Hydrophilic monomer or                    1-20%     1-20%Agent    mixture thereofHydrophilic    Itaconate or mixtures                    0         1-20%hardening    thereofagentHydrophilic    Cross-linker    1-10%     1-10%______________________________________ 
    
     The Examples recited in this specification are merely illustrative of the present invention. Many combinations are possible. Both hard and semi-hard contact lenses can be advantageously produced using the compositions of this invention. In some cases soft lenses will have advantages because of the multifunctional unsaturated organosiloxanes used. In all cases, contrary to prior art thinking in the oxygen permeable contact lens commercial field, multifunctional materials are found useful rather than monofunctional materials. Usual additives such as tints, colorants, antioxidants, stabilizers, absorbers and the like can be incorporated in the formulations of this invention if desired. All lenses can have conventional hardening agents, softening agents, wetting agents, hydrophilic hardening agents and the like incorporated therein so long as desired contact lens properties are retained. 
     In the lenses of this invention and the following claims, mixtures of monofunctional unsaturated organosiloxanes of the general formula given can be used in the combinations claimed and mixtures of the unsaturated multifunctional organosiloxanes of the general formula given can be used alone and in such combinations and are considered full equivalents included in the claimed structures. 
     A &#34;contact lens significant amount&#34; of multifunctional, unsaturated organosiloxane as used herein refers to an amount higher than previously known in contact lenses and effective to improve hardness above that obtained with the monofunctional siloxane monomers as normally used.