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Title:
POLYMER COMPOSITIONS SUITABLE FOR USE AS CONTACT LENS
Document Type and Number:
WIPO Patent Application WO/1995/009878
Kind Code:
A1
Abstract:
Disclosed are polymer compositions comprising a vinyl amide monomer, a polysiloxanylalkyl acrylate or methacrylate monomer, a styrene and/or styrene related monomer, and a cross-linking agent. These polymer compositions are capable of incorporating from about 10 to about 65 weight percent water and are useful in contact lenses.

Inventors:
MANESIS NICHOLAS T
FONG PATRICIA J
KHUSHROO GANDHI
NEIDLINGER HERMANN
Application Number:
PCT/US1994/011196
Publication Date:
April 13, 1995
Filing Date:
October 04, 1994
Export Citation:
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Assignee:
PILKINGTON BARNES HIND INC (US)
International Classes:
C08F220/54; C08F226/10; C08F230/08; G02B1/04; (IPC1-7): C08F226/06; C08F212/06; C08F220/54; C08F230/08
Foreign References:
US4182822A1980-01-08
US4661573A1987-04-28
Download PDF:
Claims:
WHAT IS CLAIMED IS:
1. A polymer composition comprising: (a) from about 30 to about 85 mol percent of a vinyl amide monomer selected from the group consisting of and where R1, R2, and R3 are independently selected from the group consisting of hydrogen and an alkyl group of from 1 to 4 carbon atoms, R4 is selected from the group consisting of hydrogen and methyl, and R5 and R6 are independently selected from the group consisting of hydrogen and an alkyl group of from 1 to 4 carbon atoms with the proviso that R5 and R6 are not both hydrogen; (b) from about 15 to about 45 mol percent of at least one polysiloxanylalkyl acrylate or methacrylate monomers having the formula: wherein X and Y are independently selected from the group consisting of alkyl substituents of from 1 to 4 carbon atoms, a phenyl substituent, and a substituent of the formula wherein A, B, C, A', B', and C are independently selected from the group consisting of alkyl substituents of from 1 to 4 carbon atoms and a phenyl substituent, R is selected from the group consisting of hydrogen and methyl, m and m' are independently integers of from 1 to 4, and n is an integer of from 1 to 5; (c) from about 0.5 to about 15 mol percent of a styrene component of the formula R7C=CHR9 R8 where R7 is selected from the group consisting of phenyl and phenyl substituted with 1 to 3 alkyl substituents of from 1 to 6 carbon atoms and R8 and R9 are independently selected from the group consisting of hydrogen and methyl; and (d) from about 0.1 to about 2 mol percent of a crosslinking agent wherein, in each case, the mol percent is based on the total number of mols of all of the components found in the dry polymer composition.
2. The polymer composition according to Claim 1 wherein the vinyl amide monomer is a compound of the formula: where R4 is selected from the group consisting of hydrogen and methyl, and R5 and R6 are independently selected from the group consisting of hydrogen and an alkyl group of from 1 to 4 carbon atoms with the proviso that R5 and R6 are not both hydrogen.
3. The polymer composition according to Claim 2 wherein the vinyl amide monomer comprises from about 50 to about 85 mol percent of the polymer.
4. The polymer composition according to Claim 1 wherein the polysiloxanylalkyl acrylate or methacrylate monomer comprises from about 15 to about 35 mol percent of the polymer.
5. The polymer composition according to Claim 1 wherein R8 and R9 are hydrogen.
6. The polymer composition according to Claim 5 wherein the styrene or styrene related monomer is selected from the group consisting of styrene having from 1 to 3 alkyl substituents on the phenyl ring wherein each of said alkyl substituents is independently alkyl of from 1 to 6 carbon atoms.
7. The polymer composition according to Claim 6 wherein said styrene or styrene related monomer is selected from the group consisting of 4tbutyl styrene, 2,4,6trimethylstyrene, and mixtures thereof.
8. The polymer composition according to Claim 1 wherein the mol percent of the vinyl amide monomer, the polysiloxanylalkyl acrylate or methacrylate monomer, and the styrene or styrene related monomer are selected so that the polymer has a oxygen permeability as measured by a Dk value of greater than 60; a Shore D hardness of greater than 75; a modulus of greater than 3; a percent elongation of greater than 75%, a tear strength of greater than 3 grams per square millimeter, and an effective water concentration of from about 10 to about 65 weight percent.
9. The polymer composition according to Claim 1 which further comprises from 0.1 to 1 mol percent of fluorinated alkyl acrylates having from 1 to 12 fluoro atoms and 4 to 12 carbon atoms.
10. A polymer composition comprising: (a) from about 65 to 75 mol percent of N,N dimethylacrylamide; (b) from about 25 to 30 mol percent of methacryloxypropyl tris[ (trimethyl)siloxy]silane; (c) from about 0.5 to about 15 mol percent of 4t buty1styrene, 2,4,6trimethyl styrene or mixtures thereof; and (d) from about 0.1 to about 2 mol percent of a crosslinking agent wherein, in each case, the mol percent is based on the total number of mols of all of the components found in the dry polymer composition.
11. The polymer composition according to Claim 1 wherein from about 10 to about 65 weight percent water based on the total weight of the polymer composition after hydration is incorporated into the polymer composition.
12. The polymer composition according to Claim 10 wherein from about 10 to about 65 weight percent water based on the total weight of the polymer composition after hydration is incorporated into the polymer composition.
13. The polymer composition according to Claim 1 wherein said composition is postcured by heating said composition at a temperature of from about 60° to about 120°C for from 1 to 24 hours or by exposing said polymer with from about 0.1 to about 3 Mrad of y radiation or by combinations thereof.
14. The polymer composition according to Claim 10 wherein said composition is postcured by heating said composition at a temperature of from about 60° to about 120°C for from 1 to 24 hours or by exposing said polymer with from about 0.1 to about 3 Mrad of y radiation or by combinations thereof.
15. The polymer composition according to Claim 11 wherein said composition is in the form of a contact lens.
16. The polymer composition according to Claim 12 wherein said composition is in the form of a contact lens.
Description:
POLYMER COMPOSITIONS SUITABLE FOR USE AS CONTACT LENS

BACKGROUND OF THE INVENTION

Field of the Invention

5 This invention is directed to polymer compositions t having properties particularly suited for use in the manufacture of ophthalmic devices, e.g., contact lenses, which compositions can also be used in other medical and non-medical devices. In particular, this invention is directed to polymer 10 compositions comprising a vinyl amide monomer, a polysiloxanylalkyl acrylate or methacrylate monomer, a styrene and/or styrene related monomer, and a cross-linking agent.

State of the Art

The use of certain polymers for human

15 applications is well known in the art and the polymer compositions are often tailored within theoretical and practical limits for the specific end use intended. In the area of contact lenses, the use of copolymers derived from acrylamide, methacrylamide or N-vinyl pyrrolidone monomers and

20 polysiloxanylalkyl acrylate or methacrylate monomers is disclosed in U.S. Patent No. 4,182,822. It is further disclosed that these materials have increased hydrophilicity, softness after hydration and oxygen-permeability. It is still further disclosed that certain properties of the therein

25 disclosed copolymers, such as hardness and strength, can be increased by copolymerizing the composition with a C, to C 20 ester of acrylic or methacrylic acid.

One problem encountered in polymers used for contact lenses is that often when the compositional amount of one

30 component of the polymer is changed to enhance the properties of the polymer for a specific end use, other properties of that polymer are also affected often in a deleteriously manner. For

* example, in the case of polymers incorporating vinyl amide and polysiloxanylalkyl acrylate or methacrylate monomers, an

35 increase in the amount of the polysiloxanylalkyl acrylate or methacrylate monomer increases oxygen permeability in the

resulting polymer but such an increase also reduces its water content. In view of the above, the tailoring of the amounts of components in a polymer for use as contact lenses requires a balancing of the amounts of each of the components so as to achieve overall requisite properties relating to hardness, oxygen permeability, water content, tensile strength, tear strength, and the like.

One particularly critical characteristic of polymer compositions suitable for use as contact lenses is that the polymer contain sufficient hardness/strength to permit machining of the polymer composition into a contact lens.

Typically, a component can be included in the polymer composition to enhance the hardness/strength of the composition to suitable levels. However, as noted above, it is essential that the added component does not so deleteriously affect other properties of the polymer composition as to render the polymer unsuitable for use as a contact lens.

Accordingly, polymer compositions which provide for more facile balancing of the desired properties are particularly desirable and especially those having enhanced hardness/strength so as to allow the polymer composition to be readily machined into contact lenses.

SUMMARY OF THE INVENTION This invention is directed to the discovery that a polymer composition comprising a vinyl amide monomer, a polysiloxanylalkyl acrylate or methacrylate monomer, and styrene or a styrene related monomer provides the requisite balancing of properties for contact lenses relating to oxygen permeability, water content, tensile strength, tear strength, and the like while having sufficient hardness/strength so as to permit the composition to be machined into contact lenses. Additionally, a cross-linking agent is preferably employed in the polymer composition to enhance the rigidity or modulus of the composition.

Accordingly, in one of its compositional aspects, this invention is directed to a polymer comprising:

(a) from about 30 to about 85 mol percent of a vinyl amide monomer selected from the group consisting of

and

where R 1 , R 2 , and R 3 are independently selected from the group consisting of hydrogen and an alkyl group of from 1 to 4 carbon atoms, R 4 is selected from the group consisting of hydrogen and methyl, and R 5 and R 6 are independently selected from the group consisting of hydrogen and an alkyl group of from 1 to 4 carbon atoms with the proviso that R 5 and R 6 are not both hydrogen;

(b) from about 15 to about 45 mol percent of at least one polysiloxanylalkyl acrylate or methacrylate monomer having the formula:

CH 2 wherein X and Y are independently selected from the group consisting of alkyl substituents of from 1 to 4 carbon atoms, a phenyl substituent, and a substituent of the formula

wherein A, B, C, A , B', and C are independently selected from the group consisting of alkyl substituents of from 1 to 4 carbon atoms and a phenyl substituent, R is selected from the group consisting of hydrogen and methyl, m and m' are independently integers of from 1 to 4, and n is an integer of from 1 to 5;

(c) from about 0.5 to about 15 mol percent of a styrene monomer of the formula

R 7 -C=CHR 9

R I . 8 where R 7 is selected from the group consisting of phenyl and phenyl substituted with 1 to 3 alkyl substituents of from 1 to 6 carbon atoms and R 8 and R 9 are independently selected from the group consisting of hydrogen and methyl; and

(d) from about 0.1 to about 2 mol percent of a cross-linking agent wherein, in each case, the mol percent is based on the total number of mols of all of the components found in the dry polymer composition.

In another of its compositional aspects, this invention is directed to a hydrogel polymer composition which comprises the polymer composition described above and from about 10 to about 65 weight percent water based on the total weight of the polymer composition after hydration and preferably from about 10 to about 50 weight percent water.

DETAILED DESCRIPTION OF THE INVENTION This invention is directed to specific polymer compositions having properties particularly suited for use in

contact lenses. As noted above, the compositions of this invention comprise a vinyl amide monomer, a polysiloxanylalkyl acrylate or methacrylate monomer, and a styrene or styrene related monomer. Preferably, the polymer compositions described herein further comprise a cross-linking agent. However, prior to discussing this invention in further detail, the following terms will first be defined.

Definitions

The term "cross-linking agent" refers to a monomer containing at least two reactive groups capable of forming covalent linkages with functional groups found on at least one of the monomers used to prepare the polymer compositions described herein. Suitable reactive groups include, for example, vinyl groups which can participate in the polymerization reaction. The reactive groups are typically substituents on a suitable backbone such as a polyoxy lkylene backbone (including halogenated derivatives thereof) , a polyalkylene backbone, a glycol backbone, a glycerol backbone, a polyester backbone, a polyamide backbone, polyurea backbone, a polycarbonate backbone, and the like.

Cross-linking agents for use in the compositions described herein are well known in the art and the particular cross-linking agent employed is not critical. Preferably, however, the reactive vinyl group is attached to the backbone of the cross-linking agent via an ester bond such as that found in acrylate and methacrylate derivatives such as urethane diacrylate, urethane di ethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, and the like. However, other suitable vinyl compounds include, by way of example, di- and higher- vinyl carbonates, di- and higher-vinyl amides (e.g. ,

CH 2 =CH-C(0)NHCH 2 CH 2 NH-C(0)CH=CH 2 ) , and the like.

Preferred cross-linking agents include, by way of example, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, tetradecaethylene glycol dimethacrylate, tetradecaethylene glycol diacrylate, allyl methacrylate, allyl acrylate, trimethylol-propane trimethacrylate, trimethylolpropane triacrylate, 1,3-butanediol dimethacrylate, 1,3-butanediol diacrylate, l,4-butanediol dimethacrylate, 1,4- butanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,6- hexanediol diacrylate, 1,9-nonanediol dimethacrylate, 1,9- nonanediol diacrylate, 1,10-decanediol dimethacrylate, 1,10- decanediol diacrylate, neopentyl glycol dimethacrylate, neopentyl glycol diacrylate, 2,2'bis[p-(7-methacryloxy-j8- hydroxypropoxy)phenyl]propane, pentaerythritol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, 1,4-cyclohexanediol diacrylate, 1,4-cyclohexanediol dimethacrylate, ethoxylated bis-phenol-A-diacrylate, ethoxylated bis-phenol-A- dimethacrylate, bis-phenol-A-dimethacrylate, bis-phenol-A-diacrylate, N,N'-methylenebisacryl-amide, and the like.

The cross-linking agent preferably has at least 2 and more preferably from 2 to about 6 vinyl functionalities and preferably has a number average molecular weight of from about 100 to about 2,500. More preferably, the vinyl functionalities are acrylate or methacrylate groups attached to a polyoxyalkylene backbone (including halogenated derivatives thereof) , a polyalkylene backbone, a glycol backbone, a glycerol backbone, a polyester backbone, or a polycarbonate backbone.

The term "hydrogel polymer composition" refers to polymer compositions described herein which, after polymer formation, are hydratable when treated with water and, accordingly, can incorporate water into the polymeric matrix without itself dissolving in water. Typically, water

incorporation is effected by soaking the polymer corαposition in a water solution for a sufficient period so as to incorporate from about 10 to about 65 weight percent water, and preferably from about 10 to about 50 weight percent water, into the polymer composition based on the total weight of the polymer composition.

The term "dry polymer composition" refers to the composition formed in the absence of added water wherein any water in the polymer composition is typically due to water impurities present in one or more of the reagents used to prepare the polymer composition and such water is typically less than 1 weight percent of the total polymer composition and preferably less than 0.1 weight percent. Such compositions are also referred to as "xerogel polymer compositions".

Formulations

The polymeric compositions of this invention comprise at least three components; namely, a vinyl amide monomer, a polysiloxanylalkyl acrylate or methacrylate monomer, and a styrene or a styrene related monomer. Preferably, the polymeric compositions further comprise a cross-linking agent. Vinyl amide monomers suitable for use herein are defined by the formula:

and

where R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 are as defined above. The preparation of each of these monomers is well known in the art

and some of these monomers are commercially available. Particularly suitable vinyl amide monomers for use in this invention include, by way of example, N,N-dimethyl acrylamide, N,N-dimethyl methacryla ide, and N-vinyl pyrrolidone. Mixtures of such vinyl amide monomers can also be used.

The vinyl amide monomer is employed at from about 30 to about 85 mol percent based on the total number of mols of all components found in the dry polymer composition, preferably from about 50 to about 85 mol percent, and more preferably, from about 65 to about 75 mol percent.

Polysiloxanylalkyl acrylate or methacrylate monomers suitable for use herein are defined by the formula

where A, B, C, R, X, Y, m and n are as defined above. The preparation of polysiloxanylalkyl acrylate or methacrylate monomers of the formula set forth above is described, for example, in U.S. Patent Nos. 3,808,178 and 4,182,822 the disclosures of which are incorporated herein by reference in their entirety. Several of these monomers are commercially available. The polysiloxanylalkyl acrylate or methacrylate monomers are employed at from about 15 to about 45 mol percent based on the total number of mols of all components found in the dry polymer composition, preferably from about 15 to about 35 mol percent, and more preferably, from about 25 to about 30 mol percent. Mixtures of such esters can also be employed.

Suitable polysiloxanylalkyl acrylate and methacrylate monomers include, by way of example, tris(trimethylsiloxy) silylpropyl acrylate, tris(trimethylsiloxy) silylpropyl methacrylate, methylbis(trimethylsiloxy) silyljpropyl methacrylate, methylbis(trimethylsiloxy)silyl]propyl acrylate, tris(pentamethyldisiloxy) silyl]propyl acrylate,

tris(pentamethyldisiloxy)silyl]propyl methacrylate, bis(trimethylsiloxy)mono(pentamethyldisiloxy)-silyl]propyl acrylate, bis(trimethylsiloxy)mono(pentamethyldisiloxy)-silyl]propyl methacrylate, mono(trimethylsiloxy)bis(pentamethyldisiloxy)-silyl]propyl acrylate, mono(trimethylsiloxy)bis(pentamethyldisiloxy)-silyl]propyl methacrylate, and the like.

Styrene and styrene related monomers suitable for use in this invention are selected from a compound of the formula:

R 7 -C=CHR 9 R 8 where R 7 , R 8 and R 9 are as defined above. Preferably, the styrene or styrene related monomer is selected from styrene or styrene having from 1 to 3 alkyl substituents on the phenyl ring wherein each alkyl substituent is independently of from 1 to 6 carbon atoms. Still more preferably, the styrene component is selected from 4-t-butylstyrene and 2,4,6- trimethylstyrene. Mixtures of styrene and styrene related monomers can be used.

The preparation of such styrene components is well known in the art and many of these components are commercially available including, by way of example, styrene, 2,4,6- trimethylstyrene, o-methylstyrene (R 7 = phenyl, R 8 = methyl, and R 9 = hydrogen) , trans-/3-methylstyrene (R 7 = phenyl, R 8 = hydrogen, and R 9 = methyl in a trans relationship with the phenyl group), 3-methyl-styrene, 4-methylstyrene, 3,4- dimethylstyrene, 3,5-dimethylstyrene, 4-t-butylstyrene, and the like.

The styrene component is preferably employed in the polymer composition at from about 0.5 to about 15 mol percent based on the total number of mols of all components found in the dry polymer composition, preferably from about 1 to about 10 mol percent, and more preferably, from about 1 to about 5 mol percent.

When employed, the cross-linking agent is employed in the polymer composition at from about 0.1 to about 2 mol percent based on the total number of mols of components found in the dry polymer compositions.

In addition to the above components, the polymer composition of this invention can optionally contain additional components such as fluorinated alkyl acrylates having from 1 to 12 fluoro atoms and 4 to 12 carbon atoms (e.g., hexafluoroisopropyl methacrylate) , which is employed at from about 0.1 to about 2 mol percent based on the total number of mols of all components found in the dry polymer composition and preferably from about 0.1 to about 1 mol percent.

In a particularly preferred embodiment, the mol percent of each of the vinyl amide monomer, the polysiloxanylalkyl acrylate or methacrylate monomer, the styrene or styrene related monomer and the cross-linking agent are selected so that the resulting polymer has a oxygen permeability as measured by a Dk value of greater than 60 [cm 3 (0 2 )cm]/[cm 2 sec cm Hg] ; a Shore D hardness of greater than 75; a modulus of greater than 3 Mdynes per square centimeter; a percent elongation of greater than 75%, a tear strength of greater than 3 grams per square millimeter, and an effective water concentration of from about 10 to about 65 weight percent.

Methodology

The polymer compositions described herein are readily prepared from a mixture comprising requisite amounts of a vinyl amide monomer (or mixtures thereof) , a polysiloxanylalkyl acrylate or methacrylate monomer (or mixtures thereof) , a

styrene or a styrene related monomer (or mixtures thereof) and a cross-linking agent. The reagents employed are typically stored and formulated in containers which prevent premature polymerization of one or more of the reagents. For example, the use of amber bottles for storing reagents inhibits photo- induced polymerization.

The mixture containing the requisite amounts of each of the monomers is then polymerized by conventional techniques such as thermal or UV induced polymerization to provide for the polymer composition. For example, thermal induced polymerization can be achieved by combining a suitable polymerization initiator into the mixture of monomers under an inert atmosphere (e.g., argon) and maintaining the mixture at an elevated temperature of from about 20°C to about 75°C for a period of time from about 1 to about 48 hours.

Ultraviolet (UV) induced polymerization can be achieved by combining a suitable polymerization initiator into the mixture of monomers under an inert atmosphere (e.g., argon) and maintaining the mixture under a suitable UV source. Preferably, UV induced polymerization is conducted at ambient conditions for a period of from about 5 minutes to about 24 hours.

Suitable polymerization initiators are well known in the art including thermal initiators such as t-butyl peroxy pivalate (TBPP) , t-butyl peroxy neodecanoate (TBPN) , benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate and the like and UV initiators such as benzophenone, Darocur 1173 (available from Ciba Geigy, Ardsley, New York) and the like. The particular thermal or UV initiator employed is not critical and sufficient initiator is employed to catalyze the polymerization reaction. Preferably, the initiator is employed at up to about 1 weight percent based on the total weight of the composition. Polymerization is typically conducted in a manner so as to facilitate manufacture of the finished contact lens. For

example, as described in the examples hereinbelow, polymerization can be conducted in molds which correspond to the structure of the contact lens. Alternatively, polymerization can be conducted so as to form a polymer rod which can be machined (lathed) to provide contact lenses of suitable dimensions. In this latter embodiment, polymerization is conducted in a silylated glass test tube and after polymerization, the test tube is broken to provide for the polymeric rod. In either case, after polymerization, a post-curing procedure is preferably employed to increase the hardness of the polymer. The post-curing procedure can comprise heating the polymer to a temperature of from about 60°C to 120°C for a period of from about 2 to about 24 hours. Alter-natively, the post-curing procedure can comprise irradiation of the polymer composition with from 0.1 to about 3 MRads of gamma (7) rays. In still another alternative embodiment, the post-curing procedure can comprise both heating and 7 radiation of the polymer (i.e., first heating the polymer in the manner described above followed by 7 radiation or first 7 irradiating the polymer followed by heating) .

Whether post-treated or not, the contact lenses prepared from the polymer compositions described herein are then soaked in a water composition (e.g., a phosphate buffered saline solution) in order to incorporate water into the polymer composition. Soaking is continued until the polymer incorporates from about 10 to about 65 weight percent water based on the total weight of the polymer composition after hydration and preferably from about 20 to about 50 weight percent water. Because of the incorporation of this amount of water, the resulting polymer composition is referred to as a "hydrogel polymer composition".

Hydration of the xerogel polymer composition is necessarily conducted after contact lens formation because the hydrogel composition lacks suitable physical characteristics,

e.g., strength, to permit lathing, etc. of the composition necessary to provide for a contact lens.

Utility

The xerogel polymer compositions described herein are suitable for use in medical and non-medical applications such as water absorbent materials useful in a variety of applications. After water incorporation, the polymer compositions described herein are particularly suitable for use as contact lenses providing requisite water content, transparency, oxygen permeability, and mechanical properties.

The following examples illustrate certain embodiments of this invention but are not meant to limit the scope of the claims in any way.

In the following examples, the following abbreviations represent the following:

BC = base curve

BME = benzoin methyl ether cm = centimeter

DMA N,N-dimethyl acrylamide EEGGDDMMAA = ethylene glycol dimethacrylate

EWC equilibrium water content

FC front curve

HFIPMA 1,1,1,3,3,3-hexafluoroisopropyl methacrylate

Hg mercury

LE linear expansion

ID internal diameter

Mdynes = megadynes min = minute mm = millimeter

MRad = megarads

OD outer or external diameter ppm parts per million tt--bbpppp oorr TTBBPPPP == t-butyl peroxy pivalate

TBS 4-t-butylstyrene

TMS 2,4,6-trimethylstyrene

T-1 3-methacryloxypropytris

(trimethylsiloxy)silane (alternative nomenclature includes tris(trimethylsiloxy)-silylpropyl methacrylate

VAZO 52 2,2 '-azobis(2,4-dimethylpentane-nitrile)

EXAMPLES In the examples set forth below, polymer compositional values are set forth for the Equilibrium Water Content ("EWC") , linear expansion, oxygen permeability, hardness, tear strength and tensile properties (i.e., tensile strength, percent elongation and modulus) . Unless otherwise indicated, these values were determined as follows:

Measurement of Equilibrium Water Content

Equilibrium Water Content (EWC) is determined by soaking the polymer samples in phosphate buffered saline solution for overnight. The samples are removed, lightly blotted dry with a tissue and subsequently weighed. The hydrated samples are then placed in a vacuum oven at 100°C overnight. The next day, the sample is reweighed. Equilibrium Water Content is calculated using the following equation:

EWC = X ~ Y X 100%

where X = mass of hydrated polymer

Y = mass of dehydrated polymer

Measurement of Linear Expansion

Linear Expansion factor is determined by measuring the diameter of the polymer sample using the Nikon Profile Projector V - 12 (available from Nippon Kogaku K.K., Tokyo, Japan) . The sample is then soaked overnight in phosphate buffered saline solution. The diameter is subsequently remeasured in phosphate buffered saline. Linear Expansion is calculated using the following equation:

LE =

where X = hydrated polymer diameter

Y = Initial (dry) polymer diameter

Measurement of Oxygen Permeability

The oxygen permeability of a contact lens is measured polarographically using a dissolved oxygen meter (available from Rosemont Analytical, Irvine, California, USA) . This dissolved oxygen meter consists of a electrode probe which has a gold cathode. The gold cathode is covered with a thin Teflon membrane. The probe is placed in a jacketed jar containing isotonic buffered saline. The saline is kept at 35°C by hot water circulating through the outside jacket of the jar. The saline is constantly stirred using a magnetic stirrer.

Initially the probe is placed in the saline solution and allowed to equilibrate. The reading on the dissolved oxygen meter should correspond to 6.7 ppm oxygen. If not the calibration knob is turned till it does so. After the calibration step the probe is taken out of the saline and the contact lens or disc is placed flat on the tip of the probe. The lens/disc is held against the Teflon membrane by a screw type device. The probe is then inserted back into the saline and allowed to equilibrate. Once the dissolved oxygen meter has reached a constant reading, this reading is noted. The lens or disc is then taken out and the average thickness of the lens/disc is measured. The oxygen permeability is then calculated using conventional methodology.

Measurement of Hardness

The hardness is measured on buttons which are at least 5 mm thick and about 12 mm in diameter. The buttons should have flat faces. The button is placed on a rigid flat surface for measurement. A calibrated Shore D durometer (available from Pacific Transducer Corp., Los Angeles,

California, U.S.A.) is used for measurements. The tip of the durometer is placed on the flat face of the button and the durometer is lowered quickly till the flat face of the durometer meets the button surface. At this point, the durometer reading is taken. Usually, the durometer has a

mechanism by which the maximum reading is recorded. This reading is then the Shore D hardness of the material.

The durometer is reset before the next measurement. An average of 5 readings is usually taken and reported.

Measurement of Tensile Properties

From a disc or a lens, a "dumb-bell" shaped specimen is cut. The sample is inspected under a microscope for nicks and cuts. If these are observed the sample is discarded. The thickness of the specimen is then measured. The sample is then placed between the clamps on an

Instron tensile tester (available from Intron Corp., Canton, Massachusetts, USA) or an equivalent instrument. The initial grip separation used is 10 mm. The sample is placed under saline during measurement to prevent drying out. The experiment is then started with the cross-head speed set to 5 mm/min. The Instron records the force required to pull on the sample as a function of cross-head displacement. This information is then converted into a stress-strain plot. The experiment continues until the sample breaks. From the stress strain plot are calculated the following:

Tensile strength: The maximum stress the sample can withstand before breaking.

Elongation: The amount of extension (expressed as a percent of original length/grip separation) the sample undergoes before breaking.

Modulus: Is the slope of the initial linear portion of the stress-strain curve.

The experiment is usually repeated with 5 samples from the same batch of polymer and the average and standard deviation are reported.

Measurement of Tear Strength

From a disc or lens a rectangular sample approximately 3.5 mm by 12 mm is cut with a die. Next a 9 mm

long slit is cut in the sample so that the sample is now "trouser" shaped. The thickness of the sample is measured.

Each leg of the trouser is placed in each of the grips of an Instron testing machine (available from Instron Corp., Canton, Massachusetts, USA). The initial grip separation used is 6 mm. The experiment is started with the speed of cross-head movement set at 20 mm/min. The Instron records the force required to tear the sample. Since an initial split has already been cut in the sample, the test measures the propagational tear strength.

The average force during tearing is calculated. This force when divided by the width and thickness of the sample gives the tear strength.

Usually, at least 4 samples are tested from the same polymer lot and the average and standard deviation is reported.

Example 1 — Preparation of Cross-Linked

Polymers in Lens Form

The preparation of the polymers of this invention in contact lens form involves polymerization of a formulation containing requisite amount of each of the monomers in a suitable mold. Initially, the formulation of monomers is prepared, the molds are then casted with the formulation and polymerization is initiated. Afterwards, the molds are decasted to provide for the polymer in lens form. The preparation of a formulation containing such monomers employs amber bottles which were used to store the requisite amount of each of the monomers, cross-linking agent and the thermal initiator. After each of these reagents are weighed (to an accuracy of 0.001 grams), they are added to the amber bottle. Upon completion of the addition of all of the reagents including the initiator, the bottle is sealed with a rubber stopper and an aluminum cap. The bottle is degassed with argon for at least 10 minutes. Afterwards, the bottle is placed in the freezer for storage prior to use.

The mold base curve is Corona treated for 0.45 seconds in air at a distance of 25 mm from the top of the mold base curve to the bottom of the Corona treatment ball and casting is accomplished by conventional techniques and the molds are processed by exposure to UV radiation for 10 minutes whereupon the molds are post-cured by heating to about 90°C for 3-24 hours (e.g., 3 hours or 24 hours). Upon cooling to room temperature the polymer composition is then de olded and are ready for physico-chemical analysis.

Example 2 — Preparation of Cross-Linked Polymers in Rod Form

Polymers were prepared by adding the requisite amount of each of the monomers, the cross-linking agent and the initiator directly into a silylated glass test tube (OD = 17.7 mm; ID = 14.7 mm; wall = 1.5 mm; length = 15.2 cm). The test tube was fitted with a rubber septum and purged with Argon for 5 minutes. Each sample was then polymerized in a water bath at 40°C to 45°C for approximately 24 hours. The resulting polymer was post-cured by heating at 90° to 110°C for approximately 24 hours in a forced air oven. Afterwards, the rods were machined into buttons and disks for physico chemical analysis.

Examples 3-10 — Preparation of Polymer Compositions

Table I below sets forth several polymer compositions which were prepared in lens form in the manner similar to that described in Example 1 above with the exceptions that in

Examples 3-7, the curing conditions were 45°C for 24 hours and the post-curing conditions were 110°C for 24 hours; whereas in Examples 8-10, the curing conditions were 40°C for 24 hours and the post-curing conditions were 110°C for 24 hours. Additionally, in each of these examples, TBPP was used as the initiator (0.75 weight percent in Examples 3-7 and 0.50 weight percent in Examples 8-10 based on the total weight of the composition) .

TABLE I

Example Mole Percent No. DMA T-1 TMS EGDMA

3 70 28 0.5 1.5

4 70 26 2.5 1.5

5 70 24 4.5 1.5

6 70 22 6.5 1.5

7 70 20 8.5 1.5

8 70 24 5.00 1.00

9 70 24 5.25 0.75

10 70 24 5.50 0.50

In Examples 3-10, 2,4,6-trimethylstyrene (TMS) was obtained from Aldrich Chemical Company, Milwaukee, Wisconsin; N,N-dimethylacrylamide (DMA) was obtained from Monomer-Polymer Labs, Windham, New Hampshire, USA; (T-1) was obtained from Huls-America, Piscataway, New Jersey, USA; ethylene glycol dimethylacrylate was obtained from Esschem Co., Essington, Pennsylvania, USA; and t-butyl peroxy pivalate (TBPP) was obtained from Atochem North America, Buffalo, New York, USA.

Each of these polymers were then evaluated for their equilibrium water content (EWC) , linear expansion (LE) and

Hardness (Shore D) in the manner described above. The results of this evaluation are set forth in Table II below:

TABLE II

Example Hardness No. EWC LE (Shore D)

3 21.0 ± 2.0 1.05 ± 0.01 71.8 ± 0.9

4 23.4 ± 1.4 1.04 ± 0.01 71.6 ± 0.8

5 25.9 ± 0.9 1.07 ± 0.00 73.6 ± 0.8

6 25.8 ± 2.0 1.07 ± 0.01 71.4 ± 1.1

7 27.0 ± 0.8 1.07 ± 0.01 74.6 ± 0.8

8 20.9 ± 0.5 1.06 ± 0.00 74.4 ± 0.5

9 22.0 ± 0.4 1.08 ± 0.01 73.2 ± 0.7

10 24.8 ± 0.1 1.07 ± 0.01 72.7 ± 0.6

Additionally, the polymers of Examples 5-10 were evaluated for tensile strength, percent elongation, modulus, tear strength, oxygen permeability, and hardness in the manner described above. The results of this evaluation are reported in Table III below:

TABLE III

Example Tensile Percent Tear Oxygen No. Strength Elongation Modulus Strength Perm. (Dk) Hardness

5 16.80 ± 4.07 44 ± 6 36.15 ± 3.31 6.62 ± 1.16 77.0 ± 6.5 73.6 ± 0.8

6 16.18 ± 2.96 51 ± 6 29.36 ± 2.60 5.07 ± 0.72 67.1 ± 2.0 71.4 ± 1.1

10

7 12.12 ± 4.14 36 ± 13 33.65 ± 2.09 3.61 ± 0.40 58.5 ± 5.0 74.6 ± 0.8

8 28.90 ± 2.70 70 ± 8 35.00 ± 3.40 10.61 ± 3.00 74.3 ± 9.9 74.4 ± 0.5

15 9 29.00 ± 2.70 88 ± 12 26.90 ± 2.40 8.78 ± 0.96 65.6 ± 4.7 73.2 ± 0.7 I tVJ

10 30.00 ± 2.90 115 ± 7 19.30 ± 0.50 7.97 ± 0.95 59.8 ± 3.1 72.7 ± 0.6

Tensile Strength is reported in Mdynes/cm2

Modulus is reported in Mdynes/cm2

20 Tear Strength is reported in g/mm2

Oxygen permeability (Dk) is reported in [x 10" 10 cm3(02) cm]/[cm2 sec cm Hg]

As noted above, the polymer compositions of Examples 3-7 were subjected to a post-curing procedure comprising heating the composition at a temperature of approximately 110°C for 24 hours. In a further post-cure procedure, separate samples of these compositions were exposed to 1, 2, and 3 MRads of radiation. The resulting compositions were then evaluated for their equilibrium water content (EWC) , linear expansion (LE) and Hardness (Shore D) and percent weight loss in methanol. This last evaluation is conducted for the purpose of determining the amount of extractables removed from the composition. Compositions having smaller amounts of extractables correspond to "harder" compositions.

Percent weight loss in methanol is determined by the following procedure. Preweighed dry polymer samples are placed in a Soxhlet extraction system using methanol as the solvent. Extraction is allowed to occur overnight. The next day, the samples are removed and placed in a vacuum oven at 50°C for 24 hours. The polymer materials are then reweighed. Weight loss values are determined using the following equation:

% Wght Loss = initial mass - mass after extr. X 100 initial mass

The results of this evaluation are set forth in Table IV below:

TABLE IV

Ex > Gamma Harein« ΪSS Wght Loss

No . Dosage EWC LE (Shore D) in MeOH

3 0 21.0 ± 2.0 1.05 ± 0.01 71.8 + 0.9 8.8 ± 0.5

1 19.2 + 0.3 1.08 ± 0.00 71.6 + 1.1 6.6 ± 0.3

2 19.6 + 0.5 1.06 ± 0.01 71.4 + 1.5 5.5 ± 0.4

3 19.1 + 0.7 1.07 ± 0.01 71.8 + 0.4 5.5 ± 0.4

4 0 23.4 + 1.4 1.04 ± 0.01 71.6 + 0.8 9.0 ± 0.4

1 21.8 + 0.6 1.08 ± 0.00 71.6 + 0.5 9.4 ± 0.7

2 20.7 + 0.2 1.08 ± 0.01 72.8 + 1.5 9.2 ± 0.7

3 20.8 + 0.0 1.08 ± 0.01 72.2 + 0.4 7.1 ± 0.3

5 0 25.9 + 0.9 1.07 ± 0.00 73.6 + 0.8 8.0 ± 0.9

1 23.9 + 0.8 1.09 ± 0.01 73.8 + 1.1 6.7 ± 0.5

2 23.2 + 0.5 1.07 ± 0.01 73.8 + 0.8 7.5 ± 0.3

3 22.7 + 0.3 1.07 ± 0.01 73.8 + 0.4 7.1 ± 0.3

6 0 25.8 ± 2.0 1.07 ± 0.01 71.4 + 1.1 8.6 ± 0.6

1 25.8 + 0.9 1.08 ± 0.00 73.6 + 1.1 10.9 ± 0.9

2 24.1 + 0.4 1.08 ± 0.01 73.6 + 1.5 9.8 ± 0.6

3 24.6 + 0.3 1.09 ± 0.01 74.6 + 1.5 8.0 ± 0.5

7 0 27.0 + 0.8 1.07 ± 0.01 74.6 + 0.8 8.8 ± 1.3

1 25.1 + 0.5 1.10 ± 0.00 74.6 + 1.1 8.1 ± 1.0

2 24.8 ± 0.2 1.10 ± 0.00 74.6 + 1.1 8.1 ± 1.0

3 25.7 + 1.0 1.08 ± 0.01 74.6 + 1.1 7.0 ± 0.2

The above results illustrate that the use of y radiation on polymer compositions already post-cured with a heating step reduces extractable levels, reduces the water content slightly, increases the linear expansion and has little effect on hardness. These last results appear to be inconsistent with the reduction in extractable levels and, accordingly, are considered anomalous results.

Examples 11-15— Preparation of Polymer Compositions

Table V below sets forth additional polymer compositions which were prepared in the manner similar to that described in Examples 1 and 2 above with the exceptions that in each of the examples, the curing conditions were 40°C for 24 hours and the post-curing conditions were 110°C for 24 hours.

Additionally, in each of these examples, TBPP was used as the initiator (0.50 weight percent).

TABLE V

Example Mole Percent No. DMA T-1 TMS EGDMA

11 73 21 5.5 0.5

12 76 18 5.5 0.5

13 79 15 5.5 0.5

14 82 12 5.5 0.5

15 85 9 5.5 0.5

In Examples 11-15, 2,4,6-trimethylstyrene (TMS) was obtained from Aldrich Chemical Company, Milwaukee, Wisconsin; N,N-dimethylacrylamide (DMA) was obtained from Monomer-Polymer Labs, Windham, New Hampshire, USA, T-1 was obtained from Huls- America, Piscataway, New Jersey, USA; ethylene glycol dimethylacrylate was obtained from Esschem Co. , Essington, Pennsylvania, USA; and t-butyl peroxy pivalate (TBPP) was obtained from Atochem North America, Buffalo, New York, USA. Each of these polymers were then evaluated for their equilibrium water content (EWC) , linear expansion (LE) and Hardness (Shore D) in the manner described above. The results of this evaluation are set forth in Table VI below:

TABLE VI Example Hardness No. EWC LE (Shore D)

11 29.3 ± 0.5 1.13 ± 0.01 77.2 ± 0.7

12 36.3 ± 0.8 1.15 ± 0.01 79.4 ± 1.0

13 41.5 ± 0.8 1.17 ± 0.01 80.6 ± 1.0

14 48.6 ± 0.2 1.22 ± 0.01 83.0 ± 0.6

15 56.3 ± 0.2 1.31 ± 0.01 84.0 ± 0.9

Additionally, the polymer of Example 12 was evaluated for its tensile strength, percent elongation, modulus, tear strength, oxygen permeability, and hardness in the manner described above. The results of this evaluation are reported in Table VII below:

TABLE VII

Example Tensile Percent Tear Oxygen

No. Strength Elongation Modulus Strength Perm. (Dk) Hardness

12 24.40 ± 3.80 142 ± 7 16.28 ± 0.74 2.97 ± 0.31 53.7 ± 4.1 79.4 ± 1.0

Tensile Strength is reported in Mdynes/cm2

Modulus is reported in Mdynes/cm2

10 Tear Strength is reported in g/mm2

Oxygen permeability (Dk) is reported in [x 10 " '° cm3(02) cm]/[cm2 sec cm Hg]

Examples 16-21— Preparation of Polymer Compositions

Table VIII below sets forth additional polymer compositions which were prepared in the manner similar to that described in Example 1 above which composition was prepared in a mold so as to provide for a product in the shape of a contact lens with the exception that the curing conditions employed in this method involved exposure of the molds to UV radiation for 10 minutes followed by a post-cure procedure of heating the polymer composition at about 50°C for about 24 hours followed by further heating the composition at 90°C for about an additional 24 hrs. Also, in Examples 16-18, 0.40 weight percent of VAZO 52 (available from E.I. Dupont de Nemoures and Company, Wilmington, Delaware, USA) was employed as the initiator whereas in Examples 19-21, 0.40 weight percent of BME (available from Aldrich Chemical Company, Milwaukee, Wisconsin, USA) was used as the initiator.

TABLE VIII

Example Mole Percent No. DMA T-1 TMS EGDMA

16 70 24 5.25 0.75

17 70 24 5.00 1.00

18 70 24 4.75 1.25

19 70 24 5.25 0.75

20 70 24 5.00 1.00

21 70 24 4.75 1.25

2,4,6-trimethylstyrene (TMS) N,N-dimethyl-acrylamide (DMA) , T-1, and ethylene glycol dimethylacrylate were obtained as described above.

Each of the polymers of Examples 19-21 was evaluated for its tensile strength, percent elongation, modulus, tear strength, oxygen permeability, and hardness in the manner described above. The results of this evaluation are reported in Table IX below:

TABLE IX

Example Tensile Percent Tear Oxygen No. Strength Elongation Modulus Strength Perm. (Dk) EWC

19 30.2 ± 7.1 225.9 ± 19.6 7.3 ± 1.5 21.8 ± 12.3 51.0 ± 11 22.2 ± 1.1

20 32.2 ± 23.5 141.7 ± 73.9 11.5 ± 0.8 16.1 ± 4.8 46.9 ± 9.8 22.4 ± 0.4

10 21 22.2 ± 21 115.8 ± 61.9 13.6 ± 3.6 14.3 ± 3.1 54.0 ± 4 20.9 ± 0.5

Tensile Strength is reported in Mdynes/cm2

Modulus is reported in Mdynes/cm2

Tear Strength is reported in g/mm2

15

Oxygen permeability (Dk) is reported in [x 10 " '° cm3(02) cm]/[cm2 sec cm Hg]

In addition to the data set forth above in Table IX, mold conformance data for six lenses prepared from the polymer composition of Example 20 are set forth in Table X below:

TABLE X

The above data in Table X above indicates that the polymer compositions of this invention provide good conformance to the mold.

Examples 22-26 — Polymer Compositions Containing Fluorinated Alkyl Acrylates or Methacrylates

The following examples were conducted to illustrate that the addition of more than about 1 mol percent of a fluorinated alkyl acrylate to the polymer composition is detrimental to the oxygen permeability of the polymer. Specifically, the compositions were prepared in a manner similar to Examples 1 and 2 above with the exceptions that in each of the examples, the curing conditions were about 40°C for 24 hours and the post-curing conditions were about 110°C for 24 hours. Additionally, in each of these examples, TBPP was used as the initiator (0.50 weight percent).

Table XI sets forth the polymer compositions used in these examples:

TABLE XI

Example Mole Percent No. DMA T-1 TMS EGDMA HFIPMA

22 70 25 4 1.0 0

23 70 24.8 4 1.0 0.2

24 70 21 5.5 0.5 3.0

25 70 15 5.5 0.5 9.0

26 70 9.0 5.5 0.5 15.0

2,4,6-trimethylstyrene (TMS) N,N-dimethyl-acrylamide (DMA) , T-1, and ethylene glycol dimethylacrylate were obtained as described above. Each of the polymers of Examples 22-24 was evaluated for its oxygen permeability in the manner described above. The results of this evaluation are reported in Table XII below:

TABLE XII

Polymer Compc >sition Oxygen of Example No. Permeability

22 64.2 ± 4.0

23 72.8 ± 8.9

24 58.1 ± 5.8

25 47.7 ± 5.4

26 37.6 ± 6.3

The above data indicates that the incorporation of a fluorinated alkyl acrylate or methacrylate material into the polymer composition provides improved oxygen permeability at low levels but detrimental oxygen permeability at high levels.

Examples 27-35— Preparation of Polymer Compositions

The following examples are offered to illustrate that other styrene monomers can be used in place of 2,4,6- trimethylstyrene. Specifically, in the following examples, 4- t-butylstyrene was used in the polymer compositions. Table XIII below sets forth several polymer compositions which were prepared in the manner similar to that described in Example 2 above. Additionally, in each of these examples, TBPP was used as the initiator (0.5 weight percent) .

TABLE XIII

Example Mole Percent

No. DMA T-1 TBS EGDMA

27 65 20 14.5 0.5

28 65 23 11.5 0.5

29 65 26 8.5 0.5

30 70 20 9.5 0.5

31 70 23 6.5 0.5

32 70 26 3.5 0.5

33 75 18 6.5 0.5

34 75 20 4.5 0.5

35 75 22 2.5 0.5

In Examples 27-35, 4-t-butylstyrene (TBS) was obtained from Dow Chemical Company, Rolling Meadow, Illinois, USA, N,N-dimethylacrylamide (DMA) was obtained from Monomer- Polymer Labs, Windham, New Hampshire, USA; T-1 was obtained from Huls- America, Piscataway, New Jersey, USA; and ethylene glycol dimethylacrylate was obtained from Esschem Co., Essington, Pennsylvania, USA.

Each of these polymers were then evaluated for their equilibrium water content (EWC) , linear expansion (LE) and Hardness (Shore D) in the manner described above. The results of this evaluation are set forth in Table XIV below:

TABLE XIV

Example Hardness No. EWC LE (Shore D)

27 26.8 ± 0.6 1.12 + 0.00 80.6 ± 1.2

28 24.0 ± 0.2 1.10 + 0.00 80.0 ± 0.9

29 20.3 ± 0.3 1.08 + 0.01 81.4 ± 0.8

30 29.6 ± 0.2 1.09 + 0.00 82.0 ± 0.6

31 27.7 ± 0.4 1.12 + 0.01 78.0 ± 0.6

32 24.4 ± 0.5 1.10 + 0.01 79.8 ± 1.2

33 34.9 ± 0.7 1.12 + 0.01 79.4 ± 0.5

34 33.8 ± 0.3 1.12 ± 0.01 80.2 ± 0.7

35 31.8 ± 0.9 1.15 + 0.01 82.2 ± 0.7

Additionally, the polymers of Examples 30-35 were evaluated for tensile strength, percent elongation, modulus, tear strength, oxygen permeability, and hardness in the manner described above. The results of this evaluation are reported in Table XV below:

TABLE XV

Example Tensile Percent Tear Oxygen No. Strength Elongation Modulus Strength Perm. (Dk) Hardness

30 25.9 ± 5.6 190 ± 35 10.2 ± 0.6 7.4 ± 0.7 62.0 ± 7.6 82.0 ± 0.6

31 30.6 ± 1.4 254 ± 7 7.2 ± 0.7 13.7 ± 2.8 68.0 ± 5.1 78.0 ± 0.6

10 33 26.2 ± 2.0 217 ± 10 8.1 ± 0.5 14.1 ± 2.7 62.8 ± 7.1 79.4 ± 0.5

34 27.0 ± 14.0 209 ± 82 7.1 ± 0.6 14.8 ± 3.7 62.0 ± 3.9 80.2 ± 0.7

35 18.5 ± 5.5 218 ± 48 6.3 ± 0.8 12.7 ± 1.7 69.2 ± 4.9 82.2 ± 0.7

15 Tensile Strength is reported in Mdynes/cm2

Modulus is reported in Mdynes/cm2

Tear Strength is reported in g/mm2

Oxygen permeability (Dk) is reported in [x 10"'° cm3(02) cm]/[cm2 sec cm Hg]

The above data illustrates that these polymer compositions provide suitable properties for use as a contact lens and, accordingly, demonstrates that styrene monomers other than 2,4,6-trimethylstyrene are suitable for use in the polymer compositions of this invention.

Examples 36-39— Preparation of Polymer Compositions

The following examples are offered to illustrate polymer compositions containing higher cross-linker contents. Table XVI below sets forth several polymer compositions which were prepared in the manner similar to that described in Example 1 above with the exceptions that in each of the examples, the curing conditions were UV exposure for 10 minutes followed by post-curing conditions of heating the polymer composition at 50°C for 24 hours and then at 90°C for an additional 24 hours. Additionally, in each of these examples, 0.40 weight percent of BME (available from Aldrich Chemical Company, Milwaukee, Wisconsin, USA) and 0.40 weight percent of VAZO 52 (available from E.I. Dupont de Nemoures and Company, Wilmington, Delaware, USA) were used as the initiator.

TABLE XVI

Example Mole Percent No. DMA T-1 TMS EGDMA HFIPMA

27 70 24.75 4.0 1.25 0.0

28 70 24.50 4.0 1.50 0.0

29 70 24.55 4.0 1.25 0.2

30 70 24.30 4.0 1.50 0.2

In Examples 27-35, 2,4,6-trimethylstyrene (TMS) was obtained from Aldrich Chemical Company, Milwaukee, Wisconsin; N,N-dimethylacrylamide (DMA) was obtained from Monomer-Polymer Labs, Windham, New Hampshire, USA; T-1 was obtained from Huls- America, Piscataway, New Jersey, USA; and ethylene glycol

dimethylacrylate was obtained from Esschem Co. , Essington, Pennsylvania, USA.

Each of these polymers were then evaluated for tensile strength, percent elongation, modulus, tear strength, oxygen permeability, and hardness in the manner described above. The results of this evaluation are reported in Table XVII below:

TABLE XVII

Example Tensile Percent Tear Oxygen No. Strength Elongation Modulus Strength Perm. (Dk) EWC

36 39.3 ± 26.1 128.5 ± 49.2 18.9 + 1.7 20.5 ± 0.3 73.9 ± 8.7 25.2 ± 0.6

37 62.1 ± 14.4 157.8 ± 12.5 20.3 ± 1.9 16.8 ± 4.9 68.2 ± 3.4 25.1 ± 0.5

10 38 30.3 ± 11.4 135.2 ± 29.1 15.8 ± 1.4 17.2 ± 3.0

39 47.9 ± 22.7 134.7 ± 24.6 22.2 ± 1.5 13.9 ± 11

Tensile Strength is reported in Mdynes/cm2

Modulus is reported in Mdynes/cm2

15 Tear Strength is reported in g/mm2

Oxygen permeability (Dk) is reported in [x 10 " '° cm3(02) cm]/[cm2 sec cm Hg]

The above data illustrates that the use of higher cross-linker content in the polymer compositions imparts excellent properties to the composition as it relates to the use of such compositions in contact lenses.