Ocular lens material and process for producing the same

Abstract: Ocular lens materials comprising copolymers obtainable by polymerizing a monomer mixture comprising: (A) an N-vinyllactam; (B) a fluorine-containing unsaturated monomer; (C) a hydrophilic (meth)acrylamide; (D) a crosslinking agent having at least 2 (meth)acryloyloxy groups; and (E) a dicarboxylic acid divinyl ester; and ocular lenses comprising these ocular lens materials. The ocular lens materials and ocular lenses according to the present invention, causing no elution and having a high water-retaining capability and oxygen permeability, are excellent in transparency, resistance to deposition, mechanical strength, flexibility, safety, durability, ability of correcting visual acuity, comfort during wear and handleability.

Description: The present invention relates to a material for ocular lenses and a process for producing the same. The present invention also relates to ocular lenses comprising the above ocular lens material and copolymers suitable as the ocular lens material. The ocular lens materials, as well as the ocular lenses, according to the present invention cause no or very little elution therefrom and have a high water-retaining capability and oxygen permeability and excellent transparency, resistance to deposition, mechanical strength and flexibility. As a result, the ocular lens materials and ocular lenses of the present invention have high ability of correcting visual acuity and excellent durability, safety, comfort during wear and handleability, and are hence suitable as ocular lenses, e.g. soft contact lens, intraocular lens and artificial crystal lens, in particular as soft contact lens. Copolymer hydrogels principally comprising 2-hydroxyethyl methacrylate have been widely used for producing soft contact lenses. This is because that 2-hydroxyethyl methacrylate copolymers, having excellent machine-cuttability and -polishability, are readily processable into lenses and that hydrogels obtained by hydration and swelling of the copolymers have an appropriate strength and flexibility. However, hydrogels of 2-hydroxyethyl methacrylate copolymers have, in general, a low water content of less than 40% by weight and soft contact lenses formed therefrom have poor oxygen permeability. Soft contact lenses from the 2-hydroxyethyl methacrylate copolymers therefore fail, when in use, to allow oxygen to be supplied to cornea in a physiologically sufficient amount. Consequently, these soft contact lenses may, when worn for a long period of time, cause the cornea tissue to suffer from anoxia, which leads to eye injury eventually. Attempts have therefore been made to develop a soft contact lens having high oxygen permeability and a material therefor, which can replace the 2-hydroxyethyl methacrylate copolymer hydrogels. Representative examples of the prior art so far developed are as follows. (1) A process for producing polymeric materials having a dually crosslinked structure usable for ocular lens, which comprises using, on producing a crosslinked polymer from two types of vinyl monomers which are hardly copolymerizable with each other, such as a combination of an N-vinyllactam and a (meth)acrylate, two types of crosslinking agents, one having a high copolymerizability with one of the 2 monomers and the other with the counterpart monomer (JP-A- 3487/1975 and 140594/1975). (2) A soft contact lens with high water content obtained by copolymerizing a composition principally comprising methylacrylamide and a fluoroalkyl (meth)acrylate and then shaping the resulting copolymer (JP-A-293520/1988). (3) A copolymer obtained by copolymerizing a polymerizable composition containing specific amounts of N,N-dimethylacrylamide and a specific fluoroalkyl (meth)acrylate and, as necessary, not more than a specific amount each of another copolymerizable vinyl monomer and a crosslinking agent; and a contact lens comprising the copolymer (JP-A-70713/1990,: US-A-4,954,587 and 5,011,275). However, the polymeric material obtained by the prior art (1), having no resistance to deposition which is essential for ocular lenses such as contact lens, causes, when a soft contact lens comprising the material is worn, much deposition on the lens. As a result, the lens may cause cornea injury or may not correct the visual acuity sufficiently.Furthermore, the contact lenses obtained by the prior art (2) and (3) have very low strength and readily break, thus having no durability, and cannot be used in practice.Contact lenses, which directly touch the eyes, are required to generate no eluates, in order to prevent eye injury and provide sufficient ability to correct visual acuity. The polymeric material obtained by the prior art (1), using the 2 types of crosslinking agents, can suppress the amount of eluate therefrom to some extent, but insufficiently.There has been proposed, in order to provide a low-elution material for contact lenses: (4) a process for producing hydrophilic polymers for soft contact lenses, which comprises polymerizing a methacrylic acid ester and an N-vinyllactam in the presence of a crosslinking agent such as vinyl methacrylate, vinyl acrylate, triallyl isocyanulate or dicarboxylic acid divinyl esters (JP-A-105992/1977 and 74049/1978 and US-A-4,184,992). However, the prior art process (4) sometimes leads to formation of an opaque polymer, which is not satisfyable for ocular lenses requiring high transparency. In this situation, there has been strongly demanded development of an ocular lens material, in particular one suitable for soft contact lenses, having high water-retaining capability and oxygen permeability, as well as excellent transparency, resistance to deposition, mechanical strength and flexibility, and causing no elution. As a result of an intensive study to develop an ocular lens material having the above features, the present inventors had found the following materials and applied patents therefor (JP-A-134029/1994, 53639/1995, 239431/1996 and 278832/1997). These materials include: i) a hydrogel comprising a copolymer obtained by polymerizingapolymerizablehydrophilic monomer, N-hydroxymethylacrylamide and a crosslinking agent; ii) a water-retaining ocular lens material comprising a copolymer of an N-vinyllactam and a specific fluoroalkyl (meth)acrylate; iii) a water-retaining ocular lens material comprising a copolymer obtained by polymerizing a monomer mixture containing N-acryloylmorpholine, a fluorine-containing unsaturated monomer and a crosslinking agent; and iv) an ocular lens material comprising a copolymer obtained by polymerizing a monomer mixture containing an N-vinyllactam, N,N-dimethylacrylamide, a fluoroalkyl (meth)acrylate and a crosslinking agent. These materials all have high water-retaining capability and oxygen permeability, as well as excellent transparency, resistance to deposition, strength and flexibility and are hence very suitable as materials for ocular lenses, such as soft contact lens. The present inventors, taking the above results into account, made a further study and found the following fact. That is, copolymers obtained by polymerizing a monomer mixture comprising the specific 5 types of monomers, i.e. an N-vinyllactam, a fluorine-containing unsaturated monomer, a hydrophilic (meth)acrylamide, a crosslinking agent having at least 2 (meth)acryloyloxy groups and a dicarboxylic acid divinyl ester, have high water-retaining capability and oxygen permeability, as well as excellent transparency, resistance to deposition, strength and flexibility and, further, cause no or very little elution to water or alcohol, thus proving excellent in safety and ability of correcting visual acuity. Accordingly, the copolymers are markedly suitable as materials for ocular lenses such as soft contact lens. The present inventors further found that, on producing the above copolymers, use of a specific thermally decomposable initiator insures still better suppression of elution from the resulting copolymers, and completed the invention based on these findings. The present invention provides an ocular lens material comprising a copolymer obtainable by polymerizing a monomer mixture comprising: (A) an N-vinyllactam (hereinafter referred to as " N-vinyllactam (A)"; (B) a fluorine-containing unsaturated monomer (hereinafter referred to as "fluorine-containing unsaturated monomer (B)"; (C) a hydrophilic (meth)acrylamide (hereinafter referred to as "hydrophilic (meth)acrylamide (C)"; (D) a crosslinking agent having at least 2 (meth) acryloyloxy groups (hereinafter referred to as " (meth)acryl-based crosslinking agent (D)"); and (E) a dicarboxylic acid divinyl ester (hereinafter referred to as "dicarboxylic acid divinyl ester (E)"). The present invention also provides an ocular lens comprising the above ocular lens material. The present invention further provides a process for producing ocular lens materials, which comprises polymerizing the above monomer mixture comprising the N-vinyllactam (A), fluorine-containing unsaturated monomer (B), hydrophilic (meth)acrylamide (C), (meth)acryl-based crosslinking agent (D) and dicarboxylic acid divinyl ester (E), with a thermally decomposable initiator having a 10-hour half-life temperature of at least 50°C. The present invention still further provides a copolymer obtainable by polymerizing the above monomer mixture comprising the N-vinyllactam (A), fluorine-containing unsaturated monomer (B), hydrophilic (meth)acrylamide (C), (meth)acryl-based crosslinking agent (D) and dicarboxylic acid divinyl ester (E). The present invention is now described in detail. As stated above, the ocular lens material of the present invention comprises a copolymer obtainable by polymerizing the above monomer mixture comprising an N-vinyllactam (A), a fluorine-containing unsaturated monomer (B), a hydrophilic (meth)acrylamide (C), a (meth)acryl-based crosslinking agent (D) and a dicarboxylic acid divinyl ester (E). The N-vinyllactam (A) used in the present invention contributes to providing the resulting copolymer with high water-retaining capability, and increasing the oxygen permeability and mechanical strength of the resulting copolymer hydrogel. In the present invention, any cyclic compound having in the ring thereof an atomic group represented by the formula -CON(CH=CH 2 )- can be used as the N-vinyllactam with no specific limitation. Examples of N-vinyllactams (A) usable in the present invention include N-vinyl-β-propiolactams, N-vinyl- γ -butyrolactams (N-vinyl-2-pyrrolidones), N-vinyl- δ -valerolactams (N-vinyl-2-piperidones) and N-vinyl-ε-caprolactams. More concretely, examples of N-vinyllactams (A) usable in the present invention are N-vinyl-2-pyrrolidones, e.g. N-vinyl-2-pyrrolidone, N-vinyl-3-methyl-2-pyrrolidone, N-vinyl-4-methyl-2-pyrrolidone, N-vinyl-5-methyl-2-pyrrolidone, N-vinyl-3-ethyl-2-pyrrolidone, N-vinyl-4,5-dimethyl-2-pyrrolidone, N-vinyl-5,5-dimethyl-2-pyrrolidone, N-vinyl-3,3,5-trimethyl-2-pyrrolidone, N-vinyl-5-methyl-5-ethyl-2-pyrrolidone and N-vinyl-3,3,5-trimethyl-3-ethyl-2-pyrrolidone; N-vinyl-2-piperidones, e.g. N-vinyl-2-piperidone, N-vinyl-3-methyl-2-piperidone, N-vinyl-4-methyl-2-piperidone, N-vinyl-5-methyl-2-piperidone, N-N-vinyl-3-methyl-2-piperidone, N-vinyl-6-ethyl-2-piperidone, N-vinyl-3,5-dimethyl-2-piperidone and N-vinyl-4,4-dimethyl-2-piperidone; and N-vinyl- E -caprolactams, e.g. N-vinyl- ε -caprolactam, N-vinyl-3-methyl- ε -caprolactam, N-vinyl-4-methyl-ε-caprolactam, N-vinyl-7-methyl-ε-caprolactam, N-vinyl-7-ethyl-ε-caprolactam, N-vinyl-3,5-dimethyl- ε-caprolactam, N-vinyl-3,5-diethyl-ε-caprolactam, N-vinyl-4,6-dimethyl- ε -caprolactam and N-vinyl-3,5,7-trimethyl-ε-caprolactam. In the present invention, these N-vinyllactams may be used either singly or in combination of 2 or more as the N-vinyllactam (A). Among these N-vinyllactams, either one or both of N-vinyl-2-pyrrolidone and N-vinyl-2-piperidone is preferably used as the N-vinyllactam (A) in the invention. The fluorine-containing unsaturated monomer (B) used in the present invention contributes to providing the resulting ocular lens material and ocular lenses therefrom, in particular contact lens, with good resistance to deposition, which prevents deposition of substances such as protein on the lenses , and increasing the mechanical strength of the lenses. As the fluorine-containing unsaturated monomer (B), the fluoroalkyl esters of (meth)acrylic acid, i.e. fluoroalkyl (meth) acrylates, are preferably used. Among fluoroaklyl (meth)acrylates, those with the fluoroalkyl group forming the ester having 2 to 15 carbon atoms are preferably used, since the copolymers obtained by polymerization of the resulting monomer mixture, as well as the ocular lens materials obtained therefrom, will have still better transparency. Examples of fluoroalkyl (meth)acrylates preferably usable in the present invention are 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3-tetrafluoropropyl (meth)acrylate, 3,3,4,4-tetrafluorobutyl (meth)acrylate, 1,1,1,3,3,3-hexafluoroisopropyl (meth)acrylate, 2,2,3,4,4,4-hexafluorobutyl (meth)acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl (meth)acrylate, 3,3,4,4,5,5,5-heptafluoropentyl (meth)acrylate, 3,3,4,4,5,5,6,6,6-nonafluorohexyl (meth)acrylate, 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl (meth)acrylate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorononyl (meth)acrylate, 5-trifluoromethyl-3,3,4,4,5,6,6,6-octafluorohexyl (meth)acrylate and 2,2,3,3,3-pentafluoropropyl (meth)acrylate. These fluoroalkyl (meth)acrylates may be used either singly or in combination of 2 or more. In the present invention, among these fluoroalkyl (meth)acrylates, in particular those represented by the following general formula (I) are preferably used, since such fluoroalkyl (meth)acrylates can provide water-retaining ocular lens materials, as well as ocular lenses therefrom, having still better optical transparency. CH 2 =C(R 1 )-COO-(CH 2 ) m -(CF 2 ) n -CF 2 H wherein R 1 represents hydrogen atom or methyl group, and m and n represent an integer of 1 to 4 and that of 1 to 10, respectively. Examples of the fluoroalkyl (meth)acrylates represented by the above general formula (I) are 2,2,3,3-tetrafluoropropyl (meth)acrylate, 3,3,4,4-tetrafluorobutyl (meth)acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl (meth)acrylate, 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl (meth)acrylate and 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorononyl (meth)acrylate. In the present invention, there may be used as the fluorine-containing unsaturated monomer (B), fluoroalkyl (meth)acrylates with their fluoroalkyl group having a hydroxyl group, either singly or in combination with the above fluoroalkyl (meth)acrylates having no hydroxyl group. Use of such fluoroaklyl (meth)acrylates with the fluoroalkyl group having a hydroxyl group, which have high compatibility with N-vinyllactam (A) and hydrophilic (meth)acrylamide (C), increases the content of the structural unit from the fluorine-containing unsaturated monomer (B), thereby providing the resulting ocular lens materials with still better resistance to deposition, optical transparency and mechanical strength. Examples of fluoroalkyl (meth)acrylates with their fluoroalkyl group having a hydroxyl group are 3-(perfluorobutyl)-2-hydroxypropyl (meth)acrylate, 3-(perfluorohexyl)-2-hydroxypropyl (meth)acrylate, 3-(perfluorooctyl)-2-hydroxypropyl (meth)acrylate, 3-(perfluoro-3-methylbutyl)-2-hydroxypropyl (meth)acrylate, 3-(perfluoro-3-methylhexyl)-2-hydroxypropyl (meth)acrylate and 3-(perfluoro-3-methyloctyl-2-hydroxypropyl (meth)acrylate. These fluoroalkyl (meth)acrylates may be used either singly or in combination of 2 or more. The hydrophilic (meth)acrylamide (C) used in the present invention contributes to increasing the hydrophilic property and oxygen permeability and minimizing decrease in the mechanical strength, of the resulting ocular lens material and ocular lenses therefrom, and providing good flexibility to the material and ocular lenses therefrom. In the present invention, all hydrophilic (meth)acrylamides can be used as the hydrophilic (meth)acrylamide (C). Among these, those represented by the following general formula (II) are preferably used: CH 2 = C(R 2 )-CO-N(R 3 )(R 4 ) wherein R 2 represents hydrogen atom or methyl group, and R 3 and R 4 each independently represents hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkyl group with a hydroxyl group having 1 to 4 carbon atoms, or R 3 and R 4 combinedly represent an alkylene group represented by the formula -(CH 2 ) n -(wherein n is an integer of 4 to 6) or a divalent group represented by the formula -(CH 2 ) 2 -O-(CH 2 ) 2 -. With the hydrophilic (meth)acrylamide (C) represented by the general formula (II), where R 3 and R 4 combinedly form an alkylene group represented by the formula -(CH 2 ) n - (wherein n is as defined above) or a divalent group represented by the formula -(CH 2 ) 2 -O-(CH 2 ) 2 -, these divalent groups each forms, together with the nitrogen atom of the hydrophilic (meth)acrylamide (C), a heterocycle having nitrogen atom. Concrete examples of hydrophilic (meth)acrylamides preferably used in the present invention are (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide and N-(meth)acryloylmorpholine. These hydrophilic (meth)acrylamides may be used either singly or in combination of 2 or more. Among these, in the present invention, acrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide and/or N-acryloylmorpholine are preferably used as the hydrophilic (meth)acrylamide (C), in view of hydrophilic property, flexibility and mechanical strength. In particular, N-acryloylmorpholine is more preferably used in view of, in addition to the above features, cuttability. Finally in the present invention, it is necessary to use, together with the above N-vinyllactam (A), fluorine-containing unsaturated monomer (B) and hydrophilic (meth)acrylamide (C), specific 2 types of crosslinking agents consisting of a (meth)acryl-based crosslinking agent (D) and a dicarboxylic acid divinyl ester (E). The vinyl group present in the N-vinyllactam (A) generally has poor compatibility with the (meth)acryloyl group present in fluoroalkyl (meth)acrylates preferably used as the fluorine-containing unsaturated monomer (B) or in the hydrophilic (meth)acrylamide (C). As a result, a mixture comprising an N-vinyllactam (A), a fluorine-containing unsaturated monomer (B) [fluoroalkyl (meth)acrylate] and a hydrophilic (meth)acrylamide will, when polymerized as it is, tend to yield, separately, a polymer principally containing the N-vinyllactam (A) and one principally containing the fluorine-containing unsaturated monomer (B) [fluoroalkyl (meth)acrylate] and hydrophilic (meth)acrylamide (C). If either one of the (meth)acryl-based crosslinking agent (D) and dicarboxylic acid divinyl ester (E) is, alone, added to a mixture of an N-vinyllactam (A), a fluorine-containing unsaturated monomer (B) [fluoroalkyl (meth)acrylate] and a hydrophilic acrylamide (C) , the resulting polymer principally comprising the N-vinyllactam (A) will hardly be crosslinked, while the other resulting polymer principally comprising the fluorine-containing unsaturated monomer (B) (fluoroalkyl (meth)acrylate] and the hydrophilic acrylamide (C) will be crosslinked; or, the resulting polymer principally comprising the N-vinyllactam (A) will be crosslinked, while the other resulting polymer principally comprising the fluorine-containing unsaturated monomer (B) [fluoroalkyl (meth)acrylate] and the hydrophilic acrylamide (C) will hardly be crosslinked. In both cases, the polymer mixture will cause significant elution. Likewise, use of, as described in the above JP-A-105992/1977, a vinyl methacrylate having both methacryloyl group and vinyl group as a crosslinking agent tends to lead to phase separation of a polymer principally comprising the N-vinyllactam (A) and another polymer principally comprising the fluorine-containing unsaturated monomer (B) [fluoroalkyl (meth)acrylate] and the hydrophilic acrylamide (C). In this case, the copolymer obtained by the polymerization would become opaque. In contrast, in the present invention, selection of the specific 2 types of a (meth)acryl-based crosslinking agent (D) and a dicarboxylic acid divinyl ester (E) is made and the two are combinedly used and added to a monomer mixture comprising an N-vinyllactam (A), a fluorine-containing unsaturated monomer (B) and a hydrophilic (meth)acrylamide (C). Then, the resulting copolymer for ocular lens material is entirely crosslinked in a good manner, causing no phase separation, so that the copolymer does not become opaque, thus having excellent transparency, and causes no or very little elution. The (meth)acryl-based crosslinking agent (D) used in the present invention is a compound obtainable by reacting a compound having at least 2 hydroxyl groups with acrylic acid and/or methacrylic acid and by esterifying the at least 2 hydroxyl groups with the (meth)acrylic acid, i.e. a compound having at least 2 (meth)acryloyloxy groups. In the present invention, compounds obtainable by esterifying the at least 2 hydroxyl groups present in a polyhydric alcohol with (meth)acrylic acid are preferably used as the (meth)acryl-based crosslinking agent (D). Concrete examples are alkylene glycol di(meth)acrylates, e.g. ethylene glycol di(meth)acrylate, 2-acryloyloxyethyl (meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate and neopentyl glycol di(meth)acrylate; polyalkylene glycol di(meth)acrylates, e.g. diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetradecaethylene glycol di(meth) acrylate, polyethylene glycol di (meth) acrylate and polypropylene glycol di(meth)acrylate; trimethylolpropane tri(meth)acrylate and 2,2-bis[p-(γ-methacryloyloxy-β-hydroxypropoxy)phenyl]propane. These (meth)acryl-based crosslinking agent may be used singly or in combination of 2 or more. Among the above, in the present invention, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate and diethylene glycol di(meth)acrylate are preferably used as the (meth)acryl-based crosslinking agent (D) in view of mechanical strength and flexibility. In the present invention, any one of aliphatic dicarboxylic acid divinyl esters, alicyclic dicarboxylic acid divinyl esters and aromatic dicarboxylic acid divinyl esters can be used as the dicarboxylic acid divinyl ester (E). Concrete examples are divinyl succinate, divinyl glutarate, divinyl adipate, divinyl maleate, divinyl cyclohexane-1,4-dicarboxylate, divinyl phthalate, divinyl isophthalate and divinyl terephthalate. These dicarboxylic acid divinyl esters may be used singly or in combination of 2 or more. Among the above, divinyl adipate and divinyl phthalate are preferably used as the dicarboxylic acid divinyl ester (E) in the present invention, in view of mechanical strength and flexibility. In the present invention, in order to obtain, smoothly and surely, ocular lens materials having high water-retaining capability and oxygen permeability, excellent transparency, resistance to deposition, mechanical strength and flexibility, and causing no elution, it is desirable to produce copolymers (ocular lens materials) from a monomer mixture containing, based on the total weight thereof , 35 to 70% by weight of the above N-vinyllactam (A), 20 to 50% by weight of the fluorine-containing unsaturated monomer (B) , 5 to 40% by weight of the hydrophilic (meth)acrylamide (C), 0.01 to 1% by weight of the (meth)acryl-based crosslinking agent (D) and 0.01 to 1% by weight of the dicarboxylic acid divinyl ester (E). It is more preferable to produce copolymers by using a monomer mixture containing 45 to 65% by weight of the N-vinyllactam (A), 20 to 40% by weight of fluorine-containing unsaturated monomer (B), 10 to 30% by weight of hydrophilic (meth)acrylamide (C), 0.2 to 0.75% by weight of (meth)acryl-based crosslinking agent (D) and 0.2 to 0.75% by weight of dicarboxylic acid divinyl ester (E). If the content of the N-vinyllactam (A) in the monomer mixture is less than 35% by weight, the resulting copolymer, as well as the ocular lens material therefrom, will tend to have a low water-retaining capability and oxygen permeability. On the other hand, if the content exceeds 70% by weight, the resulting copolymer and ocular lens material will tend to have a low mechanical strength, thereby losing durability. If the content of the fluorine-containing monomer (B) in the monomer mixture is less than 20% by weight, the resulting copolymer, as well as the ocular lens material therefrom, will tend to have poor mechanical strength, resistance to deposition and oxygen permeability. On the other hand, if the content exceeds 50% by weight, the resulting copolymer and ocular lens material will tend to have low water-retaining capability and flexibility. If the content of the hydrophilic (meth)acrylamide (C) in the monomer mixture is less than 5% by weight, the resulting copolymer, as well as the ocular lens material therefrom, will tend to have low flexibility. On the other hand, if the content exceeds 40% by weight, the resulting copolymer and ocular lens material will tend to have a low mechanical strength and lose durability. It is further desirable that the total content of the N-vinyllactam (A) and the hydrophilic (meth)acrylamide (C) in the monomer mixture be within the range of 40 to 80% by weight based on the total weight of the monomer mixture. This range will lead to producing more smoothly ocular lens materials havinghigh water-retainingcapability and oxygen permeability and excellent transparency, resistance to deposition, mechanical strength and flexibility and causing no elution. The content is more preferably within the range of 55 to 75% by weight. If the total content of the N-vinyllactam (A) and the hydrophilic (meth) acrylamide (C) in the monomer mixture is less than 40% by weight, the resulting copolymer, as well as the ocular lens material therefrom, will tend to have low water-retaining capability and oxygen permeability. On the other hand, if the total content exceeds 80% by weight, the resulting copolymer and ocular lens material will tend to have too high water-retaining capability and low mechanical strength. If the content of the (meth)acryl-based crosslinking agent (D) or the dicarboxylic acid divinyl ester (E) is less than 0.01%, which is outside the above range, the resulting copolymer, as well as the ocular lens material therefrom, will tend to generate a large amount of eluate therefrom. On the other hand, if the content each exceeds 1% by weight, the resulting copolymer and ocular lens material will tend to have low water-retaining capability and flexibility. Further with the monomer mixture, the total content of the (meth)acryl-based crosslinking agent (D) and the dicarboxylic acid divinyl ester (E) is desirably within the range of 0.02 to 2% by weight based on the total weight of the monomer mixture, more preferably within the range of 0.4 to 1.5% by weight on the same basis. If the total content of the (meth)acryl-based crosslinking agent (D) and the dicarboxylic acid divinyl ester (E) is less than 0.02%, the resulting copolymer, as well as the ocular lens material therefrom, will tend to generate a large amount of eluate therefrom. On the other hand, if the total content exceeds 2% by weight, the resulting copolymer and ocular lens material will tend to have low water-retaining capability and flexibility. The monomer mixture used in the present invention may contain, besides the above monomers, other copolymerizable monomers and/or polymers within limits not to impair the purpose of the invention. Examples of usable other monomers are aliphatic vinyl esters, e.g. vinyl acetate, vinyl butyrate and vinyl laurate; itaconic acid diesters, e.g. dimethyl itaconate and diethyl itaconate; and unsaturated carboxylic acids, e.g. (meth)acrylic acid and itaconic acid. Examples of usable other polymers are polyvinyl alcohol, polyvinylpyrrolidone, polymethyl (meth)acrylate, polyorganosiloxanes and derivatives of the foregoing obtained by introducing a polymerizable group such as vinyl group. These other monomers and polymers may be used either singly or in combination of 2 or more. On incorporation of these monomers and/or polymers into the monomer mixture, it is desirable that the content be not more than about 10% by weight based on the total weight of the monomer mixture (where polymers are incorporated, total weight of all monomers and polymers), which insures production of copolymers and ocular lens materials having the above excellent features. Further in the present invention, a color may be added to the monomer mixture on production of copolymers, in order to obtain colored ocular lens materials. The copolymers and ocular lens materials of the present invention can be produced by polymerizing a monomer mixture containing the above N-vinyllactam (A), fluorine-containing unsaturated monomer (B), hydrophilic (meth)acrylamide (C), (meth)acryl-based crosslinking agent (D) and dicarboxylic acid divinyl ester (E) as essential components and, as necessary, other monomers and/or polymers preferably in an amount of not more than the above range. On conducting the polymerization, any process generally employed for polymerizing unsaturated monomers is usable with no specific limitation. Typically, the polymerization is conducted with either one or both of a thermally decomposable initiator and an energy beam (such as light)-decomposable initiator. Of the two, use of a thermally decomposable initiator to conduct heat polymerization of the above monomer mixture is desirable, which insures production of copolymers and ocular lens materials causing no elution. On conducting heat polymerization of the monomer mixture with a thermally decomposable initiator, it is desirable to use e.g. a constant-temperature bath or a hot air circulating heating apparatus with which the temperature can be controlled easily. Examples of the thermally decomposable initiator are peroxide-based thermally decomposable initiators, e.g. benzoyl peroxide, isopropyl peroxide, lauroyl peroxide and methyl ethyl ketone peroxide; and azo-based thermally decomposable initiators, e.g. 2,2'-azobisisobutyronitrile, 2,2'-azobismethyl isobutyrate, 2,2'-azobisdimethylvaleronitrile, 2,2'-azobisisobutylamide and dimethyl 2,2'-azobisisobutyrate. These thermally decomposable initiators may be used singly or in combination of 2 or more. With the monomer mixture used in the present invention, the polymerizability of the fluorine-containing unsaturated monomer (B) [fluoroalkyl (meth)acrylate] or the hydrophilic (meth)acrylamide (C) differs from that of the N-vinyllactam (A). As a result, there tends to occur that, at early stages of polymerization, the fluorine-containing unsaturated monomer (B) and hydrophilic (meth)acrylamide (C), which are readily reactable with the polymerization initiator used, mainly polymerize; and then, at later stages of polymerization, the N-vinyllactam (A) polymerizes. In order to obtain a copolymer causing no elution, in which all monomers contained in the monomer mixture are completely polymerized and crosslinked, it becomes therefore necessary to conduct sufficient polymerization not only at early stages but at later stages. In order to make the polymerization proceed surely at early stages through later stages, it then becomes necessary to use a thermally decomposable initiator capable of maintaining its activity during heat polymerization, and to control the viscosity at a low level (keeping high flowability) of the polymerization mixture by adjusting the polymerization temperature above a prescribed level, thereby facilitating polymerization of the monomers. In view of the above, on production of the ocular lens materials (copolymers) of the present invention by polymerizing a monomer mixture comprising as essential components an N-vinyllactam (A), a fluorine-containing unsaturated monomer (B), a hydrophilic (meth)acrylamide (C), a (meth)acryl-based crosslinking agent (D) and a dicarboxylic acid divinyl ester (E), it is desirable to use a thermally decomposable initiator having a 10-hour half-life temperature of at least 50°C. Any thermally decomposable initiator having a 10-hour half-life temperature of at least 50°C can be used for this purpose. Examples of such initiators are azo-based thermally decomposable initiators, e.g. 2,2'-azobisisobutyronitrile, 2,2'-azobisisobutylamide and dimethyl 2,2'-azobisisobutyrate. The polymerization temperature for the above monomer mixture is desirably at least 40°C, which maintains the viscosity of polymerization mixture at a low level, so that the flowability of the reaction mixture will not be lost. The "10-hour half-life temperature" referred to in the present invention means the temperature at which the activity of the thermally decomposable initiator used decreases to half the initial value after 10 hours. In other words, the higher the 10-hour half-life temperature of a thermally decomposable initiator, the longer its activity is maintained under heating during polymerization. It is desirable that the amount of the initiator used, whether it may be a thermally decomposable initiator or an energy beam-decomposable initiator, be 0.01 to 5% by weight based on the total weight of the monomer mixture. The above described process can give ocular lens materials (copolymers) that cause no or very little elution, have high water-retaining capability and oxygen permeability and excellent transparency, resistance to deposition, mechanical strength and flexibility. The resulting ocular lens materials are suitable for producing ocular lenses, such as soft contact lens, intraocular lens and artificial crystal lens, in particular soft contact lens. The ocular lens materials (copolymers) of the present invention may be, as they are without being subjected to cutting or polishing, circulated or put on the market; or they may be shaped into ocular lenses and then circulated and put on the market. The water-retainable ocular lens materials (copolymers) of the present invention can yield ocular lenses by any of the usual processes having been employed for producing plastic ocular lenses, with no specific limitation. Thus, ocular lenses can, for example, be produced by the following processes. (1) The lathe-cut process which comprises polymerizing a monomer mixture comprising as essential components an N-vinyllactam (A), a fluorine-containing unsaturated monomer (B), a hydrophilic (meth)acrylamide (C), a (meth) acryl-based crosslinking agent (D) and a dicarboxylic acid divinyl ester (E) and, as necessary, other monomers, polymers and colorants shaping the resulting copolymer into a prescribed shape (such as sheet, plate or block) and then cutting and polishing the shape, to produce ocular lenses; (2) The mold process which comprises filling a mold having a cavity corresponding to the desired ocular lens, with the above monomer mixture and polymerizing and shaping the ocular lens in the mold; and (3) The spin-cast process which comprises dropping the above monomer mixture onto the surface of a mold rotating at a high speed to cast and spread the monomer mixture radially and, at the same time, polymerize and shape the monomer mixture, to produce ocular lenses. Swelling by immersion of the ocular lenses obtained above in an aqueous solution such as physiological saline solution or distilled water can produce water-retaining contact lenses such as soft contact lens, intraocular lenses and artificial crystal lenses. The ocular lens materials or ocular lenses preferably have a water content of at least 50% by weight, more preferably in a range of 50 to 85% by weight, most preferably in a range of 55 to 75% by weight, in view of flexibility and mechanical strength. The ocular lenses thus obtained of the present invention cause no or very little elution, generally having an elution ratio when immersed in distilled water at 20°C for 72 hours of less than 0.5% by weight ( substantially 0% by weight). These ocular lenses have a high water content of at least 50% by weight, a high tensile strength of at least 150 kg/mm 2 , an optimum Young's modulus for ocular lens of from 35 to 150 g/mm 2 , a high oxygen permeability of at least 40 x 10 -11 cc·cm/cm 2 ·sec·mmHg and a high light transmittance of at least 90%, and are excellent in mechanical strength, flexibility, durability, resistance to decomposition, comfort during wear, transparency, ability of correcting visual acuity and safety. The effects of the present invention can be summarized as follows. The water-retaining ocular lens materials and ocular lenses formed therefrom according to the present invention comprising copolymers obtainable by polymerizing a monomer mixture comprising an N-vinyllactam (A) , a fluorine-containing unsaturated monomer (B), a hydrophilic (meth)acrylamide (C), a (meth)acryl-based crosslinking agent (D) and a dicarboxylic acid divinyl ester (E) cause no or very little elution therefrom. Thanks to this feature, ocular lenses formed from the ocular lens materials of the present invention can be used, as they are without being subjected to extraction treatment to extract eluates therefrom, as ocular lenses, such as soft contact lens, having excellent safety, comfort during wear and ability of correcting visual acuity. Furthermore, the ocular lens materials and ocular lenses of the present invention have a high water-retaining capability and oxygen permeability, as well as high light transmittance, low haze value, high transparency, good resistance to deposition, and, besides, have high mechanical strength and flexibility. The ocular lenses are therefore most suited as soft contact lens, intraocular lens and artificial crystal lens , in particular as soft contact lens. The process of the present invention, which comprises polymerizing the above monomer mixture with a thermally decomposable initiator having a 10-hour half-life temperature of at least 50° C, can smoothly produce copolymers, which are ocular lens materials, having the above excellent features, in particular causing no elution. EXAMPLES Other features of the invention will become apparent in the course of the following detailed descriptions of exemplary embodiments. In the Examples and Comparative Examples that follow, the water-retaining capability, tensile strength and Young's modulus of ocular lens materials, the oxygen permeability (oxygen transmission rate), transparency (light transmittance and haze value), resistance to deposition and amount of eluates (elution ratio) of ocular lenses (soft contact lenses) were tested or evaluated by the following methods. Water-retaining capability of ocular lens material The ocular lens material comprising a copolymer (for producing soft contact lens) obtained in each of the following Examples and Comparative Examples was cut into a round-film like test specimen having a diameter of 15 mm and a thickness of 0.2 mm. The specimen was immersed in physiological saline solution at 25°C for at least overnight and water-swollen to saturation. After the specimen had been taken out from the physiological saline solution, the excess water adhering to the surface was swiftly removed with a sheet of absorbing paper. The specimen was then tested for the weight (Wa). The water-swollen specimen was then dried at 100°C to a constant weight and again the weight (Wb) was measured. The water content was obtained with the following formula and taken as a measure of the water-retaining capability. Water content (% by weight) = {(Wa-Wb)/Wa} x 100 Tensile strength and Young's modulus of ocular lens material The ocular lens material comprising a copolymer (for producing soft contact lens) obtained in each of the following Examples and Comparative Examples was cut into strip-shaped specimens having a length of 10 mm, a thickness of 0.3 mm and a width of 2 mm. The specimen was fixed by both ends thereof with pinches of a tensile tester (AUTOGRAPH IM-100, made by Shimadzu Corporation) and elongated at an extension rate of 50 mm/min in distilled water to breakage. The stress at the breakage was read and taken as the tensile strength. The Young's modulus (modulus of tensile elasticity) was calculated from the slope of the tangential line at the deformation starting point of the tensile stress-strain curve obtained in the above tensile test. Oxygen transmission rate of soft contact lens (1) The ocular lens material comprising a copolymer (for producing soft contact lens) obtained in each of the following Examples and Comparative Examples was cut into disks having a diameter of 15 mm and a thickness of 10 mm. The disks were cut and polished in the usual manner into 4 soft contact lenses having a base curve of 8.7 mm, a power of 0 diopter, a diameter of 13.5 mm and a thickness each of 0.05 mm, 0.10 mm, 0.15 mm and 0.20 mm. (2) The soft contact lenses prepared in the above (1) were tested for oxygen permeability in distilled water at 35°C with a SEIKAKEN type film oxygen transmission tester (made by Riken Seiki Kogyo Co., Ltd.). The obtained data were plotted on a graph with the X-axis representing the inverse of the thickness and the Y-axis the inverse of the oxygen transmission rate, and a linear regression line was drawn. The Y-intercept of the line was read and its inverse was taken as the oxygen transmission rate of the ocular lens (soft contact lens). Transparency of soft contact lens (light transmittance and haze value (1) The ocular lens material comprising a copolymer (for producing soft contact lens) obtained in each of the following Examples and Comparative Examples was cut into a disk having a diameter of 15 mm and a thickness of 10 mm. The disks were each cut and polished in the usual manner into a soft contact lens having a base curve of 8.7 mm, a power of 0 diopter, a diameter of 13.5 mm and a thickness of 0.20 mm. (2) The soft contact lens prepared in (1) above was, while being immersed in distilled water at 25°C, tested with a haze meter (MODEL TC-HIII, made by Tokyo Denshoku Co., Ltd.), using a halogen lamp as the light source. The luminosity of incident light (T1), that transmitted through the soft contact lens and distilled water (T2), that diffused by the distilled water (T3) and that diffused by the soft contact lens and distilled water (T4) were measured, to obtain the light transmittance and haze value with the following formulas. Light transmittance (%) = (T2/T1) x 100 Haze value = {(T1/T2) - (T3/T4)} x 100 Resistance to deposition of soft contact lens (1) The ocular lens material comprising a copolymer (for producing soft contact lens) obtained in each of the following Examples and Comparative Examples was cut into a disk having a diameter of 15 mm and a thickness of 10 mm. The disk was cut and polished in the usual manner into a soft contact lens having a base curve of 8.7 mm, a power of 0 diopter, a diameter of 13.5 mm and a thickness of 0.20 mm. (2) The soft contact lens prepared in (1) above was worn by a white rabbit for 2 days continuously. After the wear, the lens was taken out and projected through a magnifying projector (magnification: 10 times), and the projected image was evaluated visually. The following rating was used to show the results of evaluation. Good (O): No deposit is visible; and Bad (×) : Deposits are clearly seen. Amount of eluates from soft contact lens (elution ratio) (1) The ocular lens material comprising a copolymer (for producing soft contact lens) obtained in each of the following Examples and Comparative Examples was cut into 18 disks having a diameter of 15 mm and a thickness of 10 mm. The disks were cut and polished in the usual manner into soft contact lenses having a base curve of 8.7 mm, a power of 0 diopter, a diameter of 13.5 mm and a thickness of 0.20 mm. The soft contact lenses were tested for the total dry weight (Wc) of 9 sheets. (2) The 9 soft contact lenses prepared in (1) above were immersed in 6 ml of distilled water at 20°C for 72 hours, then taken out, dried and measured for the total dry weight (Wd). The amount of eluates (elution ratio) when immersed in distilled water was obtained with the following formula. Elution ratio in distilled water (%) = {(Wc - Wd)/Wc} x 100 (3) Separately, the remaining 9 sheets of the soft contact lenses were immersed in 6 ml of methanol at 20°C for 72 hours, then taken out, dried and measured for the total dry weight (We) of 9 sheets. The amount of eluates (elution ratio) when immersed in methanol was obtained with the following formula. Elution ratio in methanol (%) = {(Wc - We)/Wc} x 100 Examples 1 through 12 (1) To 10.0 g each of the monomer mixtures shown in Table 2 below, 0.01 g of dimethyl 2,2'-azobisisobutyrate as a thermally decomposable initiator was added. The resulting mixtures were each placed in a polypropylene test tube (capacity: 20 ml) and, after the air inside the tube had been replaced with nitrogen, the tubes were tightly sealed. The tubes were then immersed in a constant-temperature water bath at 55°C for 24 hours to effect polymerization, and then transferred to a hot air circulating heating apparatus at 100°C, where the tubes were kept for 2 hours to complete polymerization. After cooling, the resulting copolymers were taken out from the tubes. (2) The copolymers obtained in (1) above were each formed into test specimens (ocular lens materials) and soft contact lenses, by the methods described above, and then tested or evaluated for the water-retaining capability, tensile strength, Young's modulus, oxygen permeability, transparency (light transmittance and haze value), resistance to deposition and elution ratio, by the methods described above. The results are shown in Table 3 below. Comparative Examples 1 through 6 (1) To 10.0 g each of the monomer mixtures shown in Table 2 below, 0.01 g of dimethyl 2,2'-azobisisobutyrate as a thermally decomposable initiator was added. The resulting mixtures were each placed in a polypropylene test tube (capacity: 20 ml) and, after the air inside the tube had been replaced with nitrogen, the tubes were tightly sealed. The tubes were then immersed in a constant-temperature water bath at 55°C for 24 hours to effect polymerization, and then transferred to a hot air circulating heating apparatus at 100°C, where the tubes were kept for 2 hours to complete polymerization. After cooling, the resulting copolymers were taken out from the tubes. (2) The copolymers obtained in (1) above were each formed into test specimens (ocular lens materials) and soft contact lenses, by the methods described above, and then tested or evaluated for the water-retaining capability, tensile strength, Young's modulus, oxygen permeability, transparency (light transmittance and haze value), resistance to deposition and elution ratio, by the methods described above. The results are shown in Table 3 below. Reference Examples 1 through 5 (1) To 10.0 g each of the monomer mixtures shown in Table 2 below, 0.01 g of dimethyl 2,2'-azobisisobutyrate as a thermally decomposable initiator was added. The resulting mixtures were each placed in a polypropylene test tube (capacity: 20 ml) and, after the air inside the tube had been replaced with nitrogen, the tubes were tightly sealed. The tubes were then immersed in a constant-temperature water bath at 55°C for 24 hours to effect polymerization, and then transferred to a hot air circulating heating apparatus at 100°C, where the tubes were kept for 2 hours to complete polymerization. After cooling, the resulting copolymers were taken out from the tubes. (2) The copolymers obtained in (1) above were each formed into test specimens (ocular lens materials) and soft contact lenses, by the methods described above, and then tested or evaluated for the water-retaining capability, tensile strength, Young's modulus, oxygen permeability, transparency (light transmittance and haze value), resistance to deposition and elution ratio, by the methods described above. The results are shown in Table 3 below. The Reference Examples 1 through 5 correspond to the invention by the present inventors and described in the afore-described JP-A-278832/1997, or to the invention similar thereto. In Table 2 below, N-vinyllactam (A), fluorine-containing unsaturated monomers (B), hydrophilic (meth)acrylamides (C), (meth)acryl-based crosslinking agents (D), dicarboxylic acid divinyl esters (E) and other monomers are described by using abbreviations as shown in Table 1 below. Abbreviation Compound N-vinyllactam (A) NVP: N-vinyl-2-pyrrolidone Fluorine-containing unsaturated monomers (B) 3FM: CH 2 =C(CH 3 )-COO-CH 2 -CF 3 4FM: CH 2 =C(CH 3 )-COO-CH 2 -CF 2 -CF 2 H 8FM: CH 2 =C(CH 3 )-COO-CH 2 -CF 2 CF 2 CF 2 -CF 2 H 16FA: CH 2 =CH-COO-(CH 2 ) 2 -(CF 2 ) 7 -CF 2 H Hydrophilic (meth)acrylamides (C) DMAA: N,N-dimethylacrylamide ACMO: N-acryloylmorpholine HMAA: N-hydroxymethylacrylamide (Meth)acryl-based crosslinking agents (D) EGDMA: ethylene glycol dimethacrylate HD : 1,6-hexanediol dimethacrylate Dicarboxylic acid divinyl esters (E) ADVy: divinyl adipate FUVy: divinyl phthalate Other monomers MMA: methyl methacrylate MAVy: vinyl methacrylate ADAL: diallyl adipate FUAL: diallyl phthalate TAAL: diallyl tartrate The followings will be understood from the results given in Tables 2 and 3. The ocular lens materials and ocular lenses (soft contact lenses) obtained in Examples 1 through 12 have markedly low elution ratio and, in particular, 0% elution ratio in distilled water, thus causing substantially no eluates to form therefrom. The ocular lens materials and ocular lenses therefore need no extraction treatment to remove contained eluates and can be used as they are as ocular lenses directly. Furthermore, the ocular lens materials and ocular lenses (soft contact lenses) obtained in Examples 1 through 12 have a high water-retaining capability of at least 59% by weight, a high tensile strength of at least 165 kg/mm 2 , a Young's modulus of 40 to 150 g/mm 2 , a high oxygen transmission rate of at least 45 x 10 -11 cc·cm/cm 2 ·sec·mmHg, a high light transmittance of at least 99%, a low haze value of not more than 0.3% and good resistance to deposition, thus proving excellent in mechanical strength, durability, flexibility, comport during wear, transparency, ability of correcting visual acuity, safety and handling, and are hence very useful. On the other hand, the ocular lens materials and soft contact lenses containing no fluorine-containing unsaturated monomer (B), i.e. those obtained in Comparative Example 1 [ocular lens material and soft contact lens obtained from a monomer mixture containing an N-vinyllactam (A), a hydrophilic (meth)acrylamide (C), a (meth)acryl-based crosslinking agent (D) and a dicarboxylic acid divinyl ester (E)]; those obtained in Comparative Example 2 [ocular lens material and soft contact lens obtained from a monomer mixture containing an N-vinyllactam (A), a hydrophilic (meth)acrylamide (C), and a (meth) acryl-based crosslinking agent (D)]; and those obtained in Comparative Example 3 [ocular lens material and soft contact lens obtained from a monomer mixture containing an N-vinyllactam (A) and a hydrophilic (meth)acrylamide (C)], all have a low tensile strength and Young's modulus, thus proving inferior in mechanical strength and flexibility, have poor resistance to deposition and are poor in transparency and elution ratio as compared with Examples 1 through 12. These ocular lens materials and ocular lenses are therefore of low practical value. Besides, the ocular lens materials and soft contact lenses obtained in Comparative Examples 4 and 5, which correspond to the invention described in JP-A- 3487/1975 or 105992/1977 are inferior to those obtained in Examples 1 through 12 in resistance to deposition and elution ratio. The ocular lens material and soft contact lens obtained in Comparative Example 6, which corresponds to the invention described in JP-A- 293520/1988 have higher Young's modulus than those obtained in Examples 1 through 12, thus having poor flexibility, and are of low practical value. It is also understood from comparison between the results of Examples 1 through 12 and those of Reference Examples 1 through 5, in Tables 2 and 3, further improvement of no eluates (markedly low elution ratio) is realized in the ocular lens materials and ocular lenses of Examples 1 through 12 over those of Reference Examples 1 through 5, which have excellent water-retaining capability, tensile strength, flexibility, oxygen permeability and resistance to deposition. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims: An ocular lens material comprising a copolymer obtainable by polymerizing a monomer mixture comprising: (A) an N-vinyllactam; (B) a fluorine-containing unsaturated monomer; (C) a hydrophilic (meth)acrylamide; (D) a crosslinking agent having at least 2 (meth)acryloyloxy groups; and (E) a dicarboxylic acid divinyl ester. The ocular lens material according to Claim 1, wherein said monomer mixture contains, based on the total weight thereof, 35 to 70% by weight of said N-vinyllactam (A), 20 to 50% by weight of said fluorine-containing unsaturated monomer (B), 5 to 40% by weight of said hydrophilic (meth)acrylamide (C), 0.01 to 1% by weight of said crosslinking agent (D) and 0.01 to 1% by weight of said dicarboxylic acid divinyl ester (E). The ocular lens material according to either Claim 1 or Claim 2, wherein said fluorine-containing unsaturated monomer (B) is a fluoroalkyl (meth)acrylate. The ocular lens material according to Claim 3, wherein said fluoroalkyl (meth)acrylate is represented by the following general formula (I): CH 2 = C(R 1 )-COO-(CH 2 ) m -(CF 2 ) n -CF 2 H wherein R 1 represents a hydrogen atom or methyl group, and m and n represent an integer of 1 to 4 and of 1 to 10, respectively. The ocular lens material according to any one of Claim 1 through Claim 4, wherein said hydrophilic (meth)acrylamide (C) is represented by the following general formula (II): CH 2 = C(R 2 )-CO-N(R 3 )(R 4 ) wherein R 2 representsa hydrogen atom or methyl group, and R 3 and R 4 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkyl group with a hydroxyl group having 1 to 4 carbon atoms, or R 3 and R 4 combinedly represent an alkylene group represented by the formula -(CH 2 ) n -(wherein n is an integer of 4 to 6) or a divalent group represented by the formula -(CH 2 ) 2 -O-(CH 2 ) 2 -. The ocular lens material according to Claim 5, wherein said hydrophilic (meth)acrylamide (C) is at least one member selected from acrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide and N-acryloylmorpholine. The ocular lens material according to Claim 6, wherein said hydrophilic (meth)acrylamide (C) is N-acryloylmorpholine. A process for producing ocular lens materials, which comprises polymerizing a monomer mixture comprising: (A) an N-vinyllactam; (B) a fluorine-containing unsaturated monomer; (C) a hydrophilic (meth)acrylamide; (D) a crosslinking agent having at least 2 (meth)acryloyloxy groups; and (E) a dicarboxylic acid divinyl ester; with a thermally decomposable initiator having a 10-hour half-life temperature of at least 50°C. The process for producing ocular lens materials according to Claim 8, wherein said monomer mixture contains, based on the total weight thereof, 35 to 70% by weight of said N-vinyllactam (A), 20 to 50% by weight of said fluorine-containing unsaturated monomer (B) , 5 to 40% by weight of said hydrophilic (meth)acrylamide (C), 0.01 to 1% by weight of said crosslinking agent (D) and 0.01 to 1% by weight of said dicarboxylic acid divinyl ester (E), and wherein said polymerization is conducted at a temperature of at least 40 °C. An ocular lens comprising the ocular lens material according to any one of Claim 1 through Claim 7. The ocular lens according to Claim 10, being a soft contact lens. The ocular lens according to either Claim 10 or Claim 11, further having a water content of at least 50% by weight, a tensile strength of at least 150 g/mm 2 , a Young's modulus of 35 to 150 g/mm 2 , a light transmittance of at least 90% and an elution ratio when immersed in distilled water at 20°C for 72 hours of less than 0.5% by weight. A copolymer obtainable by polymerizing a monomer mixture comprising: (A) an N-vinyllactam; (B) a fluorine-containing unsaturated monomer; (C) a hydrophilic (meth)acrylamide; (D) a crosslinking agent having at least 2 (meth)acryloyloxy groups; and (E) a dicarboxylic acid divinyl ester.

Inventors: IKUO OMURA, TAKASHI MAKABE, IKUO, OMURA, TAKASHI, MAKABE, Ikuo, Omura, c/o Kuraray Co., Ltd, Takashi, Makabe, c/o Kuraray Co., Ltd
Applicants: KURARAY CO, KURARAY CO., LTD.
Application year: 1999
Main classification: C08F226
IPC codes: G02B1, C08F220, G02C7, C08F226