CONTINUOUS-WEAR LENSES HAVING IMPROVED PHYSICAL PROPERTIES

Abstract: The physical properties of highly oxygen-permeable continuous-wear contact lenses, comprising a copolymer of an organosilicone monomer, a fluoroalkyl ester monomer and a hydrophilic monomer, are improved by the further addition of a linear polysiloxane oligomeric cross-linking agent with or without neopentylglycol dimethacrylate.

Description: This invention relates to fluorine-containing copolymers which are useful for making hard contact lenses suitable for continuous wear. Contact lenses presently on the market are classified into two large groups: soft contact lenses and hard contact lenses. Hard contact lenses correct a broader range of visual defects than soft contact lenses, but are less comfortable to wear. The art has sought to increase oxygen permeability of hard contact lenses, thereby extending the length of time they can be worn without causing corneal damage or discomfort. One proposed solution has been the formation of a copolymer of methyl methacrylate and a siloxane methacrylate compound. See U.S. Patents 4,139,692 and 4,235,985. This solution has been less than satisfactory, since the lenses offered are not as hard, rigid, nor as wettable as lenses formed from polymethyl methacrylate. In addition, such lenses are fragile and have poor mechanical processability. Our copending European Patent Application No. 86 901 225 (Publication No. 0 215 817) describes an oxygen-permeable hard contact lens suitable for continuous wear, formed by copolymerizing at least one organosilicone monomer and at least one hexafluoroisopropyl ester of an unsaturated carboxylic acid. A hydrophilic monomer such as methacrylic acid may be included for wettability. A crosslinking monomer such as the multifunctional organosilicon branched-chain monomer 1,3-bis(ν-methacryloxypropyl)-1,1,3,3-tetra(trimethylsiloxy) disiloxane may also be included to control hardness. Other monomers may be added to adjust the physical properties of the lens. Our co-pending European Patent Application No. 86 901 226 (Publication No. 0 211 067) describes very highly oxygen-permeable hard contact lenses formed by copolymerizing a generically defined siloxane mono or polyfunctional acrylate or methacrylate, at least one acryloxy or substituted acryloxy fluoroorgano monomer, at least one hydrophilic monomer, and at least one crosslinking agent to control hardness, a highly multifunctional organosilicon monomer being preferred as the crosslinking agent. U.S. Patent 4,433,125 describes an oxygen-permeable hard contact lens made of a copolymer comprising a silane or siloxane acrylate or methacrylate monomer and a fluoroalkyl acrylate or methacrylate monomer. Crosslinking monomers, such as ethylene glycol dimethacrylate, may also be included, as well as alkyl acrylate and hydrophilic monomers such as 2-hydroxyethyl methacrylate. U.S. Patent 4,540,761 describes an oxygen-permeable hard contact lens in which the physical properties are improved by the inclusion of 30-50 percent of an alkyl acrylate or methacrylate. The remaining monomers comprise certain siloxane acrylates or methacrylates, certain fluoroalkyl acrylates or methacrylates, acrylic or methacrylic acid, and a crosslinking agent selected from certain glycol diacrylates or dimethacrylates and trimethylolpropane triacrylate or trimethacrylate. U.S. Patent 4,153,641 discloses oxygen-permeable contact lenses comprising cross-linked polymerizates of poly(organosiloxanes) alpha, omega terminally bonded through a divalent hydrocarbon group to a polymerized, activated unsaturated group. The hard contact lenses described in our copending European Patent Application Nos. 86 901 225/6 (Publication Nos. 0 215 817 and 0 211 067, respectively) cited above provide high oxygen permeability required for continuous wear and improved physical properties when compared to those of previously known highly oxygen-permeable lenses composed largely of organosilicon monomers in the absence of fluoroalkyl monomers. However, such polymers still show a strong tendency to chip, break and stress craze during machining to produce contact lenses and during subsequent handling and use of the lenses. U.S. 4,540,761 describes an attempt to overcome the mechanical deficiencies of organosilicon-fluoroalkyl copolymer compositions by the addition of large (30-50 percent) amounts of alkyl acrylates or methacrylates, but such addition leads to a corresponding loss of the very high oxygen permeability required for continuous wear. By contrast, the preferred crosslinked copolymer compositions of the present invention maintain very high oxygen permeability, while providing major improvements in mechanical properties as measured by tensile strength, percent elongation and toughness, resulting in elimination of chipping, breaking and stress crazing during manufacture and subsequent handling and use of the lenses. Broadly in accordance with the present invention there is provided a polymerization product of: (a) at least one fluoroorgano monomer having the formula (I): wherein R₁ is a hydrogen atom or a methyl group and Y is a fluorocarbon group having 2 to 10 carbon atoms and 3 to 21 fluorine atoms; (b) at least one siloxyl alkyl ester having the formula (II): wherein R₁ is as defined above, each R₂ is independently selected from the group consisting of methyl and phenyl groups, and a is 1, 3 or 4; (c) a member of the group consisting of: (i) at least one poly(organosiloxane) monomer having the formula (III): wherein A is an activated unsaturated group, R₃ is a divalent hydrocarbon radical having from 1 to 22 carbon atoms, each R₄ and R₅ is independently selected from the group consisting of monovalent hydrocarbon radicals and a halogen-substituted monovalent hydrocarbon radicals having 1-12 carbon atoms, and b is O or greater, and (ii) mixtures of said poly(organosiloxane) monomers, and at least one optional crosslinking monomer having the formula (IV): wherein R₁ is as defined above and R₆ is a divalent hydrocarbon radical having 2-12 carbon atoms; and (d) at least one hydrophilic monomer. The monomer percentage by weight of the total monomers present ranges from 40 to 80 weight percent, preferably 40 to 70 weight percent for component (a); from 15 to 40 weight percent, preferably 20 to 40 weight percent for component (b); from 4 to 20 weight percent, preferably 7 to 15 weight percent for component (c); and from 1 to 15 weight percent, preferably 2 to 10 weight percent for component (d). The present invention also provides a contact lens made of the just-defined polymerization product. The oxygen permeability, measured as described below, should preferably be greater than 50. Highly preferred contact lenses of this invention are formed from the polymerization product of: (a) hexafluoroisopropyl methacrylate, (b) tris(trimethylsiloxy)silylpropyl methacrylate, (c) at least one poly(organosiloxane) monomer having the formula (III) described above wherein A is methacryloxy, R₃ is tetramethylene, each R₄ and R₅ is a methyl group, and b is an integer from 10 to 50, and (d) methacrylic acid. In a distinct aspect of this highly preferred embodiment, neopentyl glycol dimethacrylate is added as an additional crosslinker. In the compound (I), R₁ is preferably a methyl group and Y is preferably a fluorocarbon group having 2 to 4 carbon atoms. As the number of carbon atoms in Y increases, the hardness of the resulting polymerization product decreases. This tendency toward decreased hardness may be compensated by employing increased amounts of neopentyl glycol dimethacrylate in the polymerization mixture. Especially preferred compounds of formula (I) are hexafluoroisopropyl methacrylate and trifluoroethyl methacrylate. Particularly preferred is 1,1,1,3,3,3-hexafluoroisopropyl methacrylate. In the compound (II), R₁ and each R₂ are preferably methyl groups and a is preferably 3 or 4. A particularly preferred compound of formula (II) is tris(trimethylsiloxy)silylpropyl methacrylate. With respect to compounds of formula (III), the term "activated unsaturated group" means an unsaturated group which has a substituent which facilitates free radical polymerization. In the compound (III), A is preferably selected from the group consisting of methacryloxy, acryloxy, acrylamido, and styryl, and more preferably is either methacryloxy or acryloxy. Methacryloxy radicals are particularly preferred. R₃ is preferably an alkylene radical, more preferably an alkylene radical having 1, 3 or 4 carbon atoms, especially 3 or 4 carbon atoms. R₄ and R₅ are preferably alkyl, cycloalkyl, aryl, aralkyl, alkaryl, haloaryl, or haloalkyl radicals having from 1 to 12 carbon atoms. Of the halogen-substituted radicals, fluoro-substituted, lower alkyl radicals having up to 4 carbon atoms are preferred. Most preferably, R₄ and R₅ are methyl radicals. Subscript b is preferably from 0 to 50, more preferably from 10 to 30. Preparation of compounds of formula (III) is described in U.S. Patent 4,153,641. In the compound (IV), R₁ is preferably a methyl group and R₆ is preferably a branched-chain, divalent hydrocarbon radical, especially a radical having 2 to 10 carbon atoms. Neopentylglycol dimethacrylate is particularly preferred, although other compounds such as ethylene glycol dimethacrylate are within the scope of this invention. Polyglycol dimethacrylates such as diethylene glycol dimethacrylate and triethylene glycol dimethacrylate are avoided because they tend to soften the polymerization product and reduce oxygen permeability. When glycol di(meth)acrylates of formula (IV) are employed in the polymerization mixture, the weight ratio of poly(organosiloxane) monomer (III) to glycol di(meth)acrylate is preferably 0.5-1.5:1, more preferably about 1:1. Hydrophilic monomers are included in the polymerization product of this invention to enhance wettability of contact lenses manufactured therefrom. Examples of suitable monomers are unsaturated carboxylic acids (e.g., methacrylic and acrylic acids), acrylic substituted alcohols (e.g., 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate), vinyl dibasic acids (e.g., itaconic and maleic acids), vinyl lactams (e.g., N-vinyl pyrrolidone), and acrylamides (e.g., dimethyl acrylamide). Unsaturated carboxylic acids (esp. methacrylic acid) are preferred hydrophilic monomers. In addition to the monomers described above, the copolymer composition of this invention may also include such additional material as the colorants known in the contact lens art, or UV-absorbing agents. Polymerization may be carried out using conventional procedures, such as by using heat or radiation treatment of a homogeneous mixture of the monomers held in sheet form between layers of a non-adherent material such as Teflon. Radiation treatment may include treatment with ionizing, ultraviolet, or infrared radiation. Free radical polymerization initiators such as peroxides, azos, or percarbonates are preferably employed, in a concentration range of 0.01 to 1 percent by weight of the total monomer mixture. The shaping of the copolymer into contact lenses can be done by usual methods. For instance, polymerization may be conducted in a mold corresponding to a shape of a contact lens to give a copolymer having a contact lens shape directly. The thus-obtained contact lens may be further subjected to a mechanical finishing, as occasion demands. Also, the polymerization may be conducted in an appropriate mold or vessel to give a lens material in the form of button, plate or rod, and the lens material may then be subjected to the usual mechanical processing (e.g., cutting or polishing) to give a contact lens having the desired shape. The following examples are illustrative only and should not be construed as limiting the invention. All percentages referred to herein are on a weight percent basis. Comparative Examples A-B and Examples 1-4 The monomers for each of Comparative Examples A-B and Examples 1-4 were formulated as shown in Table I below. To the mixture of monomers was added 0.07 percent by weight of the polymerization initiator 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane. The mixture was homogenized, degassed and placed in a polymerization cell consisting of two Teflon-coated plates separated by an elastomer gasket and held by binder clips. After filling, the cell was purged with nitrogen, sealed and placed in an oven. The heating cycle consisted of 4 hours at 70°C followed by 3 hours at 80°C and 1 hour at 110°C. The resulting transparent sheet was then further heated for one hour at 120°C. After cooling, the plastic sheet was cut into buttons which were shaped into corneal contact lenses using conventional contact lens machining procedures. The monomers of the examples tabulated in Table I are identified as follows: HFIPMa 1,1,1,3,3,3-Hexafluoroisopropyl methacrylate Maa Methacrylic acid TRIS Tris(trimethylsiloxy)silylpropyl methacrylate MMa Methyl methacrylate M2Dn M2D50 M2Dn, n=50 M2D25 M2Dn, n=25 M2D10 M2Dn, n=10 NPGMa Neopentylglycol dimethacrylate The resulting oxygen permeability and mechanical properties are listed in Table II. Oxygen permeability Dk(cm³ oxygen at STP/s)(cm/cm² x mmHg), was determined by the polarographic method of Fatt, International Contact Lens Clinic II, No. 3, March, 1984, pp. 175-183, and corrected for sample edge effects. The determinations were made at 35°C. Tensile strength (g/mm²), modulus (g/mm²) and percent elongation were measured according to the procedure of ASTM D-1708, Rockwell hardness by ASTM D-785, and Shore hardness by ASTM D-2240. Toughness (g-cm) was determined by doubling the area under the stress/strain curve. The results listed in Table II show that the high level of oxygen permeability characteristic to the Comparative Example A, having a polymer composition as described by EP-A-0 215 817 were retained or even exceeded by the Examples 1-4 of the invention. Comparative Example B, in which 5 percent of the polymer consisted of methyl methacrylate, a conventional component of hard contact lenses, showed a decrease in oxygen permeability and little if any significant improvement in physical properties. However, the Examples 1-4 of the invention showed major increases in tensile strength, percent elongation, and toughness. Modulus values were retained or increased, while Shore and Rockwell hardness were not significantly reduced. The lenses of both comparative examples showed a strong tendency to chip, break and stress craze during machining of the contact lenses and during subsequent handling and use. The improvements in physical properties as measured for the polymer examples of the invention resulted in elimination of these defects under the same conditions of machining and handling as used for the comparative examples. The copolymers of the invention were thus rendered fully suitable for the manufacture of contact lenses and their subsequent use, without impairing the high levels of oxygen permeability permitting prolonged wear. MONOMERS, WEIGHT % Example No. HFIPMa Maa TRIS MMa M2D50 M2D25 M2D10 NPGDMa A 65.00 5.00 30.00 - - - - - B 60.00 5.00 30.00 5.00 - - - - 1 60.00 5.00 25.00 - 5.00 - - 5.00 2 60.00 5.00 25.00 - - 5.00 - 5.00 3 60.00 5.00 25.00 - - - 10.00 - 4 60.00 5.00 25.00 - - - 5.00 5.00 PHYSICAL PROPERTIES Example No. DK x10⁻¹¹ Tensile Strength x10⁻³ Modulus x10⁻³ % Elong. Hardness Toughness Rockwell R Shore D A 104 1.3 51 2.2 115 78 2.9 B 89 1.2 57 1.9 118 80 2.3 1 119 1.9 53 3.8 111 77 -- 2 107 2.9 71 4.6 113 79 13.3 3 130 2.5 58 4.5 108 76 1 to 3 4 103 2.5 66 4.5 115 -- 1 to 3 Example 5 The procedure of Example 2 was repeated except trifluoroethyl methacrylate was substituted for the hexafluoroisopropyl methacrylate used in Example 2. Contact lenses produced from the resulting polymerization product had the following properties: DK of 50 x 10⁻¹¹, tensile strength of 2.5 x 10⁻³, modulus of 80 x 10⁻³, % elongation of 5.5, Rockwell hardness of 114, and toughness of 13.8.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, IT, LU, NL, SE A polymerization product of: (a) 40 to 80 weight % of at least one fluoroorgano monomer having the formula: wherein R₁ is a hydrogen atom or a methyl group and Y is a fluorocarbon group having 2 to 10 carbon atoms and 3 to 21 fluorine atoms; (b) 15 to 40 weight % of at least one siloxyl alkyl ester having the formula: wherein R₁ is as defined above, each R₂ is independently selected from the group consisting of methyl and phenyl groups, and a is 1, 3 or 4; (c) 4 to 20 weight % of a member of the group consisting of: (i) at least one poly(organosiloxane) monomer having the formula wherein A is an activated unsaturated group, R₃ is a divalent hydrocarbon radical having from 1 to 22 carbon atoms, each R₄ and R₅ is independently selected from the group consisting of a monovalent hydrocarbon radicals and a halogen-substituted monovalent hydrocarbon radicals having 1-12 carbon atoms, and b is O or greater, and (ii) mixtures of said poly(organosiloxane) monomers and at least one optional crosslinking monomer having the formula wherein R₁ is as defined above and R₆ is a divalent hydrocarbon radical having 2-12 carbon atoms; and (d) 1 to 15 weight % of at least one hydrophilic monomer. The product of Claim 1, wherein each R₁ is methyl. The product of Claim 1 or Claim 2, wherein Y is a fluorocarbon group having 2 to 4 carbon atoms. The product of Claims 2 and 3, wherein said fluoroorgano monomer is selected from hexafluoroisopropyl methacrylate and trifluoroethyl methacrylate. The product of Claim 4, wherein said fluoroorgano monomer is 1,1,1,3,3,3-hexafluoroisopropyl methacrylate. The product of any preceding claim, wherein each R₂ is methyl. The product of any preceding claim, wherein a is 3 or 4. The product of Claim 7, wherein the siloxyl alkyl ester is tris(trimethylsiloxy)-silylpropyl methacrylate. The product of any preceding claim, wherein A is selected from the group consisting of methacryloxy and acryloxy. The product of any preceding claim, wherein R₃ is a linear, divalent hydrocarbon radical having 3 or 4 carbon atoms. The product of any preceding claim, wherein each R₄ and R₅ is a methyl radical or fluoromethyl radical. The product of any preceding claim, wherein b is 10 to 30. The product of any preceding claim, wherein said optional crosslinking monomer is neopentyl glycol dimethacrylate. The product of any preceding claim, wherein said hydrophilic monomer is methacrylic acid. The product of any preceding claim formed by polymerizing 40 to 70 weight % of monomer (a), 20 to 40 weight % of monomer (b), 7 to 15 weight % of monomer (c), and 2 to 10 weight % of monomer (d). A contact lens made of a polymerization product as defined in any preceding claim. The contact lens of Claim 16, wherein said fluoroorgano monomer is hexafluoroisopropyl methacrylate, said siloxyl alkyl ester is tris(trimethylsiloxy)-silylpropyl methacrylate, A is methacryloxy, R₃ is tetramethylene, each R₄ and R₅ is a methyl group, b is an integer from 10 to 50, said optional crosslinking monomer is neopentyl glycol dimethacrylate, and said hydrophilic monomer is methacrylic acid. The contact lens of Claim 16, wherein monomer component (c) is a mixture of said poly(organosiloxane)monomer and neopentyl glycol dimethacrylate and the weight ratio of poly(organosiloxane)monomer: neopentyl glycol dimethacrylate is within the range from about 0.5:1 to about 1.5:1. Claims for the following Contracting State : ES A polymerization product of: (a) 40 to 80 weight % of at least one fluoroorgano monomer having the formula: wherein R₁ is a hydrogen atom or a methyl group and Y is a fluorocarbon group having 2 to 10 carbon atoms and 3 to 21 fluorine atoms; (b) 15 to 40 weight % of at least one siloxyl alkyl ester having the formula: wherein R₁ is as defined above, each R₂ is independently selected from the group consisting of methyl and phenyl groups, and a is 1, 3 or 4; (c) 4 to 20 weight % of a member of the group consisting of: (i) at least one poly(organosiloxane) monomer having the formula wherein A is an activated unsaturated group, R₃ is a divalent hydrocarbon radical having from 1 to 22 carbon atoms, each R₄ and R₅ is independently selected from the group consisting of monovalent hydrocarbon radicals and halogen-substituted monovalent hydrocarbon radicals having 1-12 carbon atoms, and b is 0 or greater, and (ii) mixtures of said poly(organosiloxane) monomers and at least one optional crosslinking monomer having the formula wherein R₁ is as defined above and R₆ is a divalent hydrocarbon radical having 2-12 carbon atoms; and (d) 1 to 15 weight % of at least one hydrophilic monomer. The product of Claim 1, wherein each R₁ is methyl. The product of Claim 1 or Claim 2, wherein Y is a fluorocarbon group having 2 to 4 carbon atoms. The product of Claims 2 and 3, wherein said fluoroorgano monomer is selected from hexafluoroisopropyl methacrylate and trifluoroethyl methacrylate. The product of Claim 4, wherein said fluoroorgano monomer is 1,1,1,3,3,3-hexafluoroisopropyl methacrylate. The product of any preceding claim, wherein each R₂ is methyl. The product of any preceding claim, wherein a is 3 or 4. The product of Claim 7, wherein the siloxyl alkyl ester is tris(trimethylsiloxy)-silylpropyl methacrylate. The product of any preceding claim, wherein A is selected from the group consisting of methacryloxy and acryloxy. The product of any preceding claim, wherein R₃ is a linear, divalent hydrocarbon radical having 3 or 4 carbon atoms. The product of any preceding claim, wherein each R₄ and R₅ is a methyl radical or fluoromethyl radical. The product of any preceding claim, wherein b is 10 to 30. The product of any preceding claim, wherein said optional crosslinking monomer is neopentyl glycol dimethacrylate. The product of any preceding claim, wherein said hydrophilic monomer is methacrylic acid. The product of any preceding claim formed by polymerizing 40 to 70 weight % of monomer (a), 20 to 40 weight % of monomer (b), 7 to 15 weight % of monomer (c), and 2 to 10 weight % of monomer (d). A contact lens made of a polymerization product as defined in any preceding claim. The contact lens of Claim 16, wherein said fluoroorgano monomer is hexafluoroisopropyl methacrylate, said siloxyl alkyl ester is tris(trimethylsiloxy)-silylpropyl methacrylate, A is methacryloxy, R₃ is tetramethylene, each R₄ and R₅ is a methyl group, b is an integer from 10 to 50, said optional crosslinking monomer is neopentyl glycol dimethacrylate, and said hydrophilic monomer is methacrylic acid. The contact lens of Claim 16, wherein monomer component (c) is a mixture of said poly(organosiloxane)monomer and neopentyl glycol dimethacrylate and the weight ratio of poly(organosiloxane)monomer: neopentyl glycol dimethacrylate is within the range from about 0.5:1 to about 1.5:1. A process for making a polymerization product, comprising the steps of: (1) preparing a monomer mixture which comprises: (a) 40 to 80 weight % of at least one fluoroorgano monomer having the formula: wherein R₁ is a hydrogen atom or a methyl group and Y is a fluorocarbon group having 2 to 10 carbon atoms and 3 to 21 fluorine atoms; (b) 15 to 40 weight % of at least one siloxyl alkyl ester having the formula: wherein R₁ is as defined above, each R₂ is independently selected from the group consisting of methyl and phenyl groups, and a is 1, 3 or 4; (c) 4 to 20 weight % of a member of the group consisting of: (i) at least one poly(organosiloxane) monomer having the formula wherein A is an activated unsaturated group, R₃ is a divalent hydrocarbon radical having from 1 to 22 carbon atoms, each R₄ and R₅ is independently selected from the group consisting of monovalent hydrocarbon radicals and - halogen-substituted monovalent hydrocarbon radicals having 1-12 carbon atoms, and b is O or greater, and (ii) mixtures of said poly(organosiloxane) monomers and at least one optional crosslinking monomer having the formula wherein R₁ is as defined above and R₆ is a divalent hydrocarbon radical having 2-12 carbon atoms; and (d) 1 to 15 weight % of at least one hydrophilic monomer and (2) subjecting said monomer mixture to polymerization conditions to thereby form a polymerization product. A process according to Claim 19, wherein said polymerization conditions comprise the application of heat or radiation treatment. A process according to Claim 19 or Claim 20, wherein said monomer mixture is held in sheet form during polymerization, whereby the polymerization product is a sheet. A process according to Claim 19 or Claim 20, wherein said monomer mixture is polymerized in a mold to provide a polymerization product of a desired shape. A process according to Claim 21, wherein said mold corresponds to the shape of a contact lens. A process according to any preceding claim, wherein said monomer mixture is as defined in any one of Claims 2-15. A method of manufacturing a contact lens, comprising the steps of: (1) making a polymerization product by a process according to any one of Claims 19-24, and (2) shaping the polymerization product into a contact lens by mechanical processing.

Inventors: DEICHERT, WILLIAM G.
Applicants: BAUSCH & LOMB INCORPORATED
Application year: 1988
Main classification: C08F220
IPC codes: C08F290, C08F230, G02C7, C08F220, C08F299, G02B1